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NEW Hansen Pole Buildings’ Wall Girts

NEW Hansen Pole Buildings’ Wall Girts

Clients (actually usually their choice of building erectors), have voiced concerns about our use of bookshelf wall girts. These concerns are from one or more of these areas:

Too time consuming, spacing, too hard to hit with a screw, girts sag, too much thermal transfer.

I have previously addressed some of these concerns here: https://www.hansenpolebuildings.com/2023/11/why-are-you-stuck-on-bookshelf-girts/

By using Simpson SDWS16300 structural screws for wood-to-wood attachments, required fasteners have now been cut in half (or more), this speeds installation, as well as correction of errantly placed members.

Rather than evenly spacing non-commercial bookshelf girts between splash plank and eave, we now have standardized spacing to fall so measures are evenly divisible into eight (8) feet. Examples are 32”, 24”, 19.2”, 16” all of which are keyed to markings on tape measures. With ends of girts solid blocked to columns, there really should be no need to measure anyhow (other than to cut blocks). Blocks can be cut, in quantity, speedily with a chop saw.

Too hard to hit with a screw? When we outsourced our lumber, it made it a challenge to have wood sent with little or no wane. We are first to admit how hard it is to screw into a 1-1/2” edge of a board, when one edge is round from wane. We have solved this by now shipping either 2×6 high grade msr lumber, or (for drywall ready applications) 2×8 or 2×10 PREMIUM lumber (basically, little or no wane).

Bookshelf girts sag until siding is applied, however they will do less now. Our 2×4 through 2×10 girt lumber is now all Douglas Fir. Prized by framing contractors for dimensional stability, it is far less prone to warp, cup, bow and twist than other lumber species.

We have even made it easy to quickly identify lumber to be used as wall girts – one end will arrive spray painted GREEN! If you (or your erector) need to trim a board, please trim the unpainted end, as this makes it easy for you (if you hired a builder) or an inspector, to quickly identify wood as being properly utilized!

Why not use externally mounted wall girts? With steel siding and no interior finish mounted to girts, you can specify externally mounted girts. For columns 12 foot on center (usually most cost effective) and 2×6 2100 msr lumber (over twice as strong as #2 SYP) for wall girts, when spaced 24” on center they will support up to 22.48 pounds per square foot load. For an enclosed building, with a median roof slope of 15 feet or less, this would be a Vult wind speed of 118 mph (miles per hour) with an Exposure B.

We also have limited quantities of 2×6 2850msr available for higher wind load areas.

Call 1.866.200.9657 TODAY to participate in “The Ultimate Post-Frame Building Experience”.

And, don’t forget to watch for our next article!

This entry was posted in Barndominium, Lumber, Pole Barn Design, Pole Building How To Guides, Pole Barn Planning, Pole Barn Structure and tagged , , , , on by .

Stud Walls Between Post-Frame Columns for Alternative Sidings

Stud Walls Between Post-Frame Columns for Alternative Sidings?

Reader JAKE brings up an interesting question:

“Hello! I was looking at the blog for a question I had about wall girts for post frame buildings… I was wondering that if a form of siding is installed on the building other than sheet metal, needing wall sheathing, would it be structurally sound to frame 2×6 walls between your 12’ apart posts and not have wall girts? Just attaching the wall sheathing to the posts and 2×6 walls in between? Thank you!”

Pole Barn Guru BlogMike the Pole Barn Guru says:
Before we get to your structural question, a few words. 6×6 columns are notorious for having dimensional variability. I have seen them run as much as 3/4″ over dimension. An over 5-1/2 inch dimension would mean your columns are going to project either inside or outside of your stick framed interior wall.

Now we get into structural soundness.

My concern is how to adequately transfer loads from the top of the stud wall into columns.

Walls lie within two wind zones. Zone 5 is within 10% of least building footprint dimension, with a minimum of four feet. It applies to any secondary member with over 50% of its length within this zone. Provided your building is 60 feet or less in length and width and bays are 12 foot, it would not be applicable for your case.

Wind pressure is derived from wind speed “V”. For an Exposure B (protected from wind in all four directions) site, here are applicable loads in psf (pounds per square foot) for secondary components and cladding members (with mean roof height less than or equal to 15 feet) and a fully enclosed building:

MPH       PSF (ASD – Allowable Stress Design)

95       10.527

100     11.664

105     12.86

110     14.114

115     15.426

120     16.797

125     18.226

130     19.713

135     21.258

140     22.862

All of these loads are negative, meaning your wall is trying to be sucked out of your building.

Arbitrarily picking 110 mph and a 10 foot wall height (if this is for a residence, or accessory building to a residence, then wall heights are limited to 11’7″ by IRC – International Residential Code Section R301.3):

Total load on a 12′ section of wall (by length) would be: 12′ x 10′ tall x 14.114 psf = 1693.68#. One half of this load is transferred to ground through bottom plate, and one half of remainder must be transferred through top plates to column or 423.42#.

When not nailed into end grain (through a plate into end of stud would be end grain and value is reduced x 0.67; toe-nailing reduces value x 0.83) a 10d common nail (3″ long x 0.148″ diameter) nail has a laterally loaded strength value of 102.022# with Hem-Fir or SPF lumber.

How to attach the wall section to the column is your challenge.

In order to nail through end stud into columns, connection at top of stud (nail driven through top plate) would take 423.42# / (102.022# x 0.67) = 6.19 nails. Probably unrealistic to expect to drive 7 nails into top of a single 2×6 stud.

How about toe-nailing plates to column? 423.42# / (102.022# x 0.83) = 5 nails. While ugly, this might be doable.

Ultimately, connection of top plates to columns would probably be cleanest by use of a Simpson Strongtie strap such an LSTA12.

For our example I have picked a fairly low design wind speed, so higher wind speeds will increase loads and make connections even more difficult. As building mean eave height increases beyond 15 feet, applied loads will increase. In order to meet enclosed building requirements – plan upon use of wind load rated doors (other criteria also apply to meet enclosed requirements), else applied loads may increase. Don’t have a protected site? Exposure C places a load approximately 20% greater than Exposure B on your building.

In summary, while what you propose might work, it should be checked by whatever engineer is placing his or her stamp on your building plans.

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Wall Framing, a Sloped Build Site, and Engineering for Slab

Continuing the week with more Pole Barn Guru, Mike discusses spacing of framing for wall steel, how to prepare a sloped build site, and if Hansen can provide engineering for slab on grade in Colorado.

DEAR POLE BARN GURU: If you have 2×6’s for walls in pole building that are spaced 16 inches apart, and want to put metal siding up, would I use like a wood girts every 2 feet apart in order to hang the metal siding up and down? JOSEPH

DEAR JOSEPH: I will read between lines and guess you have built stud walls between building columns. If this is your situation then you will need to have horizontal girts added in order to attach wall steel vertically. You should refer to your engineered building plans for size, spacing and attachment of these girts, as your engineer is most likely counting on your steel skin to provide needed wall diaphragm strength.

 

DEAR POLE BARN GURU: The area I want to put a pole barn has a severe slope of 6′ from one end to the other. Should I excavate this ground to make it level or build a masonry wall on low end to bring level? If I excavate I’m concerned about moisture getting into building from the high end. If I build a wall, I’m concerned about the pressure on the wall that could eventually fail or the back fill settling under the concrete floor causing cracks. Thanks so much for your help. DAN in EDDYVILLE

DEAR DAN: Well you have lots of possibilities. Given what you have provided, I would be inclined to cut roughly four feet from your high side (making your cut back another eight to 10 feet from your building) and then fill on low side, with a retaining wall eight to 10 feet beyond your building. This way you can slope grade away from building in both directions. Walls will be far enough away from building to not affect it. If you have clay in your soil, make sure to remove at least top 18-24 inches where building will be located and replace it with good, properly compacted fill.

 

DEAR POLE BARN GURU: Does your company handle all the engineering required for an interior monolithic slab? We are very interested in a pole barn home (about 1300 SQ ft) but are running into a lot of issues with the interior slab. We will be building in Fremont County, CO at 9400’ elevation. Frost heave is a huge concern. JEFF in FREMONT County

DEAR JEFF: We would need to have an engineered soil’s report as well as to know your intentions for heating (always heated or not always heated). With this information we would provide engineering for your slab on grade.

 

 

This entry was posted in Pole Barn Questions, Building Department, Pole Barn Planning, Concrete, Footings, Professional Engineer and tagged , , , , , , on by .

Why You Should Install Post Frame Roofing Before the Walls

Over roughly 40 years of post frame construction, I have seen photos of one or two (or perhaps thousands) of post frame buildings under construction. I can pretty well tell from these photos if those doing assembly are (or were) stick builders.

I grew up as a framing contractor’s son (and later working for dad and my uncles stick framing), where we built walls with sheeting (and often siding) on them and tipped them up into place. This is all fine and dandy for ‘conventional’ stick frame construction, however not necessarily easiest or best when it comes to post frame.

In post frame construction, trusses extend from column outside to column outside (plus any overhangs). If walls have been framed (girts, headers and door jambs placed) trusses will have to be jockeyed around to be lifted in place from inside the building. This is especially true in applications with bookshelf (inset) style wall girts.

Most post frame buildings have one or more columns out of perfect placement along building length. Accept it, this is just going to happen no matter how perfect you or your builder might be. Most buildings have a far greater roof purlin quantity per bay, than wall girts per bay. By framing the roof first, all purlins (assuming they are inset) can be cut to the same length in each bay, this is determined by engineered plan column spacing, less truss assembly thickness. When trusses are in place, column tops will easily move forward or backwards so all truss supporting columns end up spaced per plans. This also aids in an overall building roof length creation matching expectations.

During the truss placement process (regardless of method used) there will come times when it is highly convenient to be able to walk ‘through’ a wall. Girts in place means having to fit through girts or walk around – either of which slowing construction processes.

It is far easier to square up the roof without wall framing member resistance. Once roof sheathing or roof steel is in place, it makes it simpler to plumb building corners.

With roofing in place and walls open, a concrete slab may be installed if desired. This helps protect concrete pour from weather elements, especially heat in summer or rain. Pre-mix trucks can access and chute through any accsessible sides or ends. This can eliminate the need to pay for a pump truck.

Want your new post frame building as perfect as possible and completed quickest? Then roof first, walls after is most probably your route to success.

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A Post Frame House Photo

A Post Frame House Photo – and More

Post frame buildings are amazing, after four decades in this industry I am still amazed at what can be accomplished with them. We are just now barely scuffing surfaces of a burgeoning residential housing market!

I will begin with a disclaimer, this is not a Hansen Pole Building. In fact, I am totally unsure of what this photo’s source is. Here we are using it merely as a teaching moment.

There is a less than lovely pile of wood filling an entire corner of this photo. My framing contractor father and uncles would have had a piece of me for ever having a waste pile like this on a jobsite. My first summer working for them as a teenager, we built two three story wood framed commercial buildings with a courtyard between. My primary function was as “cutoff” man. I cut to length every stud, trimmer, sill, header, etc., for this entire project. Having been properly indoctrinated to not waste anything, when our project was completed, my wood scrap pile would not have covered a card table.

Moving forward….

From experience it is far easier to square a post frame building up when the roof is framed and sheeted before any walls are framed.

Some things I would have done different with this build:

Note level at the base of steel siding on the endwall to the left of the entry door. Bottom of the siding is lower than the bottom of the door. This precludes any ability to pour a concrete apron outside of this door without pouring up against siding (not a good choice as it leads to premature degradation of siding due to water trapped between concrete and steel), or creating a step down. Lowering this apron (landing or walkway) could result in a top surface lower than surrounding grade resulting in ice or snow build ups if in a cool climate.

Wall girts have been applied “barn style” flat on column exteriors. This building might be in a region where design wind speeds are low enough to allow these girts to meet Building Code deflection criteria. However in order to insulate and finish the interior either studwalls will need to be framed between columns, or an interior set of girts added. It would have been far easier to have accomplished all of this using bookshelf style girts every two feet.

Diagonal braces have been framed in behind wall girts. These are probably unnecessary had diaphragm strength of steel skin been factored in by a Registered Professional Engineer. So why might they be a problem? If framing in a studwall between columns, these braces will need to be worked around.

Maybe exterior walls are going to have closed cell spray foam applied directly to the inside of wall steel. If not, then a Weather Resistant Barrier should have been placed between wall girts and siding.

This building is a residence. Unless the roof deck underside is going to be insulated and attic space conditioned, my educated guess is some form of attic insulation will be blown in over a ceiling. In order to do this right, roof trusses should have been designed with a raised heel, to allow for full thickness of attic insulation across exterior walls.

All-in-all it does not appear to be overtly a bad building, but for little or no added investment it could have been so much better!

This entry was posted in Pole Barn Homes, Pole Barn Design, Post Frame Home, About The Pole Barn Guru, Building Department, Pole Barn Structure, Steel Roofing & Siding, Trusses, Professional Engineer and tagged , , , , , on by .

Putting Everything Under One Post Frame Roof

Putting Everything Under One Post Frame Roof

I have been an advocate of one larger roof, rather than an enclosed building with a roof only side shed for years. This allows for greater headroom in ‘shed’ area without having to deal with pitch breaks (transition from a steeper slope main roof to a flatter shed roof), making for easier assembly. In almost all instances, this will result in a less costly design solution.

This also happens to be a lesson I have tried to impart upon our Hansen Pole Buildings’ Design Team, however they have been slow to embrace this concept.

Reader RYAN in SUN RIVER writes:

Hansen Pole RV Storage“I have plans to build a 52x48x14 this spring.  The idea is 52×48 roofline 4/12 pitch. Under that roof is a 16×48 open side for rv parking and then 36×48 enclosed with concrete floor.  My original thoughts are to 2×6 stick frame the wall separating the open area from the enclosed area after the pad is poured (any suggestions). 16×12 insulated door and a 4’ man door on the front gable end and a 3’ man door to get in from under the open area towards the rear.

How much would you charge to draw this up with your building techniques?  

I am planning on sourcing materials local but wouldn’t mind a quote from you either.”

I do like your idea of having your enclosed portion and roof only under one gabled roof, rather than a smaller gable over enclosed portion and balance as a shed roof off one side. You gain headroom, it is easier to assemble and usually less costly.

I would frame separation wall with wall girts, rather than stick framing and having to add on horizontal framing to attach wall steel. Code also will not allow for a stud framed wall greater than 10 feet in height without it being engineered. To minimize possibilities of water from your RV area migrating into enclosed areas, your concrete should be two separate pours, with RV parking slab slightly lower at main building wall and sloping away from it.

Your choice of having a four foot wide person door is one you will not regret. For a minimal added investment you will save your knuckles repeatedly. 

As for building plans, we are not a plans’ service, however your investment in a new Hansen Pole Building does come with complete third-party engineer sealed structural plans, along with verifying calculations. This alone will usually save you thousands of dollars in engineering costs, plus you have our roughly 20,000 buildings of experience to arrive at what will be your most practical and cost efficient design.

Why people think they are somehow going to get a “better deal” by sourcing materials locally is beyond my comprehension. We have buying power an average individual (or contractor even) is never going to have, plus our control over materials being provided allows our engineers to be certain what they specify on plans, gets delivered to your building site. Some materials we have produced only for our clients – you cannot buy them elsewhere. 

For continued reading on this subject: https://www.hansenpolebuildings.com/2014/03/diy-pole-building/

This entry was posted in Pole Barn Design, Building Department, Pole Barn Planning, Pole Barn Structure, Professional Engineer, Sheds, Pole Barn Questions and tagged , , , , , on by .

North to Alaska

While Alaska is America’s last great frontier, it doesn’t mean when we go North, we throw proper structural design out of a window.

Reader CRAIG in WILLOW has more challenges going on than he has dreamed. He writes:

“Hello,

I’m building a 42Wx50D pole barn. I have 6×6 columns spaced 10’ apart on more than adequate footings. Slab on grade 5-6inches thick (poor final grading ) with 6” mesh and pens tubing. Willow has a snow load of 90:10:10. With a 4:12 pitch, truss companies up here are recommending a set of two two-ply trusses for a total of 24 trusses. 2’ overhang.
My problem is figuring out how to support the load between the trusses. They won’t give me a recommendation. I was planning on using 2×6 between top chords spaced every 2’. These would be oriented vertically and installed with joist hangers. I don’t think they’d be strong enough. The top chords on the trusses are called out at 2×6 so it’d be difficult to hang a larger member on them.

If I can’t make this plan work should I frame in between the columns and build a stick frame wall to set normal trusses on every 2 feet? What about laying some size beam across the tops of the columns and then setting trusses at 2’ centers? I’m dead in the water and want if anything to have overbuilt. Can you help? Thanks.”

Here is my response:

You have a plethora of challenges going on. This is why I always, always, always (did I mention always?) tell clients to ONLY build post frame (pole barn) buildings from engineer sealed plans produced specifically for their building at their site. It is not too late to get one involved and it will be money well spent.

Challenge #1 It is highly doubtful 6×6 columns you have placed along your building sidewall are going to be adequate to carry combined wind and snow loads. An engineer can design a repair – probably involving adding 2x lumber to one or both columns sides.

Challenge #2 Your wall girts placed on column faces “barn style” will not meet Code requirements – they will probably fail in bending and absolutely will not be adequate for deflection. https://www.hansenpolebuildings.com/2012/03/girts/
Again – an engineer can design a repair and there are several choices. You could remove them and turn them flat like book shelves between columns – you would need to add material for blocking at girt ends. https://www.hansenpolebuildings.com/2018/09/making-framing-work-with-bookshelf-girts/ Or, more girts could be added to your wall. Or, a strongback (2×4 or 2×6) could be added to your barnstyle girts to form an “L” or a “T”. My personal preference would be a bookshelf design, as it creates an insulation cavity.

Now – on to your trusses and roof purlins.

Your snow load is actually 90 psf (pounds per square foot). 10 and 10 are dead loads – you may not need ones these large. If you are using light gauge steel roofing over purlins top chord dead load can be as low as 3.3. Steel over sheathing 5. Shingled roof 7. If using steel roofing, make sure it is capable of supporting this snow load over a two foot span. If using sheathing, 7/16″ OSB or 15/32″ CDX plywood will not span two feet with a 90 psf snow load. Second 10 is bottom chord dead load. It is adequate to support the weight of ceiling joists, two layers of 5/8″ Type X drywall and blown in insulation. For a single layer of sheetrock and minimal lighting five psf is probably adequate. No ceiling – 1 psf. Important – make sure truss people are using 1.00 for DOL (Duration of Load) for snow. With your snow load, chances are snow is going to sit upon your building’s roof for a significant time period. Again, an engineer can determine what loading is adequate for your situation.

Trusses – how about placing three of them every ten feet? They can be notched into your columns from one side so you have full bearing – when two trusses are placed each side of a column, they are not acting together to load share.

Your roof purlin dimension can be larger than truss top chords – just utilize larger purlin hangers and balance of purlin can hang below top chord of truss. An engineer can confirm adequacy of hanger nails to support imposed snow and wind loads. Given your load conditions, your engineer should be looking to use something like 2×8 #2 purlins every 12 inches or 2×10 #2 purlins every 19.2 inches. You would not want to go to 2×10 unless truss top chords are at least 2×8.

You could stick frame between columns to support trusses every two feet. Any stud walls over 10′ tall do need to be designed by a Registered Design Professional (architect or engineer) as they would be outside of Building Code parameters. Your slab edges would also need to be thickened in order to support added weight. A beam could be placed from column to column to support trusses, you are probably looking at something around a 3-1/2″ x 14″ 2800f LVL.

If you are considering insulating an attic space, be sure to order raised heel trusses. They are usually no more expensive and they afford full insulation depth from wall-to-wall. https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/

With all of this said – go hire yourself a competent Registered Professional Engineer today to resolve your challenges. Otherwise you are placing yourself and your building contents at peril.

This entry was posted in Trusses, Footings, Pole Barn Questions, Professional Engineer, Pole Barn Design, Pole Building How To Guides, Pole Barn Planning, Pole Barn Structure and tagged , , , , , , , on by .

Can Wall Girts Be Installed Before Trusses?

Can Wall Girts Be Installed Before The Trusses?

In my travels over the years I have seen more than a few post frame buildings under construction. When I find one being constructed by a building contractor, if the wall girts are installed before the roof, it is an immediate giveaway to the builder having been a framer at one time.

Why?

Because the correct (and easiest) way to assemble a post frame building is to construct the roof first, then place the wall girts.
But does this sound counter intuitive??

Client ED from CLINTON wrote to Hansen Pole Buildings’ Mistress of All Things Being Delivered, Justine, recently:
“I do have another question.  I am very limited on Whidbey Island concerning  options for setting the trusses and I do not believe I will be ready for the trusses when they arrive on site, so paying the truss company to set them at the time of delivery is not an option. .  It appears that Hansen’s recommends that the trusses get placed after the skirt boards are installed and before the wall girts are installed.  Do you see any issue with installing the wall girts prior to installation of the trusses?

Mike the Pole Barn Guru Writes:

Well, there could be some issues.

The majority of our clients (as well as most professional post frame building installers) frame up portions of their roof on the ground and then lift entire bays using either post top winch boxes, or a crane. Having girts in place would make this an impossibility as the girts would be in the way of raising the trusses.

In the event you decide installing the girts first is the direction you really want to go, it is crucial to have the tops of the columns held in place along the length of the building at exactly the column spacing. It is far easier to have to custom cut a few girts to various lengths and be able to keep all of the purlins in each bay the same length.

There are always methods to our madness, which is why the Hansen Pole Buildings’ Construction Manual leads clients (or their builders) through the process of assembly in the correct order to make the process as easy and pain free as possible.

This entry was posted in Trusses, Pole Barn Questions, Constructing a Pole Building and tagged , , , on by .

The Straight and Narrow of Fascia: Hansen Building Disaster Part III

The Straight and Narrow of Fascia:  Building Disaster Part III

Look at the board on the far right. The one which resembles the coastline of New Jersey. It is what is known as a fascia board and it is pretty important it be straight.

Why?

Because not only do vinyl soffit panels attach to the underside of it, but steel trim covers the face of it. Steel trims are very happy to be installed on straight boards.

But other worries are looming in this photo.

The roof trusses were manufactured in a plant which seemingly has some challenges with plumb cutting (which was specified on our order) Read about plumb cutting here: https://www.hansenpolebuildings.com/2015/09/trusses-9/. None-the-less the builder might have stumbled upon reading in the plans or the Hansen Pole Buildings’ Construction Manual and seen the necessity to have cut the tails plumb. He instead has opted to just nail the fascia board onto the ends of the square cut tails.

This creates more problems – such as the inability to install the soffit panels. Which, since he left the framing off the sidewall to support the soffit panels, might have been why he quit where he did.

Notice, if you will, how the outside face of the bookshelf wall girts and the wall columns are in the same plane.

They are not supposed to be. The wall girts should extend outside of the columns by 1-1/2 inches. This allows for the outside of them to be flush with things such as the skirt boards, which the builder has installed on the face of the columns! I suppose the thought was the wall steel would just curve to make up the difference?

Tomorrow, the client proposes some solutions to some of the issues and I will give my take on why those solutions may, or may not work.

This entry was posted in Building Contractor, Trusses, Constructing a Pole Building, Pole Barn Structure and tagged , , , , , on by .

How Far to Lower the Trusses?

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: Good morning,

notching trussesI purchased a building back in February and just now starting to build. I have the Poles up and concrete down. Now I’m starting to install the Trusses. I have a question  about the truss layout, on drawing S-4 It shows to drop the Back truss 7-5/8” and then the next set of trusses it looks like I need to drop the outer truss 7-5/8” also which will allow my purlins to be installed on top and tie into the 2nd truss.  I have two questions. 1:  The two interior trusses I understand they must set on a 3” ledger that I cut from the post, the way the post is laid out on plans is 6×4 on the outer post and the would only leave me with just an ½” of post to attach my Trusses to. 2: I understand the drop in truss’s but the purlins actual measurement is 7-1/4 and I setting them at 7-5/8” according to drawings. I just wanted to confirm that was correct.

Thank you. CHAD IN GROVES

DEAR CHAD: Your particular building has the rear 24 foot wide by 12 foot of length fully enclosed. The balance of the building is a roof only “carport”.

At 12′ from the rear endwall only the truss towards the rear of the building (the truss with “tails”) notches into the columns 1-1/2″, leaving two inches of column remaining. The truss on the front side of the columns (without tails) attaches to the column face with 10-10d nails to each column.

This allows the rear truss to have full bearing on the columns, and the top chord will seal the enclosed portion from the carport area. The roof purlins of the carport section will bear on top of the lowered truss on the face of the columns.

Although a 2×8 physically measures 7-1/4″, because it is rotated at a 4/12 slope, the trusses themselves must be lowered 7-5/8″ to compensate. We know it sounds counter intuitive, but it actually works.

For those following along at home, you can do the math yourself. For a 4/12 slope…square four (4 x 4 = 16) and square 12 (12 x 12 = 144). Add the two together (16 + 144 = 160) and take the square root (which is 12.649). Divide 12.649 by 12 to get the slope factor for 4/12 (1.05409). Multiply the dimension of the 2×8 (7.25”) by the slope factor and the resultant is 7.642”. The closest easily measured fraction is 7-5/8” (7.625”).

Mike the Pole Barn Guru

DEAR POLE BARN GURU: I’m currently constructing a Hansen building, and as we started notching the columns, noticed that one has a split in it near where the notch will be. It will work fine if I notch it on the other side, so my question is: Can I notch one pair of interior columns on the opposite side? The purlins should be long enough. Anything else to consider? Thanks JP IN GRAND SALINE

DEAR JP: Every once in a while someone is kind enough to throw up a “softball” question (think of friendly interviews of political candidates) for me and I sure appreciate them!

As long as your purlins/eave girts and fascia boards are all long enough – it is not a problem from a structural aspect. You are all good to go!

Mike the Pole Barn Guru

This entry was posted in Pole Barn Questions, Trusses and tagged , , , , , , on by .

Loads on Barn Girts

Oops! A Girt Failure

When last we peeked in on Leroy and the boys on the pole building across the street, our hero and his crew were making slow and steady progress. I’ve figuratively hammered on why “barn style” wall girts generally do not meet the requirements of the Building Codes. The problem is one of deflection and I have probably mentioned more than once the barn girts may very well meet the requirements for bending – meaning they may very well be designed to carry the design wind load and won’t break, they just bend too far!

Well…..

Leroy’s cohorts had a wall girt fail while under a load.

Always someone to prove me wrong!

barn girtThe load, however was not from the wind (as might have been expected), but instead, it was from one of the crew standing in the middle of it!

Wood is unique in the sense that it has the ability to support higher stresses if the loads are being applied for short periods of time. This effect is quantified by the Load Duration factor, or CD for short. This helps greatly for temporary increases in loading (such as an earthquake, wheel load, wind load, etc.) will have additional strength, compared to permanent loading.

Cd for an impact load (lasting less than two seconds) is 2.0, for a 10 minute load (like wind or seismic forces) 1.6.

So how much concentrated load can a 2×4 1650msr wall girt placed placed as barn girts on the side of a building take?  If you like math – here we go…

The formula for maximum moment (refresh yourself on bending moments here: https://www.hansenpolebuildings.com/2012/09/bending-moment/) is Mmax = P x a x b / L, where P is the applied load in pounds, a and b are the distance from each end to where the load is applied and L is the length squared (all distances in inches). A 200 pound worker standing in the center of the girt would impart 4800 in-lbs (inch pounds) of force upon the eight foot long member!

4800 in-lbs / Sm (Section modulus of a 2×4 = 3.0625) = 1567.34 <= 1650 (fiberstress of the wall girt) X 1.6 for duration of load.

Moral of the story is a 200 pound worker standing on the top of the now broken 2×4 barn girt should have been able to safely be there for up to 10 minutes, and only have utilized just under 60% of the strength of the board. The caveat being if the nails in each end of the girt were adequate to support the worker’s weight!

This entry was posted in Pole Barn Design and tagged , , , on by .

Them Girts, They Be a Bending

In order to follow the deflection criteria of the International Building Codes, other than for fairly small wall column spacings with low wind speeds, pole building wall girts need to be installed in a “bookshelf” fashion.

What even is “deflection criteria”?

Dictionary.com defines deflection as, “the deviation of the indicator of an instrument from the position taken as zero.”

In layperson’s terms, when you push on something with a known force, how far does it bend (or deflect)?

Prior to the adoption of the International Building Codes, wall members which did not support a brittle finish material (e.g. drywall), were not limited in how far they could deflect.

Not so with the new code.

For those of you who care to look it up and read along, Table 1604.3 lists deflection limits. For walls with brittle finishes, the limitation is L/240 (where “L” is the span or length of the supporting member). For flexible finishes, the limit is L/120. Footnote A includes, “For secondary wall members supporting formed metal siding, the design wind load deflection shall not exceed L/90.”

The smaller the value L is divided by, the larger the allowable deflection is.

Ignoring the width of nominal six inch building columns the allowable deflection of wall girts for an 8’ bay (with steel siding) would be 1”; a 10’ bay 1.27”; 12’ bay 1.54”.

Using the least possible loads allowed by code – which would be 85 mile per hour winds, B wind exposure and a building Occupancy class of I (I = a building which represents a low hazard to human life in the event of failure) combined with the stiffest possible commonly used lumber (Douglas Fir or Southern Yellow Pine #2) and spaced 24 inches on center, some problems occur.

Using 2×6 lumber on 10’ bays the actual deflection is 1.507” and on 12’ bays 3.226”. On 8’ bays IF 2×4 #2 is actually used (it is rarely available in lumber yards), then it would deflect 0.924” and be OK. Another issue with the 2×4 girts on 8’ bays, is this style of construction is most prevalent in areas where the minimum wind speed is 90 mph.

Keeping all variables the same, except increasing the wind speed to 90 mph, increases the deflection of a 2×4 #2 to over an inch on an eight foot bay!

Shopping for your new ideal dream pole building? If so, ask specifically how the wall girts are placed. Anything other than “bookshelf” style pretty much guarantees the building being proposed, is not code conforming!

This entry was posted in Pole Barn Structure, Constructing a Pole Building and tagged , , , , on by .
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