Tag Archives: wall girts

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.

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.

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.

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

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!

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!