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Feasibility of using fiber-cement as window bucks?...

Posted by fixizin (My Page) on
Mon, Feb 22, 10 at 0:12

... in a concrete-framed opening, as found in CBS/ICF/CIP construction? I'd really like to eliminate wood from the equation, entirely. Nothing between the aluminum frame and concrete sill but more concrete... and silicone caulk... or some anchoring epoxy, if need be.

IIRC, initially fiber cement offerings only came in siding form, basically 1/4" thick. But now I notice that HardiPlank and other F-C offerings now come in thicknesses up to 3/4", maybe more, so naturally, I went "Hmmmm..."...

I have no hands-on experience doing the total window tear-out and replace gig on a CBS structure, so I'm not clear if the softness of the wood is a useful property, or conversely if fiber-cement planking is too brittle, etc. Newer codes require anchoring the window frame THROUGH the bucks, and directly into the concrete anyway. (The bucks are still anchored independently, beforehand, so they still comprise a significant portion of the shear resistance.)

What say ye, window RKIs? Thanks in advance.

Follow-Up Postings:

RE: Feasibility of using fiber-cement as window bucks?...

You can use something like a PVC/resin board (aka azek) or have a local fabricator make you some steel bucks.

I am going to go the latter route if I build my ICF home.

RE: Feasibility of using fiber-cement as window bucks?...

Oh right, the various composite (Azek/TAMKO/etc.) boards... I had considered them at one point, but they seem to be geared towards outdoor decks, and thus all the sample sizes I saw were too LARGE, e.g. 1"X6".

Steel bucks might be problematic in the humid sub-tropics, and even stainless might experience dissimilar metals reactions with aluminum alloy frames. OTOH, the Tapcons and related anchors are steel, aren't they?... hmmm....

Might have to have some aluminum pieces fabricated for a related project, so I should get familiar with some Al fabricators anyway.

Anyway, good ideas, keep 'em coming! Gotta be something better than soft pine under there... UNLESS... the soft pine provides SOUND-DAMPING action?? Hmmm... do you have any experience with the steel bucks on ICF/concrete, w.r.t. sound transmission?

PS: Have some good friends in Vancouver, WA area who built large 2-story home w/ ARXX brand ICFs. Worked out well.

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