Home Water Vapour

Water Vapour

When you heat water or anything that is damp you agitate the water molecules that are then released and float up into the air as water vapour, heat it quickly and the high amount of vapour will become visible as steam but usually 90% of vapour is invisible, you cannot watch the water rise as the sun dries a puddle. This vapour wants to form back into water again and because it is light it would naturally float into the sky where it cools and to form clouds that, when they get heavy, fall back to earth as rain. When this vapour is trapped in the home it is attracted to the coldest areas, if you take a cold can from the fridge you will instantly see that the vapour in the air will turn back to water on the outside of the can. It is the same in the bathroom when there is so much vapour that it can run down the cold perimeter walls and windows but it will not be shown on things like internal walls or doors. Vapour is present in all homes, especially the extreme amounts in the months following construction (it can take 20 buckets of water just to plaster a room that then takes 6 months to dry out). Our homes will never be rid of moisture vapour that is being constantly generated through cooking, kettles, showers, bathing, we even produce vapour when we breath, its natural.

Vapour is so small that it will actually travel through masonry, timber and plasterboard etc. If you have a room with a cold corner (such as against a windy or shaded allyway) then the vapour is attracted to this cold spot and will start to travel to the cold. As it travels through the wall from the warm inside to the cold outside, it cools and starts to turn back into water inside the wall and the wall becomes wet (most common was for it to form on the cold metal wall ties and these would rust and expand and break down the walls, especially around kitchens and bathrooms). This condensation inside the structure is referred to as interstitial condensation and is often confused as a leak or rising damp. Vapour can contain bacteria (from cooking etc) and when it is held within the structure of the building, complications will arise such as mould growth and timber degradation that will cause serious damage as it can often go un-noticed. The coldest part of the home is often the roof space and this vapour will naturally rise through the dwelling as well as being attracted up and into the cold roof space.

Vapour will not however travel through metals (foils), plastics and glass. The use of Permavent Reflect Vapour Control Layer (VCL) is an essential tool in the battle against interstitial condensation. When installed just behind the plasterboard it will reflect all vapour from entering the wall and its bright foil will increase the thermal resistance and will help to reflect the warmth back into the room. Any residual moisture that is trapped in the wall (such as during construction drying out) will be released through the breather membrane.


Fireproof breather membrane


Following the success of the Queen’s award winning Easy Verge, here at Permavent we are proud to announce the launch of the recently developed Easy VergeTrim. This latest addition to the Easy Roof System has been specially designed to meet the requirements of the Scottish and refurbishment markets.