Basement with back exit door on a landing
In the basement of our bungalow we have experienced seepage in the past. As a result we had the entire exterior of the house waterproofed professionally. The plan it to insulate the interior basement walls this summer using rigid foam against the interior concrete walls, sealing the joints with tape. Additionally, I am planning on a stud wall with roxul batts in between. I have read many of the articles on this site to get to this point.
We have a landing on the basement stairs which leads to the backyard and this is not sealed off from the basement or the upstairs. My question is whether or not this needs to be considered in my insulation strategy. It seems to me that many basements are sealed off from the outside, as well as the upstairs. I’d also like to put roxul batts in the basement ceiling to provide a sound barrier to the main floor.
I am not sure what to do on the concrete floor as there is not under slab insulation (at least that is my assumption given the age of the house) and I don’t want to lose headroom. The is some residual glue on the floor from previous carpet installations. Do I need to remove this before putting a product over top?
Any advice or article suggestions are appreciated.
Thanks!
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I am in climate zone 5/6 (Canadian zone 2).
Tylerrr, most basements are within the home's pressure boundary, meaning they are technically part of the conditioned area, though many are in an in-between state. If you're insulating your basement it sounds like you are accepting if fully into the home's conditioned area. I would recommend incorporating the landing (which I assume includes an exterior door of some sort?) into the conditioned area as well.
Insulating basement floors is a good idea for energy efficiency, comfort and mold/odor control, but it's not required by code for a basement floor, so you don't have to do anything to the floor if you don't want to. Until you are sure your moisture problems are fully under control I would not recommend installing finishes over the concrete floor, though.
Thanks for your thoughts Michael. There is an exterior door on the landing, and it is definitely part of the home's conditioned area. I suppose a future consideration would be to improve the quality of that exterior door so that is allows less air transfer with the outdoors.
We are happy with the waterproofing we've done and are confident enough to at least begin discussions on what to do on the floor. As I insulate the walls, my understanding is that condensation on the floor may become an issue, given the higher basement interior temperature. Is this true? I would also be concerned about vapour coming up through the floor and being trapped beneath whatever product goes down. One option is the Delta FL membrane with a floating floor over top. A second option being the plywood panels that have the dimpled membrane on the bottom to allow air circulation. Again though, it comes down to the glue and remnants of carpet on the floor. Should I be concerned about this organic material coming in contact with possible moisture, or do these products allow drying in such a way that this wouldn't be a concern?
The long term goal is to put a gas stove down there to add warmth.
Again, I appreciate your thoughts so far.
-Tyler
Tylerrr, both of your concerns are valid. There is likely moisture coming up through the slab, even if you don't see liquid water due to it drying quickly. The ground below slabs is usually in the vicinity of 50°F; 70° air at about 42% RH will condense at 50°, so there are definitely moisture concerns. If you don't want to raise the floor, though, your only option is to remove the slab and go down for drainage, waterproofing and insulating layers. Floor coverings may or may not be at risk of moisture damage, it depends on the material. Any floor coverings will likely exacerbate any moisture issues.
I am definitely not interested in removing the slab. There is weeping tile around the footings leading to a sump pump, which we also replaced with a high end model.
When you refer to raising the floor, are you talking about a layer of foam before other materials? If so, how think? I've got about 3 inches to spare before my head hits the ceiling so any little bit counts.
Tylerrr, if you're turning your basement into habitable space, according to the IRC you are supposed to have at least 7' of headroom, or 6'-8" for unhabitable space, with beams, ducts, etc. allowed to project below that. (R305: https://codes.iccsafe.org/public/document/IRC2015/chapter-3-building-planning). That aside, if you are confident that your existing waterproofing and drain system will work, you could put down an inch or two of EPS or XPS foam. (Preferably EPS for environmental reasons.) Cover that with a well-sealed vapor barrier, then float two layers of 1/2" subfloor over that, screwed together with seams offset. Then top that with a finished floor. You could do all of that in under 3". Alternatively, give up a bit of R-value fasten 2x sleepers directly to the slab, fill in between with foam, and cover with a vapor barrier and 3/4" subfloor.
If you think you might get some liquid water, you could start with a dimple membrane, then a layer of foam, vapor barrier, and float the double subfloor. (Floating subfloors are only a good idea if your concrete is flat.) There used to be products on the market that were made for this situation but at least one has left the market, and I don't have experience with any of them.
Ok, lots to think about. Thanks very much.
Final question (for today!): What about mechanicals that are installed directly on the concrete (furnace, hot water heater)? I read another post on here that suggested you could leave parts of the basement floor unfinished, which seems odd given that I'm assuming you want an air tight layer of foam. Is this the case, or do I need to bring everything above the layer of foam?
If you don't have much of a moisture problem, or radon problem, you're not going for super high levels of energy efficiency, the uninsulated area is not large and the slab below the equipment is in good condition, leaving a small area uninsulated won't make a big difference. Take some care to seal the vapor retarder to the slab around the un-insulated area. If the factors I listed are issues, it would be better to raise the equipment if possible.