Roof battens, membranes and ventilation
Why the concealed layers under a pitched roof are as important as the visible tiles or slates.
This is general information, not a survey, design, legal or Building Control decision. The correct scope and standard depend on the property, work, date and regulatory route.
Battens provide the fixing layout and must be the correct size, grade, spacing and support for the covering. The underlay or membrane manages wind-driven rain and drainage, but it is not a substitute for sound roof covering or correctly formed eaves and abutment details.
The roof build-up should provide the ventilation and vapour-control strategy required by its insulation and roof geometry. Do not block eaves or ridge ventilation with insulation, mortar or debris; condensation risk is a design question, not something a membrane label resolves by itself.
When recovering a roof, record the existing rafter condition, membrane, battens, insulation, roof penetrations and ventilation before closing the build-up. Use the covering and membrane manufacturer's current details.