Choosing Cladding to Improve Building Envelope
In battling a room to room temperature differentiation, I’ve also returned to my homes final checklist item: exterior cladding/envelope.
Interior has 3” closed cell foam with 3” rockwool. Current exterior is 2×10 battens faced with tarpaper and cheap vinyl siding.
I want to create additional air sealing, slight insulation, and allow drying to exterior. I considered leaving the tar paper, replacing it with house wrap, 1” eps, with wood siding and/or new vinyl siding.
I’ve also considered doubling up on tar paper and using stucco. It’s difficult to find information on properly cladding a historic home where drying to the exterior is so important – and I’m at a bit of a loss!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Starting from the inside, what do you have? Include the stud depth and sheathing. I'm confused about how you are using the 2x10 "battens". Tarpaper is a breathable membrane, but it's not air tight, and neither is "house wrap" unless it is carefully taped and detailed. Henry Blueskin is a vapor open, air tight peel and stick membrane that might work in your situation.
I’ve looked at Blueskin and it looks interesting, I just had never spoken with anyone that had used it.
The house is 2x6 baloon framing with 3” closed cell and 3” rockwool in the stud bays. The 2x10 battens run horizontally across the homes exterior. They were put in place in the 40s-50s when the original siding was removed to hold everything together in its place. Not sure what they covered it with back then, but sometime in the 90’s it was done in vinyl.
Blueskin and liquid wrb’s both have me intrigued right now. But I’m also a little lost on what siding to put over the wrb. I need it to dry outward, so I feel like vinyl would limit that.
Do the 2x10's form a solid sheathing or are there gaps between?
We're using Blueskin on our second project - very heavy and adheres very well. Maine Green Building sells a SIGA product and foursevenfive.com sells another European product, both peel and stick heavy duty vapor permeable air barriers.
Vinyl is not a tight product, so it will not interfere with drying. If you use a wood or cement product, add a rainscreen (we use 1x3 strapping) to provide an air space behind the siding.
There are probably 1/8th inch gaps on average between the horizontal boards, which might make for a lot of work if I used a liquid wrb.
By a “rainscreen” you mean just add furring strips before putting siding on so there’s a gap?
I’d been told by an old timer (which I know can be both great and terrible advice) that if I was going to stucco, I should put tar paper over the wrb before the lath.
I want to do this right, I’ve put too much work into this old house to let it rot!
3" of cc SPF is plenty air tight already. If you have room temperature issues, you have some larger air leak elsewhere (balloon framed houses can have some big uglies like missing top plates or interior wall cavities connecting up basement to attic), or your HVAC is not properly set up. Air leaks is easy to test with a blower door. HVAC will need a knowledgeable tech to get right.
Air sealing the sheathing further on the outside will do nothing for your comfort. Extra insulation on the outside would save a bit on energy use, but again will do next to nothing for comfort.
If you are re-siding, getting a WRB over the board sheathing is still important, doubly so with stucco. Keep in mind that stucco is a cladding that is very easy to mess up ie:
https://www.greenbuildingadvisor.com/question/26000-repair-and-we-still-have-water-leaking-in
So make sure the installer follows guidelines to the T ( you do want two layers of WRB, even better two layers plus air gap).
I think a standard siding install over rain screen is less fussy. Much easier to get a quality install that won't cause damage to your building. Detailing the WRB and window flashing is still important, but at least small mistakes there won't cause major issues.
Makes sense and thank you. Old standard wood clapboard would probably fit the “feel” of the house best anyway.
I think my envelope is pretty well sealed internally. My room to room a/c temp differntiation is the mostly result of aggressively sizing my mini splits. J-Calcs are difficult with the number of variables in an 1869 remodel, and I certainly didn’t want to oversize!
But with so many books and crannies, it’s always possible that I missed something. Which is why I want to air seal the outside as thoroughly as possible also while maintaining outward drying.
A third possible vapor permeable peel and stick WRB is Grace VycorEN-VS. We used it on our 100+ year old balloon framed home and found it relatively easy to work with. If you do decide to reside, it's a reasonable belt-and-suspenders, peace-of-mind addition to your wall stackup.
Did you get a good look at your attic rafters when insulating? In ours, the space between the attic floor and the wall top plates was completely open - unsealed and uninsulated - and a major leakage point.
I’ll look into that one. Thank you.
And yes, our house was the same. There was basically one long open run between the stud bays from crawlspace to attic. I sealed with closed cell from crawl space, each side of ceiling/floor between 1st and 2nd stories, and in the attic.
Have you had a blower door test? Temperature variations from room to room can indicate air leaks, which might be an easy fix, if you can find them. It's also a help (and fun) to rent a theatrical fog machine, run the blower door backwards, let the fire department know what you're doing, and watch the smoke come out the leaks.
I haven’t done this yet because I was going to wait until I did the exterior. But maybe it’s worth doing before and after.
Are there health risks with using a fog machine? I have a 9 month old baby who has skin sensitivities to chemicals, so I’ve been leery of including fog.