Barndominium wall section, zone 5
Designing our barndominium.
Is the below correct wall section for Zone 5 central OH?
We will have an insulated radiant slab, vented roof with shingles and R49 fiberglass blown insulation. Wall height of 9′ with all flat ceilings. What is a recommended truss heel height? Trying to keep all electric and ducts inside the heating envelope. Also, avoiding spray foam.
Cladding, board and batten metal siding
2×3 vertical firing strips
R 7.5 continuous insulation?
WRB
(Possibly adding Rockwool ridged board in between the purlins)
2′ O.C. 2×4 external purlins
R 21 Rockwool
Smart vapor Barrier (Siga Majex)
2′ O.C. 2×4 interior purlins
drywall
paint
I’ve done a lot of research, seeking expert opinion.
Thanks
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Replies
“What is a recommended truss heel height?”
Blown fiberglass has a surprising low R value of 2.2- 2.7
R49 / 2.2 = 22.25 inches + 3 inches of vent space = 25.25
Blown cellulose has an R value of 3.2-3.8
49/ 3.2 = 15.5 inches + 3 inches of vent = 18.5
25.25 inches of raised heal for fiberglass and 18.5 for cellulose.
https://eponline.com/Articles/2017/11/21/Right-Insulation-Material.aspx
The smart move is to keep the ducts inside the thermal envelope and out of the attic.
If some wires need to go above the ceiling drywall caulking around them should not be a big deal. Consider exposed conduit inside the thermal envelope could give the space a nice industrial vibe.
Reconsider the heated floor. Given your insulation levels the heat load per square foot will be pretty low. What that means is that if the air indoors is 68° or so the floor will be about 83° and is not going to feel warm to the touch. Seems likely you will want AC and that ton of money buried in the floor is not much help.
Great barndominium plan! I do not think I have ever put those words together.
Walta
Thank you for your response.
I noticed that in my list that I have the WRB and exterior insulation reversed. Do you have a recommendation for exterior insulation type? I read that Polyiso is not good in zone5 and better on the interior. XPS is supposed to loses its R-value over time. Which narrows it down to EPS or rockwool.
Still investigating HVAC options. I really like hydronic radiant heating. It really doesn't cost that much to run the tubing, just cost of materials. Also, considering mini splits or a drop-down ceiling or plenum trusses for ducts.
Anything you would change in my wall section? What would be the minimum R-value over the top plate or truss carriers in my case?
Since the insulation you are considering is unaffected by water, what side of the water barrier does not matter much but more dry stuff is better than more wet stuff.
The way I see it the hydronic heat only makes sense if you have a wood fired boiler, the land to supply the wood and the ambition to cut the wood and feed the boiler. That is a lot of work and how long will you be wanting to work that hard? Propane and electric boilers are too expensive to fuel and heat pump options are so expensive the math does not work. And remember you do not get the warm toes we recall from the poorly insulated homes that had huge fuel bills we experienced as a child.
Why rockwool in the walls? Maybe I am missing something but I don’t see the appeal for a premium priced product that is unseen in the walls. Yes, the stated R value per inch is 10% higher but it is batts that never fit perfectly. I like damp sprayed cellulose it costs less fills all the gaps and is about the only 100% post-consumer recycled product I can think of. OK all water is 100% post-consumer but I do not want to think about that too much.
Assuming the trussed have a raised heals and the roof has some overhang you could get the full R49 over the walls.
https://www.greenbuildingadvisor.com/article/raised-heel-trusses-make-better-enclosures
Walta
Rockwool is something that I can do by myself. But I still need to compare costs. Budget is tight.