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Posts and Collars, Girts, and Non-Vented Soffits

This week’s edition of Pole Barn Guru visits the topics of post and footing sizes, bookshelf girts for drywall, and non-vented soffits for building with spray foam insulation.

treated postDEAR POLE BARN GURU: I am currently 68 but I built pole barns as a younger man the biggest being a hay barn 24′ eaves X 80 clearspan trusses that we built X 160′ long. I am going to build a 30×60 and will use 6X6 posts 12′ to eaves, engineered trusses with 2X6 purlins 12′ span.

What diameter hole do I need?

I was thinking of using a 16 or 18 sonotube top of an 8″ footing below pour.

Does that sound reasonable?

I am in Grant county Wa.

Thanks for your time 🙂 JOSEPH in SOAP LAKE

DEAR JOSEPH: We have had clients much older than you, with no prior experience, successfully erect their own beautiful post frame buildings. Your 80 foot clearspan x 160 foot long and 24 foot eave must have been quite impressive structure!

Most of your area’s building sites are Exposure C for wind (open to the wind in one or more directions – https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/), which is default value for Grant County. If this is indeed your case, neither 6×6 posts or 18 inch diameter holes would be adequate. One of our Building Designers will reach out to you to further discuss your building needs.

 

DEAR POLE BARN GURU: After reading all of the advantages of bookshelf girts I still find the idea of installing drywall sheets vertically over them a bit perplexing. Is vertical “strapping” of some sort required in addition to the girts or is there enough rigidity between the girts to keep the seam together? I’m assuming this would require the use of 5/8 thick sheets. We are planning on doing as much of the work as possible so our plan would be to have all of the ceilings hung by a pro and do the vertical wall hanging ourselves. All of the details for top of wall to truss connections and the prep make perfect sense to me, why does this detail escape me.
Always thankful for all of the useful info we have learned from your site. We are getting closer by the day to being ready to have our plans prepared for building. RUSS in PIPERSVILLE

DEAR RUSS: Thank you for all of your kind words, they are appreciated. The horizontal bookshelf girts will be stiff enough being attached to both the exterior siding (whether wood or steel) as well as the interior drywall to keep your seams together, without need for blocking at seam edges. You will find your sheetrock joints will be much smoother with vertical installation across these girts (https://www.hansenpolebuildings.com/2019/09/11-reasons-post-frame-commercial-girted-walls-are-best-for-drywall/). I used 5/8″ Type X drywall in my own shouse (shop/house) – because it is much more durable, absorbs sound better and provides fire resistance, however 1/2″ would have worked equally as well for standard performance.

 

DEAR POLE BARN GURU: I am looking at purchasing / installing a 30’X50′ pole barn style building with 16′ ceilings, including two 12’X50′ lean-to on each side and 12′ ceilings
I want to enclose about 12’X25′ of the left side lean-to for a canning kitchen area.

I am going to have a non-vented insulated roof assembly since we are using a closed cell foam spray, My question is would using 12″ closed soffit overhang be acceptable for the entire building.

Thank You in advance for the support, SAMUEL in CORINTH

DEAR SAMUEL: In my humble opinion most buildings without overhangs look overly industrial. Overhangs help to keep your building sidewalls cleaner and push rain runoff away from your structure. We can provide non-vented soffit panels and they would work perfectly for your application.

 

 

 

This entry was posted in Insulation, Pole Barn Questions, Building Overhangs, Pole Building How To Guides, Pole Barn Structure, Ventilation, Concrete, Footings, Columns and tagged , , , , , on by .

Flash and Batt Insulating Barndominium Walls

Flash-and-Batt Insulating Barndominium Walls

We’re in a seemingly never ending cycle of racing towards net zero post frame homes, shouses (shop/houses) and barndominiums (read more on net zero post frame here: https://www.hansenpolebuildings.com/2019/01/net-zero-post-frame-homes/). 

One possible design solution involves what is known as “flash-and-batt” where two inches of closed cell spray foam insulation is applied to steel siding interior surface between barn style wall girts, then balance of insulation cavity is fitted with fiberglass batts.

Today’s expert opinion is rendered by Martin Holladay, former editor of the Green Building Advisor web site. You can read more about Martin at www.MartinHolladay.com.

Even though thicker is always better with any type of insulation, applying a thin layer of spray foam is a good way to get air-sealing benefits at considerable cost savings over full-thickness spray foam.

Some spray-foam contractors dismissively call the technique “flash-and-dash”; they point out that fiberglass batts may fail to remain in contact with the spray foam, creating an air space and the potential for convective air currents through the insulation. But I think this is a relatively insignificant problem, particularly if the cavity is fairly airtight. Besides, it’s easy to minimize the chance of a potential air space by simply choosing a thicker batt. In fact, batts that are compressed slightly as they are installed will yield higher R-values than ones that just fill the cavity.

Another concern is that in a heating climate, the flash-and-batt method creates a vapor retarder on the wrong side (the cold-in-winter side) of the fiberglass batt. But whether the spray foam actually becomes a vapor retarder depends on the type of foam used. Open-cell foams — that is, foams with a density of about 1/2 pound per cubic foot — are very vapor-permeable. However, since many low-density-foam manufacturers, including Icynene, recommend against the flash-and-batt method, most proponents use closed-cell foam with a density of about 2 pounds per cubic foot.

One inch of closed-cell foam has a permeance of about 2 perms, while 2 inches has a permeance of about 1.2 perms, so closed-cell foams are effective vapor retarders.

But does installing a vapor retarder on the cold-in-winter side of a wall create a problem? Actually, research has shown that exterior foam can safely be used as part of a cold-climate wall or roof — as long as the foam is thick enough. As a rule of thumb, walls with exterior foam sheathing or flash-and-batt closed-cell foam will avoid condensation problems as long as the foam is at least 1 inch thick in climate zone 5 (Pennsylvania, Iowa, Nevada) or 2 inches thick in climate zone 7 (northern Minnesota).

Since exterior foam reduces a wall’s ability to dry to the exterior, it’s important to choose an interior vapor retarder that allows drying to the interior — such as kraft-paper facing or vapor-retarder paint — instead of sheet poly.

This entry was posted in Building Interior, Pole Barn Homes, Post Frame Home, Barndominium, Insulation, Pole Barn Planning, Ventilation and tagged , , , , , , , on by .

Participating in Rick’s Post Frame Cabin Planning

Participating in Rick’s Post Frame Cabin Planning

Happy readers have been following Hansen Pole Buildings’ Designer Rick’s journey towards constructing a new cabin. Rick has graciously asked me to jump in with sage advice (yep, Rick and I are both old guys), as well as answering some questions he has posed.

Rick mentions using a vapor barrier under his thin concrete slab. This should be a minimum 10 mil with 15 mil being even better in resistance to possible tears prior to floor being poured.  (https://www.hansenpolebuildings.com/2017/11/vapor-barriers-slabs-grades/)

I’d believe Rick’s cabin floor could be insulated with closed cell spray foam two inches thick, providing approximately R-14. Any wiring or plumbing extending through sub-flooring could be routed directly vertical through foam and this should not pose a challenge of access for any future system modifications.

As only incidental heat will be provided into crawl space areas, using rigid foam insulation boards beneath a thin concrete slab might very well prove to be an undue expense.

Rick’s sub-slab insulation boards (if used) and approximately two inches of concrete will not pose any design issues when used with a 2×8 pressure preservative treated splash plank. With top of floor OSB three feet above grade, a clear height in crawl space of two feet will exist under the floor joists. A row of stub columns at building center will carry beams designed to support joists. Given relatively small floor joist and beam spans, there would be 20 inches or more between concrete and the bottom of beams.

A consideration for wall insulation might be to use a flash coating of two inches of closed cell foam against siding, then fill remainder of wall cavity with BIBs. This would eliminate a need for a Weather Resistant Barrier beneath siding and would provide as much as R-35 insulating value. If looking to super insulate and eliminate any thermal bridging, two inches of insulation board could be glued to inside of framing, further increasing R value.

So far, I am liking Rick’s plan of attack and look forward to reading more along his path to his best possible design solution.

This entry was posted in Concrete, Footings, Insulation, Pole Barn Questions, Pole Barn Planning, Pole Barn Structure and tagged , , , , , on by .

Plan to Avoid Failure, Closed Cell Foam, and Addition to Building?

DEAR POLE BARN GURU: We are planning to build a pole barn in the near future and, I need some advice on the footings. depth width etc. We are planning to use rough cut 6×6 pine for the posts and plan to use anchors. The soil here on the property is very sandy. I’ve set some treated corner post for our fence 4 ft down, easiest digging I’ve ever done with post hole diggers. It’s pretty sandy here.
Here’s the link to the barn we will be building.

https://bioengr.ag.utk.edu/Extension/ExtPubs/Plans/T4161.pdf

Thanks DAVID in CASSATT

DEAR DAVID: My advice is to invest in a complete ENGINEERED post frame building kit package from a reputable supplier. You will get all of the correct answers on not just the holes, but every component of the building – it takes away the guesswork and minimizes the probability of a failure.

 

Engineered means the building plans are sealed by a RDP (Registered Design Professional – architect or engineer) specifically for your building at your site.

 

DEAR POLE BARN GURU: We are building an air conditioned metal building using 2×6 studs 16″ OC with 1″ deep hat channel running horizontal instead of C-purlin. The metal panels will attach directly to the hat channel. Drywall will be attached on interior of 2×6 studs. Open cell spray foam will be applied. My question is should we apply spray foam directly to metal panels or should we use a house wrap in between the hat channel and the metal panels and apply spray foam to house wrap? We live in a hot humid climate, so moisture in the wall system is a concern. AMBER in BULVERDE

DEAR AMBER: My problem is with the open cell spray foam, in my humble opinion – use closed cell foam as it has a higher R-value per inch, it seals to reduce air infiltration, it is highly water-resistant and it does not store water. Yes closed cell is more expensive, however you can eliminate the need for building wrap to help offset some of the added investment. Some studies have shown closed cell spray foam to increase the racking strength of walls as much as 300%.

I recently added an elevator shaft to the side of my post frame building, which has steel roofing and siding. My choice of insulation was closed cell spray foam.

DEAR POLE BARN GURU: Can you add onto an existing pole barn? RHONDA in SALEM

DEAR RHONDA: In most cases, yes. There are some things you can do which will help your Building Designer. The best thing is for you to provide them with the original engineered plans and sealed prefabricated roof truss drawings. It would behoove you to confirm the eave height on the building, matches what is on the plans, as this is an area of frequent variation.

Engineer sealed pole barnAt the very least, confirm all dimensions and the roof slope, as well as provide digital photos showing all fur walls, both inside and out, as well as up at the roof system from the inside both at the end bays and in the middle of the building.

 

 

Know how far away your addition must be from other buildings, property lines, etc., as well as the total area which is allowable for the existing building and the addition.

 

This entry was posted in Footings, Professional Engineer, Insulation, Pole Barn Design, Pole Barn Planning, Concrete and tagged , , on by .
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