What is sarking and does my roof need it?

A roof covering is the primary barrier and sarking is the secondary one. Water that gets past a tile lap in driving rain, or condensation that forms on the underside of metal sheeting on a cold night, lands on the sarking and runs down into the gutter instead of onto the ceiling.

What it does

• Catches wind-driven rain that gets past the covering.
• Manages condensation, which is a growing problem as homes become better sealed and insulated.
• Provides some protection during the period between removing an old roof and finishing the new one.
• In some products, adds a reflective layer that reduces radiant heat gain into the roof space.

The catch with retrofitting

Sarking sits under the roof covering, so adding it to an existing roof means removing and reinstating the covering. On a tile roof that is possible but substantial, and it is usually only worth doing as part of a re-roof or a major restoration. On metal it effectively means a new roof.

Where it matters most

Exposed and high wind sites, low pitch roofs, and cold climates where condensation is a real risk. If you are re-roofing anywhere in those categories, including sarking is a small proportion of the total cost and it addresses the exact failure mode that produces mysterious storm leaks.