Ventilation to a “cold roof” is an essential part of the design as lack of adequate airflow will result in condensation forming to the underside of the sarking felt and rafters etc.
Ventilation can be incorporated in various ways; at eaves, with over fascia vents, or soffit vents, ridge and within the roof covering via in-line tile or slate ventilators.
Ventilating felt can also be used to assist air-flow through the roof space and in some cases provides adequate air flow without the need for additional provision at ridge and eaves.
The basic requirements for ventilating a traditional cold loft space are that air should enter the loft at the lowest point on one side of the roof and exit on the opposite side of the roof.
Water vapour rises up through quilt or fibrous insulation, and meets the air in the loft, where some of the moisture is absorbed - the quantity depends on the air temperature.
Warm air can absorb more water vapour than cold air. If the air layer directly above the insulation is constantly changing it stands a good chance of absorbing most or all of the water vapour and take it outside. The warmer the air in the rooms below the insulation, the higher the amount of moisture that can be absorbed.
The cooler the loft, the less moisture that can be held before condensation forms.
Consequently if air leakage into the loft is full of moisture then the risk of condensation forming in the loft increases. This can be reduced if a vapour check layer is introduced below the insulation such as foil backed plasterboard, or a layer of polythene, along with sealed holes and openings.
We have completed many ventilation projects over the years and regularly work with domestic and commercial clients from across Kent, Surrey, Sussex and London, including East Grinstead, Tonbridge, Bromley, Croydon, Orpington, Maidstone, Aylesford, Canterbury, Ashford, Sevenoaks, Medway, Brighton, Reigate and Burgess Hill.