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internal rain screen or liquid air barrier?

stolzberg | Posted in Green Products and Materials on

Hi, we bought a 1900 farmhouse in northeastern Massachusetts that has real 2 x 4 framed walls, no insulation, and board sheathing, a layer of wood shingles covered by a layer of cement shingles. We don’t think we can afford to redo the exterior, so thinking about removing interior plaster and lathe on outside walls and air sealing and insulating from interior.  A number of options or combination of options under consideration: 1) spray foam or dense pack cellulose the 4″ bays and sheet rock, 2) create internal rain screen with blocked rigid foam and then spray foam or dense pack cellulose, 3) create rain screen with caulked membrane held out with batten in middle of bays and fill with dense pack and sheet rock.  Also thinking about furring out studs with strip of rigid foam and 1×3 or cross strapping to get more depth.  Any opinions on best option at reasonable cost?  Do we need an internal rain screen? Is it worth thickening and thermally breaking walls? (we’re planning to replace single pane windows and sash weight cavities at same time so have opportunity to extend jams)  Do we need any vapor adjusting membranes under sheetrock?  And random question: can you paint a vapor permeable air barrier such as StoGuard on the back of the sheathing and then insulate to interior? Thanks, I’m total amateur at this stuff, but love learning from the discussions here on GBA.

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  1. user-2310254 | | #1


    I'll give your post a bump. The usual guidance in these situations is to focus on increasing air sealing and attic insulation. But let's see what the experts suggest.

  2. stolzberg | | #2

    Thanks. I just focused on wall questions in this post, but we're also hoping to insulate the attic ceiling. The house has slate roof over gapped board sheathing with what looks like crumbling tar paper. Based on what I've read on GBA about slate roofs, I was thinking about creating a small vent space with rigid foam and either caulk/foam to air seal or spray a layer of foam, then build interior ceiling frame connected to existing rafters with gussets (like a larsen truss hanging from roof) and fill with cellulose.

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