Fabcab

Fabcab https://fabcab.com We are a professional boutique architecture/design firm. Universal/Inclusive design is also a focus in our work.

Our approach offers design flexibility and customization, a high-quality timber frame and SIPs structural building system, and classically modern interior finishes. Founded in 2011, FabCab is headquartered in Seattle, Washington, U.S.A.

05/22/2026

"SIPs will rot if moisture ever gets in."

It's one of the most common concerns we hear.

EPS insulation, the solid foam core inside Structural Insulated Panels, does not absorb water. It is not fiberglass batt. It does not wick, hold, or migrate moisture through the core the way cavity insulation does.

Moisture risk in any wall assembly comes from air movement through gaps at transitions. Joints, window openings, penetrations. SIPs construction reduces the number of those gaps and concentrates the ones that remain at predictable, sealable locations.

That does not mean detailing does not matter. It does. Proper joint sealing and transitions at windows and roof connections are critical in any high-performance assembly.

But the claim that a SIPs wall will silently rot from a single leak does not hold up against how these systems actually behave.

→ The full explanation of how SIPs manage moisture: https://hubs.ly/Q04hh4fX0

05/16/2026

"SIPs are just foam and OSB. Won't they go up in flames and release toxic fumes?"

No. And the claim does not hold up under scrutiny.

Premier SIPS are tested to 1-hour fire-rated wall assembly standards (ASTM E119). With approved gypsum detailing, they meet or exceed code-required fire performance, including Wildland Urban Interface (WUI) requirements where stick-frame assemblies often need multiple additional product layers to reach the same compliance level.

On the off-gassing claim: EPS and GPS insulation cores are chemically inert. They do not release harmful gases when exposed to heat. The rigid foam is also treated with flame retardant during manufacturing.

There is another advantage most people miss. SIPs buildings are inherently airtight. That limits the oxygen that fuels fire spread. And unlike vented attics and eaves in stick-frame construction, SIPs eliminate the paths that embers exploit during wildfires.

Every building material will eventually degrade in a sustained fire. The question is how your assembly performs before it gets there. SIPs meet the codes.

More common SIPs questions answered: https://hubs.ly/Q04gDfTT0

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