Insulating/Sealing Walls From Exterior

Maybe

Nick

I would just leave the bats and add tyvek and, if your remodel would allow for it, insulated foam board to the outside.

Actually the foam boad goes under the tyvek. Some may say no need for tyvek if you use foam board.

Anyway, the advice is free.

Are you sure it is cotton and not cellulos loose fill that will fall out if you take off the wood

Yes, the insulation is cotton batts, I put them in when I remodeled the interior side. They are _so_ much nicer to work with than fiberglass batts. Speaking of cellulose fill (with a binder), does it create an effective air barrier? Should I consider pulling out the batts and spraying in cellulose? It's more economical than foam.

Cheers, Wayne

Well, I fall on the felt side of the tyvek vs felt argument, so I'll be using 30 lb felt. The siding is cedar shingles, and at least some cedar shingle manufacturers recommend felt instead of tyvek. I may use cedar breather (1/4" thick mesh) under the shingles as a mini rain screen.

As to the foam board, is there any value to 1/4" foam board? Would it be an effective air barrier, and what would I use to tape the seams?

I don't want to make the wall any thicker than it is, as I don't want to mess with the frieze board and molding details at the top of the wall. So I'll be leaving 2-3' of the 7/8" plank sheathing at the top of the wall, and there I'll just have to seal the gaps in the sheathing with spray foam.

But the new sheathing will be 1/2" or 3/8" CDX, and I'll have 3/8" or

Cheers, Wayne

Well, this is a nice idea, but I'm afraid that aesthetic concerns preclude it. Unless there is some way to make this work with cedar shingles on top? :-)

As to the computations, let's see. 1050 Btu is the daily insolation per ft^2 in Berkeley on an average January day, and 0.9 is a correction factor for vertical walls given the angle of the sun in January, yes? My interior design temperature is 68F, not 70F, but that's a small difference. Why is the heat loss resistivity during the "day" R1 instead of R6.2? 48.7F must be the average January temperature (average low temperature?), seems like it would be more accurate to use one temperature during the 6 hour "day" and another during the 18 hour "night". Not that it really matters, as the heat loss is an order of magnitude less than the solar heat gain.

Did I get all that right? Thanks for the education. Oh, and why does the thermosiphon require a 2" air space? I assume the 1050 Btus/day is an average of sunny and cloudy days, how much insolation can I expect when it is raining? It does that alot in Berkeley in January, and so I imagine this heat source would be very uneven day to day.

Cheers, Wayne

I would definitely get that out of there and replace it with a modern conventional insulation, it will work better and be far less to cause vermin or other problems.

Umm, these cotton batts are a "modern conventional insulation", they are treated with borates to provide fire and vermin resistance. See, e.g., . Cotton batts are a much nicer alternative to fiberglass batts, but more expensive.

Anyway, the original question was about batts insulation in general, and sealing the batt/framing interface.

Cheers, Wayne

Maybe I need to get up to speed. I have not seen any for many years and it was old then. I did not even know they were selling the stuff. It sounds like they have done the same kind of work on it as the cellulose stuff.

What is the R value of ultra touch, that web site did not display it.

Yah, their site is a bit unclear, you have to go to "Technical Library" to get the specs. They make R-13 at

Wayne

Blue jeans have a good R value, I have cedar, I removed it, ran 2" of R