Use Styrofoam under hardwood flooring over crawlspace
Hi all,
New to this forum but it looks like this is the right place to pose this question.
I have a room that is built over a crawlspace that is very cold. What I’m thinking about doing is to tear up an existing Pergo type floor that is installed in this room and to put in a layer of 1 inch thick pink or blue styrofoam and then to install a new hardwood floor over the top of this foam underlayment. The reason I’d like to do this is the crawl space itself is very low clearance and, while I can pretty easily install a moisture blocking layer of pastic sheeting to cover the ground, I don’t see any good way to put insulation in between the joists, plus what I’m seeing is that fiberglass batting is not the preferred method for this type of project. So, I know you can use styrofoam over concrete as a subfloor, won’t it also work over a plywood subfloor over a crawlspace? For the finished floor I think an engineered floating floor might be the best choice. Note – I don’t have a concern with the added thickness of the flooring, no issues with limited cceiling height. I will have to raise the entry door a correspnding amount but this is doable.
So, what do you all think? Is this going to work? Is there a problem with this approach? Any precautions or changes to my plan?
Thank you
Replies
if insulating from the crawl space isnt an option then this is your next best choice. Make sure you air seal the new insulation properly. Tape the seams and use foam to seal the exterior edges against the wall. the only precaution would be to take care to not abuse the foam walking on it while being installed. this will depend greatly on your size. I am 6'4'' 235lbs, and one of my guys is pushing 300lbs...hands and knees on bare foam has been problematic. we use a ez-kneeler or something like it.
no spray foam at edges
If your planning to use a floating floor (or any wood floor), then you should leave a gap at the wall (3/8-1/2" usually) for seasonal movement of finish flooring. Foaming the edges would not be a good idea because that material is not made to expand and contract. It would be a waste of time and material to spray seal this gap. Even foam backer rod would be better than spray foam. However, If you are concerned about doing a good job air sealing the wall plate, then cut out the bottom section of wall board and air seal with caulk or a peel and stick membrane as necessary. If you remove your base moulding and cut your wall board just below to top of your finished base height, then you can caulk your seam and avoid refinishing the wall before reapplying base
A better solution may be to condition the crawlspace. This would mean adding insulation to the exterior walls of the crawl, adding a moisture barrier, and possibly foam on the "floor" of the craw. You'd want to air seal it also. Essentially, you would treat the crawl as an extension of your living area. Then it wouldn't be cold and you'd not need to insulate the floor.
Adding one inch of foam gives you an R value of 5. Not so much for a lot of work and expense.
Further info about my problem
I should have noted that this room is for a cabin that we go to for weekends (during the winter) and longer periods during the summer. Anyway, I do keep the place only warm enough to prevent things from freezing (around 45 F) and then turn up the heat when we get there (actuallly remote call in alllows me to change from vacation mode to regular heating). The problem is that the flooor of the rooom is cold and takes a long time to warm up to make the room comfortable. Thats one of the big reasons I was thinking the styrofoam under the flooring (I plan to replace the flooring anyway) might do a great job of making the room comfortable more quickly. If the place wass always kep warm, like a regular home, then the need might be different.
I do intend to try and enclose and insulate the crawlspace itself this year, but it isn't going to be all that easy (low clearance). Also, there are no plumbing, heating lines under this portion of the crawl space.
Area rugs help a lot, infact they make the difference between being comfortable and not. Thats what got me to thinking about the styrofoam.
So my plan for the room is to: tear up the old Pergolike flooring, put in a layer of styrofoam, install a poly vapor barrier, install new hardwood (engineered) flooring. While I'm at it, I will have to pull up the old baseboards and will take a look at the walls and will run that vapor barrier up the sidewalls (maybe a foot).
I'm still researching things so I love all the thoughts and feedback.
new subfloor
One solution (probably your best) is get an insulation contractor to spray closed cell form (definitely closed cell, not open cell) between joists and fill the band joist, minimum 2" to create a moisture barrier. If this works in your situation, it is almost certainly the cheapest and quickest way if you aren't wanting to replace the Pergo for other reasons, but if your insulation sub is competant and honest they can look at the situation and advise you.
This is NOT a DIY job unless you want to get really messy (which doesn't even save you money, my installer sprays for $1 ft. per inch whereas the store kits cost more then that without labor, even assuming you use the whole kit and don't throw 1/2 of an unused cannister away).
I did this in a house I bought where the kitchen was dropping 22 degrees on a cold winters day (really!) and the kitchen was immediately the same as the rest of the house (actually, the whole house got warmer as I did the whole basement). You may pay more then $1 for a small job since they have to marshall their equipment. On that job I was doing all the basement walls (there was a full basement plus crawl space section) so I also sprayed the walls and floor of the crawlspace and am very glad I did, all the moldy basement smells were immediately gone. It has been 2 years and everything has been fantastic.
If your floor is flat and you are taking up the Pergo anyway, you could also look at DriCore sub floor panels which I have used and been very happy with. They are about $1.50/sf and come as 7/8" x 24" x 24" T&G panels that have a dimpled plastic underside and OSB top. What I like is they are easy to handle and fast to install for unskilled labor IF YOUR FLOOR IS LEVEL and the need to shim is minimum. They definitely warm the room significantly and make the floor installation easier and more reliable.
I use tapcons every 3rd to reduce movement (though I am installing over slab, so if you are over wood I'd check their recomendation), then glue and nail the floor to it like a standard install.
I did not use these on a recent below grade floor at my own house because of low ceiling heights and cost and I _really_regret it. Because we didn't have the dricore I chose to float the floor instead of gluing it, big mistake. Even though our moisture tests were good, I had to take up and reset part of the floor when summer humidity caused it to buckle, whereas the first floor I did 10 years ago with dricore is as solid as the day it was done (it was my fathers basement, so I get to see it regularly) even though he wanted a bamboo floor product that doesn't handle moisture well. The floor is also not as comfortable as my fathers, as I didn't get the same insulating value in floating the floor over the underlayment.
There is a slightly cheaper way using Delta FL + OSB sheets for big jobs, but I found it isn't worth it, the dricore is much easier to carry downstairs and handle, especially when you have to make cuts close to walls, sump pits, etc.
For a really big job (1800 sf) I had it quoted at $5.50 sf delivered to the garage by home depot (I don't love HD, but my yard does not stock dricore and HD does, so I just get it there).
They also make a new product DriCore R+ which is basically a higher R value because it has a XPS panel instead of the dimpled plastic, though still in a convenient 24x24 form factor. I have not used it.