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Who is Responsible for Verifying Design Loads?

Who is Responsible for Verifying Design Loads by Contract?

Disclaimer – this and subsequent articles on this subject are not intended to be legal advice, merely an example for discussions between you and your legal advisor.

Please keep in mind, many of these terms are applicable towards post frame building kits and would require edits for cases where a builder is providing erection services or materials and labor.

DESIGN LOADS/CONDITIONS: Plan, drafting, engineering or calculation changes needed due to Purchaser’s failure to adequately confirm criteria in this section, or Purchaser’s desire to change building dimensions or features, will result in a minimum $xxx charge.

It is solely upon Purchaser to verify with Purchaser’s Planning and/or Building Departments, or any other appropriate government, or non-governmental agencies, the ability to construct purchased building(s) at location anticipated, as well as to apply for and obtain any needed permits. All due diligence to comply with any architectural or aesthetic covenants must be done by Purchaser, and Purchaser agrees to absorb any costs associated with compliance.

Purchaser acknowledges verification/confirmation/acceptance of all Building Code, Plan and Design Criteria included on Instant Invoice. Information Purchaser has verified includes, but is not limited to: Applicable Building Code version, Occupancy Category, Ground (Pg) and Flat Roof (Pf) Snow Loads, Roof Snow Exposure Factor (Ce), Thermal Factor (Ct), Wind Speed (vult or 3 second gust) and Wind Exposure, Allowable Foundation Pressure, Seismic Zone and Maximum Frost Depth, as well as obtaining for Seller any unusual code interpretations or amendments.

Seller’s designs are all per specified Building Code and include the use of NDS Table 2.3.2 Load Duration Factors (Cd) as well as ASCE 7, Eq. 7-2 for slippery surfaces. Seller’s designs rely solely upon occupancy category and structural criteria for and at specified job site address only, which have been provided and/or verified by Purchaser.

It is Purchaser’s and only Purchaser’s responsibility to ascertain the design loads utilized in this Agreement meet or exceed the actual dead loads imposed on the structure and the live loads imposed by the local building code or historical climactic records. Purchaser understands Seller and/or third party engineer(s) or agents will NOT be contacting anyone to confirm.

Dead loads specified on engineered roof truss drawings include the weight of the roof truss. Roof trusses are NOT designed to support ANY hanging loads or ceiling loads other than those specified as special truss loads in the Agreement. In the case of design roof truss bottom chord loads of less than five (5) psf (pounds per square foot) the bottom chord dead load may be sufficient only to cover the truss weight itself and may not allow for any additional load to be added to the bottom chord.

Roof truss top chord design loads of 5 psf (or less) are not adequate for roofing other than light gauge steel.

Seller recommends use of A1V (aluminum/single air cell/vinyl) radiant reflective barrier, an Integral Condensation Control (I.C.C. – Dripstop, Condenstop or similar), solid sheathing (with appropriate underlayment) or Purchaser applied 2″ or thicker closed cell spray foam insulation to help control roof condensation.

In no case is Seller liable for any condensation issues. An I.C.C., when ordered, is manufacturer applied to roof steel panels only. Seller makes no representation of any R or U value for any insulation or insulation products supplied. In the event Purchaser opts to utilize snow loads, wind loads, wind exposure factors, seismic loads or ventilation of less than those recommended by Seller, or soil bearing capacities greater than those recommended by Seller, Seller and third party engineer(s) are totally absolved of any and all structural responsibility.

Any windows and/or doors provided by Seller are NOT wind-rated, unless specifically noted as such.

Any possible design responsibility for this building is null and void should any structural materials and/or construction be substituted, replaced, depart, deviate, or are otherwise altered from the Seller’s original building kit they belong to, including structural materials from suppliers not authorized in writing by Seller’s owner, or if building is constructed at an address other than as specified on plans.

This entry was posted in Professional Engineer, Pole Barn Design, Building Department, Pole Barn Planning and tagged occupancy category, wind speed, thermal factor, flat roof snowload, seismic zone, engineering changes, design criteria, calculation changes, design loads, roof snow exposure factor, wind exposure, allowable Foundation, ground snow load, maximum frost depth on June 10, 2025 by Rick Ochs.

Exactly Identical and 20% Less

There is always someone willing to sacrifice quality and/or service to get to a lower price. I have seen it over and over again for decades now.

Price shoppers, or deal hunters, seem to be most interested in the lowest price. Unlike value shoppers who are willing to pay more in favor of an increased sense of value, deal hunters will only pay less and are willing to accept less.

I had an interaction recently with a potential client from rural North Dakota, who is looking to invest in a new post-frame building for a garage/shop. He had received a quote for a similar dimension building from a large vendor who advertises they will save customers big money and their price was quite a bit lower.

In my humble opinion, this client really wanted to do business with us – he was a value shopper, not a price shopper. He did offer to share his quote with me and I found it to be interesting, as it was a multi-page list of materials, rather than stating possibly important things such as building dimensions, design loads, etc.

My goal has always been to assist clients to help them avoid making choices they will regret forever.

Below is my response to this client:

Thank you for your patience while I have gone through xxxx quote. Here are some things I noticed:

xxxx building is not engineered and there is no stated design wind speed or exposure, both of which are critical for adequate structural design.

xxxx is furnishing nailed up columns, with 22′ ones being spliced. I did destructive testing of steel plate reinforced nail-lam columns at Oregon State University. Didn’t work out as well as I had hoped – as the center member takes twice as much load as outer plies (due to nails from both sides going into center member) and failed every time.

They do not furnish posts for either side of entry doors

Their quote included OSB under roof steel, however screws do not hold in OSB and a 1″ screw would penetrate only 1/2″ into blocking between trusses, if added.

Their quote did not include wall OSB or housewrap.

Entry doors – builder grade, primed only, in wood jambs, as opposed to insulated commercial steel, in steel jambs, factory finish painted.

We used to buy overhead doors from Clopay (parent company of Ideal). Ideal doors typically have very low cycle springs and use nylon hinges as opposed to steel.

Our buildings utilize double trusses aligned with interior sidewall columns, to avoid the possibility of a single truss failing and pulling the balance of the roof down with it.

Ventilation should be intake at eaves, exhaust at ridge for best airflow. Endwall soffits should be non-vented and there should be no gable vents.

There is no Z trim on xxxx quote between wainscot and steel panels above.

Delivery not included from xxxx.

Attached quote is how I would want my own building…..

Commercial wall girts for insulation (2×8 on eave sidewalls), framing is included to be drywall ready. https://www.hansenpolebuildings.com/2019/09/11-reasons-post-frame-commercial-girted-walls-are-best-for-drywall/

Trusses with raised heels, so ceiling insulation will be full depth from wall-to-wall https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/

Raised panel (not industrial looking ones xxxx quoted) insulated WIND-RATED overhead doors https://www.hansenpolebuildings.com/2014/12/wind-load-rated-garage-doors/

Roof steel with an Integral Condensation Control https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/

Besides fully engineered plans, showing location and connection of every component, you get our 500+ page step-by-step construction manual and unlimited free technical support from people who have actually built post frame buildings.

Will this potential client actually order his new building from Hansen Pole Buildings? There is a distinct possibility and if his choice is to invest elsewhere, at least he has hopefully gained enough insight to make an informed decision.

This entry was posted in Constructing a Pole Building, Pole Barn Planning, Pole Barn Structure, Building Contractor, Trusses, Budget, Insulation, Pole Barn Questions and tagged wind speed, OSB, Post-Frame, insulated steel entry doors, commercial wall girts, wind exposure, nail-lam columns, house wrap on June 13, 2023 by admin.

Wind Exposure and Confusion Part III

Cliff Notes for Wind Exposure
Been following along reading my articles on wind exposure? OK – so here is my “Cliff Notes” version – in generalized, simple terms:
Wind Exposure B is a site protected from wind in all four directions, within 1500 feet, by trees, hills or other single-family home sized buildings. This would include building sites in residential neighborhoods and wooded areas. If your picturesque view is under ¼ mile, then this is probably you.

Wind Exposure C is open to wind in one or more directions, for 1500 feet, with only scattered obstructions generally less than 30 feet tall in any direction. This would include building sites in flat open country and grasslands. Can you see ‘forever’ in one or more directions and your ‘forever’ does not include a body of water over a mile wide? You are Exposure C.

Very few people actually have Wind Exposure D. This would be areas facing unobstructed large bodies of water (over 5000 feet in width) or within 600 feet of a qualifying shoreline (water over 5,000 feet in width), whether unobstructed or not. Examples include ocean shorelines, wide lakes or rivers (Columbia, Missouri, Mississippi, etc.).

I am always amazed when I get a request for a quote from someone claiming Exposure D…and they are in mid- Kansas with not even a river, much less a lake within 100 miles!
I also have those folks who insist the “prevailing wind” comes from the one direction they have “protected”, so they want to claim Wind Exposure B – when other three sides are basically totally exposed. Exposure B determination doesn’t care what side IS protected –just all four
sides ARE protected. And, although it doesn’t hurt to claim a more restrictive exposure “just to be safe”, it will cost more in many (but not all) cases. When in doubt, stand on your building site and take photos in all 4 directions, and then take them to your building department for a wind exposure determination. It’s always best to have your local Building Officials working with you from project beginning.

This entry was posted in Pole Barn Planning, Pole Barn Homes, Post Frame Home, Barndominium, Pole Barn Design, Building Department and tagged wind exposure, wind exposure C, wind exposure B, wind exposure D, prevailing wind on June 30, 2022 by admin.

Wind Exposure and Confusion Part II

WIND EXPOSURE & CONFUSION – Part Deux
For those of you who needed an energy drink to survive Part I….
To get the information needed, glance over IBC Section 1609.4.2‐‐Surface Roughness Categories. “A ground surface roughness within each 45-degree sector shall be determined for a distance upwind of the site as defined in Section 1609.4.3 from the following categories, for the purpose of assigning an exposure category as defined in Section 1609.4.3.”
1) Surface roughness B: “Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions having the size of single-family dwellings of single-family dwellings or larger.”
2) Surface roughness C: “Open terrain with scattered obstructions having heights generally less than 30 feet. This category includes flat open country and grasslands.”
3) Surface roughness D: “Flat, unobstructed areas and water surfaces. This category includes smooth mud flats, salt flats and unbroken ice.”
Hold on, we still haven’t determined what our Exposure Category is.
In IBC Section 1609.4.3‐‐Exposure Categories, we finally get information we want. Exposure is based on roughness determined earlier and once again broken into Categories B, C, or D:
1) IBC Exposure B: “For buildings with a mean roof height of less than or equal to 30 feet, Exposure B shall apply where the ground surface roughness, as defined by Surface Roughness B, prevails in the upwind direction for a distance of not less than 1,500 feet. For buildings with a mean roof height greater than 30 feet, Exposure B shall apply where Surface Roughness B
prevails in the upward direction for a distance of not less than 2,600 feet or 20 times the height of the building, whichever is greater.”
wind damage Surface roughness B = Exposure B with these restrictions:
a) Roughness B prevails upwind for greater of at least 2,600 feet or 20 times mean roof height
b) If mean roof height is 30 feet or less, upwind distance is reduced to 1,500 feet
IRC Exposure B: “Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions having the size of single family dwellings or larger. Exposure B shall be assumed unless the site meets the definition of another type exposure.”
2) IBC Exposure C: “Exposure C shall apply for all cases where Exposure B or D does not apply.”
IRC Exposure C: “Open terrain with scattered obstructions, including surface undulations or other irregularities, having heights generally less than 30 feet extending more than 1,500 feet from the building site in any quadrant. This exposure shall apply to any building located within Exposure B type terrain where the building is directly adjacent to open areas of Exposure C type
terrain in any quadrant for a distance of more than 600 feet. This category includes flat, open country and grasslands.”
3) Exposure D: “Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance of not less than 5.000 feet or 20 times the height of the building, whichever is greater. Exposure D shall apply when the ground surface roughness immediately upwind of the site is B or C, and the site is within a
distance of 600 feet or 20 times the building height, whichever is greater, from an Exposure D condition as defined in the previous sentence.”
IRC Exposure D: “Flat, unobstructed areas exposed to wind flowing over open water, smooth mud flats, salt flats and unbroken ice for a distance of not less than 5,000 feet. This exposure shall apply only to those buildings and other structures exposed to the wind coming from over the unobstructed area. Exposure D extends downwind from the edge of the unobstructed area a
distance of 600 feet or 20 times the height of the building or structure, whichever is greater.”
Surface roughness D = Exposure D with these restrictions:
a) Roughness D prevails upwind for greater of at least 5,000 feet or 20 times building height
b) Exposure D extends inland from a shoreline greater of 600 feet or 20 times building height
Is choosing an Exposure Category now clear? If not, as a generality, roughness = exposure.
Memorizing all details isn’t necessary, but being able to recognize these letters is probably a good idea.
In my next article, I will give a Reader’s Digest version of how to determine Wind Exposure.

This entry was posted in Building Department, Pole Barn Planning, Pole Barn Homes, Barndominium, Pole Barn Design and tagged wind exposure, surface roughness, IBC Exposure B, IBC Exposure C, IBC Exposure D on June 28, 2022 by admin.

Wind Exposure and Confusion

WIND EXPOSURE AND CONFUSION
If you are a registered design professional, or a building official, then you are trying to make sense out of this subject on a daily basis. Most people who are selling buildings (either constructed or kit packages), tend to ignore wind exposure, or pretend it somehow doesn’t exist.
What adds into confusion, for all involved, is (even though written by same group of experts) IBC and IRC definitions do not exactly align!

Choosing a proper wind exposure is crucial to your building’s proper structural performance. Exposure C buildings must withstand a roughly 20% greater wind force than Exposure B and Exposure D, yet another 20%! This can result in one or more of deeper and/or wider column embedments, more concrete required to prevent uplift, larger columns and/or more closely
spaced, larger dimension and/or higher grades for wall girts and roof purlins, changes in truss design (larger and/or higher graded chord lumber, more webs, larger steel connector plates), ‘beefier’ connections, etc. In a nut-shell, it can change nearly every structural member and connection. To ignore proper wind exposure can result in catastrophic failures.
For utter confusion’s sake, I’ll list 2021 code sections (just in case you need some “put me to sleep” late night reading material.)
(HINT: At end, I include a broad generalization providing a close idea for most building sites.)
Picture entering a code book resembling a surrealistic painting by Salvadore Dali.
IBC Section 1609.4‐‐Exposure Category: “For each wind direction considered, an exposure category that adequately reflects the characteristics of ground surface irregularities shall be determined for the site at which the building or structure is to be constructed. Account shall be taken of variations in ground surface roughness that arise from natural topography and vegetation as well as from constructed features.”
IRC Section R301.2.1.4 Exposure Category: “For each wind direction considered, an exposure category that adequately reflects the characteristics of ground surface irregularities shall be determined for the site at which the building or structure is to be constructed. For a site located in the transition zone between categories, the category resulting in the largest wind forces shall apply. Account shall be taken of variations in ground surface roughness that arise from natural topography and vegetation as well as from constructed features. For a site where multiple detached one- and two-family dwellings, townhouses or other structures are to be constructed as part of a subdivision or master-planned community, or are otherwise designated
as a developed area by the authority having jurisdiction, the exposure category for an individual structure shall be based on the site conditions that will exist at the time when all adjacent structures on the site have been constructed, provided that their construction is expected to begin within year of the start of construction for the structure for which the exposure category is determined. For an given wind direction, the exposure in which a specific building or other structure is sited shall be assessed as being one of the following categories:”

Exposure determination is not relegated to a nice, comfortable chart or table. This section’s main part explains ground roughness variations from natural topography and vegetation need to be take into account when determining Exposure Category.
IBC Section 1609.4.1‐‐Wind Directions and Sectors “For each selected wind direction at which the wind loads are to be evaluated, the exposure of the building or structure shall be determined for the two upwind sectors extending 45 degrees either side of the selected wind direction. The exposures in these two sectors shall be determined in accordance with Sections 1609.4.2 and 1609.4.3 and the exposure resulting in the highest wind loads shall be used to represent wind loads from that direction.”
Here we get started in determining Exposure Category, but this process is three‐step from here.
Breaking this babble down to something making sense isn’t easy, but a list helps:
1) Select wind direction for wind loads to be evaluated
2) Two upwind sectors extending 45° from either chosen wind direction side are markers.
3) Use IBC Section 1609.4.2 and Section 1609.4.3 to determine exposure in those sectors
4) Exposure with highest wind loads is chosen for this wind direction
Got all this? If not, you aren’t the only one. But wait, there’s more! Tune in next time for yet
another fascinating installment!

This entry was posted in Pole Barn Structure, Pole Barn Design, Building Department, Pole Barn Planning and tagged wind exposure, Wind Exposure Category, wind load, IRC building code, vegetation, IBC building code, wind direction, topography on June 23, 2022 by admin.

Who is Responsible for Verifying Design Loads?

Roof truss top chord design loads of 5 psf (or less) are not adequate for roofing other than light gauge steel.

Any windows and/or doors provided by Seller are NOT wind-rated, unless specifically noted as such.

This entry was posted in Pole Barn Design, Building Department, Pole Barn Planning, Professional Engineer and tagged thermal factor, flat roof snowload, seismic zone, engineering changes, design criteria, calculation changes, design loads, roof snow exposure factor, wind exposure, allowable Foundation, ground snow load, maximum frost depth, occupancy category, wind speed on July 9, 2021 by admin.

Buildings Designed/Built to Code

Designed / Built to Code

Sounds pretty impressive to think you are going to be investing in a new building designed and/or built to “Code”.

Right?

Well – maybe not so much. To begin with “Code” happens to be bare minimum requirements to adequately protect public health, safety and welfare. This does not mean a structure built to “Code” will withstand all possible circumstances. As an example, residential structures (R-3) are designed so as there is a 2% probability of their design loads being exceeded in any given calendar year!

So, how does a consumer best protect their interests?

BE AN INFORMED BUYER

Whether investing in a complete building kit, or having a builder provide materials as well as erection labor – if you receive a proposal stating only “to Code” or not mentioning “Code” at all…..

RUN

All proposals and agreements for buildings should mention what Code and Code version is being used. IRC (International Residential Code) and IBC (International Building Code) do have some differences between them. Every three years there is a new Code version published. Each version has latest updated changes due to testing, research and new products being introduced. Your new building should either match your jurisdiction’s adopted Code version or (if no structural permits are required), most recent version.

ENGINEERING

Unless you are building within prescriptive ‘cook book’ restrictions of a Code, I am a firm believer of buildings being fully engineered. Not just engineered trusses (as an example) but every component and connection being checked and verified by a Registered Professional Engineer specific to your building’s features on your site. This is for everyone’s protection (not just yours, but also your provider and any hired builder).

WHAT TO LOOK FOR ON PROPOSALS AND AGREEMENTS

Beyond applicable Code version, there are other factors you should have included:

Ground Snow Load (Pg) in areas where it snows. Ground snow load is not the same as roof snow load, but is important as it affects drift zones on each side of roof ridges. In these areas, roof purlins often must be closer together, larger dimension or higher graded material to compensate for drifting.

Flat Roof Snow Load (Pf) is usually calculated from Pg and incorporates factors such as Occupancy (low risk buildings get a 20% reduction), wind exposure (an exposed building has snow blow off, a protected site has snow sit) and temperature (heated or unheated and well or poorly insulated). Some jurisdictions mandate a minimum Pf, ignoring applicable laws of physics.

No snow? Then Lr applies, rather than Pf. Lr is a reduced uniformly distributed roof live load ranging from a minimum of 12 to a maximum of 20 psf (pounds per square foot), depending upon the area being carried by a given member.

Design Wind Speed in either V (basic design wind speed, sometimes expressed as Vult) or Vasd, in mph (miles per hour). These values are directly correlated as Vasd equals V multiplied by square root of 0.6.

Wind Exposure – rarely mentioned and extremely important. Most buildings will be on Exposure C sites, meaning they must resist a 20% greater wind force than a fully protected Exposure B site. Become more knowledgeable by reading here: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/

If wind exposure is not delineated on a proposal or agreement, it is not a good sign.

Allowable Foundation Pressure – most people are not interested in having their buildings settle. This value relates to your site’s soil being able to support a given value per square foot of building weight INCLUDING roof and floor live (or snow) and dead (permanent) loads. Keeping it simple, easier to dig equals lower values. In an ideal world, a geotechnical engineer has tested your site’s soils and can provide an exact measure of soil strength in his or her report. Many providers assume a value of 3000 psf, this would exclude soils including any silts or clays and using this as a value could compromise structural integrity.

Seismic Zone: for single story wood or steel frame structures with low or no snow and more than just bare minimum design wind forces, seismic forces will not dictate structural design. However, they should be checked.

If you are negotiating with a provider or builder who is not clearly stating all of these factors, you are very well paying hard earned money for something you are not getting.

Contact your local jurisdiction so you are aware of what Code minimum requirements are. Ask your provider or builder for any additional investment to upgrade to a greater roof load and/or design wind speed – in most cases it is negligible and it allows you to make informed choices as to risk/reward.

This entry was posted in Pole Barn Structure, Professional Engineer, Pole Barn Design, Building Department, Pole Barn Planning and tagged allowable foundation pressure, wind exposure, flat roof snow load, ground snow load, International Building Code, design wind speed, International Residential Code, Registered Professional Engineer, seismic zone on June 16, 2021 by admin.

Building Department Checklist Part I

BUILDING DEPARTMENT CHECKLIST 2020 PART I

I Can Build, I Can Build!

Whoa there Nellie…..before getting all carried away, there are 14 essential questions to have on your Building Department Checklist, in order to ensure structural portions of your new building process goes off without a hitch. I will cover the first seven today, finishing up tomorrow, so you have a chance to take notes, start your own home file folder of “what to do before I build”. Careful preparation will be key to having a successful building outcome (whether post frame or some other structural building system).

Provide answers to these questions to your potential building providers!

IMPORTANT SIDE NOTE: Building Departments’ required snow and wind loads are absolute minimums in an attempt to prevent loss of life during extreme events. They are not established to prevent your building from being destroyed. Consider asking your providers for added investment required to increase wind and/or snow loads beyond these minimums.

#1 What are required setbacks from streets, property lines, existing structures, septic systems, etc.?

Seemingly every jurisdiction has its own set of rules when it comes to setbacks. Want to build closer to a property line or existing structure than distance given? Ask about firewalls. If your building includes a firewall, you can often build closer to a property line. Creating an unusable space between your new building and a property line isn’t very practical. Being able to minimize this space could easily offset a small firewall investment. As far as my experience, you cannot dump weather (rain or snow) off a roof onto any neighbor’s lot, or into an alleyway – so keep those factors in mind.

#2 What Building Code will be applicable to this building?

Code is Code, right? Except when it has a “residential” and also has a “building” version and they do not entirely agree with each other.

Also, every three years Building Codes get a rewrite. One might not think there should be many changes. Surprise! With new research even things seemingly as simple as how snow loads are applied to roofs…changes. Obviously important to know what Code version (e.g. 2012, 2015, 2018, 2021) will be used.

#3 If building will be in snow country, what is GROUND snow load (abbreviated as Pg)?

Make sure you are clear in asking this question specific to “ground”. When you get to #4, you will see why. Too many times we’ve had clients who asked their building official what their “snow load” will be, and B.O. (Building Official) replied using whichever value they are used to quoting. Lost in communication was being specific about “ground” or “roof” snow load.

As well, what snow exposure factor (Ce) applies where a building will be located? Put simply, will the roof be fully exposed to wind from all directions, partially exposed to wind, or sheltered by being located tight in among conifer trees qualifying as obstructions? Right now will be a good time to stand at your proposed building site and take pictures in all four directions, and then getting your B.O. to give their determination of snow exposure factor, based upon these photos.

#4 What is Flat Roof Snow Load (Pf)?

Since 2000, Building Codes are written with flat roof snow load being calculated from ground snow load. Design snow load has become quite a science, taking into account a myriad of variables to arrive with a specific roof load for any given set of circumstances.

Unfortunately, some Building Departments have yet to come to grips with this, so they mandate use of a specified flat roof snow load, ignoring laws of physics.

Make certain to clearly understand information provided by your Building Department in regards to snow loads. Failure to do so could result in an expensive lesson.

#5 What is “Ultimate Design” or Vult wind speed in miles per hour?

Lowest possible Vult wind speed (100 miles per hour) only applies in three possible states – California, Oregon and Washington for Risk Category I structures. Everywhere else has a minimum of 105 mph. Highest United States requirement of 200 mph for Risk Category III and IV buildings comes along portions of Florida’s coastline (although there are scattered areas nationally defined as “Special Wind Regions). Don’t assume a friend of yours who lives in your same city has your same wind speed. City of Tacoma, WA has six different wind speeds within city limits!

Vult and nominal design wind speed (Vasd) are different and an errant choice could result in significant under design (or failure). Make certain to always get Vult values.

#6 What is wind exposure (B, C or D)?

Please Take a few minutes to understand their differences:

(https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/).

A Building Department can add hundreds, or even thousands, of dollars to your project cost, by trying to mandate an excessive wind exposure. Once again, a good place for photographs in all four directions from your building site being shared with your Building Department. Some jurisdictions “assume” worst case scenarios. Meaning, your property could very well have all four sides protected and easily “fit” category B wind exposure requirements. However, your jurisdiction may have their own requirement for every site in their jurisdiction to be wind exposure C, no matter what. It’s their call.

#7 Are “wind rated” overhead doors required?

Usually this requirements enforcement occurs in hurricane regions. My personal opinion – if buying an overhead door, invest a few extra dollars to get one rated for design wind speeds where your building will be constructed. Truly a “better safe, than sorry” type situation.

I’ve covered seven most important questions for your Building Department Checklist, and they really weren’t so difficult, were they? Come back tomorrow to find out the last seven!

This entry was posted in Pole Barn Design, Building Department, Pole Barn Planning and tagged ground snow load, firewalls, Residential Building Code, Vult wind speed, wind exposure C, building setbacks, setbacks, nominal design wind speed, Building Code, wind exposure, flat roof snow load on August 25, 2020 by admin.

Getting the Best Deal on Your New Post Frame Building

A price quote is merely a number without a complete understanding of exactly what is or is not included in said quote.

You have requested quotes for your new post frame building from a dozen or more providers and actually gotten four back, even after having to hound all of them for pricing! Frustrating when you are ‘knocking at their door’ trying to spend your cash.

One quote stood out above all others with an exceptional price, so you place your order. Only after “everything” arrives and you try to assemble it do you find out what you thought you bought and what you really purchased are not quite equal.

Disappointing.

If you prefer to read books by starting with the last chapter, you can skip to there to find a solution.

Here are a few points to be aware of:

Will Your Building Meet Minimum Building Code Standards?

Those quotes you got….few, if any, will specify what loads your building are designed for.

Some of them will just be a list of materials! Are they right? Is there even enough there to construct a building?

Every quote should include (at a minimum): engineer sealed plans specific to your building at your site. Complete Building Code information – including Code version (there is a new one every three years), Ground snow load (Pg), Flat roof snow load (Pf), Design wind speed (Vult or Vasd), Wind Exposure (there is a big difference between Exposure B and C) and assumed soil bearing pressures.

You can easily acquire this information for yourself, so you have a point to check from: https://www.hansenpolebuildings.com/2019/01/building-department-checklist-2019-part-1/

If Code information is not on a quote, chuck it.

Do Roof Trusses Quoted Meet Your Needs?

Here is where investing in an engineered building comes into play, as your Engineer of Record (person who seals your building plans) should be reviewing prefabricated roof truss drawings for their adequacy for his or her building.

Planning on supporting a ceiling, either now or at a later date? If so a ceiling load of no less than five pounds per square foot (psf) should be indicated on engineered plans as well as a BCDL (Bottom Chord Dead Load) to match on sealed truss drawings.

At Hansen Pole Buildings, we ran into this situation so often, we decided to upgrade all trusses up to 40 foot clearspan to support a minimum five psf load.

How is Roof Steel Condensation Being Controlled? Most providers are not even going to mention this. Most of us prefer it not to rain inside of our new buildings.

I answer questions online every Monday. Problem/question number one is regarding condensation.

From cheapest up – a Radiant Reflective Barrier (aka bubble wrap – if going this route you only need single bubble, six foot wide rolls with an adhesive pull strip); Integral Condensation Control (https://www.hansenpolebuildings.com/2017/03/integral-condensation-control/); Sheathing with 30# felt; Closed cell spray foam.

Planning on insulating and finishing walls? If not using closed cell spray foam you will want to apply a Weather Resistant Barrier between wall framing and steel siding.

What Written Warranty Comes With Your Building?

If it does, how long does it last? What does it include? When it comes to Post Frame Building kits, Hansen Pole Buildings stands alone with a Limited Lifetime Structural Warranty (https://www.hansenpolebuildings.com/2015/11/pole-building-warranty/).

Are Assembly Instructions Included?

Hansen Buildings Construction Manual If not, there is plenty left to chance. Hansen Pole Buildings provides a fully illustrated, step-by-step 500 page Construction Manual. And, if you get stuck, there is unlimited FREE Technical Support from people who have actually assembled buildings!

How About Your Potential Provider?

How long have they been in business 2 years, 5 years? How about 18 years? How many post frame buildings have they provided? How about roughly 20 thousand buildings located in ALL 50 states!

Here is how to vet any potential provider: https://www.hansenpolebuildings.com/2015/01/pole-building-suppliers/

I promised you a solution (aka Last Chapter of Book)

We are offering to shop for you. Seriously? Yes! You provide up to three names of competitors to Hansen Buildings, where you can purchase a complete wood framed post frame building kit package, and we will shop them to get quotes for you.

Now we say three, because frankly, some people just are not very prompt or cooperative when it comes to getting back with price quotes.

Why would we do this? Comparing “apples to apples”, we know our price will beat theirs, every single time. We offer to do this for your peace of mind. We guarantee all other prices will be higher. And we will provide you with documentation to prove it!

There is a catch…..before we go shopping you have to place your order for your new Hansen Pole Building kit….. subject to us “proving our point” by going shopping. Your payment to us will not be processed for ten calendar days. Within seven days of order, you’ll have competitive quotes in hand, or our documentation of having hounded them every week day for a week trying to get pricing for you (seriously, if you have to hound someone for a price, what kind of after sale service will you get?).

After we email you proof, if you seriously want to purchase from one of these competitors, just let us know before ten days pass and we tear everything up and go away friends.

This entry was posted in Barndominium, Pole Barn Planning, Shouse, Trusses, Budget, Pole Barn Design, Pole Building Comparisons, Post Frame Home, Building Department and tagged wind exposure, building code standards, complete building code information, ground snow load, flat roof snowload, design wind speed, engineer of record, engineer sealed building plans, Warranty on February 18, 2020 by admin.

Free Post Frame Foundation Building Calculator

Free Post-Frame Building Foundation Engineering Calculator

No, such a thing as a free post-frame building foundation engineering calculator does not exist. However there always seems to be someone out there who is in search of “engineering for free”.

Reader KELLY writes:

“Guru,

Do you have a link to a pole foundation engineering calculator?

Looking for column depth / diameter for:

40x60x14

10 ft column spacing

35 PFS load

115 wind load.

No floor for constraint.

thanks.”

Mike the Pole Barn Guru responds:

There is no such thing as a “pole foundation engineering calculator” therefore, there is also no link to one. The design of post frame (pole) building foundations is one which is best left in the hands of RDPs (Registered Design Professionals – architects or engineers). When provided with all the pertinent information about your proposed building, they can design not only a structurally sound column embedment, but also your entire structure (which I whole heartedly recommend).

You’ve provided some of the information a RDP would require, but I will expand upon it:

Will the building have adequate sheathing (which could be roll formed steel roofing and siding) to transfer wind loads from roof to ground through endwalls? And will the sheathing be adequately fastened to underlying frame to take advantage of sheathing stiffness? If yes, diaphragm design can be utilized in your building design.

The difference in forces carried by sidewall columns with and without an adequate diaphragm is a factor of 4! If diaphragm design cannot be utilized, expect significantly larger columns, deeper holes and more concrete around columns.

What type of soil is at building site? Strength and stiffness of your soil will impact both depth and diameter of holes.

How are you measuring your 14′? It should be from bottom of pressure preservative treated splash plank, to underside of roofing at sidewalls. It does make a difference.

Does your building have overhangs?

What is the roof slope?

What is wind exposure at your site? The difference in force against columns between Exposure B and Exposure C is roughly 20%.

In the event you are not interested in procuring services of a RDP, the NFBA (National Frame Building Association) has available a Post-Frame Design Manual and you could attempt to do calculations yourself. For more information please see: https://www.hansenpolebuildings.com/2015/03/post-frame-building-3/.

Of course you could always invest in a fully engineered post frame building kit package. Besides engineer sealed blueprints and calculations, you would also get materials delivered to your site and a multi-hundred page Construction Manual to guide you through to a successful completion.

This entry was posted in Pole Barn Questions, Pole Barn holes, Pole Barn Design, Constructing a Pole Building, Pole Barn Planning, Pole Barn Structure, Trusses and tagged RDP, roof slope, NFBA, overhangs, post frame building kit package, sheathing, building site soil, wind exposure on February 22, 2019 by admin.

500 Year Storm and Wind Exposure

500 Year Storm and wind exposure.

Allstate® Insurance has a TV commercial featuring actor Dennis Haysbert. Haysbert sits in an open field and questions why there have been 26 “once in 500 years storms” in last decade, when term alone implies they should only happen every 500 years.

View Allstate® commercial here: https://video.search.yahoo.com/search/video?fr=crmas&p=Allstate+once+in+500+years+storm+commercial#id=1&vid=b134fa05aba0ff046debaea22891c23d&action=click

IBC (International Building Code) in Chapter 16 (https://codes.iccsafe.org/public/document/IBC2018/chapter-16-structural-design) Table 1604.5 lists Risk Category of Buildings and Other Structures.

Risk Category I includes buildings representing a low hazard to human life in event of failure – agricultural buildings and most detached residential accessory buildings fit into this category.

Risk Category II would be most homes and many low risk commercial, industrial and manufacturing buildings.

Risk Categories III and IV cover buildings with high occupancies or are essential to fire, life and safety (like fire stations).

IBC offers Minimum Design Loads modified by a given factor depending upon Risk Category. For a previous article about this subject please see: https://www.hansenpolebuildings.com/2018/08/minimum-design-loads-and-risk/.

Reflect, if you will, back upon paragraph one above and a 500 year storm.

wind damage Risk Category I buildings are based upon a once in 25 year probability of minimum design loads being exceeded. Risk Category II once in 50 years, while Categories III and IV are once in 100 years.

So, what does one do to protect against a once in 500 years storm?

When planning your new post frame building, this becomes relatively easy – have it designed for greater loads than bare Code required minimums. While this sounds simple, very few clients consider asking for it and even fewer post frame building sales people offer it!

Why would it not be offered?

Price

People are selling buildings using price rather than value. Most are afraid to suggest increasing building price by a few percentage points, because they think it will cost them a sale!

I know there are numerous members in our post frame industry who are reading this article. To you I offer this challenge – as an option start offering to every potential client an ability to have their building designed for an extra even five or 10 psf (pounds per square foot) of snow load (in snow country of course). And, give them an option of withstanding greater wind speeds than Code minimums. Even upgrading wind Exposure B sites to Exposure C will increase ability to resist wind loads by about 20%.

A short wind exposure story can be found here: https://www.hansenpolebuildings.com/2011/11/wind_exposure/.

Now, sell your potential client benefits of having last building standing when Mr. Haysbert’s storm rolls through.

Sold itself, didn’t it?

This entry was posted in Pole Barn Design, Building Department, Pole Barn Planning, Pole Barn Structure and tagged risk category 1 building, Risk Category II, Risk Category III, Risk Category IV, wind exposure, snow load on November 1, 2018 by admin.

It Is Exactly the Same Building Part I

Well, maybe not exactly the same building.

In April of this year we had a client invest in a brand new 36 foot wide by 60 foot long post frame building kit package with a 16 foot eave height. Three months later, the building has been delivered, and one of the group which ordered the building sends us a quote on “exactly the same building” from a worthy competitor. And, of course, the competitor’s quote is way less expensive!

Now the competitor’s sales person advised the client the quotes were exactly the same, other than he had quoted a 25 psf (pounds per square foot) roof snow load, whereas we provided a 40 psf load, which is 60% more snow carrying capacity!

Turns out there were maybe a couple of other differences as well……

Things we have and they do not:

4/12 roof slope vs. 3/12 The steeper roof slope will look less industrial as well as more readily will shed snow.

C wind exposure vs. B wind exposure (for a detailed explanation of wind exposure please read here: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/). The benefit of an Exposure C wind load is it makes the building roughly 20% stronger in resisting wind forces, than the B exposure.

12″ enclosed overhangs vs. 18″ open overhangs. Not only are enclosed overhangs far more attractive, they provide ventilation and eliminate the wonderful nesting locations for flying critters which are provided by open overhangs.

12’x14′ residential overhead door vs. 14’x12′ commercial overhead door. If the client wants to get something taller than 12 foot through the other guy’s door, it just isn’t going to fit no matter how big a run one gets at it. Residential overhead doors come with “dog eared” openings and a far more attractive in a residential setting. Here I discuss why 14 foot wide doors are not what they are cracked up to be: https://www.hansenpolebuildings.com/2016/05/14-foot-wide-doors/.

One more entry door. Insulated commercial steel entry doors with steel jambs do not come cheap, especially when they are four foot wide!

Integrated J Channel on windows. So much easier to install than having to cut four pieces of steel trim to fit around a window and have them not leak!

The reflective radiant barrier with pull strip attached adhesive tab on one side vs. Metal Building Insulation (MBI) under the roof steel to minimize condensation challenges. My personal horrors of installing MBI can be visited here: https://www.hansenpolebuildings.com/2011/11/metal-building-insulation-in-pole-buildings-part-i/.

Lifetime paint warranty on steel vs. 40 year pro-rated. Your post frame building is going to be around for a long time, might as well have the best paint warranty available to minimize the effects of fade and chalk.

Base trim – keeps those creepy crawling critters from entering the building through the high ribs of the wall steel.

Top of wall trims – Even though roll formed steel siding lengths are controlled by a computer, they do vary slightly from panel to panel. The bottom of the panels should be kept at the same height as “stair steps” at the base of the walls is quite noticeable. Easiest way to hide any variants is to place the top edge into a piece of trim which covers any fluctuations.

Jamb trim on Overhead Door– exposed wood overhead door jambs are very popular in some parts of the country, however they do turn grey and then eventually black if not kept painted. The idea of a steel covered post frame building is to minimize future maintenance. Having to paint raw exposed wood does not meet with this criteria.

Heard enough? No? Then come back tomorrow for Part II. You won’t be disappointed!

This entry was posted in Pole Barn Design, Pole Building Comparisons, Building Overhangs, Pole Barn Planning, Pole Barn Structure, Pole Building Doors, Ventilation and tagged base trim, integrated J channel, lifetime paint warranty, reflective radiant barrier, wind exposure, enclosed overhangs, roof slope, commercial entry door on July 26, 2017 by admin.

Airplane Hangar Exposure C

Why Your Airplane Hangar is Probably Exposure C

I had the joy of growing up “hanging out” (pun intended) at airplane hangars and doing a lot of flying including having my hands on the controls of a Cessna 182 for many hours before I became a teen. One thing for certain about airplane hangars – they are always built with the idea of being able to take off and land the airplanes which are housed inside, somewhere in the general vicinity of the hangar!

Yes, I know this reads like a mission for Captain Obvious.

After all, what would be the use of a hangar if not to be able to fly the plane?

Airplanes do require a certain amount of space to be able to land and the runway better be fairly flat, as well as not obstructed by things like other buildings and trees. Those tall things generally tend to make the life of a pilot miserable.

A Hansen Pole Buildings client recently ordered a new post frame hangar with an Exposure B for wind. This is the short version of the definition of a B exposure:

Wind Exposure B is a site protected from the wind in all four directions, within ¼ mile, by trees, hills or other buildings. This would include building sites in residential neighborhoods and wooded areas.

Whereas, Wind Exposure C is a site where there is open terrain with scattered obstructions having heights generally less than 30 feet high. (Commonly associated with flat open country and grasslands).

If you are curious and want to know all there is to know about Wind Exposure here is some good late night reading: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/.

Being a fairly simple guy, I am scratching my head at this wondering how the plane is going to takeoff through all of this protection.

Hansen Pole Buildings’ Managing Partner Eric did a quick Google search of the site and let me know it is in the middle of a field!

In the event you are in need of a new airplane hangar and you are getting quotes from providers which do not specifically indicate on the Exposure C for wind, chances are good you are being quoted for Exposure B. The difference in design strength for resistance to wind loads is roughly 20%.

Think about it…..

Do you actually want your several hundred thousand dollar airplane to be parked in a building which is under designed for the actual wind conditions which could be applied to the building?

This entry was posted in Pole Barn Questions, Pole Barn Design, About The Pole Barn Guru, Building Department, Pole Barn Planning and tagged wind exposure, Wind Exposure Category, airplane hangar, Wind speed maps on April 12, 2017 by admin.

Wind Speed

Just Another Windy Conversation

Hansen Pole Buildings’ Designer Rick asked me this question today: “Mike, I got a guy who wants to compare an over wind rated building to a Quonset hut at 150 mph” (miles per hour).

Of course I jump right onto this one off the get go, “So the Quonset people have an engineer’s seal on a 150 mph building?” (Just call me a skeptic) “And even if they do – how functional is a Quonset hut?”

I’ve pointed out some Quonset challenges in a previous article: https://www.hansenpolebuildings.com/blog/2011/07/quonset-huts/

Rick, “I’ll check it, but for now I am about to call this guy back, the question is how high can I go up on the wind load and be reasonable?”

Hansen Pole Buildings has created a proprietary pole building design and pricing program which does some truly amazing things….but Rick had me stumped with this one!

retail-pole-barn For this particular client’s building site the Code wind speed design would be for 90 mph. There is a nifty little formula to convert mph to wind pressure (.00256 X wind speed squared). This makes a 150 mph wind speed applying 277% of the load force of 90 mph.

On this particular 40’ x 60’ x 13’ pole building, the difference in investment for the 277% more force….?

Under 20% more!!

On many pole buildings, designing for extra wind resistance is minimal. For anyone considering a new building, I would certainly encourage them, at the least, to investigate an increase of 10 or 20 mph, at the least.

Next Rick decided to try a 200 mph wind speed (even though no Building Department anywhere in the United States has this requirement). We are now talking wind speeds only an EF-5 tornado would surpass!

Not surprising – our program would design the building…..at 200 mph!!

The sidebar to this story…..

The client wants to be able to pull a trailer out of his new building to live in if his house goes down!

This entry was posted in Uncategorized and tagged pole barn wind speed, wind design speed, wind exposure on April 14, 2015 by admin.

Dear Guru: What is the Highest Wind Speed You Design For?

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays. With many questions to answer, please be patient to watch for yours to come up on a future Monday segment. If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: Hello, I am interested in this construction method, but I was wondering what is the maximum wind load that your buildings can take? Thank you for your time. WHISTLING IN THE WIND

DEAR WHISTLING: We’ve designed pole buildings resist wind speeds up to 170 miles per hour. For all practical purposes, we could design for any wind speed and exposure condition desired.

DEAR POLE BARN GURU: What is the mil thickness of plastic to lay down in a

pole barn before the rock for moisture protection and do you carry the

product? MOIST IN MISSOURI

DEAR MOIST: If you are not intending to pour a concrete floor, then a black visqueen of at least 6 mil thickness should be used. For use under a concrete slab, the best product would be A2V insulation, which is available for direct purchase at:

www.buyreflectiveinsulation.com

There is an insulation calculator on the website to help you figure out how many rolls to purchase.

DEAR POLE BARN GURU: I am planning on constructing a 48’ x 48’ roof only pole barn. I would like to put a couple bags of sakcrete in the bottom of hole and then pour the rest when I pour the pad. I am planning on putting rebar down into both sakcrete and have it stick up so it will connect to the other concrete. Will this be ok? If not, recommendations? STUCK ON SAKCRETE

DEAR STUCK: Sakcrete can be a great and practical solution to many problems, however this application is not any of those.

To begin with, a couple of bags of sakcrete will not provide an adequate footing under the columns. With your loading conditions, a 30 inch diameter by eight inch thick footing pad would be required. It would take eight 90 pound bags of sakcrete to pour each footing. It may not be practical to haul home almost four tons of sakcrete.

Even if you do pour adequate footings, you are quickly going to find out how challenging it is to work on a roof only structure, where the columns are not stabilized. Even with the columns braced in all four directions (which is going to require investing in a lot of extra material), there is going to be a significant amount of movement in the columns, as the roof system is framed and roofing installed.

Why fight it?

My recommendation would be to just concrete backfill the columns and footings monolithically in a single pour. It will take about nine yards of redi-mix, so it isn’t like there is going to be some big savings by waiting to pour the balance of the holes with the floor.

This entry was posted in Pole Barn Questions, Pole Barn Design, Building Department and tagged wind exposure, floor moisture protection, sakcrete, reflective radiant barrier on November 4, 2013 by admin.

Tornado! What We Didn’t Learn in Moore

Tornado! What We Didn’t Learn in Moore

wind damage On the afternoon of May 20, 2013, an EF5 tornado, with peak winds estimated at 210 miles per hour (mph), struck Moore, Oklahoma, and adjacent areas, killing 23 and injuring 377 others. The tornado was part of a larger weather system which had produced several other tornadoes over the previous two days. The tornado touched down west of Newcastle, OK staying on the ground for 39 minutes over a 17-mile path, crossing through a heavily populated section of Moore. The tornado was 1.3 miles wide at its peak. Despite the tornado following a roughly similar track to the even deadlier 1999 Bridge Creek-Moore tornado, very few homes and neither of the stricken schools had purpose-built storm shelters

Between 12,000 and 13,000 homes were destroyed or damaged, and 33,000 people were affected. Most areas in the path of the storm suffered catastrophic damage. Entire subdivisions were obliterated, and houses were flattened in a large swath of the city. The majority of a neighborhood just west of the Moore Medical Center was destroyed. Witnesses said the tornado more closely resembled “a giant black wall of destruction” than a typical twister.

The Oklahoma Department of Insurance said the insurance claims for damage would likely be more than $1 billion. Total damage costs have been estimated as high as $2 billion.

How did all of this happen?

Home builders protest the estimated cost of $2,000 to $6,000 for home tornado shelters would make houses unaffordable. How much is a human life worth? If it is one of my loved ones, a whole bunch more than this.

Some of the fault might be placed upon local government, as well as the Building Departments which provide recommendations for design wind loads for structures. The design wind speed for the Moore area, by Code? 90 mph or roughly 20.736 psf (pounds per square foot). Consider 210 mph is over 107 psf – more than FIVE TIMES the design wind load!!

Anyone wonder why the photos were as astonishing as they were?

Not trying to be confusing….the values we use for wood design are based upon 40% of a 5^th percentile figure. As an example, if 100 random pieces of lumber were tested for strength, and the values plotted on a curve, take the 5^th lowest value from the bottom, and use 40% of this value. This does afford a certain amount of cushion for safety in designing wood structures.

At the least, I’d recommend increasing the required design wind speed to something in the range of 150 mph (57.6 psf) to 170 mph (74 psf). While this would not eliminate all destruction, it would certainly tend to be better than what exists currently.

In examining a fairly significantly sized full enclosed pole building kit package (40 feet wide by 60 feet long and 14 foot tall), the price increase from 90 to 150 mph design wind speeds was just over 10% (not much more than $1200).

Post frame construction lends itself naturally to being resistant to extreme wind loads. With columns embedded in concrete backfill, there is no weak point at ground level, as found in conventional stick frame construction, or manufactured housing.

With a minimal number of mechanical (nails, etc.) connections, as compared to stud wall buildings, pole buildings run a far lower risk of compromising these crucial joints. Over the years when I have examined “why” buildings fail (either pole buildings or stick framed), it was most often the connections which failed.

Play it safe – play it in a post frame building designed to actually support the types of loads with which it could be hit.

This entry was posted in Pole Barn Design, Pole Barn Structure and tagged storm shelter, wind loads, wind exposure, damaged homes on June 20, 2013 by admin.

Things You Never Wanted to Know About Snow Load

Yes I know, it is white (at least it starts out that way).

From a design standpoint there are lots of things to know about snow loads.

Cautionary Warning: The information contained herein is fairly technical in nature. We use ALL of this information in the design of your new Hansen Pole Building. Some clients will think this is all very cool, for others, it may cause your head to explode. I’ve been waiting three decades to pass along this information to a client, as I’ve always felt the understanding of it is pretty impressive.

1. GROUND SNOW LOAD (otherwise known as Pg). This is based upon a once in fifty year (probability of event greater than design loads happening is 2% in any given year). The use of unrealistically high Pg values causes issues with the design for drifting snow.

The International Code specifies design snow loads are to be determined according to Section 7 of a document called ASCE 7. This document provides for all roof snow loads to be calculated from ground snow loads, however not every Building Department follows this procedure. When discussing snow load with anyone, it is crucial to have a clear understanding as to if the load is a ground or flat roof snow load.

Pf is FLAT ROOF SNOW LOAD – If, as a consumer, your concern is snowfall and you want to upgrade the ability of your building to carry it, THIS is the value to increase. Often changes of five or 10 pounds per square foot result in minimal differences in cost.

Pg is converted to Pf by this formula:

0.7 X Ce X Ct X Is X Pg = Pf

2. Ce is the wind exposure factor for roofs.

For an Exposure B or C for Wind; Fully Exposed = 0.9; Partially Exposed = 1.0; for fully sheltered (e.g. nestled in tightly amongst conifer trees as an example) Exposure B = 1.2, Exposure C = 1.1 (how you could have Exposure C and fully sheltered is beyond me)

We use partially Exposed (Ce = 1.0 as a default)

3. Ct is the effect of temperature (building heating), where:

Ct = 1.0 for heated structures (climate controlled)

Ct = 1.1 for Structures kept just above freezing and others with cold, ventilated roofs in which the thermal resistance (R-value) between the ventilated space and the heated space exceeds 25h – ft^2 – degreesF/Btu

Ct = 1.2 Unheated

We use Ct = 1.2 as the default value

Most truss designers will use a Ct value of 1.0 or 1.1 in their designs. This results in a decrease in the ability of the roof to carry snow loads. These values should only be used when appropriate.

4. “Is” is the IMPORTANCE FACTOR

ASCE I is a structure which is a low hazard to life in the event of a failure. Is = 0.87

ASCE II residences and frequently occupied commercial buildings (a warehouse or storage building is probably ASCE I) Is = 1.0

ASCE III Is = 1.1

ASCE IV Is = 1.2 (these are “essential” essential facilities – police/fire stations, hospitals)

5. There is also a Minimum Roof Live Load (known as Lr) of 20 psf (defined by Code) (psf = pounds per square foot) which accounts for weights such as construction loads, when Pg values are very low.

Lr is adjusted based upon the area the roof member supports and can be as low as 12 psf, in cases where a roof member supports over 600 square feet of area.

Doing the math, it would be unusual, using the laws of physics, for Pf to be greater than Pg – however, some jurisdictions have established Lr values which defy the laws of physics (e.g. State of Oregon, where most of the state has a minimum Lr of 25 psf – exceptions being some locations along the coast, where it is 20).

From Pf, Pr (Pressure on the roof) values are calculated depending upon whether the roof is a slippery surface or not, whether building is heated or not and the slope of the roof.

The Top Chord Live Load (TCLL) of any roof trusses will be the greater of Pr or Lr.

6. Duration of Load (DOL) for Snow is typically 1.15. DOL can play a part in some snow areas, where the Building Official (BO) has made the determination snow will remain upon the roof for extended time periods. Some Examples of this include Higher elevations in Utah and Kittitas County, WA where the BO has declared DOL = 1.0. In areas with little or no snowfall (where Lr > Pr) DOL = 1.25.

Yes, I know this is a lot of stuff to carry around in your head. Trust me, I know all too well, and my character analysis consistently reads “does not like numbers”! All these numbers and “code requirements” are why we not only ask, but insist you must take the page of our quote with the Design Criteria to your building department to get their blessing on it, and ask if there is anything else they require. With over 7000 building departments in the U.S., it would be the greatest feat on earth if we could keep up with all of them, and which ones change on any given day. My last caution is to be careful when asking your building department about snow load. Be sure you keep “roof” and “ground” snow loads separate. Because when it comes to getting your building designed, priced and finally plans signed off by your building department, there is a difference!

This entry was posted in Uncategorized and tagged ground snow load, International Building Code, wind exposure, flat roof snow load on February 3, 2012 by admin.

Building Codes: Wind Exposure C

We all know what Assume Means…

Bob is a builder in Northern California. He made a request for a quote on a building recently, via the Hansen Pole Buildings website.

The building he had in mind was to be 30’ wide x 80’ long. Bob told me the roof snow load was 100 pounds per square foot (psf) and wind speed 60 to 100 miles per hour (mph).

Bob called to discuss the project, which was to have one long sidewall open, so recreational vehicles, tractors and other equipment could be parked. I asked Bob how wide the openings between the sidewall columns would need to be – to which he replied 12’. Quickly doing the math, I suggested he might want to consider 84’ in length, as 12’ evenly divides into 84’. Bob liked that idea.

We discussed wind exposure. I asked Bob, “If you stand in the middle of the building site, with your arms parallel to the ground, and at 90 degrees to each other, and then turned in a circle, would the area between your arms ever be exposed to the wind?” This would be Exposure C. The alternative being a site which is protected from the wind on all sides, or Exposure B. Bob advised, once the three walls were up, it would be protected from the wind, because the “local winds never come from the open side”.

Somehow, I just do not think we were communicating.

For once, I listened to the little voice in my head and suggested to Bob that he give me the address of the site and I would call the Building Department to verify the loading requirements. While the building purchaser must ALWAYS confirm the code and loading information with their Building Department prior to placing a building order, I felt an ounce of prevention would be worth a pound of cure in this case.

Now Bob has been a registered contractor in California for over five years, in the area where the building will be constructed. The pleasant lady at the Building Department even guessed who he was, when I gave her the jobsite address. Obviously, he is known, and knows the area.

Well it turns out the design roof snow load was 60 psf, not 100. This will save Bob’s client thousands of dollars. The wind speed requirement is for 85 mph, however the entire county uses C for wind exposure.

There is a moral to all of this. Just because one hires an experienced registered contractor to construct a building, does not mean the contractor necessarily knows or understands the proper design criteria. Having the correct information on loads, saved the building owner thousands of dollars by using the correct snow load, and prevented a possible collapse from using an incorrect (and under designed) wind exposure.

This entry was posted in Building Department, Pole Barn Planning and tagged design criteria, building codes, wind exposure on November 7, 2011 by admin.