No good quality roof vents leak when installed correctly. If a slate or tile vent is suspected of leaking, the circumstances should be considered.
It is possible for rainwater and condensation to run down the roofing underlay and drip though the opening cut into the underlay. This will usually be apparent on the outside of the vent, or on the underlay. To prevent this, the underlay should be cut and dressed around the opening to divert any rainwater or condensation around the opening in the roof.
If water is draining through a ceiling extractor fan, it is most likely that it is condensation forming in the ducting and draining back to the fan. To minimise this, the ducting should be as short as possible and lagged with insulation where it passes through a cold roof space. If this is not possible, or the problem persists and a condensation trap has not been fitted above the extractor fan, then this should be done.
In very extreme conditions, such as experienced during the ‘Beast from the East’ in 2018, extremely low temperatures combined with fine dry powdery show can create a situation where small amounts may enter through the ventilator. It is not possible to produce a ventilator cost effectively that will allow the free flow of ventilating air and not the very fine snowflakes.
In these situations, in-line or flush fitting ventilators often perform better due to an internal rainwater trap rather than those that rely on a covering hood or cowl.
