Underlays
For Roofing, Cladding and Weathering Applications.
An underlay is normally used to isolate the lead sheet from the substrate and allow the lead sheet to expand and contract freely with changes in temperature.
The main requirements for underlays are that they should:
- Allow the thermal movement by reducing the amount of drag between the substrate and the lead sheet.
- Help to protect the lead sheet against corrosive attack from stone, concrete, or discharge from timber and roof condensation.
- Provide an even surface and to level out any imperfections such as nail heads, board edges and knots which could damage the lead.
- Fully support the lead sheet so that it cannot sag or be punctured.
- Reduce the risk of moisture being tapped between the lead and the substrate.
- Not be adversely affected by heat when in-situ welding takes place.
- Be free of any substance which could be deleterious to lead sheet.
