PYC: fixings through airtight board don’t impact airtightness

This article was originally published in issue 52 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €15, or click here to receive the next issue free of charge

The test was conducted on a passive house project using off-site manufactured I-beam timber frame panels with the Smartply Airtight Board as the internal vapour control layer. The panels were insulated offsite with Warmcel cellulose fibre insulation, which has itself been shown to improve airtightness by as much as 30 per cent, as previously reported in Passive House Plus. The boards and taped joints provide the primary air barrier.

All board joints and panel connections were sealed with Pro Clima Tescon Invis, with Tescon Primer and Tescon Vana XL used at the wall-to-slab junction. Pro Clima tapes were also applied at all window and door interfaces. PYC says this approach has achieved airtightness results as low as 0.08 air changes per hour at 50 pascals on previous projects.

On this build, initial pressurisation and depressurisation tests on the exposed fabric returned an average of 0.32 air changes per hour at 50 pascals. Each exposed stitching screw head was then individually taped with Tescon Invis, and two further tests were carried out. The average result remained at 0.32, indicating no measurable improvement.

PYC says the findings confirm its working assumption that fixings penetrating the airtight layer self-seal, as the screw compresses the 12 mm board tightly against the I-beam flange. The screw heads sit flush with the surface and do not create a pathway for air leakage. Taping over exposed fixing heads is unnecessary, the company says, even at passive house levels of airtightness.