Basement insulation options

[Tom7227]

I am thinking about insulating the basement of my daughters 1960's single story home in Minneapolis. Right now the basement is about 10 degrees colder than the upstairs. The city's specs call for 2 inches of closed cell foam and then a 2x4 wall. That gives an R-10 and will cost about $750 or so for the insulation if we do the entire basement.

I am wondering if using spray foam makes sense, both from the increased R value and also economics. I don't have any bid for the spray foam so I don't know what the cost may be.

If we were going to spray then next thing is does it make sense to build the 2x4 wall and run the electric but to set the wall 2 inches of so off the wall. That way it would give a full insulating break from the outside wall and also an increased R value. I have been told that anything more than an R10 isn't needed in a basement.

There isn't any ductwork in the basement and installing it seems like a pretty large expense. My idea based on the economics is to wire it for electric baseboard and only install it if the basement is ever going to be used for living space. There is a rec room with a fireplace, a room that may be used for a bedroom in the future, a laundry room and a furnace room. Not sure if doing the furnace room makes sense as it can be closed off with a door.

So any ideas what the foam might cost for a 1200 square foot house? Does the increase in R value make economic sense? Does it make sense to offset the stud wall to allow for more foam and the higher R value?

Thanks for your time.

Tom

[rundrave]

I just had spray foam done in my most of my basement a couple months ago and I love it. Keeping in mind I am doing most of my basement finish as a DIY'er I chose to hire the foam out. The time it saved me alone in just labor was worth it compared if I did the close cell foam, batts, cutting etc. and all that myself. Plus it saved me a little bit of room not having to do the sheets of foam and I then having frame up against those for my the basement walls. I just put my studs about 1" off from the walls around the perimeter.

I framed up the basement and ran my wiring and the spray foam crew of 2 guys did that area including the walls of my garage and were in and out in one morning and gone before lunch.

There is no way I could have got the same R-value especially up around the rim joists in the basement. it was a little more expensive up front but I think it will be worth it. Its nice and toasty down there even in this cold and I dont have any heating runs ran yet.

The other thing I liked about the foam in the basement is that I live on a rural property with a high water table and I pump alot of water out of my sump. Worst case scenario if I ever get water in the basement the spray foam should fair alot better than the bats would if I got wet.

I dont know my exact sq/ft of work done on the exterior walls in the basement. That included 3" of foam in rim joists and 2" of foam on that walls and that was about $1400. I dont have the exact measurments because I had some storage areas left out because they were full of stuff and I wasnt moving it all out.

I also had just the the walls in my 32x28 garage done with 2" foam also and that was about $1300.

i would say get some bids just to price it out, of course the spray foam is gonna be little more spendy but it sure saved me a lot of time on my project.

[leechlake]

from reading that the time savings would be a huge benefit especially since you're doing this in your "spare time." Probably save you 2-3 days I'd guess unless you've got some young industrious "free" helpers which you may have. I'd assume you have to balance that with the fact your daughter is probably paying some or all of the tab (none of my business no need to answer that question).

This project is giving me flashbacks to our first house, great memories of a simpler time in life. My wife's dad and my dad were over all the time helping us learn the ropes of DIY stuff. I lived at the M store that luckily was right down the road.

[LightningBG]

The spray foam is great, but a LOT more expensive. I think Rundrave got off pretty cheap. Who knows why. Maybe a struggling business trying to get a gig? Maybe just cheaper down in SD? People are paying more than he did just to get their ice shack sprayed.

Personally I don't think I'd do it in a basement unless I had cash to burn or a new fancy house in which a lot of time was going to be spent in the basement.

I'd do the closed cell sheets, 2x4 wall, then batts in the stud bays. Use the extra money to add insulation to the attic or upgrade some windows.

No question about it. We are doing exactly that at our cabin which we recently gutted the basement in.

[Tom7227]

Well I am not young but I am cheap labor - free. Being retired means that I don't have much to do and looking for projects. The windows in the house need some attention but that will be waiting a bit.

Anyone with knowledge on whether something more than an R10 makes any sense? Advice from a retired builder was that it was enough and that even putting fiberglass in the stud cavities wasn't worth it. Lightening the only differences I see is that the Mpls specks call for 2 inches of foam boards, and for some reason placing the 2x4 the 'other' way so that the drywall is only 2 inches away rather than 4. That makes no sense to me as it creates problems running the wiring.

[rundrave]

The spray foam is great, but a LOT more expensive. I think Rundrave got off pretty cheap.

[LightningBG]

As for the rigid foam. If the house was 30'x40', you'd be looking at approximately 35 sheets (assuming ceilings 8' and no odd shapes).

If it were me, and I was doing it today.....

I'd go get (Qty: 35) JM AP Foil™ 1"x4'x8' R-6 Polyiso Rigid Foam Insulation

on sale at the M store for $12 a sheet, $420.

Then you'd need studs, but you'll need those anyways. so that is moot in the comparison.

Then I would buy batts. These: CertainTeed 3-1/2" x 15" x 40' R-11 Unfaced Fiberglass Roll - Covers 50 Sq. Ft. at a cost of $6 per roll.

Lets say 105 stud bays. ((140-lf x 12in)/16 inches per stud) Each roll will fill 5 bays. 21 rolls, buy 22 @ 6 = $132.00

You will also need some odds and ends, like glue, but for the insulation itself, you'd be looking at approximately $550.

R value would be approximately R-17. Approximately equivalent to 3 inches of closed cell foam or 4.6 inches of open cell.

(but I would also check to make sure that foil faced insulation is ok up against a basement wall. I've always used the pink or blue stuff, but the foil is higher R value and a smokin deal currently.)

[LightningBG]

You can router the foam to run wiring behind the studs if they are laid flat, but unless you are desperate for the extra 2 inches of floor space, I wouldn't do it.

Does Mpls "require" 2 inches or suggest? Are you pulling a permit? I wouldn't.

[Tom7227]

Here is the info from Mpls.

http://www.ci.minneapolis.mn.us/www/groups/public/@regservices/documents/webcontent/convert_270212.pdf

[LightningBG]

Looks like it just needs to be 10 or greater, so I would imagine the R5 and batts would work. Overall, their requirements are pretty poorly designed. R-0, good. R-5, no good. R-10, also good.

Here is the full energy code sheet. I wouldn't agree with much of it.

Energy Code

[delcecchi]

In reality the return for insulation depends on how far underground you are. Rim and exposed block lets out a lot of heat. 5 feet underground, not nearly as much.

[LightningBG]

In reality the return for insulation depends on how far underground you are. Rim and exposed block lets out a lot of heat. 5 feet underground, not nearly as much.

Very True. If you're just interested in getting it a little better down there, but not dead set on going all out, you could buy an inexpensive infrared thermometer and shoot it at various areas (different walls, rims, etc) and see which areas are coldest, insulate those areas first.

If there aren't any vents down there, I cant see it holding the same as upstairs, no matter what the insulation (but it may be close enough)

[BoxMN]

When we built cabin (walkout in 2008) our contractor did what LightningBG said about the on-sale foil foam sheets next to the block, with all seams taped - it might be 1.5" but I am pretty sure it is not 2" - I recall R12 with a 2" space between foam and wall, but I can't recall for sure. He recommended no further insulation (actually told me NOT to do it), just the 2x walls. On the framed walls in basement (above grade) he used unfaced and put vapor barrier plastic over it, taping all seams and around windows. Spray foamed the rim joists.

[leechlake]

I'm taking a guess here but the "new" way to finish a basement just looks weird. My buddy in Maple Grove had his basement finished last Winter and I thought it was the goofiest thing I'd ever seen. In his case the 2x4's were placed facing "flush" towards the wall with the insulation between the wall and 2x4's. I still don't get it but that's how it had to be done in MG.

[311Hemi]

I'm taking a guess here but the "new" way to finish a basement just looks weird. My buddy in Maple Grove had his basement finished last Winter and I thought it was the goofiest thing I'd ever seen. In his case the 2x4's were placed facing "flush" towards the wall with the insulation between the wall and 2x4's. I still don't get it but that's how it had to be done in MG.

You sure it HAD to be done that way? I can't see that being a requirement anywhere. They may have done that to save space, but I can't see I have seen it done line you are suggesting.

My house was built 1.5 years ago and the builder wrapped all of the foundation block in 2" foil faced rigid insulation, all seams sealed. Rim joist was sprayed insulation. Frames walls were bat insulation with vapor barrier on inside. Still researching the best way to finish it.....but not in a big hurry there.

What was up against the wall (or was it just block), and where was the plumbing and electrical ran?

[amateurfishing]

The spray foam is great, but a LOT more expensive. I think Rundrave got off pretty cheap. Who knows why. Maybe a struggling business trying to get a gig? Maybe just cheaper down in SD? People are paying more than he did just to get their ice shack sprayed.

Personally I don't think I'd do it in a basement unless I had cash to burn or a new fancy house in which a lot of time was going to be spent in the basement.

I'd do the closed cell sheets, 2x4 wall, then batts in the stud bays. Use the extra money to add insulation to the attic or upgrade some windows.

No question about it. We are doing exactly that at our cabin which we recently gutted the basement in.

This is how I finished our block wall split level basement cept no fiberglass, pink rigid glued and taped against block, then frame, then sheetrocked. Inspector even laughed, said rigid insulation on block was unnecessary cause whole neighborhood is insulated on outside below grade.

[Pinusbanksiana]

The spray foam is great, but a LOT more expensive. I think Rundrave got off pretty cheap. Who knows why. Maybe a struggling business trying to get a gig? Maybe just cheaper down in SD? People are paying more than he did just to get their ice shack sprayed.

Personally I don't think I'd do it in a basement unless I had cash to burn or a new fancy house in which a lot of time was going to be spent in the basement.

I'd do the closed cell sheets, 2x4 wall, then batts in the stud bays. Use the extra money to add insulation to the attic or upgrade some windows.

No question about it. We are doing exactly that at our cabin which we recently gutted the basement in.

this is how I finished my basement. Went from freezing in winter to tolerable. Also put that rigid EXP in rim joists, seal with great foam.

[Tom7227]

If you have to build a sheetrock wall how much glue should you use on the foam board? Just dabs in the corners to hold it up? The glue is pretty expensive and it seems that the stud wall would hold it up.

BTW the specs call for the 2x's to be put up the 'wrong' way. Doesn't make sense to me and that's not how I am going to do it.

[Pinusbanksiana]

If you have to build a sheetrock wall how much glue should you use on the foam board? Just dabs in the corners to hold it up? The glue is pretty expensive and it seems that the stud wall would hold it up.

BTW the specs call for the 2x's to be put up the 'wrong' way. Doesn't make sense to me and that's not how I am going to do it.

The effectiveness of the foam (EXP) is all hinged on having an air tight fit to the block. I put mine up in the winter so it was immediately evident to me. Even not taping the seams I could feel the cold coming through between the sheets. I didn't use the sheets that lap, but if I did it again I would. I also left about an inch of air space between the EXP and the stud wall. So my suggestion is to bite the bullet on the expensive glue and put it on liberally. I think a tube per two sheets is what we averaged. Build a contraption to hold it tight to wall until the glue dries.

[amateurfishing]

I had no problem glueing to blocks but I do remenber reading directions on tube and says apply liberally in weave or "s" pattern, it can b messy but should not matter as covering uo with sheetrock anyway.

[nofishfisherman]

I remember when gluing my sheets of insulation to the wall I had to brace them in place with 2x4's until they dried in place. Not sure if it was due to the cold concrete since I did it in the winter. I used plenty of glue on each piece.

Once in place i liberally taped each seem and used plenty of the expanding foam where needed.

I also left a gap between the insulation and the stud wall. I think it went anywhere from 1 to 3 inch gap in order to make my stud wall straight.

[SkunkedAgain]

My basement is the same as your daughter's situation. A few years ago I put the rigid foam in place with PL300 adheasive. I don't remember having to hold anything against the wall as it was tacky enough. I then taped the boards and used more PL300 to seal gaps, then built the stud wall against the foam. I didn't fill the bays with insulation and then just sheetrocked. It made a huge difference. The biggest heat/cold issue comes from top of the block and joists. I put rigid foam up there and sealed with the PL300 as well.

All of this raised the temp from 15 degrees colder than the rest of the house to about 8 degrees (68 upstairs and typically 60 in the basement). I installed a subpanel and three baseboard heaters under each window connected to a thermastat on the inside wall. It's perfect....along with adding pad & carpeting.

[bobberineyes]

They make a metal "z" stud for this application. Foam gets glued to the block and the z stud not only locks the foam sheets together but the sheet rock gets screwed in to as well. Most of the commercial jobs are done this way.

[Pinusbanksiana]

They make a metal "z" stud for this application. Foam gets glued to the block and the z stud not only locks the foam sheets together but the sheet rock gets screwed in to as well. Most of the commercial jobs are done this way.

With this method you are missing the added R value of the fiberglass batting. Also, I am not sure how you could easily wire in some outlets or switches. I agree that it sounds easy and probably not expensive.