Roof Ventilation

The method of ventilation should be established prior to the assembly of the roof covering. The position of the roof insulation will affect the method of ventilation where the insulation is at ceiling height (cold roofs) and at rafters (warm roofs). The ventilation methods must also take into consideration the type of underlay that will be used, e.g. bituminous felts, vapour permeable underlays.

The method of assessment given in BS 5250 should be used and where the risk of condensation is identified appropriate ventilation should be provided and / or a vapour control layer should be incorporated within the structure.

The recommended method and amount of ventilation of the roof void depends on two critical factors: the degree of sealing or air tightness of the ceiling below the roof void and the type of roofing underlay used. If a ceiling contains a loft hatch without an effective seal, unsealed pipe or service or other penetrations then high level ventilation of the roof void should never be installed without adequate low level ventilation of the same void regardless of the type of underlay. In the absence of this low level ventilation warm, moist air from the living space can be drawn up into the roof void through the holes and gaps in the ceiling to replace air sucked through the ridge thereby raising the risk of harmful condensation occurring in the roof void. Well sealed ceilings can be constructed to help meet the need for more energy efficient dwellings and other buildings. These better sealed ceilings allow the use of vapour permeable underlays for felting the roof void. With such modern construction high level ventilation of the roof void only is sufficient to ensure adequate control of condensation risk even during the drying out stage of newly constructed buildings. Furthermore with a well sealed ceiling external air is encouraged into the roof void at low level through the tiles and laps in the underlay, in preference to moist air from the living space, thereby creating an effective method of ventilation without the need for an eaves ventilation product.

Which products can be used to ventilate a roof?

Dry Vent Ridge, Dry Vent Monoridge, Abutment Ventilation System, Over Fascia Vents and Area Tile Vents