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Skip the plywood, go right ot the Comfortboard IS

Blake Olson | Posted in Plans Review on

I live in central Vermont, heating zone 6, hoping to get a little bit of feedback on the wall system I have in mind for a 4 season workshop (barn), with small efficiency apartment on the second floor.

From inside out: (1) Proper vapor retarding latex paint and primer, (2) air tight drywall system gaskets caulking and all, (3), freshly milled, green, 2×6 stud-wall, utilizing efficient framing techniques, and let-in bracing. (5) Cellulose or mineral wool batts in stud cavities (6) Comfortboard IS over stud-wall(7) Typar or Tyvek type WRB over Comfortboard IS (8) strapping (9) board and batten siding.

Also, considering using a variation of this in the roof system. swap (7) for an more appropriate roof WRB and (9) metal roofing, standing seam or Channel Drain.

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Replies

  1. Malcolm Taylor | | #1

    Blake,
    Why the green framing lumber?

  2. D Dorsett | | #2

    I too am wondering how well air-tight drywall will hold up on air tightness over time if starting out with green lumber. (A flexible smart vapor retarder detailed as the interior side air barrier may be more reliable over the long term.)

    The siding attachment method is not mentioned in the stackup. Board & batten has more rain penetration issues than clapboard or ship lap siding, but with deep roof overhangs and 2x lumber girts establishing the drying gap it should be OK.

  3. Blake Olson | | #3

    (1) Green framing lumber, primarily because it's available to me, have a mill and already harvested the lumber prior to hatching this plan, that said, we are also looking to keep the budget low.

    I should also mention the species I'm working with is eastern white pine. Which should keep shrinkage, twisting, and checking to a relative minimum.

    (2) Can a flexible vapor retarder, also work as a air barrier? I was under the impression that holes during installation were inevitable. Perhaps I am not clear on the type of product you are referring to, is there a particular product I can investigate?

    (3) And for siding attachment I was thinking of nailing directly over the strapping. and decided on board and batten because I can mill out the boards fairly easily and without having to fiddle around with a table saw.

    Additional since it will be put up green, I can nail in only one side of the batten and wait until the wood dries for a year to nail in the other side, Helping to deal with gaps that might develop with shrinkage.

    (6) Just curious what might you consider deep over hangs?

  4. Blake Olson | | #4

    Also not clear on what you meant by "2x lumber girts establishing the drying gap "?

  5. User avatar GBA Editor
    Martin Holladay | | #5

    Blake,
    There are a few unusual aspects to your plan. As long as you realize that the methods are on the fringe of normal practice, and are somewhat experimental -- and as long as you are willing to accept a few surprises -- your plan can work.

    If you take your time, and build slowly, you'll give the framing lumber some time to dry before you have to install drywall and finish materials. The slower you build, the better the result. Joists and beams will get smaller, so the house will settle. If you have any large beams supporting joists in the center of your house, the floors can develop a slope when the beams dry.

    The nature of green framing lumber usually means that your drywall job will have a few extra screw pops. Like Dana, I don't think these facts are particularly compatible with the airtight drywall approach.

    Personally, I like exterior sheathing -- for strength and for added airtightness. But it's possible to build a house without exterior sheathing.

    I wouldn't build a roof assembly without roof sheathing without talking to an engineer. Mineral wool laid over sloped rafters, without any exterior sheathing, doesn't sound like a good idea to me. When your roof has a few feet of snow on it, the mineral wool will compress against the tops of the rafters, and you will break all of your roof flashing (around chimneys and vent pipes, for example).

    If you have a bandsaw mill and some pine logs, make yourself some 1x6 and 1x8 boards, and use them for wall sheathing and roof sheathing. You won't regret it.

    And if you have the time, sticker all your lumber carefully and cover you lumber piles with metal roofing and heavy stones. Then wait a year. You'll have better lumber if you do.

  6. User avatar
    Dana Dorsett | | #6

    A couple of flexible air barrier "smart" vapor retarders would be Certainteed MemBrain (https://www.menards.com/main/paint/drop-cloths-plastic-sheeting/poly-film/8-x-100-membrain-smart-vapor-retarder-air-barrier-film/p-1902435-c-8188.htm ) or Intello/ Intello Plus (http://foursevenfive.com/?s=intello ), any of which can be detailed as an air barrier, in much the same way polyethylene vapor barriers can be (but without the moisture trap risk of polyethylene sheeting).

    The board & batten have to be mounted to something- I doubt you intend to long-nail them though the Comfortboard. I suppose the girts are what you listed as "...8) strapping...". While 1x lumber for that strapping is good enough for other siding types, it's probably worth going to 2x with board & batten. That's also true since it's going over rock wool, which is more compressible than foam. The extra rigidity of the fatter lumber will deliver a flatter wall surface.

    A roof overhang of 1 foot for every 10 feet of wall height provides substantial protection against rain-wetting of the siding in most areas. (In high wind coastal areas, not so much.) For a 30' tall barn it's typically only the rake of the roof that needs to project out a bit to meet that at the gables, since the eaves are usually more like 15-20' up. An extended rake near the ridge is a fairly common feature even on traditional barn designs, and that can be accomplished in several ways.

    https://s3.amazonaws.com/loablogs/barn%2010.jpg

    http://www.featurepics.com/FI/Thumb300/20081017/Rustic-Barn-Scene-935434.jpg

    http://st.houzz.com/simgs/76e1a5260151a6fa_4-5667/traditional-garage-and-shed.jpg

    http://www.sandcreekpostandbeam.com/content/Images/slideshows/homepage/1_photogallery.jpg

    While the extended ridge pole was often designed into the barn to hang a hay-loft hoist, it has the additional benefit of less rain penetration of the siding & doors below the ridge. (As if keeping the hay dry was important ! :-) )

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