# Insulating a basement wall have questions.



## kossuth (Aug 15, 2009)

Basement has been waterproofed and has I guess you could call it a vapor barrier installed so that any water that would get through would get channelled down into the sub drain the contractors put in. I have the furring strips attached and was starting to get things in order to insulate the walls and I started questioning myself (I guess I suffer from OCD because most people probiably would just run with it) what type of insulation should I use? Should I use the non foil lined Styrofoam or the foil backed stuff? I thought for a moment and considered it a possibility that I was creating two vapor barriers and that could lead to problems being the wood furring strip would take the brunt of the moisture if I were to use foil backed stuff. Am I correct in my concern? If so just regular 1 1/2" styrofoam insulation would be the ticket yes or does it not matter? I know that fiberglass is a definate no-no due to mold concerns etc. Pictures attached so you can get an idea if my description isn't good enough. Thanks guys.


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## bluebird5 (Jan 24, 2011)

i would use the pink foam by owens' corning but at 3/4 thick you are oinly going to get r2 ir is going to take 2 inch to get r10


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## bgibson11 (May 15, 2011)

No matter whether you use pink board or blue board you are getting the same product. Just different manufacturers (Dow, Owens Corning)... However - I could not tell how far along your project was. I know if it were me (for a basement) I'd substitute the 2" of Foam Board with 1.5" - 2" of Closed Cell Spray Foam. The Closed Cell Spray Foam will create its own (seamless) vapor barrier. Free of joints. It also will bond 100% to the concrete substrate. This can stop vapor drive into the basement. Definitely will not stop a water problem tho (if that is the case). 

I'd consider it. And, my guess is you are getting the 2" foam board for near $1.00 + per square foot. You can get a reputable contractor to spray Closed Cell Foam at $1.00/board ft. in our area. For the extra money - it will be well worth it. Just my 2 cents...


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## kossuth (Aug 15, 2009)

Thanks guys, so just regular foam board without the foil backing then. I did think about the using the spray foam but decided against it being I didn't know of anybody local that could do it in a timely manner, not to mention I'm not 100% of the way done framing the basement out. Doing it in stages I guess.


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## Rbneron (May 8, 2011)

From what I've read, you want to attach the foam board directly to the basement wall with the proper adhesive, then attach the furring strips through the foam into the concrete using screws (tapcons or similar). Follow by vertical 1x3 furring strips in vertical direction, 16" on center, using regular screws into first set of horizontal furring strips. 

Drywall then attaches using regular drywall Screws into second set of furring strips. You can dig out the foam slightly as required to allow using standard electrical boxes, and can easily run wire either vertically or horizontally in chase created between sets of furring strips. TOH has video online showing entire process.


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## HomeInsulation (May 25, 2011)

*Insulating Basements - Best Practices*

The standard accepted method for insulating a basement is fairly straightforward. 

1. Glue or screw 2" thick XPS, Extruded Polystyrene, foam insulation board to the concrete block walls. XPS is semi-permeable so it won't trap moisture behind the walls creating mold and rot. 2" of XPS = R10. Foil Faced Poly Isocyanurate like Dow TUFF-R is impermeable and will trap moisture in basement walls.

2. Tape the seams between the foam board panels with Tyvek tape, or some other strong acrylic based tape. This will prevent air from leaking through the XPS foam insulation board at the seams.

3. Use expanding foam insulation like Great Stuff to seal any gaps between the foam board insulation and the floor. Also air spray the foam in any service penetrations where your electricity, phone, cable, gas and water mains enter your basement.

4. Air Seal your rim joists and bottom plate with scraps of the XPS foam board and Great Stuff. Start by cutting pieces close to the right dimensions. Glue those pieces to the rim joist. Air seal around the perimeter with Great Stuff.

5. Frame a 2X4 wall in front of the insulation. Use a piece of Trex or composite decking for the bottom plate to prevent water from wicking up into the framing.

6. Run your electrical wires, outlets, light switches, plumbing and HVAC ductwork through the walls. 

7. Drywall, tape and mud. But be aware that the paper on drywall is food for mold spores. The new types of paperless drywall offer the promise of mold-free basements.

For extremely cold climates, adding 3 1/2" of fiberglass insulation or rockwool insulation between the studs will boost your r-value. Insulating the floor with 2" of XPS and installing a plywood subfloor over top will also increase comfort and energy efficiency.


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## HomeInsulation (May 25, 2011)

*Controlling Moisture in Basements*

One other thing I forgot to mention...

If your basement seems to be damp or have mold or moisture problems, you probably have a lot of moisture in the soil that surrounds your basement. This moisture can pass through concrete block and poured concrete walls very easily.

In order to control the moisture in your basement, you need to eliminate the water that is getting into the soil around your foundation.

Most of this water comes from your gutters and downspouts. Connect extensions of some kind to your downspouts. Make sure the water is sent at least 10 ft. away from your foundation. Although I'd personally channel it to the street, drywell or french drain for extreme weather situations.

The other way water gets into the basement is through improper grading. Improper grading is when the grass or landscaping next to your foundation is lower than the soil near by. Water always follows gravity and so it flows down hill and collects right next to your foundation.

Proper grading directs water away from your foundation. It may require adding extra soil next to the foundation to raise the grade. Or you can remove the high spots near foundation walls.


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## Gary in WA (Mar 11, 2009)

I wouldn't recommend using composite for a bottom plate or a filler against the concrete slab. It will mold from the wood composition if a vapor barrier is missing under the slab (most older houses). A foam sill sealer is better for a thermal/capillary/air seal there. Add using the ADA and fire-blocking to the previous-posted good information: http://www.buildingscience.com/docu...rs/air-barriers2014airtight-drywall-approach/

http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec002.htm

Gary


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## Lilbear79 (Aug 8, 2011)

Would you use faced or unfaced batt insulation in the wall cavity thats infront of the 2" xps board to get a higher R-value? And for free standing walls in a basement family room that are not up against any exterior wall, what type of insulation would you use if I plan on using 2x4 studding in the walls also? And thanks for all the good info , its really been helpful.


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## Gary in WA (Mar 11, 2009)

Always unfaced, you don't want to slow the moisture coming through the wall. Insulating for sound, or thermal? Against concrete? 
http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation

There are more links at the end of the articles; http://www.buildingscience.com/docu...rol-for-new-residential-buildings?full_view=1

Gary


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