Insulating basement that’s already framed with electrical
IndyGopher
| Posted in Energy, Heating & Insulation on
| First, let me own my novice DIY status and say I probably screwed up. I bought a new house last year in the Indy area (5b) and immediately went to work finishing the basement. The builder attached batts of insulation to the top half of the poured concrete walls to just below grade. I framed the walls just off those batts, so several inches from the foundation. Didn’t consider any other insulation as I assumed like a novice that I’d just insulate the stud cavities after everything was done. It’s only recently I’ve become aware that the preferred option is rigid foam attached to the concrete walls from top to bottom for moisture control. I’ve now got a 2000 sf basement fully framed with electrical run and I’m wondering what my best and most cost-effective course of action is for insulation…and I’m posting this all over the internet, lol! If it makes a difference, I learned today that the builder used a waterproofing membrane (Hydra-Guard?) on the exterior of the foundation. Also, here’s a link to a couple pictures if that helps: https://photos.app.goo.gl/1Kq5uGx6XoicXFBJ9 |
Replies
Looks like a fairly new house. if there is no moisture problem, you can put more fiber insulation,
or you can pull down what is already on the wall, and put up foam boards, as your internet research suggests.
you might be able to slip boards sideways behind your stud wall without too much disruption. some come in 2 ft widths.
another option is to spray foam the whole thing, and this has its own issues.
You really would be best off to slip some foam behind the studs. That also helps to keep humid summer air from condensing on the cool concrete. I wrote a little on this topic a few years back. https://www.finehomebuilding.com/2005/03/01/the-no-mold-finished-basement
Thanks for both replies! I'm now heavily leaning towards using foam boards after posting the same question and getting similar replies on several sites. I'll take down the glass, "thread" the boards through, then use the glass in my stud bays afterwards. I'll have to purchase more to finish the job, but I should be able to get out around $1000 total if I use EPS. I think that's well worth the cost and the effort of installing them.
And pay attention to details. I picked up a pro foam gun to seal, and it does a great job.
you can also cut and use foam boards and foam to fill the gaps on the rim joists and top of that poured foundation. connect it all to the foam you put along the inside of the wall, and you will be in a happy place.
Foil tape or tyvec tape will do a good job sealing between the sheets too, if you have clean straight but joints.
Closed cell spray foam will quickly do the job, 1" is enough though they say 2" is a complete vapor barrier. Installed cost will almost certainly be cheaper than the rigid panels and work much better as well.
If you go this route I'd price removing the fiberglass and spraying up to and including the rim joist, you won't regret it. I have done this in a many basements (including my own old house) with minimal hvac and they stay comfortable and dry.
Make sure you specify CLOSED CELL foam, not open.
@UncleMike42: Thanks for additional advice! Had read about using tape on the joints and will definitely do so. Where did you spray foam? I've read to keep EPS off the floor, so I was thinking of spraying about 1/2" between floor and the sheets. Any other spots?
@qualityjob: I was originally thinking spray foam since it would be easy, but I figured it would be WAY more expensive than foam board -- especially something on the cheap end of the spectrum like 2" EPS (currently under $12/sheet after rebate at Menards). I can definitely get an estimate from an installer in my area, but general prices I see online for closed cell are between $1 - $1.50 per board foot. My rough calculations have me needing over 1,600.
why use sheets at all, just as expensive for material and labor intensive to install and you still have seems to seal?
I'm talking about bringing in a professional spray company, $0.80/bf in my area. If your walls including rim are 9' and you have for example 150lf of wall sprayed 1" on the wall and 2" on the rim then you are looking at maybe $1500 ... because it is a small job they will likely charge you more unless they are hungry for the work or you are a builder and they want an in with you.
I used the foam to fill between cut sheets and edges, and along the floor.
this is two inch foil faced, cut a bit short to make it easier to place, then glued with foam, and sealed around the edges.
While I am at it, here is what I did to insulate the walls. this is an outside basement wall, block and brick, was thin paneling on furring strips which were nailed to the block with hardened cut nails.
I put half inch between the furring strips, then 2 inch foam, secured with half inch plywood screwed into the furring strips, with adhesive in selected areas.
https://www.awarehousefull.com/dow-great-stuff-pro-enerfoam-sealant-and-adhesive-30oz-pro-can/
I used enerfoam with a gun from these guys. bit of a learning curve, but it is very nice to be able to control the flow rate, stop and reuse a couple days later.
I used a tie wrap to secure the plastic extension tubes to the end of the gun for hard to reach places.
Dang, @UncleMike42! Appreciate the pictures and suggestions. Really good stuff and super helpful! I've started a shopping cart at Menards with supplies, but I'll look at that spray foam you linked for sure. Thanks a ton -- very helpful!
why use sheets at all, just as expensive for material and labor intensive to install and you still have seems to seal?
I'm talking about bringing in a professional spray company, $0.80/bf in my area. If your walls including rim are 9' and you have for example 150lf of wall sprayed 1" on the wall and 2" on the rim then you are looking at maybe $1500 ... because it is a small job they will likely charge you more unless they are hungry for the work or you are a builder and they want an in with you.
Help me here, I’m a little confused. Do you mean apply the spray foam to foundation wall before framing? If after, how do you get a good barrier and prevent rot of the framing?
We’re about to install the foam board on a home we just purchased and then frame in with steel. I’m curious to hear more about your approach.
Thanks for the suggestion and that would definitely be easier, but I talked with two spray foam companies and both were charging over $1.50/bf for closed cell spray foam. I read online that's a pretty typical price, so I'm not sure where you live that it's so cheap. I'm a little over 160 lf, so with 9' walls and another 1' for the rim joists, I'm looking at over $2500 at a minimum. All the materials to do the foam boards would be around $700.
Spray foam after framing will work fine if there are gaps between the framing members and the masonary.
One thing to keep in mind with spray foam, is that the feedstock chemicals are not kind to living things, and the mixing process is not perfect.
the lesson is for applicators to use proper breathing protection, and for homeowners to plan for good ventilation to let the remaining feedstock chemicals dissipate. I would want a couple weeks with windows open and fan running.
really important for pregnant women and small children.
https://www.epa.gov/saferchoice/potential-chemical-exposures-spray-polyurethane-foam