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VikingDinKC 01-16-2012 11:06 PM

Foam Insulate All Basement Walls?

I am in the planning phases for finishing my basement. I have been reading that it is a good idea to use rigid insulation foam board. My question is, do I use this foam board on all walls? My basement is a day light basement meaning one basement wall has 3 good sized windows. For this wall, half of the wall is below ground level and the other half is above ground level. On the other side of the basement, the walls are completely underground. Some of the wall faces the garage and the remaining are under the front porch. For these walls, do I need to use the foam insulation against? I am thinking the temperature remains pretty consistent size it never sees the sun. Please advice, when using the foam insulation, should I cover all basement walls? Even the walls in the furnace room? In live in Missouri.

Thanks in advance for your time and knowledge.

Just Bill 01-17-2012 06:05 AM

yes, insualte all walls. I use 2" XPS foam board, and prefer the type with notches in it to allow furring strips. I glue the foam to the wall then screw the furring stripsthru the foam, to the wall with tapcons. The guarantees the foam will stay in place and gives you a place to hang drywall or other wall covering.

mikegp 01-17-2012 07:24 AM

Be careful with the furnace room. All foam needs to be covered because it is flammable and creates overpowering fumes when it burns. If you're not planning to build a wall in front of it in certain areas then you should not use it. I think all cities require it to be covered by code.

VikingDinKC 01-17-2012 10:00 AM

Thank you for the response. I was going to use the 2Ē XPS foam board and use liquid nails to attach it to the concrete. As for the furnace room, this is just a storage area. It will be walled off from the main finished basement. I was going to put storage shelves in this area. So it sounds like I should NOT put the foam on the walls in this storage/furnace area. Since this is not living area, I probably do not need to insulate those walls at all, correct? Just leave the concrete exposed. As for foam board, I should use it any where I am going to stud in front off and then put sheet rock over, even the finished basement bathroom, correct?

mikegp 01-17-2012 10:05 AM

Yes, you should use it on all perimeter walls that you are also planning on framing and finishing a wall in front of. Use canned spray foam and tape to seal it up. I believe 2 inch will act somewhat as a vapor barrier, so I don't think you want to put any 6 mil poly up. Some people say not to put any vapor barrier in a basement anyway.

Rooki 01-17-2012 11:07 AM

Foam Board
I would check on the use of Liquid Nails for foam board....

Im also putting up 2 inch XPS on my basement walls and bought specific foam board adhesive because most of the others will melt the foam board.

I was informed that liquid nails could not be used for XPS board.

mikegp 01-17-2012 11:15 AM

PL300 works well. I'll double check, but I think that's it.

Trucon01 01-17-2012 12:08 PM

Hey Viking. I'm doing the same thing with the XPS. Here is what I go back from the Drylok folks.

"Thank you for contacting us. In regard to your question, once the final coat of DRYLOK Extreme has been cured for a full 48 hours, you can lay the foam up against the DRYLOK. In order to do this, you would need to use a water based construction adhesive such as Liquid Nails to adhere the foam. It is important to use a water based adhesive as a solvent, polyurethane, or epoxy based adhesive will bite into the DRYLOK and will soften it.
Hope this helps to answer your question. Please let us know if you have any additional concerns.

Liquid nails Heavy Duty does work with XPS foam, I checked on that too.

concretemasonry 01-17-2012 01:23 PM

Many of the problems with compatibility of adhesives come from using EPS foam that is not really acceptable or practical for insulation. There are many adhesives that work well with XPS because of the foam density and chemistry.

Adding Drylok into the situation adds some problems because it is a "paint-type" coating. there are other wall coatings that are well established through the years and are more resistant to chemicals and are more compatible with concrete walls.


psilva8 01-17-2012 02:50 PM

I am assuming that you will be putting 2" foam on walls (approx. R10) and a R12 batt in the framing? Have you weighed the difference in price between this method and spray foaming the basement?

Secondly, I would still insulate the furnace room by more traditional means with 2x4 construction and batt insulation. I would go the whole nine yards and insulate the entire basement.

VikingDinKC 01-17-2012 10:25 PM

Thank you for all the wonderful feedback. I was thinking about Drylock as well. I paid extra to have my exterior foundation waterproofed so I think I have a 10 year warranty on that if there are any water issues. I have been in my home for 13 months now and have zero water issues (crossing my fingers just in case). Since I have the exterior waterproofed, gutters that push all water away from the foundation, a slight grade away from the house, a sump pump and no current water issues, should I put Drylock on my walls? I have been reading a lot about it and there appears to be 2 completely different thoughts. Some say it should be done where others say sealing both sides of the wall does not allow it to breath and can create issues. Any feedback? Also, when applying the foam board to the wall, spaces where I have PVC pipes, for example sewer drain pipes, do I get the foam board as close to the PVC pipe as I can and then spray foam such as Great Stuff behind and around it. How have others insulated around unmovable items near their walls? I would like to do what is right but I also donít want to spend money to do something if it does not add value.

mikegp 01-18-2012 06:59 AM

Exactly. What I did was cut a U shape out of the foam board and then slid it up under the pipe. Then I put back the portion of the U that would fit above it and spray foamed around it. You should trim the pieces a little to leave a space for the canned foam to fill. Hope that makes sense.

Gary in WA 01-18-2012 06:06 PM

Go to the chart below the map to find your Zone:

If in Zone 4, you don’t want interior foam board in front of the existing basement wood frame wall (daylight) because it is a Class 2 vapor retarder.

If in Zone 5, the foam will work only if

1. Describe the wall materials, please. Stucco, builder’s paper, foamboard, studs, etc.
2 .Which Zone are you in?

No interior vapor barrier paint if already done on the outside. The below-grade portion of the wall would not be allowed to dry to the inside, pp7-9;


VikingDinKC 01-18-2012 10:13 PM

Thank you for the feedback on how to insulate around pipe. Do you use this same approach around the utility (breaker) box? Not sure how close I want the foam and spray foam to be next to the utility box since I do not want it to be a fire hazard/

In response to what zone, I live in Kanas City MO, which appears to be the top of zone 4. So, based on your response it sounds like I should use the foam on concrete perimeters surfaces that will be finished but should not put it over the wood framed walls which are above ground level. This works for me since I am most likely going to put a little ledge where the concrete transitions to the wood frame.

As for materials, here are the notes I have put together. Any feedback you have is appreciated.

How to finish the walls
• Do not drylock interior concrete walls since the exterior was waterproofed. Below grade portions of the wall will not dry if they are sealed from both sides.
• Install extrude polystyrene insulation boards – minimum of 1-1/2 inches of rigid insulation board – probably go with 2 inch XPS foam board. All perimeter walls that get framed and finished should have the foam board against it. Do not put foam board in the furnace room since it is flammable and creates overpowering fumes when it burns. Also, do not foam board wood framed walls which are above ground level.
• Use an all-purpose adhesive that’s approved for Styrofoam (not liquid nails)… when applying to the wall, it should be a tight fit
• Tape each joint with construction tape, by taping the joints you are helping keep moisture and cold air from infiltrating into the stud wall cavity (Tyvek Tape or Dow Construction Tape). Also, use adhesive in the foam joints.
• Seal top and bottom of the foam board using spray foam from a can (Great Stuff) so it acts as a vapor barrier
• Frame basement wall – leave 1 inch gap between foam and framed wall to allow for air flow.
• Insulate stud wall cavity – install fiberglass insulation in the wall cavities to create a final composite R value that meets the energy code requirements (R13)
• Install rim joist insulation – use spray foam, foam board or fiberglass insulation
• Complete needed electrical, plumbing, etc.
• Vapor barrier - the best vapor barrier is a polyethylene plastic sheet (4 or 6 mil) spread over the studs and stapled in place – not 100% sure this is needed if the foam board is sealed but the cost is low so I am thinking of doing it
• Finish wall surfaces with sheet rock

mikegp 01-18-2012 10:26 PM

You probably don't want to put up the 6 mil vapor barrier. It could cause more harm than good. You don't have to leave any space between the studs and xps, but you can if you want. Try to avoid fiberglass insulation. It can absorb moisture and start to mold. Try something like roxul instead.

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