Building a retirement home in climate zone 5B
user-4221191
| Posted in Energy Efficiency and Durability on
I plan on doing my retirement home as owner/builder soon.
I have done several homes in zone 2B. Two have been alternative systems.
My question is what is the most effective shell construction type? Effective to me is the most bang for the buck. I’m thinking of a traditional stem wall, possibly insulated on the inside of the block? Exterior walls would be framing. How should it be framed and insulated? House would have a partial loft and pitched metal roof. Should I use trusses?
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Replies
R. Ferd,
If you have already built several houses I'm surprised that you haven't developed any firm preferences.
In many areas of the country, "traditional stem walls" aren't made of block. They are made of poured concrete.
Walls should be 2x6 with exterior insulation or double stud walls, in my opinion.
I don't know what a "partial loft" means -- does that mean a cathedral ceiling with a loft at one end of the house?
Roof trusses are usually more cost-effective than solid lumber rafters.
In zone 5B the exterior insulation over a 2x6 frame wall should be at least R7.5 (more is better), at which point you don't need an interior side vapor retarder to protect the sheathing from wintertime moisture build up (a problem you DON'T have in zone 2B.) Having more exterior-R is even better- 2" of rigid rock wool or 2" of EPS would put you over R8.
IRC code-min would be R20 between the studs, no exterior insulation, but another R8 on the exterior buys both resilience & comfort as well as a medium term ROI on heating energy use.
I have preferences for a different zone. Rastra has served me well.
Most every stem I've seen in the are is CMU.
Partial loft means overlooking the great room in the center of the house.
Double stud wall means 2X4 staggered with gussets and a 2-3 inch space between the walls? Any thing in that space? Does polyiso and cellulose work the same as on the 2X6?
I have thought of doing 2X6 with exterior 3 inch polyiso over 1 inch EPS over OSB. Filling the void with dense packed cellulose?
R Ferd,
There is lots of information on double-stud walls on GBA. If you type "double stud wall" into the GBA search box, you'll have a lot of articles to read. Here is a link to one to get your started:
Double-Stud Walls.
Double stud walls don't necessarily need gussets. The two rows of 2x4s don't need to be staggered (although they can be) and you can put them as far apart as you want. Dense-packed cellulose is a good choice of insulation material.
If you are planning a great room with a cathedral ceiling, make sure that you get the insulation details right. Here is an article to read: How to Build an Insulated Cathedral Ceiling.
I am not entirely sure what you meant by 3" polyiso over 1 EPS over OSB. So 4" of total foam?
Have you read the post about "R-5 beats R-6 in cold climates" (or similar) - regarding the quick decline in performance of Polyiso in cold temperatures.? Since Martin didn't mention it - might be a minor (or none?) concern in 5b...vs 6 or 7. Not exactly sure on winter situation in 5b (appears to have a wide swath of fairly varied areas....)
Found it:
https://www.greenbuildingadvisor.com/blogs/dept/musings/cold-climates-r-5-foam-beats-r-6
If you do a polyiso + EPS stackup, the EPS goes on the exterior (cold side in winter) to get better overall performance, since EPS performance increases at colder temps, and polyiso performance falls off a cliff for the layers with an average layer-temp below 40F.
In zone 5B with R20-R23 in the 2x6 stud bays you'd want to make that 2" polyiso + 2" EPS, not 3" & 1".