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Window Buck with Wood Fibre Insulation

Matt_VT76 | Posted in Green Building Techniques on

We’re starting the process of CLT build design and we’re trying to figure out the best way to design the window RO layers.

We’ll be installing about 3 inches of rigid wood fibreboard (Steico duo) on the exterior of the CLT and are planning our windows to be on the exterior edge of the CLT plane on a 7-inch thick wall (3 in of CLT, 3 in of Wood Fibre insulation, 1 in rainscreen batten). The CLT will be exact due to it’s CNC cutting, so I’m hoping to avoid needing plywood or timber bucks going into the CLT layer.

The plan would be to install the WRB to the CLT plane and attach a sloped sill to the top of the wood fibreboard on the bottom side of the rough opening bringing it out to the edge of the rainscreen layer.

My question is, would the wood fibreboard act as a suitable window buck if I attach the 1″ rainscreen battens around the RO perimiter, or do I need 4″ window bucks attached directly to the CLT?

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  1. spaget52 | | #1

    Good question! I have the same question and a search brought up your post. My structure is sheathed double-stud walls with rainscreen siding. To minimize thermal bridging at the window frame, I was thinking of using a wood fibre insultation for the bucks, but am not sure if the density of the wood fibre is sufficient to hold fasteners from the window frames. Did you employ thermal fibre bucks with your CLT project? Any others with input on this topic?

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