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Is a standard ‘Home Slicker – 6 mm’ for under wood shingle siding adequate for Cape Cod, MA area ?

PROJECTSUSTAINABLE | Posted in Green Products and Materials on

There are two types of slickers by Benjamin Obdyk …. the 6mm is perfect for what Iwant to do, but there is also a 10mm which is required by code in certain parts of Canada. Is there a 10mm code requirement for rainscreens in MA ?

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  1. Expert Member
    Michael Maines | | #1

    The thicker product is best for very wet or very cold areas, to assist with moisture removal. In most of the US the thinner product is more than enough to break capillary attraction. I don't know what code you're using but I would put the Cape in the gray zone--6mm is probably fine but thicker is better. There is more to it of course, but that's the quick version.

  2. GBA Editor
    Martin Holladay | | #2

    As far as I know, there are no requirements in the Massachusetts code for rainscreen installations. You are free to choose your rainscreen specifications based on your own research.

  3. Expert Member
    Dana Dorsett | | #3

    MA codes are pretty much straight-ahead IRC 2009 at this point, with few exceptions. There is no rainscreen requirement of any type/depth in MA.

    In a typical Cape style house will have almost no roof overhangs (or very minimal overhang) to make them more wind-resistant under gale/hurricane force winds, and as a result gets 100x more bulk wetting of the siding than a bungalow in the same location with 18-24" overhangs on all sides. One reason shingle siding has long since been the standard on Cape Cod is that it's inherently back-ventilated (though not as much as vinyl siding), and will dry quickly once the rainy nor'easter passes, and that's with NO explicit rainscreen gap. In less windy parts of MA where the average and peak wind speeds are lower there's less wind-driven rain penetration, and less risk to building the roofs with large overhangs.

    For dealing with the wintertime interior moisture drives of the colder NW part of MA a rainscreen gap of 6mm is fine, as is using inherently back ventilated siding such as vinyl or shingles.

    Larger rainscreen cavities are more important when the siding is stucco or masonry, where it can store large quantities of dew/rain and release it quickly when heated by the sun. For wood or fiber cement siding etc a 6mm cavity vented to the exterior at both the bottom and top is plenty for any local MA climate.

    Other than for insect & critter access control I don't see much benefit to the mesh style products for establishing rainscreen gaps. Furring or lath works just fine, and putting strips of mesh at the bottom & top vent access points does a decent job of keeping wasps etc. from turning that cavity in to a condo complex. But if you're OK with the 6mm Obdyke product, it gets the job done.

    Even in rainy western B.C. where 10mm rainscreen is current code, 6mm of air (no mesh) does just fine for drying the sheathing & siding on 1 & 2 story houses with minimal roof overhangs. There is quite a bit of ongoing testing of different wall assemblies on no-overhang test hut in Vancouver, much of which is documented here:

  4. davidmeiland | | #4

    The benefit of the mesh style products is installation speed and low waste factor. I've used a lot of the Obdyke 1/4" product and it goes up in seconds and very little ends up in the trash. I would probably use furring over exterior rigid foam, but Obdyke over sheathing is so easy a caveman could do it.

  5. Expert Member
    Dana Dorsett | | #5

    Sure, a caveman COULD do it, but do caves really need rainscreens? :-)

    I hear ya- it goes up quick, but it's apparently in lieu of going with exterior foam, which is far more protective of the sheathing than any rainscreen alone.

  6. davidmeiland | | #6

    So far, I've installed Obdyke on remodels where there isn't going to be exterior foam. You can slap-staple it up over felt quite easily, and then start siding.

    With exterior foam, you could put Obdyke up with long fasteners, but the requirements of the siding and trim lead you towards furring over the foam, so Obdyke won't seem as appealing.

    I don't see it as being in lieu of foam, but rather a good product to use if you're not using foam. I'm designing a project now, considering thick walls vs exterior insulation, and if we do thick walls, they'll have Obdyke over felt on the walls. Everything I do is cedar siding. If I did stucco or lick/stick stone then I wouldn't dream of using it.

  7. davidmeiland | | #7

    In case you have a few moments to waste...


    Thanks everyone for your answers. Helped me make an informed decision.

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