30 March

How not to get an “F” in AVB chemistry

“Don’t know much about chemistry” might be a catchy tune, but it’s a sure way to earn an “F” for failure when it comes to AVB system failure.

Design professionals who want to ensure mandated air and vapor continuity must focus on the often-overlooked spaces between adjoining systems. The challenge comes when choosing from among the abundance and variety of transition products on the market today.

But the choices aren’t easy since many accessories and AVB products don’t mix due to problems caused by chemical resistance. Chemical resistance is the strength of a material to protect against chemical attack or solvent reaction. A low chemical resistant product that touches a corrosion resistant material is likely to swell or soften, causing the material to lose serviceability.

For example, silicone sealants should not be used for detailing when the primary air barrier membrane contains asphalt because these compounds are not compatible with one another.

When designing or evaluating materials for a high performing building envelope consider that the primary air barrier membrane must be compatible with:

•  Window and door flashings

•  Termination mastics & sealants

•  Through wall flashings

•  Contact adhesives

•  Sealants

•  Roof-to-wall connections

•  Below grade waterproofing connections

Fortunately, manufacturers provide technical data sheets to guide you through the chemical compatibility minefield. Visit their websites often for the most updated information so each of your projects earn an “A” for mission accomplished, rather than an “F” for membrane failure.

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