Basement insulation

shortys7777

Feeling the Heat
Nov 15, 2017
322
Smithfield, RI
Turning part of my basement into a playroom for the kids. It was a half done room with zero insulation and no outlets. Wouldn't mind keeping the 2x4 studs but not a deal breaker. I could gut it entirely and use the 2x4 for a wood storage over hang for my stacks out back. What is the best insulation to go with? I will be installing pex baseboard heat down there from the same zone as my master bedroom.
 

heat seeker

Minister of Fire
Feb 25, 2011
3,195
Northern CT
I would strongly suggest, if you can, a separate zone for the basement. The heating requirements will probably be very different from the bedroom above.
 

EbS-P

Minister of Fire
Jan 19, 2019
528
SE North Carolina
I did quite of bit of thinking and reading about insulation for my basement. I have moister issues than in need to fix before I do any insulating. I decided that the best solution was closed cell spray foam. Its cost prohibitive given my climate and budget. Next best thing was a rockwool product that went right up on the concrete. Then if you wanted needed more insulation you could insulate the stud wall. Again this just my felling and have not used any of this. I can tell you that just sticking foam bbetween the studs that doesn’t fit tight isn’t that great. Insulation is all about air sealing. And in a basement that also means moisture control.

my two cents. I just ended up painting the bock wall. I’m considering adding a mini split unit.
 

MTY

Feeling the Heat
Jan 9, 2019
438
Idaho
I ripped 2" blue foam board to fit the stud bays, glued those to the concrete, and foamed the top, bottom and sides of each foam board. Behind each stud I filled the void with foam.
On the non concrete walls, I had blown in batt done. The house is right at 2500 square feet, and starting in November the three electric bills so far were $66, $120, and $118. Deduct about $30 each month for a service connection fee to figure out the actual electric cost.

This is for an all electric house, occupied 4 days per week. R60 above, R23 walls, heated 4' crawl space under half the house. Full basement under the rest. The crawl space walls are covered with 2" foam and the rim is foamed and stuffed with R20 batts. There are no breezes blowing through the house.
 
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shortys7777

Feeling the Heat
Nov 15, 2017
322
Smithfield, RI
I will look into those . As for the heat my master hardly ever gets turned on. My heat in general hardly ever turns on from my stove running all the time.
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,205
Eastern Central PA
I exclusively use foam board in the basement. But after all moisture and water issues are resolved. I love cellulose but not in the basement. Also i put the board either behind the studs or in front of them for best rValue not in between. Thats less work as well. Foam board is so much cheaper than spray foam and very good r value.
 
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stoveliker

Minister of Fire
Nov 17, 2019
538
Eastern Long Island NY
I exclusively use foam board in the basement. But after all moisture and water issues are resolved. I love cellulose but not in the basement. Also i put the board either behind the studs or in front of them for best rValue not in between. Thats less work as well. Foam board is so much cheaper than spray foam and very good r value.
Just make sure there is drywall covering the foam board per fire code.
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,205
Eastern Central PA
Just make sure there is drywall covering the foam board per fire code.
That sort of goes without saying. Of course the foam has to be covered with moisture resistant drywall if possible. I usually keep it off the cement half an inch or more and always use treated lumber for the stud base plate.
 
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MTY

Feeling the Heat
Jan 9, 2019
438
Idaho
I agree with putting it behind the studs. My helper beat me to the job that day, and he had the concrete portion of the basement walls framed out by the time I got there. We stayed off the concrete 1.5" with the framing. That is why I cut the foam to fit the stud bays. The framing left me adequate room to foam behind the studs. I figured since he was already framed, it might work for the OP.
 
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zrock

Minister of Fire
Dec 2, 2017
1,035
bc
I would never use a spray foam or foam board that is not fire rated/retardant. the fumes that come off that will harm you before you realize what is happening. Does not matter if it has drywall over it or not if the fire gets to it or starts behind the walls its gonna be toxic. I have used the roxul and that is great stuff and fire proof so if a fire starts in that area its not going to spread as fast...
 
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Seasoned Oak

Minister of Fire
Oct 17, 2008
7,205
Eastern Central PA
I would never use a spray foam or foam board that is not fire rated/retardant. the fumes that come off that will harm you before you realize what is happening. Does not matter if it has drywall over it or not if the fire gets to it or starts behind the walls its gonna be toxic. I have used the roxul and that is great stuff and fire proof so if a fire starts in that area its not going to spread as fast...
You could say the same for vinyl siding and foam in furniture.
 
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DickRussell

Feeling the Heat
Mar 1, 2011
261
central NH
The building science relating to insulating a basement wall has been very well understood for some time, yet people still do it the wrong way, often resulting in a smelly, mold-infested mess. Basically, a porous, vapor-open insulation like rock wool or fiberglass should not be installed directly against a buried concrete or block wall, nor should there be a poly vapor barrier on the interior side of the assembly. Basically, the right way to do it is with rigid foam board or closed-cell spray foam against the wall, covered with sheetrock for thermal and ignition protection of the foam. If desired, additional batt insulation can be installed between 2x framing over the foam, and the sheetrock over the foam/batt assembly. If there is no batt insulation over the foam, 2x framing flat side out can be installed over the foam board to create a 1.5" cavity for shallow electrical boxes. All of the science behind how to do it right and plenty of variations and related information is easily found by a search on insulating a basement wall. Here is one: https://www.finehomebuilding.com/2015/07/11/adding-insulation-to-basement-walls
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,205
Eastern Central PA
Basically, the right way to do it is with rigid foam board or closed-cell spray foam against the wall, covered with sheetrock for thermal and ignition protection of the foam.
Pretty much zero chance of burning that way.
 

stoveliker

Minister of Fire
Nov 17, 2019
538
Eastern Long Island NY
@DickRussell Question: My basement is partially below grade, concrete. It has a sewer line running along the wall from the back to the front of the ("wide" rather than "long") home - covering 2/3 of the back wall, all of the (shorter) right side wall, and 1/2 of the front wall before exiting the home.

The wall/finishing is therefore (mostly) about a foot in front of the concrete wall, b/c that pipe runs behind it. I thus end up with a concrete wall, about a foot of empty space, then a fiber glass bat-insulated 2x4 wall with drywall on the inside. Other than the drywall (?) there is no vapor barrier that I know of.

(The bays in the floor assembly at the walls are also, erroneously, stuffed with fiberglass, and the ceiling is an "office looking panels on aluminum profiles" drop ceiling - and I am planning to have the bays between the floor joists spray-foamed sometime in the next two years when I redo the ceiling.)

What is the best way of insulating the walls, with that gap from the 2x4 wall to the concrete wall?

We don't currently have moisture or mold issues in the finished basement (though I don't know how it looks behind the drywall...). We do run a dehumidifier in summer and the stove (dry) in winter from the basement.
 

DickRussell

Feeling the Heat
Mar 1, 2011
261
central NH
....... Question: My basement is partially below grade, concrete. It has a sewer line running along the wall from the back to the front of the ("wide" rather than "long") home - covering 2/3 of the back wall, all of the (shorter) right side wall, and 1/2 of the front wall before exiting the home.

The wall/finishing is therefore (mostly) about a foot in front of the concrete wall, b/c that pipe runs behind it. I thus end up with a concrete wall, about a foot of empty space, then a fiber glass bat-insulated 2x4 wall with drywall on the inside. Other than the drywall (?) there is no vapor barrier that I know of.

(The bays in the floor assembly at the walls are also, erroneously, stuffed with fiberglass, and the ceiling is an "office looking panels on aluminum profiles" drop ceiling - and I am planning to have the bays between the floor joists spray-foamed sometime in the next two years when I redo the ceiling.)

What is the best way of insulating the walls, with that gap from the 2x4 wall to the concrete wall?

We don't currently have moisture or mold issues in the finished basement (though I don't know how it looks behind the drywall...). We do run a dehumidifier in summer and the stove (dry) in winter from the basement.
Since you don't have apparent moisture issues in the basement, that takes care of your first step - making sure leakage isn't a problem. As for that sheetrocked wall in front of the foundation wall with the pipe along it, if it's well sealed against air currents leaking around it, then a couple coats of latex paint provide a decent vapor retarder layer to keep most of summer air moisture off the (likely) cooler foundation wall. However, much of the year there could be ground moisture migrating inward through the wall or upward from the footing, creating mold-favorable conditions behind the wall.

You spoke of later insulating under the floor above, yet you have a dehumidifier running in the basement in summer (likely a good thing), and you run the stove in winter. The other approach would be to forgo insulating that floor and just insulate the basement walls. You might think of getting behind that wall in front of the sewer pipe and applying rigid foam board above and below it as best as you can. You can seal the gap between pipe and foam with can foam. Then there shouldn't be any problem having that framed wall in front of the pipe, as long as there is no polyethylene sheet sandwiched in there behind the sheetrock. Allow for access to any cleanouts in the sewer pipe. Having part of the wall built in a way that it is easily removed for access is one thought.

When you do get into redoing the ceiling of the basement, the right way to insulate the bays at the perimeter is with closed-cell foam, either sprayed on or with "cut & cobble" application of rigid foam board sections with the perimeters sealed with canned foam. Additional batt insulation could be applied over that. As things stand (per your description), having porous insulation not totally sealed at the edges allows moisture from the air to migrate easily to the rim board, which will be cold in the winter.

Those are my thoughts, based solely on what you have described. There could be other aspects to it that would call for doing some of what I suggest somewhat differently.
 

stoveliker

Minister of Fire
Nov 17, 2019
538
Eastern Long Island NY
Since you don't have apparent moisture issues in the basement, that takes care of your first step - making sure leakage isn't a problem. As for that sheetrocked wall in front of the foundation wall with the pipe along it, if it's well sealed against air currents leaking around it, then a couple coats of latex paint provide a decent vapor retarder layer to keep most of summer air moisture off the (likely) cooler foundation wall. However, much of the year there could be ground moisture migrating inward through the wall or upward from the footing, creating mold-favorable conditions behind the wall.

You spoke of later insulating under the floor above, yet you have a dehumidifier running in the basement in summer (likely a good thing), and you run the stove in winter. The other approach would be to forgo insulating that floor and just insulate the basement walls. You might think of getting behind that wall in front of the sewer pipe and applying rigid foam board above and below it as best as you can. You can seal the gap between pipe and foam with can foam. Then there shouldn't be any problem having that framed wall in front of the pipe, as long as there is no polyethylene sheet sandwiched in there behind the sheetrock. Allow for access to any cleanouts in the sewer pipe. Having part of the wall built in a way that it is easily removed for access is one thought.

When you do get into redoing the ceiling of the basement, the right way to insulate the bays at the perimeter is with closed-cell foam, either sprayed on or with "cut & cobble" application of rigid foam board sections with the perimeters sealed with canned foam. Additional batt insulation could be applied over that. As things stand (per your description), having porous insulation not totally sealed at the edges allows moisture from the air to migrate easily to the rim board, which will be cold in the winter.

Those are my thoughts, based solely on what you have described. There could be other aspects to it that would call for doing some of what I suggest somewhat differently.
Thanks. Your thoughts make sense. Indeed, the idea is to have closed cell spray foam in the bays (and then stuff the rest of that unused space with fiber glass - cheap and won't cause trouble anymore after foaming). It's too much work to do foam board sections in these bays, reaching over that stud wall...

So, when you're saying "get behind that [stud] wall in front of the sewer pipe and apply rigid foam board", you mean putting the foam board on the concrete wall, right (not on the back side of the stud wall)? So not putting the foam boards on the back side of the stud wall (putting the sewer pipe outside of the foam board envelope)?
(I also read that I may then need a fire retarding (wood board) layer on top of those foam boards before the floor joists are reached?)
 

velvetfoot

Minister of Fire
Dec 5, 2005
10,038
Sand Lake, NY
I did the rim joist with several layers of foam board. I did it with a tight fit and yes, it did take a long time. I fastened 2" foam boards to the wall and held them in place with furring strips that were screwed into the concrete. I had to mill out channels for wires. I put tyvek tape over the joints. I put a second layer of 2" foam with channels milled into them to go over the furring strips and glued it on. I then screwed drywall onto the furring strips. I think it turned out well but it was a hassle. Forget about adding non-surface electric circuits. I had a sewage trap that I thought about it a little: I think you'd want to keep that exposed to the warmth of the interior so it doesn't freeze (it was on an above-ground section of basement wall. I never did finish the basement: I put in a pellet boiler, with, like, 6 tons of pellets instead. That is one sturdy wall though-you could run at it full force and nothing would happen to the wall.
 

DickRussell

Feeling the Heat
Mar 1, 2011
261
central NH
....
So, when you're saying "get behind that [stud] wall in front of the sewer pipe and apply rigid foam board", you mean putting the foam board on the concrete wall, right (not on the back side of the stud wall)?....
Yes, put the foam board right up against the concrete. You can find online various ways of attaching it. One is to glue it with PL-300 (Loctite). Another is with screws through fender washers, foam, and into the concrete. Sheetrock goes over the foam, even though it's inside that framed cavity. When I said "get behind" that wall, I had in mind removing paneling from the framing and pulling studs here and there as needed to be able to slip foam boards behind the framing, If there is space between pipe and concrete, you can slip the foam board sections in there. If the pipe is tight to the wall, you'll have to fit the foam section-wise up tight to the back curve of the pipe and perhaps seal the edges against the pipe.
 
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shortys7777

Feeling the Heat
Nov 15, 2017
322
Smithfield, RI
So your saying cement foundation, foam board, sheetrock, 2x4 studs with insulation between them, then sheetrock again on the inside to be finished and painted?? My basement got a very small spot of water from some big storms but I had clogged gutter drains. I have since ran those way away from my foundation. Couple storms should really see if it fixed it. I do some drainage work in the summer when I landscape. My basement is generally really dry. The dehumidifier turns on when needed in the summer months. I will probably put another small one in the finished room since it'll be separated from my workshop area.
 

velvetfoot

Minister of Fire
Dec 5, 2005
10,038
Sand Lake, NY
So your saying cement foundation, foam board, sheetrock, 2x4 studs with insulation between them, then sheetrock again on the inside to be finished and painted?? My basement got a very small spot of water from some big storms but I had clogged gutter drains. I have since ran those way away from my foundation. Couple storms should really see if it fixed it. I do some drainage work in the summer when I landscape. My basement is generally really dry. The dehumidifier turns on when needed in the summer months. I will probably put another small one in the finished room since it'll be separated from my workshop area.
That's a lotta sheetrock
 

DickRussell

Feeling the Heat
Mar 1, 2011
261
central NH
So your saying cement foundation, foam board, sheetrock, 2x4 studs with insulation between them, then sheetrock again on the inside to be finished and painted??....
Mmmmm, the double sheetrocking likely is not needed. If the cavity is sealed off by sheetrock on the framed wall in front of the foamed foundation wall, so that there is no ready access to the cavity behind it, then arguably the sheetrock right over the foam could be skipped. But that might be a matter to run by local code enforcement for interpretation.
 
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Seasoned Oak

Minister of Fire
Oct 17, 2008
7,205
Eastern Central PA
So your saying cement foundation, foam board, sheetrock, 2x4 studs with insulation between them, then sheetrock again on the inside to be finished and painted??
Whats the insulation between the studs for ,if you dont have the required Rvalue just use thicker foamboard. Works better anyway as there is no thermal leakage through the studs. .
 

stoveliker

Minister of Fire
Nov 17, 2019
538
Eastern Long Island NY
Whats the insulation between the studs for ,if you dont have the required Rvalue just use thicker foamboard. Works better anyway as there is no thermal leakage through the studs. .
But R19 in foam board gets to be rather thick...?
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,205
Eastern Central PA
But R19 in foam board gets to be rather thick...?
Any foam is higher R value per inch than most other insulation. You can use 2 2in thick sheets if you cant find 4in foamboard. Savesa lot of work cutting something else for in between studs for less r value . I just did a exposed basement wall from the outside under a front porch with 2 in. Since the basement will not be living space with separate heating. And doing the out side has a number of additional benefits.
 
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