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Will I need house wrap and /or rainscreen?

origano | Posted in General Questions on

Existing exterior is Textured 111 plywood (with vertical groove 8″ o.c.) over stud with 1X4 interior , exterior corner, window, door and soffit (header) trim.

Would like to reface with Western Red Cedar 1X8 T&G vertical siding (WWPA Profile 1600). Would like to install over new horizontal wood furring (that would bridge the existing T-111 groove which would remain open and unobstructed) and have some of the existing trim act as furring. The bottom and top new siding will be slightly routed out in the back (simulating the existing T-111 groove) to allow for drainage and breathing (circulation). All this without the use of house wrap and/ or rain screen. (The T-111 is now breathing). Yes, cedar will have all surfaces and edges factory sealed. I would like to have the existing T-111 grooves act as my rain screen.

Will this work without using house wrap and/or rain screen.

Comments and/or other suggestions please.

Aristides “Steve” Cagos
781-890-0937
Please confirm the receipt of this question.

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Aristides,
    Building codes require, and building scientists recommend, that every exterior wall include a water-resistive barrier (WRB) like housewrap or asphalt felt. This WRB needs to be integrated with your window flashing and door flashing. (By the way, do you have a window flashing plan?)

    For more information on this issue, see All About Water-Resistive Barriers

    Although you wrote that you are planning a wall "without a rainscreen," in fact your new exterior furring strips will create a rainscreen gap. That's a good thing.

    You should install your WRB (probably housewrap) between the existing T-111 and the new horizontal furring strips that you plan to install.

  2. Eric Padgett | | #2

    He said the furring strips would be horizontal with vertical siding. Can horizontal furring against a house wrap be a rain screen? Just want to know for my own info. Will the gaps in the T-111 be enough when covered with house wrap over them?

  3. Malcolm Taylor | | #3

    Eric,

    "Rain screen" describes any break between the cladding and the underlying sheathing or WRB. In other words it encompasses a range of assemblies.

    The three main attributes of a rain screen are:
    - A capillary break.
    - A vented cavity
    - A drainage plane.

    Running the furring strips horizontally means you only get the first benefit. The question is how important is that? Depending on what cladding you use you may still get some drying to the exterior, and you would need an awful lot of bulk water to intrude for the drainage plane to be necessary.

    It really depends on your climate and wall assembly how important the additional attributes are. But yes, either way it's still a rain screen.

  4. User avatar GBA Editor
    Martin Holladay | | #4

    Eric,
    I agree with Malcolm's answer. For more information on this issue, see All About Rainscreens.

    In that article, I wrote, "It’s possible to install cedar shingle siding over horizontal 1x3 furring strips. Even though the resulting gaps won’t have drainage, the installation works fine — because not much liquid water gets behind the shingles, and any water that does can evaporate quickly. (If you’re the type of builder who worries about drainage, you can cut kerfs on the back side of your horizontal battens, use corrugated plastic battens with drainage holes, or buy notched battens at a roofing-supply outlet. But I don’t think that level of obsession is necessary.)"

  5. origano | | #5

    Origano responding:
    Yes, I understand the new wood horizontal furring will create a rain screen and the existing T-111 vertical grooves will allow for drainage and air circulation (furring to bridge existing grooves). The existing T-111 has been exposed and breathing for the last forty years. Does anyone agree with me that the "house wrap" would be overkill? Kerfs will be cut behind the new vertical siding at the top,where the existing trim is being used as furring, to allow for the chimney effect .Existing windows and doors already have flashing.
    :

  6. User avatar GBA Editor
    Martin Holladay | | #6

    Origano,
    The fact that the existing T-111 isn't rotten tells you nothing with respect to the question of the need for a WRB with your new siding.

    If your existing windows are now properly flashed -- and they have sill pan flashing that directs water to the exterior of the T-111 -- that doesn't mean that the existing flashing will work after your new siding is installed.

    It sounds as if you want to use T-111 as a WRB. Or perhaps there is a layer of asphalt felt under the T-111, and you are assuming that the existing asphalt felt will continue to operate as an adequate WRB.

    It might. Whether or not you get away with this approach depends on the depth of your roof overhangs, the exposure of the house to wind-driven rain, and the local climate. But it seems like an unnecessary risk -- just to save the cost of a roll of housewrap.

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