New in-line solar PV and air permeable underlay guidance

*Please note, however, that NHBC acceptance is subject to their own separate approval process.

As an air permeable, low resistance (APLR) membrane, Proctor Air reduces the risk of issues occurring in roof spaces due to poorly installed vapour control layers or ventilation. And because it provides a more uniform flow of air than standard ventilation solutions, it means the roof requires no other ventilation measures.

Proctor Air has proved a popular solution since its launch. However, an update to the NHBC Technical Standards created confusion around the use of in-line solar PV with APLR membranes. Housebuilders and developers have therefore been reluctant to specify the two together, despite wanting to use APLR products.

With rooftop solar expected to be made compulsory on new-build housing , the adoption of PV panels will only intensify as specifications adapt to the lower carbon emissions required by the Future Homes Standard. And as those same homes become even better insulated and more airtight, they will rely on the performance of air permeable membranes to help reduce condensation risk in loft spaces.

To overcome the confusion, Proctor Group undertook industry-leading research to investigate the issue, engaging Glenfeulan Consulting to undertake modelling using RoofCond software. The renowned Fraunhofer Institute then validated the reasearch findings and agreed with the conclusions.

Equipped with a more thorough understanding of air and moisture movement through pitched roof coverings, Proctor Group has developed a recommendation for pitched roof specifications featuring in-line solar PV and Proctor Air.

Throughout, Proctor Group consulted with the BBA, who reviewed all of the research. Proctor Air’s BBA certificate has been updated to reflect the new recommendation and to serve as independent verification that the underlay can be used with inline PV panels, without additional ventilation in either the loft space or the batten space, assuming our installation instructions are used.