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Best rainscreen with reverse board and batten design? Strapping versus blocking?

Kail_Z | Posted in Green Building Techniques on

I am in climate zone C4 and will be using rough cut reverse board and batten to side my new house. I have been planing on attaching the board and batten on horizontal dimensional 1×3 strapping that will be attached over my wrb and 1″ of rigid foam. I know others in the area that have been installing blocking on the inside of there sheathing to attach there board and batten. Does anyone have any advice on this? If I were to eliminate my strapping and just screw through the foam and sheathing to pre-installed blocking this would simplify triming out my windows and bug screening and other tasks. Would the reverse board and batten attached directly to the wrb and foam ventilate enough? Would the blocking take up too much space in my 2×6 wall cavity where insulation should be?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Kail,
    If I understand correctly, you want to install reverse board and batten siding on a wall with exterior rigid foam.

    There are several ways to do it, but the easiest way is to attach the battens directly to the rigid foam with long screws that extend back to the OSB or plywood sheathing. In this case, the battens serve two purposes: they are part of your siding system, and they are also vertical furring strips that create a rainscreen gap.

    The main objection to this approach is that attaching siding to sheathing is not as secure as attaching siding to framing. To overcome this objection, you can install horizontal 2x4 or 2x6 blocking between your studs, 24 inches on center. That solution works -- I've done it -- but it involves a lot of fussy work.

  2. Kail_Z | | #2

    Martin, thanks for your advice. Would you worry about the space in my wall cavity that the 2x4 blocking would be taking away from insulation? or is this nominal? It also seems like a lot more screw penetrations through the rigid foam, any issues with this?

  3. Chaubenee | | #3

    Personally, Kail in my opinion- I wouldn't worry about either of those considerations very much. You cannot avoid putting fasteners through the foam, and what good will your foam insulation be if your siding does not stay attached, anyway. You wouldn't need the blocking of you knew you were right on the framing studs, though. And if you were doing boards that were cut to fit the same width as the stud spacing. Are you using pine or cedar? Will you be putting something at the bottom to prevent pests from getting in? Also, is this going to be a fully ventilated assembly with air coming in at the bottom and venting up at the top of the siding?

  4. GBA Editor
    Martin Holladay | | #4

    Kail,
    You are correct that blocking between your studs will increase thermal bridging. If you want a better insulated wall, you should make your rigid foam layer thicker. The rigid foam layer is doing most of the work; it's a more important layer than the insulated between your studs.

    As I wrote in my first response, there are several ways to do this. If you are worried about thermal bridging through blocking, you can skip the blocking and instead install horizontal 2x4 nailers on the exterior side of the rigid foam, 24 inches on center, installed flat to the foam (creating a 1.5-inch-deep air space). The nailers should be secured to the studs with long screws through the foam. You will find that installing these horizontal nails will go much faster than installing blocking between the studs.

    Then you can attach your reverse-board-and-batten siding to the horizontal nailers.

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