Insulated old house from exterior?
I’ve got a 1950’s Cape Cod in Albany, NY
2×4 exterior construction with 3/4″ shiplap on the outside, tar paper, then cedar shingles, then looks like 1/2″ styrofoam that was “molded” to fit behind the vinyl siding.
The “insulation” is the old “alfoil” product. Due to this, and a few other reasons, I had cellulose blown in 8 years ago into the exterior walls from the outside, but there’s a few areas that got missed or were inaccessible to make a 2″ hole (stud placement, you don’t really know where things are from the outside), and the alfoil kinda trapped things. Better than it was before, but not what I’d like.
I REALLY don’t want to have to remove all the drywall (I’d have to remove the crown molding, furniture, etc. re-hang, mud, tape, etc.)
I was debating about having the siding removed (I can do that easily enough), remove the cedar shingles, tar paper, and the 3/4″ shiplap and then basically spray foam from the outside (plus it’ll let me replace the two main windows that I need to as well and use “new” install models).
The problem with this (that I see) is that I either have to fill the entire 2×4 void with foam (expensive), or add on another 1″ of rigid foam after I put new sheating on. But I am worried in that setup that I’d end up with moisture/water problems. (not so much water leaks, but we have high humidity in the summer here).
In other words:
a) spray foam 1″, re-use cellulose or add fiber glass, then the OSB, Tyvek, 1″ foamboard, and then vinyl siding (I think this would get me close enough to the existing “thickness” with the 3/4″ shiplap and cedar shingles). But worried about sealing bad things in (or would there be enough air movement between the OSB)?
So here’s some other options:?
1) spray foam 1″, then re-blow the cellulose in (I can save what I would take out and re-use it), put OSB, tyvek, and vinyl siding back on.
2) spray foam 1″, then just use unfaced fiber glass, put OSB, tyvek, and vinyl siding back on
3) Spray foam entire void (well 3 to 3.5 inches), put OSB, tyvke, and vinyl siding back on
any other ideas that may work better?
Replies
It's pretty cold
in Albany, right?
I would go with either
1) 3-1/2" of closed cell foam in the stud bays plus 2" of XPS or EPS over the sheathing, with new housewrap and existing siding. Might consider a rain screen but have no experience with vinyl siding. Advantage of this is that you will air-seal your walls nicely.
2) 2" of XPS/EPS over the existing shiplap, plus new wrap/existing siding. Big advantage of this is that you can avoid destroying the shiplap. You can get someone with a thermal camera to find the voids in the cellulose. You can get someone with energy modeling software to compare the payoff periods for the two jobs, and I suspect that the significant extra cost of the spray foam will take many years to recover.
As with any/every project where you are tightening the house, there are many unintended consequences to consider, and should read this http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing to be sure that 2" is enough foam outsulation.
Yeah, getting someone with a thermal camera to come in and "shoot" things this winter would probably be a good idea. If you can fix the major "holes" and also address air sealing (probably mainly at floor level and in the attic) then you'll likely improve things considerably, without major expense.
Thank you both for the options and advice. I'll check around and see what the cost for the thermal camera job is. I kinda like the idea of going over the shiplap with 2" of foam or thereabouts.
Another good resource for this type of question
are the forums at Green Building Advisor -- http://www.greenbuildingadvisor.com/qa -- there are a lot of energy nerds there.
and I mean 'energy nerd' in the best way possible :)