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Community and Q&A

Wall detail for exterior foam and … (wait for it) … SHINGLES

kjhkjh | Posted in Green Building Techniques on

We’re in the process of building a home in MA and committed to external foam on walls and roofs

There’s a ton of great detail here on exterior foam and I’ve followed / read it and Martin’s other posts on rainscreens.
We’re still struggling with the best practical assembly for traditional shingles rather than clapboard.

There are the 3D mesh rainscreens that Martin suggests in his “All About Rainscreens” article, but if those are used, how do you provide a nailbase for the shingles? If thye are used is thee sheathing put at the outside?

This is an old house so there will be existing sheating, so is the sequence (inside to out)

– Original sheating
– Housewrap? (or fully adhered ice and water? ($$)
– 2″ Polyiso
– 2″ of XPS (Sorry dana) ;-*
– 1/2 Sheathing
– 3D matrix (see below)
– Shingles/Shakes

There’s a ton of 3D matrices
1. Are these the best practical approach?
2. Any preference?

(from Martin’s article)
Benjamin Obdyke Home Slicker mesh is 1/4 inch thick.
Stuc-O-Flex WaterWay Rainscreen drainage mat can be ordered in several thicknesses, ranging from “nominal” 1/4 inch to “nominal” 3/4 inch.
MTI Perforated Control Cavity creates a gap of about 3/16 inch.
Colbond EnkaMat is about 3/8 inch thick.
DC 14 Drainage Mat is about 1/4 inch thick. Because it is made of polystyrene and has a low permeance (1 perm), it depends on ventilation drying through air channels rather than diffusion drying.
Cosella-Dörken Delta-Dry is about 1/2-inch thick. Delta-Dry is a membrane made of 22-mil high-density polyethylene that has a three-dimensional egg-carton configuration. Like DC 14 Drainage Mat, Delta-Dry is a vapor barrier. The product depends on ventilation drying through air channels rather than diffusion drying.

Thanks to all for you what you do on this site every day

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  1. GBA Editor
    Martin Holladay | | #1

    Your plan is fine, as long as you remember to install a WRB on the exterior side of the outermost layer of plywood sheathing. The plastic mesh is a good idea, but it's optional.

    My house has exterior EPS and cedar shingle siding. Back in the early 1980s, when I installed the siding, I decided to install horizontal 1x3 furring strips on the exterior side of the EPS. Since the cedar shingle courses are spaced at 5 inches, the furring strips cover more than 50% of the wall. That's a lot of furring strips, so I'm not sure if I was being clever or not. But it worked.

    One more point: In Maine, I noticed that builders who were installing cedar shingle siding over rigid foam were using nailbase. For more information on this option, see Nailbase Panels for Walls.

  2. kjhkjh | | #2

    thanks Martin,
    1. Any reason for ice and water over original sheathing in preference to tyvek? _ worth the $ premium?
    2. Is a second WRB needed over outer layer of sheathing?

    3. Anyone have ROI ( pricing/ease of use/performance) for any of the 3D matrix materials?
    4. I've seen some posts on irregularity with sight lines with these matrix products. Issue for shakes or only clapboard?

  3. GBA Editor
    Martin Holladay | | #3

    The main advantage of Ice & Water Shield in this location is to create a good air barrier. But if you are building a new house, the Ice & Water Shield isn't necessary. You should be able to create a good air barrier by taping the seams of your plywood or OSB wall sheathing.

    For more information on tapes, see Return to the Backyard Tape Test.

    As I noted in the first sentence of my answer, you need a WRB (for example, plastic housewrap) on the exterior side of the outermost layer of plywood sheathing.

    The purpose of the plastic mesh (if you decide to use it) is to help the shingles dry faster after a rainstorm. I can't imagine how anyone would estimate the return on investment for this measure; the only "return" would be the (possible) longer life for shingles over the mesh -- but this longer life is speculative. Probably, your cedar shingles will last as long as you do, no matter how you install them.

    I doubt whether plastic mesh under cedar shingles is associated with waviness or problems keeping the siding co-planar -- but I welcome other opinions from GBA readers.

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