Does my roof need ventilation?

Does my roof need ventilation?

Any new roof should include both high and low level ventilation.  Roof spaces need adequate ventilation in order to prevent condensation.  Condensation can be a really significant problem, especially in modern, well insulated and airtight houses.

The problem occurs because of the amount of water vapour we create in our everyday lives.  Showers, cooking and washing all create steam which moves around the house.  Warm air rises, so typically warm damp air rises up through the house and ends up in the roof.

If the roof is not adequately ventilated, then the water vapour condenses on the underside of the roof tiles, causing damp.  This can be a really significant problem, soaking insulation in the roof and potentially causing mould and rot on the roof timbers.

The only effective way to prevent this problem is to have adequate ventilation at both low level and high levels.

Low level ventilation is provided by a gap, created between the insulation and underlay at the eaves so that air comes into the roof space and out the other side.  High level ventilation is situated at or near the ridge of the roof.  This creates a stack effect, drawing air up and out of the roof, whatever the weather conditions.

This method has always been recognised as an effective way to ventilate roof spaces, but over the last decade or so there has been a trend to use unventilated roof designs.  These rely on vapour permeable roofing underlays to allow humidity to escape.

However, the last two cold winters have seen a dramatic increase in the number of problems related to condensation, and this has demonstrated that vapour permeable underlays are not sufficient on their own.

It is always worth checking that your roofing contractor is designing your new roof to include both high and low level ventilation.  This will ensure you never experience the problem of condensation.