Finish basement floor insulation
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I’m thinking of finishing my basement utlizing the tecniques outlined in Andy Engel’s article titled “the Stay Dry, no mold finished basement in the March 2005 issue of Fine Homebuilding.
I’m Ok with putting carpet over the two layers of plywood and insulation, but in some areas, I want to put ceramic tile. Does the EPS foam insulation have enough compressive strength or stability for ceramic tile? I would assume that where I put ceramic tile, I would replace the 2nd layer of 1/2 inch plywood with some type of tile underlayment like HARDIBacker underlayment.
Also, I plan to put a pool table in one carpeted area. Should I add some sleepers where the legs would fall?
Last I don’t know how to end the insulated floor in areas like the furnace room. Since I can’t pick up the furnace, I planned to enclose it in a mechanical, workshop room with a louvered door connecting it to the rest of the insulated basement. I would suppose the uninsulated basement walls and floor will be damp in the summer months and require a significant amount of dehumidification. With an arangement like this, do I run the risk of getting humid air from the mechanical room under the insulation and defeating the purpose of the insulation?
Replies
I've never tiled over the floor system from my article. That said, the air that's under most subflooring has no compressive strength, and according to the Tile Council of America, you can tile on 1 in. of plywood over joists in an L/360 floor. Attached properly to the concrete (I'd actually use more Tapcons for under tile than in the article), I wouldn't hesitate. To be certain, you could use 3/4 ply.
You'd probably be fine without sleepers below the plywood, but I'd probably throw them in for peace of mind.
I would not substitute backer board for the top layer of plywood. Backer board isn't as strong as plywood, it just sticks better to thinset. By all means, add a layer of backer board, but don't skip the second layer of plywood. I'll get a lot of flak for saying this here, but there are a lot of floors where the tile is laid on plywood that hold up just fine. You don't want that where there's likely to be a lot of water, or where deflection is an issue, but again, according to the TCA, tile over 1 in. of plywood is acceptable for residential applications. The other concern I have with tile is that it's vapor impermeable. Water trapped below there is going to stay there, maybe resulting in a musty smell. If it's a very dry basement, you'll probably be fine. Your call.
The floor in the furnace room in the article didn't get finished. It's a small area, and it's probably going to be fine. All construction, and particularly all renovation, is nothing but deciding on the best compromise between budget, time and conditions. It's never perfect, but if it performs well and the customer is happy, then it's right. To finish the edge of the floor there, just substitute some 5/4 PT for the foam. I wouldn't use a lovered door into the furnace room. Add make up air ducts as I describe in the article, and there's no need for the louvered door. When you insulate and seal the walls, you've most likely removed the source of make up air for your furnace. These ducts aren't optional.
Andy
Andy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Edited 3/7/2005 2:01 pm ET by ANDYENGEL
Andy - I just finished reading your article as well. I have a question about the EPS. I heard one person say that if the EPS does take on some moisture, it will start to smell pretty bad. I was wondering what you thought of that?
Another question I have is, does the EPS (on the walls) replace the standard fiberglass insulation?
One last question: My basement floor now is concrete >> thin tile >> carpet. Originally I had planned on recarpeting over the tile (just to avoid trying to remove the tile). In your article, you mentioned using EPS, then plywood, then carpet. In my basement though, headroom is limited. I could get away with adding 1-1.5" more on the floor, but that's about it. Any thoughts about that?
I plan on purchasing Drylok (latex-based) masonry waterproofer and Drylok Fast Plug to fill holes. I wanted to combine that with the EPS (along with proper drainage from the gutters outside, and proper landscaping slope) to have a "best-effort" job. How do you feel about that idea?
Thank you very much!
-> Jason
The idea behind using eps (as opposed to xps) is that eps allows the transmission of water vapor. Dampness in basements is practically unavoidable. XPS will trap it, and that can lead to smells. EPS will allow moisture to move. You must dehumidify the basement. That can be done with central air, or with a dedicated dehumidifier. By drying the air in the basement, any moisture under the floor should dry as well. Dry foam, no smell.
Yes, the wall insulation is in place of fiberglass. I don't recommend fiberglass in basements, or in very many other places for that matter.
Definitely pull up the existing carpet. Carpet on an uninsulated concrete floor is a bad idea. The concrete can be cool enough to allow condensation, and damp carpet's a great breeding ground for dust mites, mold and assorted allergins.
You could use a thinner foam on the floor - 1/2 in. can probably be found.
I see no harm to using Drylock, unless you're counting on it to deal with a known leak. If you've got liquid water entering your basement, you need to deal with that at the source, and be utterly certain that it's not coming back, before finishing the basement.
AndyAndy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Andy - Thanks for your info. To reply back to some of your comments:
>>>XPS will trap it, and that can lead to smells. EPS will allow moisture to move.
I will look for the EPS for sure.
>>>You could use a thinner foam on the floor - 1/2 in. can probably be found.
Ok sounds good. Does the foam experience any crushing, even with the plywood on top of it? I plan on installing a bar, dining room set, heavy things like that. I'm guessing the plywood helps dispurse the pressure on the foam.
>>>If you've got liquid water entering your basement
No liquid watering in the basement that I can see. However, on the old drywall that I tore down, there was mold on it. I've posted pictures of my progress on another website, and if you would like to see it, here's the link: http://forums.vwvortex.com/zerothread?id=1769432 My name on that board is "pooz01wolfsburg".
Thanks again,
-> Jason
The foam thickness shouldn't matter.
The moisture for the mold behind the old finishes could have been trapped by vapor barriers such as poly, foil-faced insulation, vinyl wall paper, or oil or shellac based paints.Andy Engel
Senior editor, Fine Woodworking magazine
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
Wedi board is an insulating foam backerboard that you can use on floors, and you can tile directly on top of it. But it can be hard to find and expensive compared to EPS. You are probably better off following Andy's method and using 1/4" cement backer thinsetted and screwed to the plywood. You can get a greater safety margin from tile/grout cracking by using a Ditra membrane instead of the cement backer over the plywood.
Billy