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Issue with HardiBoard over exterior foam and strapping

user-4310370 | Posted in Green Building Techniques on

I will be building new soon and found a builder willing to do 1.5-2″ of external foam (zone 5) our plan is either brick veneer or a craftsman style with hardiboard siding. The plan was to use strapping (1×3 – 1×4) over the foam for a place to nail the siding, however, the siding contractor rightfully pointed out that hardiboard is fragile and if struck between the strapping the hardiboard could snap. His preference (and the manufacturer specified) method is to have a continuous backing under the hardiboard. He mentioned success in attaching the board directly through 1.5″ foam but I am unsure of the viability of this method.

Has anyone used hardiboard over external foam board and if so how was it attached?
Any other gotcha’s?
(and yes we thought about smartside but most general’s around here are wary of it and the two siding contractors I talked to refuse to use it as they say within 5 years it no longer looks good ???)


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  1. Expert Member

    The manufacturer supplies rain screen details for both Hardi-panel and Hardi-plank showing their approved method of installation on vertical furring. On all multi-family and commercial applications that's the only way they will allow it to be installed.
    Here is one link:

  2. user-4310370 | | #2


    I will pass the info along to the builder and contractor. I do see the risk the siding guy mentions I have hardi board on a garage and to clean up I just snapped the large pieces to toss in the garbage, takes no muscle at all. Hopefully 16" spaced and wide furring strips gives it enough strength.

    I have noticed that the GC's and trades tend to be very conservative and go with what they know. It's understandable when you might have warranty issues 5 years down the road so the only thing you are sure of is materials and methods that have been used for a while. It just makes it difficult when you want to try newer and presumably better techniques.

  3. Expert Member

    I'd say Hardi siding and similar products now are used on 90% of the dwellings built in British Columbia, and all are required to be installed on rain screen. It really can't be considered a novel way to build anymore.
    While it does snap easily, when installed each edge is supported. I suppose a really well placed kick could break a piece, but if people are going around kicking your house, the broken siding is probably the least of your concerns.

  4. user-4310370 | | #4

    Thanks, a good answer and a laugh all in one :0)

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