A vapour control layer limits the passage of water vapour through a construction. Its role differs from the outer roof covering that resists rainwater.
What does this mean on your roof?
The location and properties of this layer need to suit the complete roof assembly. Junctions and interruptions around pipes or roof windows form part of that arrangement.
A correctly named product does not, without suitable installation, provide a complete answer to moisture questions in an existing roof.
Additional insulation can alter conditions within the construction. Have existing layers and indoor conditions assessed before adding material or closing a ceiling. Ask which product information supports the proposal and how the layer connects to retained components. Keep documentation and available installation photographs, because the layer usually becomes difficult to inspect once internal finishes are completed.
Frequently asked questions
Does vapour control mean waterproof roofing?
No. Managing water vapour and resisting rainwater are different functions within the roof assembly.
Can it be omitted because roofing exists above?
The covering’s presence does not answer that question. Assess the complete moisture-control arrangement.
Consulted 19 September 2026. Check requirements for your own address and selected system.