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Fiber-cement lap siding — Back vent or not?

GBA Editor | Posted in Energy Efficiency and Durability on

I’m installing fiber cement lap siding on the second and third floor exterior walls in a hot humid climate, subject to relatively high rain fall and high winds.—8 1/4″ x 5/16″ with 7″ revaeal on wood frame 2×6’s on 24″ centers, above 20′ from ground.

I have several questions involving durability. My goal is to install a reasonably durable system, but I’m running into differences in what seems to be recommended vs what is typically done in my area. Perhaps this is a case of general construction having not yet caught up with best practice. I would appreciate any comments on the following.

First, should you fur it out? Most of what I’ve read indicates that durability of the FC and dry out of the wall system is significanly improved by so doing. Yet, it doesn’t seem to be common practice.

Second, most of what I’ve read indicates that durability of the FC is significantly improved by back-priming. Yet , again not commonly done. Is this important?

Third, If back priming of the FC is important, then how is use of bare wood fur strips justified or consistent?

Fourth, most of what I’ve seen recommends fur strips on 24″ centers (even BSC papers for hurricane areas). It appears to me from looking at the Hardie wind charts, that you can’t get hurrican wind load ratings on 24″ support spacing. Should I add an intermediate fur strip (essentially strips on 12″ centers)?

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Replies

  1. homedesign | | #1

    John W,
    I know this does not answer your question....
    In a perfect world it seems like "best practice" would be to build exactly as BSC Suggests
    Very easy to suggest......not-so-easy to construct.
    may the force be with you....

    If you do decide to go Sans Furring Strips...there is a compromise solution...
    It may not "vent" as well as 1x4 furring strips...but it looks to me like it would drain and dry.

    I have always thought this looked pretty clever.....
    Look at the photo of the Felt Furring strips in post #9
    http://forums.taunton.com/tp-breaktime/messages/?msg=124481.1
    Just a thought

    There's also some interesting ideas using corroplast strips(Rollie's Delores house) further down in the thread.
    JB

  2. homedesign | | #2
  3. homedesign | | #3

    John W.
    Concerning the Hardi siding nailing schedule
    Check it again... It may not allow blind nailing a 24 oc ... but may allow face nailing
    I'm not sure about this so check with the latest James Hardie info

  4. John Walls | | #4

    JB, If I'm reading the charts right, you can get 105 to 110mph, Category C, 3-second gust ratings (depending on which code you select) at 24" spacing face nailing (what they call "through overlap"). It may be that the BSC paper is based on a Category B, which would bump it to 125-130 mph which would meet hurricane winds (although some local jurisdictions are higher, I think).

  5. John Walls | | #5

    TREATED LUMBER?

    How about using treated lumber for the furring strips?

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