Solving Yet Another Post Frame Condensation and Insulation Challenge
Long time loyal readers will sigh as yet another post frame building has been erected without thoughts to how to properly insulate and control condensation. Had our new friend invested in a Hansen Pole Building, chances are good we would not be having this question and I would have had to write about something else today! Our Building Designers follow with these recommendations: https://www.hansenpolebuildings.com/2019/11/post-frame-building-insulation/.
Our new friend COREY in POST FALLS writes:
“I have a 36×48 pole building with trusses on 12’ with BCDL 5psf, the roof is plywood sheeted with composition roofing with ridge vent and gable vents. The wall Purlins are on the exterior of the poles and there is no vapor barrier. I would like to install a ceiling with insulation and insulate the walls. I am looking for vapor barrier and insulation recommendations. Was thinking of installing 2×4 on 24 centers to bottom of trusses and installing OSB and blown in insulation, and then framing in between poles adding batt insulation and sheeting with OSB, but am unsure of controlling vapor. Thank you.”
Mike the Pole Barn Guru responds:
Small world, many years ago I graduated from Post Falls High School!
A vented ridge relying upon gable vents as an air intake is usually very inefficient. You should make sure your vents in each end are located in the top half of your attic and have at least 415 square inches of net free ventilating area on each end. This means you are probably going to have to add more vents. Effective ventilation of this area is essential to preventing mold and mildew in your attic.
Wall girts flat on column exteriors are inadequate to carry imposed loads and will not meet deflection limitations. I would suggest you reinforce each of them to create either an “L” or a “T”. Assuming you have 6×6 wall columns, you could place a 2×8 bookshelf style girt on top or bottom of each girt, nailing through 2×8 into existing girts with a 10d common nail at say 12 inches on center. This will create an insulation cavity and allow for easy interior finish.
For ceiling joists between your trusses, 2×4 will not be adequate you should use 2×6 #2 with joist hangers on each end.
Unless you have a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between framing and wall steel, my recommendation would be to have two inches of closed cell insulation spray foam to the inside of wall steel. Then fill balance of wall cavity with BIBs insulation: https://www.hansenpolebuildings.com/2011/11/bibs/ with a well sealed vapor barrier towards the inside space.
Tstud™ for Post Frame Bookshelf Wall Girts
I have been somewhat enamored of Tstuds’ potential since one of our clients asked if they would be a viable option last summer.
First I had to find out what a Tstud even was, as I had never heard of them before. Once you skip past ads at the start of this video, it gives a pretty good idea of how Tstuds work in traditional stick frame construction: https://www.youtube.com/watch?t=140s&v=mxDSulcLpAE.
Framing with Tstuds minimizes air infiltration, reduces carbon footprints and saves on electrical energy costs.
A lumber frame is obviously great for providing post frame buildings’ structural integrity. However, this same framing is also a massive weak spot in a wall insulation system – where external air can easily infiltrate. Traditionally a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) is used to cover a post frame home, shouse (shop/house) or barndominium and blanket those weak points.
Tstuds are a new engineered framing product, essentially framing lumber with an insulated core. Tstuds consist of two long wood 2×3 members connected by crisscrossing dowels factory filled with closed cell spray foam. A 2×6 has an R-5.5 value, where a similarly sized Tstud is R-20 (or equivalent to a 2×6 wall cavity filled with fiberglass batt insulation).
Tstud’s thermal benefits are undoubtedly their main draw. Their closed cell foam core gives it roughly three times as much insulation value as a typical 2×6 bookshelf girt. By framing with Tstud wall girts and filling in wall cavities with batt insulation, there is no need to consider having to add exterior insulation. As long term readers of this column are aware, exterior insulation, for post frame buildings, takes away or eliminates diaphragm strength of steel siding.
Another structural benefit with using Tstuds for bookshelf wall girts is they have engineering tests showing they are up to three times stronger than a #2 graded 2×6!
Now some possible downsides, distribution and availability is highly limited. And (according to Tstud), “We are retailing about the same price as an LVL stud but we are obviously a 5 in 1 solution. In the future we will be about the price as an LSL stud”.
The Home Depot® currently has a 2x4x8 foot LVL stud at $50 or $9375 per thousand board feet. This would make a 12 foot long 2×8 Tstud wall girt roughly $150 or over 11 times more than equivalent sized dimensional lumber. Picking arbitrarily a 36 foot by 48 foot post frame building with a 12 foot eave, this would add nearly $10,000 to your cost of materials! While nifty in design, it is not for the pocketbook faint of heart.
Continued from yesterday’s blog:
(1) Storage – if you ever believe anyone might ever in the future desire to climate control then provision should be made for making it easiest to make future upgrades.
At the very least a reflective radiant barrier (single cell rather than wasting the money for the extra approximately 0.5 R from double bubble), an Integral Condensation Control (https://www.hansenpolebuildings.com/2017/03/integral-condensation-control/) or sheathing with 30# felt should be placed between the roof framing and roof steel to minimize condensation.
If a concrete floor is poured (in ANY use building), it should be over a well sealed vapor barrier.
For now we will assume this building is totally cold storage. If it might ever (even in your wildest dreams) be heated and/or cooled include the following in your initial design: Walls should have a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between the framing and the siding. Taking walls one step further would be ‘commercial’ bookshelf wall girts (https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/).
In the roof – have the trusses designed to support a ceiling load ideally of 10 pounds per square foot (read about ceiling loaded trusses here: (https://www.hansenpolebuildings.com/2016/03/ceiling-loaded-trusses/). Trusses should also be designed with raised heels to provide full depth of future attic insulation above the walls (https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/).
Make provision for attic ventilation, by having an air intake along the sidewall using enclosed ventilated soffits and exhaust with a vented ridge.
Any overhead doors should be ordered insulated – just a good choice in general as, besides offering a minimal thermal resistance, they are stiffer against the wind.
(2) Equine only use: Same as #1 with an emphasis upon the ventilation aspect.
(3) Workshop/garage and (4) Garage/mancave/house are going to be the same – other than whatever the client is willing to invest in R value, being the major difference.
Adding onto #1 for the walls the low end would be unfaced batt insulation with a 6ml visqueen vapor barrier on the interior. Other options (in more or less ascending price and R values) would be Mineral wool insulation as it is not affected by moisture (https://www.hansenpolebuildings.com/2013/03/roxul-insulation/), BIBs (https://www.hansenpolebuildings.com/2011/11/bibs/), closed cell spray foam in combination with batts and just the closed cell spray foam (https://www.hansenpolebuildings.com/2016/07/advantages-spray-foam-over-batt-insulation/).
For added R value and a complete thermal break, add rigid closed cell foam boards to the inside of the wall.
Once a ceiling has been installed, blow in attic insulation.
For (4) a Frost-Protected Shallow Foundation (https://www.hansenpolebuildings.com/2016/11/frost-protected-shallow-foundations/) with sand on the inside rather than a thickened slab is an excellent and affordable design solution.
For insulation solutions which follow the roof line, the best bet is going to be the use of closed cell spray foam, as it solves the potential condensation on the underside of the roofing and does not require ventilation above.
In most cases, the steel trusses fabricated for post frame buildings are either not designed by a registered engineer, are not fabricated by certified welders or both – so it makes it difficult for me to recommend them as part of a design solution.
With scissor trusses, they can be treated the same as a flat ceiling would be, provided the bottom chord slope is not so great as to cause blown in insulation to drift downhill.
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.
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.