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Q&A Spotlight

Rainscreen Details for a Board-and-Batten Retrofit

A homeowner plans to replace tired vinyl siding with new cladding, but needs help with exterior insulation details

A continuous layer of rigid mineral wool insulation on the exterior of the house helps reduce thermal bridging. An owner/builder in Alberta is looking for the guidance on how to attach board-and-batten siding to the assembly. Photo courtesy Shannon Cowan and Patrick Walshe.

One thing on Drew Goldsack’s spring cleaning punch list this year is removing the vinyl siding from his Alberta home and replacing it with cedar board-and-batten siding.

As he explains in this Q&A post, the plan is to install 1 1/2-inch Comfortboard mineral wool insulation, a rain-screen drainage mat, then horizontal 1×4 furring strips before adding the yellow cedar siding. His initial question concerns the fasteners he should use to make sure the siding stays put.

“I have been unable to find a local building code that specs fastener penetration for cedar board and batten (3/4″ thick boards and approx. 7/8″ thick battens),” Goldsack writes. “However I did come across the Western Red Cedar Lumber Association specs that recommend a minimum 1-1/4″ fastener penetration for installation of board and batten.”

Goldsack had thought that a 3/4-inch penetration of ring-shank nails into the furring would be enough, but now he’s not so sure. Would that be enough? Should he switch to screws instead, or make the furring strips thicker?

Those are the questions that start this Q&A Spotlight.

Consider stiffer furring strips

Russell Miller reports “zero issues” when he’s used 3/4-inch plywood or 3/4-inch pine or fir furring strips. Either should work, he says, unless Goldsack is building in a coastal or tornado-prone area. “Even then,” he says, “tighter nailing of siding is the main issue.”

But GBA Editor Brian Pontolilo raises another issue—the difficulty of keeping mineral wool flat under 1×4 furring.

“Have you specifically used 3/4 inch furring strips over exterior mineral wool?” he asks. “I’ve heard that thicker furring strips, mainly 2x4s, make it easier to keep the furring strips in plane for a flat siding install and that 1x material bends too easily and therefore compresses the insulation.”

In either case, Pontolilo suggests…

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5 Comments

  1. Russell Miller | | #1

    I thought that I had made a second reply to this question but, must not have. YES 2x4s make it stay flatter "easier", if there is an easier way. The total build out thickness on existing homes can be a bear to work out.

    Another thing we have done is to use UV stable, even though its hidden from the sun, pipe (pvc, etc.)to act as a sleeve over the screws to make the installation near perfect. Most of the time this level of precision is unnecessary.

    Ive heard builders complaining about the "FOAM WAVE" many times. They've never experienced the ROXUL WAVE I have been blessed with always having decent reclaimed foam.

    I should be doing one right now, it would've made great pictures for you.
    SADLY, after the current pandemic is settled down it may be YEARS before I get to fur another house out. We have gone from a busy year to an open schedule.

    1. Vlad Shpurik | | #4

      Could you please elaborate on the PVC pipe/sleeve technique you've used to limit compression of the mineral wool? I am just about to start installation of Rockwool on the exterior and contemplating whether to do something like that. Wouldn't this sleeve introduce quite a bit of thermal bridging, if not by itself, but by creating a fairly large hole between the sleeve and the screw?

  2. Expert Member
    Malcolm Taylor | | #2

    This Q&A Spotlight dovetails nicely with Martin's latest blog.

    https://www.greenbuildingadvisor.com/article/wrinkled-housewrap-behind-exterior-rigid-foam

  3. Expert Member
    Dana Dorsett | | #3

    >"--mineral wool is indeed a capillary break.."

    Indeed mineral wool is NOT a capillary break, as Peter Yost explains in some detail.

    But that isn't particularly important in this assembly, since the air gap provided by the furring very much IS a capillary break.

  4. Kieran Lavelle | | #5

    How much are builders paying for Rock Wool? In the PNW, I'm paying about $1.10/sqft/inch of thickness for the rock wool. Any comparison from other parts of the country?

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