Can a cottage built on a concrete piers ever be as warm in Canada as one with a full foundation?
sarah_1978
| Posted in Energy Efficiency and Durability on
Hi-
I am trying to minimize the use of concrete in the design of a cottage on flat sandy-ish soil near Huntsville, Ontario. I have heard from contractors that a cottage on piers will always be drafty and that I should go for a full 4 ft insulated concrete perimeter foundation (crawl space).
My question is this – in reality (not theoretically) – can I insulate the floor of a building built on piers enough that it could match the full foundation? What would it take?
Thanks in advance for your help. It is one of those basic questions that no one I have talked to seems willing/able to answer.
Best!
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I live on the Canadian shore of Lake Superior. I live year-round in a 20'x30' cabin built on concrete piers on a sandy soil. I had the cabin built in 1992 and I have lived in it year-round since 2004. It was built to the Building Code of 1992 but I have exceeded the code in a few areas.
The walls and attic are insulated to R-20 with fiberglass batts. The floor is R-20 fiberglass batts and an outer layer of 2" blue styrofoam insulation. I carefully sealed all seams in the vapour barrier with caulking. Any opening in the vapour barrier (like windows, plumbing, phone/tv cables, etc.) was sealed with caulking. The gap between the bottom wall plate and floor was sealed with caulking. Etc. etc.
There are no drafts in the building. The floor is warm (I heat with 3 electric baseboard heaters). The previous cabin on the property was built in 1954 and I converted it to year-round use (similar insulation levels as the new cabin) in 1982. It was built on concrete piers but the building shifted over the years and the floor was not level. This building was drafty and a cold air layer at the floor. The main heating source was a wood stove that got its combustion air from inside the cabin - this added to the cold air draft problem.
So the lesson learned is that a cottage built properly on piers can be draft-proof. However, my heating bill is on the high side. For my next cabin I will probably still use concrete piers (on the sloping bedrock site of the 1954 cabin) but go super-insulated and even more airtight (probably use SIPS panels for floor/walls and ceiling).
I’ve designed homes in the SW US Mountains with floors over concrete piers, where we installed blown cellulose between floor joists and 2-1” layers of sealed, tapped and staggered foam sheets under.
I would imagine if I was building in Canada or really cold climates, I would use at least 2-2" layers of sealed, tapped and staggered foam under the floor system to improve on the air sealing, or 4-1" layers as BSC did in their walls & roof.
How is an exposed floor any different, thermally, than an exposed wall? Armando's plan sounds good to me. I'd be leery of vinyl flooring, just as I would visqueen on the walls, but in Canada you'll likely be OK. That's one to ask locals about, or a pro here can voice an opinion.
Sarah,
As most of the previous comments have indicated, the problem with cold floors is almost always an air leakage issue, not an R-value issue. Most builders find that either spray foam insulation or rigid foam insulation creates a more dependable air seal than systems that are insulated with fiberglass batts.
If your builder understands airtight construction techniques, a house on piers can have warm floors.
I recommend the following article:
How to Insulate a Cold Floor
Back to the original question: is there an advantage of the full perimeter foundation over a pier foundation?
Joel,
Of course. With a full perimeter foundation, it's much easier to keep the pipes from freezing.
Can it be surrounded with an insulated skirt? I was wrestling with a similar problem last weekend (frozen pipes), albeit in a milder climate.
Yes, you can definitely build a super-insulated and well-sealed pier foundation. My husband and I built a passive house in Vermont, and it's entirely on piers. Our crew sealed it with ZIP sheathing/tape, plus expanding foam tape at some of the tricky junctions, and the box (built from 11-7/8" I-joists) is insulated with dense pack cellulose and 4" of rigid polyiso. Our blower door results were 0.28ACH50 (91 CFM).
Martin is right that freezing supply pipes are an issue -- we had a minor problem when the temps dipped to -10F last week, but we have a few ideas for solutions, one of which we'll implement soon.
You can see photos and details about our foundation at:
http://vermontpassive.com/category/blog-subjects/foundation
Andrea,
I'm glad you are working on solutions. In a cold climate, the only foolproof way to keep pipes from freezing (if your house is on piers) is to use electric-resistance heat tape. That's why off-grid homes need a basement or sealed crawl space -- in my opinion.
Hi Everyone - I am overwhelmed and totally grateful. It is so nice to hear from people that have 'been there, done that'. Your responses have helped me realize that you can really do it the wrong way (as in Joel's 1954 cabin) or the right way - you just have to pay attention to a bunch of really important variables (I hadn't even thought of the impact the wood stove would have on pulling in drafts). Martin - the link you provided to that article was fantastic. So straight forward finally! Andrea, Joel and Armado - you give me good ideas of how this can be done. Thank you thank you thank you!! (Note of warning - now that I know how great you guys are - I may be back with more questions :).
Sarah, If I could make one further suggestion - that you consider a hybrid foundation. That is build the house on piers but incorporate a small insulated core made of concrete for the services to enter and exit the house. This core doesn't have to be very big and also has the added benefit of providing some shear (sideways) strength to the foundation.
Make sure you're building sustainable, something that lasts for many human(e) generations.
An externally insulated foundation/floor can be eaten away in areas with termites, ants, rats etc. very quickly.
Leading to increased energy bills, moisture problems and structural instability:
http://www.aecb.net/forum/index.php?PHPSESSID=428tfv12ph1t6sbds0e82uvi44&topic=3770.0
A couple of things to bear in mind, Sarah: critters could shelter under the building (if you've ever had otters at your styrofoam you'd understand), so it's imperative to have something under the joists - like plywood. Attaching this will have its own problems, but it's not impossible. But since plywood in a floor is considered a vapour retardant and/or barrier in its own right, then the insulation you put in there should probably be foam or you'll have moisture penetrating it over time and rotting it out from the inside. An extra couple inches in joist depth is probably cheaper than adding polyiso after the main insulation. A skirt around the perimeter would reduce critter infestation.
As to make-up air for wood-stoves (in particular), you'll find the manufacturers advise the hole being under the stove itself. (Other make-up air is usually introduced under the fridge.)
The BC code doesn't allow a dwelling to be completely on stilts - there has to be one concrete wall. Check with your local BI for adherence to your code. The best point about stilts, in my opinion, it that if settlement occurs, you can shim up the low points. The second-best point is that you won't have to be doing a lot of excavation, renting of forms, etc, and footings can be formed with a mixer and navvy-jack at your own speed.
There are electrical heating cords to wrap around your water and waste lines - one good power outage could be havoc, so a well-insulated enclosure would be necessary (take it below frost line) in a pressure-treated or aluminum shroud of sorts.
And finally - I've found some houses on crawl spaces that are draftier and colder than those on well-constructed and insulated houses like you propose.
Peter, Good point about protecting the foam - luckily I've only had problems with small rodents and ants not otters! Are you sure about the need for a concrete wall on pier type foundations in BC? I can't find anything in the code (9.15.2.4.(1). Maybe it's elsewhere?
Hey Peter, Where is the referenced code section you mention about the requirement for one concrete wall? This code official is not familiar with it. Is that a British Columbia code req.?
Donald,
Peter may be ahead of us on this one. The just released revisions to BC'c code have for the first time brought in seismic requirements for Part 9 residential structures. In reviewing them I didn't think to look at how they affected pier construction.
Jim Iredale at Landmark Passivehaus suggests using 24inch webbed floor trusses installed to the passivehaus standard. This should give you the Rvalue required.