There are two categories of premium underlay:
Building papers
- Conform to BS 1521 / AIF
- Are suitable for smooth plywood decking (underside of decking must be ventilated.
- Can prevent chemical attack from smooth concrete, stone or oak surfaces.
- Must be fitted over whole substrate area.
Geotextiles
- Are needle punched, non-woven, Geotextile polyester materials in two unit weights -200 and 220 g.m-2
- Are suitable for more uneven surfaces, e.g. Traditional timber boards.
- Do not rot or cause adhesion.
- Allow space for air flow between led sheet and substrate
