Reduce drag arising from thermal movement; assist against condensation and chemical attach; protect against uneven surfaces.
Building Paper to BS 1521/AF
Advice on use:
- When using wood roll, fit them over the underlay;
- Lay underlay in strips across the fall of the roof, lapping the upper layer over the lower and staple the lengths in position (do not use nails as they may cause damage to the underside of the lead);
- Create an upturn at abutments. Avoid draping underlays downwards at edges, as moisture will be drawn into the roof by means of capillary action;
- Take care when lead welding as flames will ignite paper and melt textiles;
- Ensure that the lead sheet is laid onto dry substrate and underlay.