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AndrewF 02-25-2009 11:36 AM

Insulating - Rim/Header Joist - Basement
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I searched the forums and wasn't able to gather the ideal way to do what I want.

We have an unfinished basement that is always cold, generally between 55 and 58 degrees. This results in the first floor floors being cold regardless of the temperature up stairs.

I am considering buying a DIY spray foam kit to spray 2" of foam on the rim/header joist. When I put my hand up there now, I feel cold air coming in...(not just radiating in). My infrared thermometer shows that this area is about 20 degrees warmer than the outside temperature.

This house has a basement that is 52' x 31' and has 2x12s as the floor joists. The basement is poured walls and the exterior is brick down to the top of the basement wall.

Is using spray foam the best option here vs hard foam board or batted insulation? Is it worth the cost?

I live in Southern Ohio.

I've seen the soyfoam product, as well as sprayfoamdirect and other suppliers and while itappears it may cost around $600, it should qualify for the 30% tax credit offered this year for insulation.

mountainmike 02-25-2009 12:27 PM

If the problem is air infiltration you could buy a much smaller foam kit and just foam the edges of the rim joist where the air is coming in. Then use fiberglass batts for the rest. That would save you some money and work just as good as going all foam.

Also if you have anchor bolts be sure to foam around them as the notches/holes around them will allow air to move through.

I also noticed in the photos you have the windows look old. You may want to put some insulation over them to cut down on heat loss. It will make your basement dark though.

Bob Mariani 02-25-2009 12:31 PM

Foam will be the way to go. Batt insulation will not yield as much R-Value.
And the mice love to nest in it.

AndrewF 02-25-2009 12:39 PM

The plan is to replace the basement windows this year and convert one of them to an egress window.

I bought blue board to put over them, but havent had time to do it...and now with it finally getting warmer, I may not do that anyways.

The problem is two-fold. Air infiltration and the the cold that radiates in.

jaros bros. 02-25-2009 01:13 PM

The only thing the building inspectors like to see is foamboard or spray foam, unless your outside joist is offset and you have the rim joist insulated on the outside with foam. There is too much thermal mass there and in cooler weather fiberglass will allow moisture to condense. You will see frost on the rim joist and it will start to rot it out and possible wick through to your subfloor. The foam kits are the best.

AndrewF 02-25-2009 01:30 PM

I doubt the outside joist is insulated with anything more than the 1" insulation board that is behind the brick. This house was built in the mid 70s and is an all brick exterior.

sweaty 02-25-2009 01:32 PM

I just insulated my rim joists and it has made a big difference. It even made the top floor warmer by reducing the stack effect.

I bought 2'x8' sheets of 2" thick extruded polystyrene from Lowe's. Using a long carpet knife, I cut it to the approximate size of the spaces between floor joists. I then sealed around it with caulk or spray foam.

simonb 02-26-2009 11:10 PM

I was thinking of doing the same thing Andrew. Pink just isnt cutting it and i know its going to get moist and cause rot and mold eventually. Cutting foam board then sealing might work in some cases, but its allot of work IMO. With the spray foam you know you get a good seal if its done properly.

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