# 4×4 or Double 2×4 Bay Roof Purlins?

4×4 or Double 2×4 for 12’ Bay Roof Purlins?

“If you have trusses spaced at 12 feet, can a 4x4x12 or two 2x4x12’s span the distance given the minimal snow loads in Arkansas? I know this is question #2 but what kind of joist hangers do you use (Simpson Number or equivalent) for purlin attachment to trusses?”

We typically would use 2×6 #2 on edge for these recessed (between truss pairs) roof purlins. Here are the calculations:

Assumptions:

Roof slope = 4:12 (18.435° roof angle)
Trusses spaced 12-ft. o.c.
Purlin span = 11.75-ft.
Purlin spacing = 24 in.
Purlin size 2″ x 6″ #2
Roof steel dead load = 0.63 psf steel American Building Components catalogue
Roof lumber dead load = 62.4 pcf * 0.55 lbs/ft.3 / (1 + 0.55 lbs/ft.3 * 0.009 * 0.19) * (1 + 0.0019) * 1.5″ / 12 in./ft. * 5.5″ / 12 in./ft. * (12′ – 3″ / 12 in./ft.) / 12′ / (24″ / 12 in./ft.) psf in purlin weight based on 0.55 G NDS = 0.963 psf

Bending Stresses

Fb: allowable bending pressure
Fb‘ = Fb * CD * CM * Ct * CL * CF * Cfu * Ci * Cr
CD = 1.25 NDS 2.3.2
CM: wet service factor
CM = 1 because purlins are protected from moisture by roof
Ct: temperature factor
Ct = 1 NDS 2.3.3
CL: beam stability factor
CL = 1 NDS 4.4.1
CF: size factor
CF = 1 (not applicable to SYP)
Cfu: flat use factor
Cfu = 1 NDS Supplement table 4A
Ci: incising factor
Ci = 1 NDS 4.3.8
Cr: repetitive member factor
Cr = 1.15 NDS 4.3.9
Fb =1000 psi NDS Supplement Table 4-A
Fb‘ = 1000 psi * 1.25 * 1 * 1 * 1 * 1 * 1 * 1 * 1.15
Fb‘ = 1437.5 psi

fb = (purlin_dead_load + Lr) * spacing / 12 * cos(θ) / 12 * (sf * 12 – 3)2 / 8 * 6 / b / d2 * cos(θ)
Lr = 20 psf using the appropriate load calculated above
fb = 21.593 psf * 24″ / 12 in./ft. * cos(18.435) / 12 in./ft. * (12′ * 12 in./ft. – 3″)2 / 8 * 6 / 1.5″ / 5.5″2 * cos(18.435)
fb = 1060 psi ≤ 1437.5 psi; stressed to 73.7 %

Deflection

Δallow: allowable deflection
Δallow = l / 180 IBC table 1604.3
l = 141″
Δallow = 141″ / 180
Δallow = 0.783″
Δmax: maximum deflection
Δmax = 5 * Lr * spacing * cos(θ * π / 180) * (sf * 12 – 3)4 / 384 / E / I from http://www.awc.org/pdf/DA6-BeamFormulas.pdf p.4
E: Modulus of Elasticity
E = 1400000 psi NDS Supplement
I: moment of inertia
I = b * d3 / 12
I = 1.5″ * 5.5″3 / 12
I = 20.796875 in.4
Δmax = 5 * 20 psf / 144 psi/psf * 24″ * cos(18.435° * 3.14159 / 180) * (12′ * 12 in./ft. – 3″)4 / 384 / 1400000 psi / 20.796875 in.4
Δmax = 0.559″ ≤ 0.783″

2×4 #2 and 4×4 #2 Southern Pine have Fb values of 1100

Sm (Section Modulus) of a 2×6 is 7.5625; (2) 2×4 nailed together would be 1.5″ width x 3.5″ depth^2 x 2 members = 6.125 I would = 10.71875; 4×4 would be 7.146 with I = 12.5052

The (2) 2×4 would be stressed to 82.7% in bending however Δmax = 1.085″ so would fail due to being over deflection limits

How about a 4×4? 70.9% in bending Δmax = 0.9296″ so would also fail due to being over deflection limits

For our 2×6 purlins, we specify a Simpson LU26

# Building Department Checklist 2019 Part 1

BUILDING DEPARTMENT CHECKLIST 2019 PART I

I Can Build, I Can Build!

(First published six years ago, it was more than past time to update to reflect current code requirements!)

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 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 post frame building outcome.

#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 the small investment of a firewall. 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. IBC (International Building Code) only applies to post frame buildings, not IRC (International Residential Code:

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 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 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. Now 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.  Don’t assume a friend of yours who lives in your same city has your same wind speed.  The city of Tacoma, WA has six different wind speeds within city limits!

Vult and nominal design wind speed Vasd are NOT the same thing. Make certain to always get Vult values.

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

Take a few minutes to understand the differences:

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 the 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!

# When is it Time to Remove Roof Snow?

Regardless of what side of the climate change argument one is on – it has been snowing in Massachusetts this winter.

A lot.

Late January’s Winter Storm Juno alone brought up to 36 inches of snow in some parts of Massachusetts. https://www.weather.com/storms/winter/news/winter-storm-juno-snow-totals-wind-gusts

As if Juno wasn’t enough, another storm followed – leaving so much snow on the ground it forced the postponement of the celebratory parade through Boston for the Super Bowl Champion New England Patriots. https://www.cbsnews.com/news/flash-freezing-now-the-big-concern-in-northeast/

So, how much snow is too much for one’s roof?

As a basic rule of thumb, consider saturated snow weighs in at approximately 20 pounds per cubic foot. This weight is based upon a 25% moisture density, which may be conservative or liberal, as the actual moisture content of snow can range from approximately 1% to 33%.

Using the 20 pounds per cubic foot, this means every inch of snow will add 1-2/3 pounds per square foot of weight!

Any ice build-up on roofs would need to be added in as well. Use 5.2 pounds for each inch of ice depth.

For those who want to get scientific, the actual roof snow load can be checked by cutting a one foot square the full depth of the snow and ice build-up on the roof, dumping into a plastic bag and weighing the contents.

Modern buildings are designed for a snow load which assumes the roof snow load will be exceeded anywhere from once in 25 to once in 100 years, depending upon the Risk Category of the structure. The actual International Building Code language on risk categories can be read at: https://publicecodes.cyberregs.com/icod/ibc/2012/icod_ibc_2012_16_par023.htm

Buildings which were not constructed under Code requirements are often at far greater risk to collapse under snowfall. When rain falls upon snow, the weight of the roof snow can increase rapidly. Heating a building, in an attempt to melt the snow off a roof, can result in ice dams at the eave sides of the building – compounding the load problems.

Please be aware of the potential dangers of shoveling or raking snow from a roof. Besides the potential damage to the roofing materials and structure, there are such factors as a person sliding off the roof, falling off a ladder, overexerting themselves, or injury from snow sliding on top of them.

I can’t make recommendations on when to remove snow from any particular roof. It is up to the individual building owner to consider the benefits and dangers of snow removal and determine their own course of action. If your structure is in question, it is always best to consult a registered professional engineer.

# Revolutionary Roof Monitor System

Revolutionary Roof Monitor™ System Poised to Transform Market

Most people have the mistaken belief International Building Code (IBC) snow loading requirements will give them a roof structure which will hold up literally forever. The truth could not be further from this belief!

All buildings are categorized in the IBC by Risk Category (See https://publicecodes.cyberregs.com/icod/ibc/2012/icod_ibc_2012_16_par023.htm )

Each Risk Category has a multiplier to the roof snow load which relates to the probability of the design load being exceeded. For Category I, it is once in 25 years. Category II, once in 50 years. Categories III and IV once in 100 years.

Buildings can be designed to IBC snow load requirements and yet still fail!!

Still in the planning stages? Then the solution may be to either increase the design roof snow load, or to building to a higher Risk Category.

For existing buildings with valuable contents or very large buildings, technology now offers a safeguard.

Across the country, businesses are preparing for several more months of snow and forecasts call for an abnormally wet winter, roof collapses continue to make headlines. Collapses this year alone have already caused millions of dollars in damage and revenue loss, the elimination of hundreds of jobs, serious injuries, and numerous deaths.

If there were ever a time to reevaluate how to better protect roofs, this is it.

RoofMonitor™ is more than just reevaluation. It’s a revolution.

Developed by roofing industry veteran Brad Beldon, Roof Monitor™ is the first and only technology-based system designed to monitor live loads of snow and water. Roof Monitor™ has been created, tested, and perfected during the last decade, dramatically updating an antiquated process which — up until now — has relied upon rough estimates and gut-checks, all complicated by the fact clearing snow from a roof too early can be just as expensive a mistake as waiting too long.

Roof Monitor eliminates surprises and guesswork. Providing real-time data courtesy of wireless sensors, the system helps building owners and professional roofers make fact-based decisions about snow and water removal to save lives, jobs, and money.

“Roof Monitor™ received our first round of inventory in November of this year,” says Beldon. “We are ready to go, and yet, I know there are thousands of roofs blanketed with snow that will have to wait until spring to install our system. It’s been frustrating and often heartbreaking watching reports of collapses this year, knowing that we finally have the means to prevent many of them.”

A new video details the inspiring Roof Monitor™ backstory, as well as the intricacies of the system. (Watch the video here: https://www.youtube.com/watch?v=bPpy3NRULFQ)

How Roof Monitor™ operates, at-a-glance:

•     Wireless sensors. Patent-pending, wireless sensors installed on the exterior surface of the roof measure live loads and provide real-time information on even small changes in the environment.
•     Ethernet-based controllers. Roof Monitor™ controllers receive the wireless signal from sensors and send data to multiple redundant cloud-based servers in data centers across the country for added security.
•     Web-based interface. The Roof Monitor™ user-friendly, web-based interface delivers a pictorial representation of live loads providing the customer real-time data at their fingertips. The custom, intelligent interface works with any operating system and uses inferential data to reduce false alarms.
•     On-call monitoring and alert service. Roof Monitor™ monitoring and alert service operators have access to live data and, when it is necessary to take action, can dispatch information simultaneously to multiple users, including service representatives.
•     Certified dealer network. In a strategic alliance with National Roofing Partners, Roof Monitor™ offers a certified dealer network for servicing customers. Dealers are tied into the monitoring portal and have crews available for dispatch with pre-negotiated snow and water removal rates.

“Every year, thousands of roofs collapse in the U.S. alone,” Beldon says. “I know Roof Monitor™ can help drastically decrease that figure. 2015 is going to be a different story for roof collapses.”

To learn more about how Roof Monitor™ works and if it’s a smart fit for your roof, schedule a demo or call (844) 4WARNING. https://www.roofmonitor.com

# Dear Pole Barn Guru: Why Didn’t You get the Snow Load Right?

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: I recently ordered a pole building kit package. The agreed snow load was 35. A minimum of 34 is required in our area. The calculations supplied are for 28, not 34. So now we are out another \$800 and

back to square 2.

What can be done, and how fast? SNOWING IN SNOHOMISH

DEAR SNOWING: We’d all like to believe Building Department Plans Examiners are infallible. The reality is, the IBC (International Building Code) is a huge and complex document, which is further complicated by its references to numerous other outside documents.

The agreed upon snow load which you purchased, was 35 pounds per square foot (psf) as a GROUND SNOW LOAD (or Pg). The Code references a document called ASCE 7-10 (for the 2012 version of the Code). ASCE 7-10 gives the formula to convert Pg to flat roof snow load (Pf). This formula takes into account factors such as Building Importance, if Building is heated or not and the roof’s exposure to the wind. The roofing material also comes into play with the heating or not of the building.

Pf is also adjusted for roof slope, to get to the design sloped roof snow load (Ps).

In your particular case, our office made a call to your plans examiner who has now been happily educated.

For further reading on this subject, please see the article I wrote for Structural Building Components magazine: https://sbcmag.info/article/2011/it-isnt-your-grandpas-barn-tips-technicians-designing-post-frame-trusses

DEAR POLE BARN GURU: I have an old metal barn that needs new doors and hardware. A pair of sliding doors that are each 10′ wide by 14′ tall. We had a storm that blew them off and damaged the tracks and channels. We live in Fowler, Colorado. Do you have a dealer here in Colorado? Or can we get them from you to install ourselves? Any information would be appreciated. CAUGHT IN COLORADO

DEAR CAUGHT: Sliding doors can be a challenge in wind storms. If they are not correctly designed, installed, or kept closed and latched during high winds, they can all too easily end up as an unusable pile of rubbish. Sliding door frames which are built either partially or all from wood, are especially susceptible to failure under load.

Hansen Pole Buildings provides sliding door systems and components direct to builders and end users in all 50 states. The doors are designed for the average individual to successfully assemble and install their own sliding doors, by following the detailed step-by-step instructions.

Call us and we will get you started on the path to replacing those doors.

DEAR POLE BARN GURU: Hello, I am helping a friend build and install sliding doors on his pole building. The building is otherwise complete. The door openings are pretty much ready to go as I can see. They are framed in and the upper track is installed. So here I come with a pile of steel siding, steel studs, track for SIDS and button of doors, rollers (pendant) and screws… The instructions he has are very vague. Can you provide me with any plans, prints, instructions of any kind please? Also a photo or diagram of what the finished product should look like?

They have a binder with instructions that supposedly came with the kit and your logo on the front of it. I’m not there at this time so if you need the model name/# I can send it to you this afternoon when I get there.  WONDERING IN WASHINGTON

DEAR WONDERING: While our sliding door systems are relatively simple for the average individual to install – having the detailed step-by-step instructions included in our Construction Guide, in hand would be a serious assist.

The manual devotes 18 pages which include actual photos, as well as diagrams showing how to properly (as well as most quickly) assemble and install each component. Check the manual for these pages and then let me know if you still need help. Often people think the instructions come with the door and we’ve found having them in the Construction Guide makes them easier to find.