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Retrofit insulation in walls with no sheathing or WRB?

My house is a one-and-a-half story bungalow built in 1906, in Portland, OR. Balloon framing. Rabbeted shiplap 1x6 siding nailed directly to the studs, no sheathing or felt. Lath and plaster on the inside. The siding is in good shape and there's little evidence of water in the studwall cavities (that I've seen.)

What options, if any, do I have for insulating the walls that won't risk accumulating moisture in the cavities or result in rotting the siding or loosening the exterior paint?

Asked by Ray Sten
Posted Jul 3, 2014 12:51 PM ET


6 Answers

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Here is a description of the two most common techniques. Both methods assume that you have removed all of the lath and plaster, and are looking at open stud bays from the interior.

1. Line each stud bay with asphalt felt. The felt should be cut so that it is as long as the stud bay is tall, but about 2 inches wider. Create two 1-inch tabs, one on each side, and staple these tabs to the sides of the studs, so that the asphalt felt is up against your siding. Then you can install any type of insulation you want.

2. Install 1" by 1" sticks in the corners of each stud bay, up against the siding. Then install a layer of 1-inch-thick rigid foam in each stud bay, so that the foam is up against the sticks, and there is a 1-inch air space between the rigid foam and the siding. Seal this rigid foam in place with caulk or canned spray foam. Then you can insulate the stud bays with any insulation you want.

Answered by Martin Holladay
Posted Jul 3, 2014 2:17 PM ET
Edited Jul 3, 2014 2:18 PM ET.


Here is a link to a blog that mentions Method #1: Sticking With Spray Foam for My Renovation.

Answered by Martin Holladay
Posted Jul 3, 2014 2:21 PM ET


Thanks, Martin, for the quick reply. I should have mentioned that gutting the interior is not an option. (Although tearing down the whole house might be. Just kidding. Sort of.)

Answered by Ray Sten
Posted Jul 3, 2014 2:53 PM ET


I don't recommend filling the stud bays with cellulose the way they are -- although if your house has very wide roof overhangs, and the siding stays dry, it's worth considering.

If you can't open up the stud bays from the interior, the other option is to attack the house from the exterior-- for example, by attaching exterior rigid foam and new siding.

Answered by Martin Holladay
Posted Jul 3, 2014 3:10 PM ET


I found compelling the principles you articulated in your posts on the dubious economics of the Deep Energy Retrofit, and it's beginning to look like those principles apply to my house. Its siding, windows, and plaster are in good shape, and I'm not willing to tear them out for the sake of a somewhat lower heating bill. We are, though, planning some remodeling that will expose part of one exterior wall, and an addition that will open up the entire length of one of the others, so those walls can be upgraded in the course of things. Also, the entire front wall of the house is protected by a 7' overhang, so I suppose we could go ahead and put cellulose in it. In all, we'll be able to insulate nearly half of the total exterior wall area. Better than nothing.
Thanks for your advice.

Answered by Ray Sten
Posted Jul 4, 2014 4:57 PM ET


not to thread hijack, but I find myself in a similar predicament, except in austin tx (32" rainfall vs 39" but it seems a *lot* less). would open cell in stud bays allow sufficient drying to the interior, or is that water vapor vs water liquid? we can gut interior, so martin's methods might apply, but I think historic commission might frown on adding a rainscreen and hardie plank over the original shiplap.

Answered by Matt Desloge
Posted Jul 7, 2014 12:54 PM ET

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