Capping a Foundation for Winter (and staying in it)
skot_fortin
| Posted in General Questions on
Long time reader, first time poster.
GBA & its contributors have been immensely helpful during the design and early construction stages of a Pretty Good Ski House in Madrid Township, Maine- climate zone 6A. (Pronounced Mad-Drid).
I’m reaching out for advice on a less than ideal situation: Capping a Foundation for Winter.
The piece of land my fiancé bought in the spring for a ski getaway came with an abandoned 1-story house and 9, that’s right, 9 outbuildings that needed to be demolished and disposed of prior to site work, septic system repair, and footings poured by a local contractor. This weekend is the start of ICF assembly for the foundation walls.
I’ve accepted the fact there will not be a house built on top of this foundation before winter. Realistically, I can get the foundation done, first floor deck on, and backfilled before old man winter arrives.
My choices for accommodations this winter are now between moving a yurt or partially completing the basement apartment that was originally planned as phase 3 of construction. We’ll only be staying there for 1-5 days at a time when ski patrolling at nearby Saddleback Mountain.
Either way I go on accommodations, I’ve read that I need to protect the foundation, basement floor, and footings from frost to prevent heaving (though there is 4-12” of high quality 3/4” crushed rock underneath the slab & footings). When I am not staying there, I’d keep the basement at 40 degrees with some heat source- electricity, propane, etc.
Attached is a detail that I’m thinking about applying to the first floor deck this Fall that would allow us to stay in the basement. With the exception of EPDM roofing, it’s made of materials that will be used during the house construction so waste is minimized. I tried to follow best practices for keeping certain layers warm/cold to prevent condensation / mold which seems to be rampant in foundation caps and could ruin these building materials. Air sealing happens via taped ICFs and a sheet of poly or other membrane on the bottom of the floor trusses.
Feedback on this plan? Cautionary tales? Does this rise to the level of a Pretty Good Foundation Cap?!
Thanks in advance,
-Scott
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Replies
Scott,
Over the years we have has several neighbours live in their basements as they competed their builds. The big challenges were humidity and comfort. The first is easier to remedy than the second. The sequence of construction means you won't have many of the things that we expect a living space to have. Maybe y0u will be okay with that, but it's worth really diving into what that temporary living space will be, and how much time it will take to create it.
The second hurdle is that you will not have an occupancy permit, meaning you can not legally inhabit the space. That has implications beyond those just related to your permits, it also voids your COC insurance.
Thanks for the reply, Malcom. Great points and more real-world evidence that people in fact, do this.
I've been rooftop tent camping while at the job site for the past 4 months, so comfort issues are relative and manageable in my opinion.
I'll plan to dehumidify the space to control the humidity issue you referenced.
Legal-wise, the township is 'unorganized' and there seems to be no occupancy permit process through the State- just a self attestation once construction is complete in 2025. They offer an optional paid inspection process where they come out and examine the work- but only to the extent I did what I said I was going to do in the permit application process. They don't inspect for code compliance, etc. That burden is on me & any contractors I use.
This is an owner-build so I've opted to not carry insurance (COC was a new acronym to me). The risk of inhabiting the space / damaging the foundation through the winter is totally on me. I work in information security & risk management and can apply some of those principles here: I am willing to accept aforementioned risks with compensating controls to protect my investment (thoughtful detail to foundation cap, dehumidification, 40-degree set point to avoid frost heaving, smoke/CO detectors, etc).
Scott,
So back to your original question: What you are proposing looks good, you just need to make sure the ratio of foam to batts in the roof is sufficient to avoid condensation. You can find that in this link: https://buildingscience.com/documents/building-science-insights-newsletters/bsi-100-hybrid-assemblies
Seems to me changing the order of operations to accommodate your vacation plans will not happen without some cost. The cost may not all be monetary it seems like this will delay the project and distract you form working on this build.
What you seem to be preposing has no heat, toilet, running water, shower or stove. Not exactly my idea of a vacation.
Seems like the smart move would be to buy a used travel trailer with a good furnace `use in during the construction and resell it afterword for about the same price.
If you check your building permit, I am guessing it expires in 360 days. Getting one short extension is pretty easy. After that even the most relaxed building departments tend to get cranky.
Walta
Thanks for the reply, Walta.
Good points about cost: My money, sweat, and brain power are all running low!
Friends & family have also suggested a travel trailer / RV and I'm still considering one for next spring. My truck has a roof-top-tent that got me through this summer of site & foundation work. Running an RV through the winter is possible, but more difficult if you are only there on weekends+
The word vacation wasn't used in my OP; Around here, you either pickup a winter-time activity (skiing is mine) or you get bored, cold, and fly south for the winter. I'm used to staying in a ski-yurt with less than half of the amenities you listed. The capped foundation will have heat (40 degrees unoccupied, 70 degrees occupied). My plan is to find a freebie toilet, sink, and shower and hook those up to the septic system. Water will be carry-in. Actually finishing the basement is phase 3 but the temporary basement toilet, sink, and shower will provided added comfort during next construction season.
Your point about the building permit caused me to check the expiration date. Project must be started 2 years from issuance and completed 5 years from issuance.
I think it might be simple to build a shallow pitch roof using the materials you'll need for the upper floors.
For example, you can put say a 2x10 or 2x12 on edge down the center of the floor and run 2x4/2x6 rafters off the top of it towards the edge of the house. Cover this with whatever material you'll use for your sheathing, CDX/OSB/ZIP all work. Over the whole thing drape a heavy duty tarp (single piece is less likely to leak) and hold it down with 2x2 (watch especially edges, once draped over the side, those need to be held down). If you have a coil or plastic strip nailer, Scrails are your friend for this type of temporary build.
For extra insurance, you can tape the seams of the roof deck as well as the floor bellow, in case the tarp fails, this will keep most major leaks out of the space bellow.
I would not install anything underneath that would mind getting partially wet. No drywall, no fiberglass.
I have build something similar as temporary roofing when adding an extra story. Holds up quite well as long as the tarp is well restrained.
Even with some screw holes in it, a big tarp like that will come in handy down the road.
Good suggestion, Akos!
I was trying to figure out a method to incorporate a pitched roof to help shed bulk water that didn't involve buying lots of extra 2x8,10,12+ rafters and cutting them. Your design accomplishes the pitched roof with minimal material- some of which I have lying around in a pile from ICF bracing.