Do all roofs require a ventilated counter batten?
Close-fitting roofing materials, such as clay and concrete tiles do not allow much airflow through the laps and joints. It is, therefore, necessary to provide a 50mm ventilated batten cavity above the underlay and below the tiles (comprising a 25mm-deep counter batten and 25mm-deep tiling batten). This cavity should be ventilated equal to 25mm at the eaves and 5mm at the ridge.
This recommendation should be followed for all types of roof construction where close-fitting tiles and vapour permeable underlays are specified, as it will minimise the risk of harmful condensation or moisture build-up in the batten space.
If it is not practical to install a counter batten, a non-vapour-permeable underlay should be used with traditional low- and high-level ventilation (below the underlay and above the insulation) in accordance with BS 5250 - Control of condensation in buildings.
For more information, take a look at our roofing FAQs.