16 - Formance Sips with Membrane roofing
Membrane roofs are often used with Formance structural roof panels on shallow pitch roofs.
This bulletin sets out best practice for these situations.
The recommended build-up of layers is as below.
- Formance reinforced or thermal roof panel selected from the appropriate table in the Formance Design Guide
- Breathable roofing underlay suitable for the application for example (Proclima Solitex Extasana Adhero)
- H3.2,12mm F8 plywood – fixed to the panel with fully threaded 10g x 30mm stainless steel screws. (200mm centres to the perimeter and rows of screws at 200mm centres - 400mm apart to the middle of the sheet) It is recommended to set the plywood sheets out in a brick pattern to avoid SIP & plywood joints aligning. (Plywood can be substituted with approved membrane substrates such as PIR board – check with manufacturer regarding suitability)
- Selected roofing membrane installed in accordance with the manufacturer's recommendations.
Important points to note.
- All panel joints and junctions on the inside of the building must be completely airtight to prevent any potential dewpoints occurring under the membrane.
- It is recommended that a light colour roofing membrane is used to lessen heat absorption.
- The membrane is to be installed correctly by a competent, qualified, and accredited installer.
- It is strongly recommended that if there is any structural steel needed to support the roof panels that it is placed on the inside of the thermal envelope (not in the same plane as the panels)
- The top skin of the roof panel must have a moisture level of 18% or less prior to installing the plywood
