How2:Insulating Joist/Wall Plate & Concrete Walls

I have a walk out poured concrete (8"x8') basement (~800+ ft^2). One of the four walls is exposed and has a sliding patio door and two double hung windows. One wall is shared with the garage at the same level. That leaves two walls below grade. The basement is always cold because the Vigilant is on the main floor and the oil furnace barely runs. Basement temperatures drop into the high 40's when outside temps hold in the teens. Cold uninsulated floors as you'd guess. I'm seeking input on how to solve two insulating problems. I like to get ideas about what would be the best material to use in each application.

The first problem is air infiltration at the floor joist voids where they are perpendicular to the wall. I didn't realize how much air was infiltrating until I ran a gas powered generator on the side of the house where the grade covers the wall. I discovered that the basement filled with exhaust fumes! Where I had the generator, the floor joists are perpendicular to the wall. There is about an 8" section that the joist cantilever out past the wall to hold a zero clearance wood burning fireplace/chimney assembly. I always thought the builder placed wood blanks at the wall in between the joists (I would have!). Apparently not A skirt board covers the rest of the way. Fiberglass insulation is between each joist above the wall. I think there's another 16' in the same condition where the kitchen bumps 2' over the wall. 24' total that are just filled with fiberglass.

• What should I use to seal and insulate these voids?

After that one, here's the second question: What insulation technique/materials should I use on the below grade concrete walls and then the exposed wall? It will have to be an inside instalation, not going to dig up the two sides. Once last year when the outside temperatures were -12*F, the exposed concrete wall measured 22*F. Can't leave either of these two conditions unchanged when I hook up the Koker (finally).

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http://www.homeconstructionimprovement.com/how-to ... ent-walls/

http://www.contractortalk.com/f18/basement-concre ... ons-93754/

I was think Styrofoam or SprayFoam too. The sprayfoam crated a vapor barrier and give as much or more insulation than a standard 3.5" thick fiberglass. LIke 2-3" of sprayfoam is like R19 or more.

Thanks for the links.

Has anyone done this job before?

Still trying to figure what to do with the space between the cantilevered joists that are open to the outside. Only filled with fiberglass and that doesn't stop air from moving. I'm thinking cut blue board foam to fit, foam it into place and then replace the chunk of fiberglass that's there now. Thoughts?

I spray foamed under the floor of my house last summer. It's not a bad job; just make sure to wear all the protective gear because that stuff really sticks to whatever it gets on. I have a similar cantilever setup on the addition I'm building. I used fiberglass on one side of the house and I don't notice any air movement. Of course I put in the wood freeze blocks between the joists and cement board along the bottom of the joists so it's pretty tight. I haven't done the other side yet but I'm going to spray it. Makes an airtight seal and it's closer to grade so I didn't want to have to worry about moisture getting to the fiberglass. I have sprayed foam onto the blueboard and it seems to stick fine if you want to go that route. I think just spraying would be a lot easier than fooling with cutting the blueboard. You can build the foam up to whatever thickness you want.

David78 - what did you use for spray foam? Do you have access to professional equipment or did you use kits?

I used a kit. I got mine from http://www.sprayfoamdirect.com No complaints. I think the prices are about the same wherever you get it.

david78 wrote:I used a kit. I got mine from http://www.sprayfoamdirect.com No complaints. I think the prices are about the same wherever you get it.

Yep, Use the Closed-cell version to create a 1 inch thick vapor barrier, then fill the rest of the void in with Open-cell or fiberglass batting.

MY .02 DOLLARS.

Spray foam is fairly expensive - over $1 per board foot just for materials but does a great job due to it's ability to fill every gap.

Spray foaming the joist band will seal the air infiltration.

The overhang should have the underside board taken off and have barrier blocks installed in the joist band area. Spray foam the band underside of the floor in the overhang to seal it up.

Do not leave foam exposed to the living area. It is flammable. It will burn vigorously and emit toxic gases in a fire situation. Stud out the area after installing foam board or spray foam and cover with drywall to add a fire barrier. The studs will add a chase for electrical if you ever want to have more power in the basement.

steamup wrote:MY .02 DOLLARS. ...8<...
The overhang should have the underside board taken off and have barrier blocks installed in the joist band area. Spray foam the band underside of the floor in the overhang to seal it up.

Do not leave foam exposed to the living area. It is flammable. It will burn vigorously and emit toxic gases in a fire situation. Stud out the area after installing foam board or spray foam and cover with drywall to add a fire barrier. The studs will add a chase for electrical if you ever want to have more power in the basement.

Steamup, thanks for the tips! I wouldn't have considered some of them myself. I would have spray foamed the inside of the joist/floor/wall space after blocking it with wood. Never considered the fire considerations.

Does anyone know if there is a specification for which type of foam board to use on the inside of the wall with the following exposures?

• concrete below grade
• concrete above grade

Does it have to 'breath' if it's against a wall that's below grade and that wall has a mastic barrier outside covered by earth? I'm wondering about where to use different foam board types - closed cell unfaced or faced, open cell unfaced or faced. I guess the facing is a foil style barrier. I haven't begun to shop for what I'll need so I'm open to more suggestions, especially from those that have been there

Dew point is the consideration...
Insulation 'rules' are a moving target as it depends what theorist is preaching...
What you do not want is the temp at which the moist inside air condenses 'dew point' to be...
where organics are...
Short answer...
below grade 2" spray foam closed cell will keep the dew point in the concrete...
not organic, not an issue as the concrete will breath...
the perm factor is variable...
Everything breathes because nothing is perfect...
Think like moist air and don't let it condense in a place where it can't escape...
If you have a high ACH factor and control the humidity it helps....
The humans...

ACH factor

VigIIPeaBurner wrote:ACH factor

Average _____ Humidity?

Air Changes per Hour...
It is what the pressure door test with the fan tells you...
Sealed up houses tend to have high indoor humidity...
combined with cold outdoor temps...
makes for wet insulation if...
The dew point is in the middle of your organic insulation...

Houses that have higher ACH also have better air quality...

Does anyone know if there is a specification for which type of foam board to use on the inside of the wall with the following exposures?

• concrete below grade
• concrete above grade

Does it have to 'breath' if it's against a wall that's below grade and that wall has a mastic barrier outside covered by earth? I'm wondering about where to use different foam board types - closed cell unfaced or faced, open cell unfaced or faced. I guess the facing is a foil style barrier. I haven't begun to shop for what I'll need so I'm open to more suggestions, especially from those that have been there

There is no specific requirements for insulation on the inside of a concrete wall, above or below grade. There are three basic types of board foam on the market for insuation. Polystyrene (the white bead type), Polyurethane foam (pink or blue) and Polyisocyanurate which is commonly coated with foil on one side. R-value per inch and cost per board foot increase from Polystyrene to Polyisocynurate. Put up a vapor barrier on the warm side and then protect the foam with a fire resistive material such as drywall. Taping the foil face seams and punctures of polyiso will work but is not a perfect solution. Do some research.

With the vapor barrier on the warm side, there should be no need to have the wall "Breath"