Insulating Unvented Conditioned Crawlspace
I bought a 120 year old cottage with a vented crawl space which was very damp. I got rid of the mold, replaced a few beams, levelled things, and encapsulated the crawl space. Vapor barrier on ground and walls, insulated walls, and ceiling mounted dehumidifier draining to outside. I have an electric baseboard heater in there in the winter set at 40 to keep the pipes from freezing. I did not do anything with ceiling joists as wanted to keep those nice and dry.
However, the front of crawl space is under the front porch which is not insulated so was close to -20 this weekend. The rest of crawl is under the cottage which is kept at 40 all winter and is well insulated
I realized that I am loosing a lot of crawl space heat through the flooring in porch, plus the rest of cabin has very cold laminate floors even when heated to 70.
I am considering insulating the ceiling of this non vented conditioned / heated crawl space. Two areas.
1. The area under the front porch (not insulated and gets very cold). I’m sure I’m losing crawl space heat through here. I am considering using 2 inch rigid foam and installing to joists and running straight across, instead of cutting to fit in the uneven joint spaces. I would Vapor tape edges and spray foam any gaps. This would leave a 10 inch air gap between foam and floor boards. Does this sound ok. Could I cause dampness in the cavity as the area will no longer be open to the conditioned heated crawl air.
2. The rest of area under well insulated cottage living space which is heated minimally in winter, but the floor remains very cold when we stay there and turn heat on. Ie cottage 72 but crawl 10, so floors very cold. Should I do the same there, ie attach rigid foam to joists. Again, would I be created an environment within joist cavities with no air circulation.
if I do try entire ceiling of crawl space with rigid foam, is there any point in having a dehumidifier as the joists etc will be on other side of foam acting as vapour barrier. Essentially I will have a closed space that would be easy and cheap to keep warm over winter to prevent pipes from freezing when away. Any suggestion of what I should do. Was planning to screw the foam board to joists using screws and washer.
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I see no one has replied. IMHO, you really don't have your crawlspace "Encapsulated". Encapsulated means it needs to be cut off from the outside air, and the porch is preventing that. IMHO, once again, you need to build a wall and cut off the rest of the crawlspace from the porch so you can condition it.
Your crawl either needs to be vented or (semi) conditioned. Since you have already done work to insulate it to make it a conditioned space, and since you have pipes down there you need to protect, and since a living space over a conditioned crawl is much more comfortable than one over a vented crawl, my inclination would be to continue on the path of having a conditioned crawl.
Thus you are asking the correct questions on how to protect the joists under the front porch. If air leaks between the floor boards, water can also leak between the floorboards in a driving rain or snow. Whatever you do needs to include a way for that water to escape. Horizontal insulation does not lend itself to water escaping. However, if the area is extremely protected and rarely gets water, your strategy may be different. I would try to build a wall in the crawl space, directly under the wall between the conditioned space and the front porch. You can air and water seal that wall, and have a completely sealed and semi conditioned crawl under your conditioned living space, and the space under the front porch could still dry out.
To clarify, the front port is enclosed and watertight. It just has no insulation in exterior walls. The walls between porch and cottage is insulated as is rest of cottage. Cottage is kept at 40 over winter if no one there, porch has no heat and is cold. The crawl space runs under the entire cottage. When I bought it there was no insulation whatsoever. i chose to leave porch uninsulated. So crawl space is encapsulated with plastic on ground all walls are plastic/ insulated. Ceiling of crawl is open joists and floor boards / flooring above... Question is (1) floors are cold in insulated cottage, and (2) ceiling is opne to uninsulated porch, so I imagine heat is escaping.
It seems to me the current situation of being semi conditioned is the riskiest possible choice.
I think the smart move is to separate the two crawlspaces and install large vents under the porch and insulate all 4 walls if the conditioned crawlspace turn up the heater and dehumidifier enough the keep the space almost the same temp and humidity as the rest of the house.
Walta
Thank you Walta. I'm confused.. Why is this the riskiest scenario of all. Many cottages would be watertight but not heated over winter.
I could treat the undersurface of the porch area as an exterior wall, and vapor barrier it with insulation, and leave the ceiling of rest of crawl open as it is now... However, the floor is still very cold in winter. ie heat cottage to 72 but crawl is only 10, so floor cold. Was hoping insulation under floor would help.
The house survived for 120 years likely because the crawlspace was well vented and the rot only began when someone decided sealing up the crawlspace was a good idea.
Your crawlspace is risky because the dew point of the air in your crawlspace is likely to be higher than the surfaces so water condenses on the cooler surfaces and things get wet and start growing mold then thing start to rot. That is what makes a semi conditioned crawlspaces are a risky code violation.
The underside of the porch needs a water proof layer IE a roof to keep rain out of the crawlspace I don’t think you have a way to add one.
Walta
There is no dew in crawl space as its dehumidified in summer, and dry in the winter.
Perhaps, i should rephrase question, I have an encapsulated crawl space (floor sealed, and walls sealed and insulated with rigid foam). The ceiling of crawl space is open.
In the winter when we heat cottage, the floors are very cold as crawl space is much colder.
My question was, would it be ok to install a ceiling of rigid foam across joists in crawl, so essentially, the crawl is its own conditioned space and heated to 40 in winter to keep pipes from freezing.
The porch is more like a sunroom, ie fully enclosed with windows (so no rain) but walls not insulated. In winter we leave the "exterior door" (between cottage and sunroom) closed and heat the rest of cottage, which is fully insulated.
“There is no dew in crawl space as its dehumidified in summer, and dry in the winter."
If that were true, did you have to repair rotten wood?
Until the unvented crawlspace is more or less the same temp and humidity as the rest of the house it is a risky code violation.
Walta
When I bought the place it was vented with moldy insulation in floor joists and rotting wood.
I removed the insulation, replaced any damaged wood, sealed the floor with thick vapor barrier, sealed vents and installed foam board up all the sides, and ran a dehumidifier until it was bone dry... In summer I have a dehumidifier under there but hardly turns on. In winter, without heat, the crawl space stays above freezing. I have a baseboard heater in there, just in case.
I realize this is an old post. Nothing wrong with insulating the ceiling. I’m fact that’s exactly what I did to my house (same issue as you essentially - cold floor in winter because despite insulated walls in unvented crawl space, the floor of the crawl space isn’t insulated and the ambient temperature in winter there is about 43 degrees). Crawl space is 4 feet high and around 2000 square feet. I have a standard residential 70 pint dehumidifier running and used Rockwool for the insulation in the joists. I have various humidity sensors throughout the crawlspace and the humidity never goes above about 45 percent. I think as long as you keep humidity down you won’t have any issues.