Roofing foils (or more precisely – vapor-permeable-waterproof foils and vapor barriers) are, only at first glance, not so important building elements. However, these are indispensable elements in today’s modern construction, because in many positions it is not enough to install only insulating material according to attic insulation contractor durham.
It used to be common for roofs to be built with two ventilating layers, so the only requirement that was placed in front of the roof foils was exclusively watertightness, i.e. protection from the penetration of rain and snow.
Today’s styles of roof construction, and thus the installation of thermal insulation materials and supporting elements, imply the use of sophisticated materials of high quality, which guarantee the longevity of the construction. So, these are not ‘ordinary, PVC foils’ that you will often find in warehouses and construction sites, but high-quality membranes from reputable manufacturers, which offer a full range of these products, for different purposes.
We divide roofing foils into two large groups, depending on their purpose and the place where they are placed:
- Vapor-permeable foil – prevents the penetration of rain and snow into the roof structure (it is waterproof – so it is placed on the upper side of the insulation, towards the outside), but also to allow water vapor, which eventually reached the roof structure from the living space, unimpeded evaporation, ie. passing through it to the outside (therefore it must also be vapor permeable).
- Steam dam – prevents the sudden penetration of water vapor from the heated space into the roof structure, where it can condense.
Namely, if you use the attic as a living space (and not as an attic), you produce water vapor every day by staying in it and all your activities, ie. moisture (cooking, showering, ironing, washing, drying clothes inside, etc.).
Depending on the location, dimensions and depth of the leak, building elements located in the immediate vicinity of the leak site may be damaged. Moreover, if moisture penetrates the insulating material, its insulating properties can be reduced by one sixth, compared to dry material. Reduced thermal insulation properties lead to the accumulation of moisture in the structure, thus causing a chain reaction that inevitably leads to serious damage to the structure. The steam dam controls this process and that is why it is placed under the insulation, ie. towards the interior.
ON WATER STEAM AND CONDENSATION
Water vapor is formed by the evaporation of water and occurs at all temperatures (the rate of evaporation is affected by temperature, air flow, the existing amount of water vapor in the air). With the appearance of water vapor, a process called water vapor diffusion takes place.
Water vapor diffusion is the appearance of the movement of water vapor molecules from a place of higher concentration (higher pressure) to a place of lower concentration (lower pressure) with a tendency to equalize.
Condensation of water vapor occurs in two cases: when the air is supersaturated with water vapor and when the saturated air cools, which is a phenomenon known as “dew”. The problems of water vapor diffusion and condensation are directly related to the vapor permeability of the material.