Insulating basement before finishing half of It


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Old 02-11-16, 04:38 PM
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Insulating basement before finishing half of It

Ok, looking for some advice here as I am clearly overthinking this. I am preparing to finish half of my 900 sq ft basement. Right now its a blank slate and I want to do this right the first time so looking for help. My main concern, even though the basement is dry all the time (in that no water pours in when it rains), is that basements are humid and I know that adding a heat source in part of the basement will create moisture. I want to avoid a situation where I create an environment for mold. Some background first:
  • the house is 3 years old
  • the basement is poured concrete
  • we live in central Pennsylvania (temps tonight in the low teens and 0 forecasted this weekend). According to the IECC Climate Zone Map, we are Zone 5 and 4 marine.
  • ceiling insulated with batts (R19 I think) between the joists
  • the sill plate currently has batts cut to fit and jammed up against

My first task right off the bat is get rid of the fiberglass insulation on the rim joist as I've read that this can create the perfect environment for mold. I was going to cut rigid foam to fit and then fill gaps with Great Stuff.

Then I was going to use the right adhesive to attach 4x8 sheets of rigid foam to the poured concrete walls. Again, taping seams and filling gaps with Great Stuff to create a barrier stopping moisture from getting to the cold concrete wall. For the top of the wall (where the concrete is exposed because it is wider than the 2x6 plate), I was going to cut pieces to fit, almost like a cap. This way, no concrete is left exposed.

So, my questions:
  1. Should I use XPS or Polyiso between the joists on the sill plate? I've read that Polyiso actually loses R-value the colder it gets...true?
  2. What adhesive is the right adhesive?
  3. If xps, is a 2 inch piece enough? In other words, is R10 going to cut it in our zone? Or would you add another inch?
  4. What tape is the best to use on xps...if that's the material I should end up using?
  5. If I am only finishing half the basement, should I only worry about the foam board on the walls that will be finished? 2 of my finished walls will be up against the concrete foundation, the other 2 studded out in the middle of the room. I am leaving space for storage. With the unfinished part being bare concrete walls, am I being inefficient and leaving myself open for cold getting in?
  6. On the 2 walls that aren't against the foundation, are batts in between the studs enough to combat the situation above (unfinished part of basement not being insulated)?
  7. Should I still insulate between the studs on the walls where the foam board is installed? Or is R-10 good enough?
  8. Would you fill the inch or so space at the bottom of the wall (between the stud wall and the foam board) with Great Stuff to stop air/moisture from getting to the concrete foundation wall?
  9. Thoughts on the concrete floor? Is a roll of foam (the stuff you'd put down under a laminate floor) enough for moisture? Or what is best practice there?

There's probably more, but that's it for now I suppose. Thanks in advance for reading and for any input you can give.
 
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Old 02-12-16, 08:33 AM
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OK, that's a lot of questions but I'll take a crack at some answers.

1. General consensus is for XPS. Polyiso R value does decrease when colder, unlike XPS and EPS (and fiberglass batts) which all get a little better when colder.

2. I know PL premium works well. Some folks like foam board adhesive. PL quick grab has the advantage of requiring less bracing while setting, but a lot of people complain it is very stiff and hard to dispense. You want decent ventilation when using any of these. You will find all the adhesives recommend mechanically supporting the foam for a day or so. My local inspector required this, so I reluctantly used a few tapcons in each panel.

3. You may want to check local building code to see if they have a minimum, many now do. But R10 is about the minimum you would want in your zone. IIWM, I'd put 3.5" unfaced fiberglass in the stud cavities in addition to the foam. This will make the room more comfortable and save a little on energy costs. You could use another inch of foam, but I think the FG will be cheaper and won't eat anymore depth.

4. I like the 3M red construction tape; sticks well to just about everything, including foam. Others use tyvek tape. With either, make sure you remove all dust and press it down tightly; a j roller is ideal.

5. Personally, I would do the whole space, storage area included, especially if that space is heated and/or cooled because you are wasting a lot of energy. If the space isn't conditioned at all, then I would make the separating wall 2x6 and insulate it very well. On that wall only you will need a vapor barrier on the conditioned side. You said the ceiling is insulated, which normally would not be needed, but definitely is if the space isn't conditioned.

6. See 5 above.

7. See 3 above

8. First, you don't have to have a space between the studs and wall. It does often make it easier to get the stud wall straight and plumb. If you put the studs tight to the foam it may count as the support mentioned above. If you do leave a space, I wouldn't bother to can foam the gap.

9. I suggest following manufacturers recommendation and warranty requirement for below grade installation. Most here will say laminate doesn't belong below grade. You can do a moisture test (probably best to do it in spring in your area) to see if you have much moisture coming through the slab. A lot of folks use dricore to be safe, but it adds a lot of cost and work.

Some things you didn't mention:

Firestopping. You need it. See here: How to Firestop Your Basement | Contractor Kurt

Foam sealed with can foam in the rim joists is good, but needs a thermal barrier in front of it. Roxul safe and sound works well for this. Can also double as fire stop if you do it right. Doesn't support mold and isn't bothered by moisture.

You made it sound like you are considering adding an unvented gas heater. Don't. Use a vented heater, electric baseboards, a mini-split...almost anything other than unvented heater.

Hope that helps. I'm sure others here will chime in as there are alternatives to all of this, each with pros and cons.
 
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Old 02-12-16, 01:15 PM
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Very helpful!

I think I am going to go with the 2" XPS between joists up against the rim joist. I'll Great Stuff it into place and probably put my batts back in once I put my firestopping in...

Speaking of which, I am glad you mentioned this as I had forgotton to put it down. But I knew I had to since the Dow Company requires its use with their foam board anyway.

So a few more after reading your reply:
  1. What would you recommend in the space between the bottom of the fireblocking and the top of the foundation? If I use 22/32 OSB nailed to the bottom of each joist, and the sill plate is 1.5", I figure that's 3/4" of exposed foundation (since I'm bringing the foam board on the wall flush with the top of the concrete foundation). Just put strips of 1/2" foam board in and liberally apply Great Stuff to compress it? If that doesn't make sense, there's good reason for it. I might be getting too hung up on the notion that every last bit of concrete behind the framed wall needs to be covered over to limit the moisture coming in contact with it. Maybe I am wrong??
  2. If I frame my wall right up against the foam board, does the "every 10 foot of fireblocking" still apply? Or is that only if the wall is framed with a cavity behind it?
  3. Regarding heating/cooling, the basement is not tied into the HVAC of the rest of the house. It currently has no heat and no AC. Does that change anything you wrote under #5? I plan on heating the 450 Sq Ft with an electric heater that is rated to handle a 1,000 sq foot room. The room stays comfortable in the summer and we have a dehumidifier to keep moisture under control. If you think it better to tie into the existing HVAC though, I would consider it.
  4. The plan was to leave the unfinished part alone and not do anything (just from a cost standpoint). If I put foam board on the walls where the basement is unfinished, am I then forced to frame them, drywall them, and take into account all other firestopping codes? I think i'd rather insulate the crap out of the interior walls to keep the cold in the unfinished part and the heat in the finished part. But again, I want to do this right, so...
 
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Old 02-12-16, 03:41 PM
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1. I meant to mention this. If you cut the foam a little short, say 1/4 inch, so it's not up tight against the fire stop, it will do two things. First, it will faster to cut and install because it doesn't have to be perfect, and second, it gives you room to stick the can foam straw in there and fill that whole space with foam. If you don't want to use that much can foam, you can stick strips in there, but the can foam will seal better and it's pretty cheap.

2. Assuming you are getting this inspected, you should ask your AHJ. My inspector was fine with me putting an extra stud in tight against the foam every 10 feet. In other words, every 10 feet I sistered one of the studs with another that was pressed back tight against the foam. So building the wall tight against the foam would be equal to that except at every stud. But I have read that some inspectors require the fireblock to go all the way to the masonry wall, interrupting the foam. I wouldn't do it that way unless AHJ forced me. (you would have to use pressure treated, too). My inspector also gave me option of tightly stuffing safe and sound in the gap every 10 feet.

3/4. So that means the storage area is unconditioned and you already have insulation in the floor, so I would build the 2x6 wall with insulation and vapor barrier on the "inside", and call it a day. You're right, you can't put foam on the walls and not cover it unless you use fire rated foam that has some thermal barrier built in.

It will be cheaper in the long run to tie it into the house HVAC, energy cost wise, but you would have to determine if your equipment has the extra capacity to handle it.

You may want to consider using a cheap exterior door between the two spaces so you get weather stripping and a bottom seal. Plus the door will be insulated.
 
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Old 02-23-16, 08:07 PM
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How timely as I an in the process of this very project!

Curious about using great stuff low expanding foam for the panel adhesive instead of the PL line.. Been reading a lot of horror stories about how tough the PL stuff can be to use.

Also, I found that link for the firestopping an excellent read.
 
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Old 02-24-16, 05:56 PM
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I think you are talking about the Great Stuff Pro panel and subfloor adhesive?

I've not used it, but it is designed for that application and seems like it would work well and you get a lot of coverage per can. I think you will still need to mechanically fasten or brace the panels and it may actually be worse with the foam since it does expand a little after dispensing.

Big negative for me is the propane propellant; I hate using products with that indoors. Especially when you will be using a lot of it. Unfortunately, as far as I know all the can foams use propane for propellant except for the CRC brand.
 
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Old 03-09-16, 02:01 PM
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I used Dow EnerFoam to adhere most of the foambaord to my concrete foundation. It was relatively inexpensive when purchased on Ebay in a 2 or 3 can set. But of course I ran out right before the end of the project....at that point I switched over to the Window and Door Great Stuff (low expansion, the light blue can). If you can swing the $$$ Id highly recommend buying one of the foam insulation guns (again, off Ebay). Probably the best $30 I spent on the basement project....its SO much easier to use and get an accurate bead with, and allows you to use the big cans of EnerFoam or Great Stuff pro so you get quite a bit of panels adhered before needing another can. And there is no waste....release the trigger and it basically stops coming out, unlike the one-time-use cans.

I did what you are proposing: sheets of foamboard against the vertical walls, strips of foamboard where the top of the wall is exposed before the sill plate of the first floor walls and rectangles of board in each joist cavity slightly undersized and filled in with foam. I have a bandsaw so getting long strips at the right width was really easy.
 
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Old 03-14-16, 09:24 AM
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update

So here I am a bunch of weeks later with not a lot to show. Had the radon tested in the basement and it came back at 44 ("safe" is less than 4) so had that remediated and now we sit at 1.2, so its back to work.
  1. cut all the xps to fit between joists and filled the gaps with great stuff expanding foam.
  2. fire block is done.
  3. I've pre-cut my 2 inch XPS sheets to fit and am ready to attach. I looked at Home Depot and they have a PL specifically for foam board. It's engineered to setup quick (in about 15 minutes). So I am going to use that.

Once that's done, I was going to start framing my 2x4 walls. I've done enough reading now to realize that FG batts is not the way to go. While it may be more expensive, I am going to go with Roxul batts to fill the stud cavity. Then Drywall over that.

So questions:
  1. Any issues I am not thinking about?
  2. Anyone have experience with Roxul? It seems to handle moisture/air flow better and is more resistant to open flame.
  3. What type of drywall is best? I've seen moisture "resistant" and mold "resistant", but is there anything better? If I have a nice sealed wall, is a wood panel an ok option?
  4. I still see and read about people using plastic barrier between the drywall and the insulation. Isn't this bad? I'd think that if I tape all my seams on the XPS, this is the way to go?



- - -
 
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Old 03-14-16, 09:34 AM
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Any issues - not that I can see, but they always pop up It took me 2.5 years to get my half finished basement to the point of framing so all I can suggest is take your time! Actually...are you using steel studs or wood? If wood, Roxul is easy to find, but if you use metal and put them at 16" OC, you'll most likely need to special order the right size (from Lowes or HD) or hit up an actual building supply.....because of the "channel" in a steel stud, your insulation needs to be 16" wide, instead of made for 16" OC (which is truly 14.5" wide).

Roxul - Yep, I used it on my basement remodel too. Two pieces of advice: get a mask or better yet a respirator (pretty much true for any insulation) and get yourself a couple cheap bread knives. Roxul cuts great with a bread knife since it doesnt compress like fiberglass

I used "resistant" drywall, only because I didnt need many sheets and it wasnt much more expensive. If you really want it to never grow mold you need to use something like DensArmor which is a pain to cut and a bigger pain to finish (although in the end I had someone do the drywall for me, so it would have just cost me more $$$ instead of more time). Biggest key is to keep the bottom of the drywall clear of the floor. I had mine cut about 1" short of the floor....if we get 1" of water we have a problem (I had a sump system installed, even if the pumps fail there is 100' of 4" diameter pipe to hold the water...if that fills up we have REALLY big problems)

If you are doing the ridgid glued and taped to the foundation, do not use a vapor barrier behind the drywall. Basement walls cant dry to the outside since you have a big concrete insulator in the way, so any moisture that does form needs to be able to dry to the inside. A vapor barrier would prevent that from happening, so you'd end up with moisture between the back of the barrier and the Roxul. The ridgid foam can technically breath a very little bit so vapor can make its way through, eventually.

The PL foamboard stuff is handy for situations where you dont want to use the spray foam. When I did mine I used the foamboard with lap joints.....I used the PL stuff where the lap joints met and used spray foam to adhere them to the concrete
 
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Old 03-14-16, 10:19 AM
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There are two types of Roxul insulation. Safe and Sound and Comfort Batt. SnS is the mineral wool version that is specifically designed for fire stop and for sound insulation. It is not intended for thermal insulation (says so right on the bag) and the spec sheet does not list an r-value.

I use SnS where I want sound deadening (it is not a miracle cure in this respect, but helps a little) or as fire blocking or as a thermal barrier (such as to cover foam on rim joists).

[edit to correct incorrect information]The Roxul comfort Batt is a stone wool product intended for thermal insulation.

So if you are using for thermal insulation and want to use stone wool, use the comfortbatt product.
 

Last edited by CarbideTipped; 03-14-16 at 12:37 PM.
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Old 03-14-16, 12:21 PM
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Yes, wood studs

So, I guess I need to do more research on Roxul. I knew they had the Sound product, which isn't what I was planning to use, but didn't realize that the ComfortBatts was so much like fiberglass insulation.
 
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Old 03-14-16, 12:36 PM
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I apologize...the comfort batt is stone wool, *not* fiberglass; I confused it with another product....so go ahead and use the comfort batt! I will edit my previous post.
 
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Old 03-14-16, 12:47 PM
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So Roxul

is good as a fire stop? If so, that's my ticket right there. And if so, still do traditional drywall or could you do a wood panel? I'm less and less concerned about moisture, which is good, but rather the ability of the roxul to act a fire stop in place of the drywall.
 
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Old 03-14-16, 01:47 PM
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When did you do all this? Satisfied with the results? I'm all about doing things right the first time and not have to rip it out down the road and do it again. Thanks for the input!
 
 

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