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1850’s clapboard over studs – WRB & air sealing suggestions needed

Otherdrysock | Posted in General Questions on

My father and sister are in the middle of a gut rehab of an 1850’s house in Michigan – climate zone 5a. The clapboards are in good shape, but are fastened to the studs; there is no sheathing. The house is in a historic district, so removing or siding over the existing clapboards may not be an option. 

Concerns are the lack of sheathing, no ability to get a WRB outboard of the studs, and the inherent challenges with air sealing in this situation. 

Can anyone point me to where this topic has been previously addressed?

Short of removing the clapboards or sheathing over them (with WRB and air sealing, of course) would any of the following be options?

1) Flash and batt with open cell foam and mineral wool. Intelligent vapor barrier on the inside. Concern is the lack of a drainage plane. My thinking with open cell is that it is permeable which would help to preserve the drying potential of the wall given the lack of a proper WRB.  

2) Using Zip from the inside (cut and cobble) and flashing the bottom of the panel to create a drainage plane over the rim. Foam the joints. Mineral wool batts. Intelligent vapor barrier on the inside. 

I appreciate any suggestions you have to offer. 

Ryan

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Replies

  1. Expert Member
    AKOS TOTH | | #1

    Ryan,

    This has indeed come up a number of times, searching for it is not very easy.

    The big issue with clapboard over studs is getting an air gap behind it. Without some air movement, water leaks have nowhere to go and you end up with moldy insulation and peeling paint.

    Probably the simplest would be to staple some 1x1 into the corners of the stud bays and than put either a house wrap or a layer of foam over it to create an air gap. The remaining cavity you can then fill with your choice of insulation.

    Since you are probably looking at a balloon framed house, the best bet is a full fill with OC spray foam. I don't think a flash and batt buys you anything in this case except a lot more labor.

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Ryan,

    As Akos pointed out, you don't want to install insulation to the back side of the siding because you want the siding to be able to dry in both directions. And you need an air barrier.

    So, once you have determined how to create that air space, you could install some kind of backing for spray foam, which would then create an air barrier, or you could install rigid foam and seal it in place with canned spray foam. Depending on the cavity depth, you could then install fibrous insulation.

    This article will answer all of your questions in more depth than I can here: http://www.greenbuildingadvisor.com/article/insulating-walls-in-an-old-house-with-no-sheathing

  3. Otherdrysock | | #3

    Perfect! I appreciate the assistance.

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