air sealing below the knee walls in a cape cod?

[Cdshakes]

my cape cod is very poorly insulated... each year i add more and more to it. The back of the knee walls on the 2nd floor aren't insulated at all--that's a project to do before it gets hot again. I keep reading about air sealing just below the knee walls on the unfinished side-- blocking the conditioned air between the 2 floors from escaping into the unfinished portion of the lower attic.
In the front of my house, no problem--i can do this. In the backside of the house, the X style wood braces that keep the floor joists from flexing/bowing are right in the way. Is it worth it to put the air sealing rigid foam on the unfinished side and trying to seal off the couple of inches on top? Or how should i handle this?

Colin

[crokett™]

Got pics? Sounds like you either need blown in or sprayed foam insulation to get around the braces. Blown-in you can do yourself, sprayed foam is much better though.

[Cdshakes]

on many sites, i see suggestions do put rigid foam blocking just below the knee wall and spray foam or caulk it in, like shown here:


on the front side of my house, you can see the X brace is set back a little, so no problem here.


But in the back, the X braces are just beyond the knee wall-- no way to get a piece of rigid foam behind them.

[crokett™]

that's a little different than what I was picturing.

Are the gaps too big to simply seal around the brace with expanding foam from the BORG?

If so then the way I see it your options are

a) remove the brace, insulate, replace the brace
b) build an l-shaped rigid foam cap that goes over the brace and seal it to the joists, the ceiling below the brace and the sill plate on the kneewall with canned spray foam. Actually I'd spray some foam on the brace stick the cap in place then seal all the edges.
c) put in a form, then get something like this

http://tigerfoam.com/sprayfoaminsulation...UU9EaAjec8P8HAQ

and spray around/over the brace to seal everything up.

[Phil Thien]

Most people use the blocks of foam held with spray foam as a poor-mans closed-cell spray job.

Home centers now cell smaller closed foam kits, however, and they aren't that terribly expensive. And I imagine they'd save a ton of time, and be a little more effective, too. if you would have enough room to get the gun in/around the brace, maybe you could just spray instead?

[EricU]

I'm thinking of spraying where I have to in my basement rim joists. At both ends of the house, there is about 2" of clearance between the last free-span joist and wall beneath. A bit of a pain, since that's where it would be easy to put rigid foam if there was enough clearance.

[Cdshakes]

EricU said:

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I'm thinking of spraying where I have to in my basement rim joists. At both ends of the house, there is about 2" of clearance between the last free-span joist and wall beneath. A bit of a pain, since that's where it would be easy to put rigid foam if there was enough clearance.

---

i did rigid foam in my rim joists up in my crawlspace. I used this special foam that's supposed to have better fire rating or something-- was expensive-- like 70 bux for a 4x8 sheet. I kept reading if you have exposed spray foam, you're supposed to cover with drywall. No way i was going to put drywall in my crawlspace's rim joists.

I'd prefer to stay away from spraying the whole X brace and opening-- ideally to get access to them again would be nice--i always seem to be running a wire of some sort... whether replacing 110v stuff, or low voltage stuff (speakers, ethernet...etc)

Colin

[Phil Thien]

Well you can always caulk everything to stop the air infiltration, and then add fiberglass.

[vernonator]

I had someone come in and do ours with closed cell foam along with the rim joist cavities - it has DRAMATICALLY reduced our heating costs. Our house is a 10yr old 1 1/2 story with daylight windows. We also foamed the exterior walls in the basement.

In the 5yrs since we did this it has paid for itself (we are on propane).