Ventilation of Roofs to Prevent Condensation

Pitched Roofs

  • A pitched roof is defined as a roof with a slope of 15 degrees or more.
  • To ensure adequate ventilation of the roof space, every pitched roof should have openings at the eaves, between the ceiling and the roof itself.
  • The total area of roof strips required under the eaves is equal to 10 mm times the perimeter of the roof. Or the area a 10 mm thick roof strip would take if it ran continuously under the entire eave.
  • Roofers must ensure that the insulation does not block these openings; this can be arranged through acquiring and using components designed to enable air flow through insulation at these gaps.
  • Those pitched roofs which have a single slope that runs up to a tall wall have less opportunity for ventilation at the eaves level. Thus these types of pitched roofs should have a high level ventilation system installed where ventilation through the roof covering or at the upper wall roof junction is arranged with a total area of 5 mm x the length of the junction.

Flat Roofs

  • The roof space of a flat roof, between the roof and ceiling, must also have ventilation to prevent condensation and building damage.
  • Flat Roof spaces should be 50 mm in width for adequate air flow.
  • To enable optimum cross ventilation through the roof space, openings should have a total area of the eave length x 25 mm. The ideal design is to have enty points for air flow at opposite ends of the roof.
  • Pitched roofs that have the ceiling following the roof structure have a similar design to flat roofs. However as the ceiling blocks the air flow, an escape strip of at least 5 mm x in area must be placed along the ridge of the roof.
  • If the span of the roof is in excess of 10 metres or has a shape more complex than a rectangle, higher levels of ventilation may be necessary to prevent condensation from developing. A good guideline is to calculate 0.6% of the total roof area and add that to the ventilation width.

BPM Maintenance is a property maintenance company based in Bath that is proud of the high quality roofing work it consistently offers to clients all around the Bath and Bristol areas.


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