Fire Rated Exterior Sheathing

Hi all,

I am working on a single-family home in the Wildland Urban Interface (WUI), so we need 1hr rated exterior walls. Instead of using DensGlass sheathing, we are specifying LP Flameblock OSB. Does anyone know of lower carbon exterior sheathing? Or healthier options?

I am particularly concerned with the recyclability and reuse of OSB.

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Hi Brian, I inherited a WUI house project that was already sheathed in plywood. We gave it a housewrap, then two staggered layers of 1-1/2" 9 lb mineral wool boards, We then plastered directly onto the mineral wool. We used a clay based plaster, to keep the carbon footprint minimal, but lime plaster would be an option.

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We’ve been working with various earthen walls with heavy timber or a timber & hempcrete (or cob) infill for the mass and fire resistance. The mass is critical. All borrowed from Northern European practice with a bit of QA/QC. Thing about fire is the radiant energy through the windows. The RE alone can ignite interior fabrics and some surfaces if the structure is enveloped. So you need fire shutters or something similar as well.


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following <3

Thanks Bob and Michael!
I should mention, we are using a charred cedar rainscreen over the sheathing.
Though, I would love to use earth, clay, and/or lime on other projects. Not sure our clients are open to that just yet. Also the setbacks on the project have restricted us to 8" walls to create the desired interior layouts.

So when mass is not achievable, what are the low-carbon options for sheathing?

worked on a project without adequate water supply in the WUI and that was not fun… we also used char siding - the AHJ required the application of a fire retardant coating of the shou sugi ban. :roll_eyes: