Lead underlay

There are four main reasons why we recommend using a good underlay:

1. Lead underlay gives you a smooth, even surface to work on, so you don’t have to worry about exposed nail heads, rough edges or wood knots

2. Lead underlay isolates the lead sheet from the substrate – reducing the drag between the two and allowing for thermal movement

3. Lead underlay reduces risk of damage caused by trapped moisture between lead and substrate. It also protects the lead against corrosion 

4. Lead underlay stops the lead from sagging or puncturing

Recommending lead underlay to your clients

If you’re working on behalf of a client, you might recommend lead underlay as a solid investment to preserve the lead and prolong the roof’s lifespan. But it’s important to choose a lead underlay with care:

• The wrong type of underlay can cause buckling and splitting

• In hot weather, some materials with a bituminous surface can become sticky. If the lead then bonds to the substrate it could restrict normal thermal movement

• It’s important to recommend an underlay that won’t be affected by heat – particularly where welding will take place