Interstitial Condensation In Roof

Condensation in a cold roof.

Interstitial condensation in roof.

The position of the insulation means that the roof deck and most of its structure has no protection from low temperatures during the winter. It is the result of the interaction between a complex set of factors. The moisture laden air can penetrate into hidden interstitial wall cavity through the exterior in a warm humid outdoor period and from inside the building during. Interstitial condensation commonly occurs when moist air permeates through elements of the building fabric across which there is a temperature difference typically but not always when warm moist internal air moves towards the cooler outer parts of external walls or roofs driven by a pressure difference.

Only through fasteners such as screws brick ties and roof screws would be at risk in such high rh environments. Interstitial condensation is a form of structural damp that occurs when warm moist air penetrates inside a wall roof or floor structure. Interstitial condensation can occur in solid and cavity wall properties and happens when pressure and temperature differences force warm humid air through hygroscopic water absorbing materials until they reach a point cold enough for it to condense upon a surface. Inside the roof wall or floor elements.

How to find the dew point in buildings when does moisture condense on surfaces and in cavities. Interstitial condensation is condensation which occurs between layers of the construction i e. Interstitial condensation is different from surface condensation such as that caused by cold bridging and its occurrence within the roof or wall structure of a building is difficult to detect without investigation. Condensation risk analysis for the glasgow school with the dew point indicated under the membrane.

The incorporation of adequate insulation and ventilation in the roof void of a cold roof construction or sufficient insulation and vapour control layer in a warm roof construction will prevent the formation of interstitial condensation in the normal range of environmental conditions experienced. When that moisture laden air reaches a layer inside the interstitial structure that is at dew point temperature it condenses into liquid water on that surface. The standard of roof ventilation varies widely but the current building regulations specify that 270mm mineral wool should be used to insulate your a roof space at a minimum. Interstitial condensation can create structural dampening that occurs when moist air penetrates inside the hidden space within an enclosed wall roof or floor cavity structure.

Moisture will condense in this zone to form interstitial condensation. The dew point defines when moisture will begin to condense on building. Interstitial condensation is a particular problem in cold deck roofs where the insulation is placed in between the joists in the void above the ceiling.