Let your roof breathe

It is important to ventilate your roof space to reduce the risk of condensation, which can lead to excessive damp and fungal decay (see photo) in the roof timbers. Condensation is caused by warm, moist air, created by activities in the house such as cooking and showering, rising into the roof space. When that air meets the cooler air in your roof it releases the moisture as droplets that settle on surfaces. This is known as condensation. Water droplets can also fall onto ceilings, causing damp patches.

Most houses built since the mid-1990’s, or those that have had their roofs re-covered since then, will have a breathable, or vapour permeable, underlay (such as protect) incorporated above the rafters/trusses. These are water resistant but allow the passage of water vapour and so help to prevent condensation. However, older underlays are impermeable and if ventilation is not provided condensation can be an issue. Ventilation can be particularly difficult to achieve if a roof has been converted as thermal insulation around the rooms in the roof may obstruct airflow.

Ventilation can be provided by proprietary tile vents installed into the sloping surfaces of the roof, or air bricks inserted into gable walls. Ideally ventilation should be provided at the ridge and as a continuous 25mm slot along the full length of the eaves.

When insulating a roof, care needs to be taken to ensure the insulation is not pushed right into the eaves as this can block the flow of air through any existing vents.

If you are concerned about condensation, contact Woodward Chartered Surveyors to arrange for an inspection.

Kate Farrar MRICS is a Chartered Surveyor and Director of Woodward Chartered Surveyors.

Woodward Chartered Surveyors cover an area from East of Oxford, High Wycombe, Beaconsfield, Amersham, Berkhamsted, Watford, Rickmansworth and into London, Northwood, Uxbridge, Harrow, Ealing and Mayfair.