Universal rafter trays which adjust to the correct roof pitch and can be used in new-build, or in refurbishment without disturbing the roof covering. Provides guaranteed actual ventilation opening of 25 000mm2/m at 600mm rafter centres (RV655) or 400mm rafter centres (RV635). RV635 can also be used at 450 - 600mm rafter centres; one per rafter provides not less than 10 000mm2/m. For use with existing roofs (pushed into place) or new buildings (fixed to wall plate). 600mm rafter spacings. 25,000mm2/m ventilation. Lightweight and durable. Easy to install.