Condensation/Sweating on garden office roof

The condensation/sweating on this garden office roof is a problem I get asked about many times.
Condensation or sweating in lofts, cold roofs or unvented roofs is a big problem. When you are in the garden and you have construction moisture thrown into the equation you have an even a bigger problem!
Sweating on the underside of a flat metal roof is even more difficult to stop. Condensation through conductivity of the roofing material is really what we are talking about. If your roofing membrane is thick, and therefore insulates the topside of the roof, the problem of the roof sweating in the cold months of the year would not happen as much. Unfortunately, this is why we see so many GRP (fibre glass) roofs failing. So, to explain the problem - the underside of the roof covering is getting cold and the rising air containing moisture from the room below or from the air passing through the venting, condenses on the cold underside of the roofing deck. The water vapour in the warmer air hits the colder surface and changes from a gas to a liquid.
The environment around the base of the home office is also important to how the roof vents
Moisture from the environment around the garden room or office will rise and go through the vents of the cold roof. This moisture in the winter will be what condensates on the back of the roofing boards and the colder the roofing boards the more likely the sweating or condemnation will be. So the external environment of the home office or garden room is very important to how the roof works if it's a cold roof that is vented correctly. you should also make sure that the AVCL (air vapour control layer) is correctly installed above the plasterboard and under the insulation, in the roof, the AVCL (air vapour control layer) is extremely important in stopping moister from inside the cold roof of the office green from rising up into the vented space and adding to condensation that may be drawn in from the surrounding areas.

I will post the link to the author of the drawing below when I find out who it was as this is a very good diagram.

This viewer sent me photos of his sweating cold flat roof that hadn't been build incorrectly and was now sweating so much that water was dripping through into the room below. He hadn't fitted ventilation to between the joists and he hadn't added an AVCL (air vapour control layer) he had cut lights into the ceiling and air was pouring into the cavity. Mould on the timbers and on the back of the roof decking was starting to grow. So the question is "Can I save my sweating cold flat roof" Using information from some ware on the internet I took some research that shows that plasterboard has a good vaper resistance and the fact that the ceiling is airtight should solve the problem. airtightness in flat roofs is always the biggest problem I come across. People get all hung up about the vapour control layer and forget that more moisture gets into the roof through the movement of air than through a vapour barrier.

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Steven Dickinson
London flat roofing
07802300099
info@londonflatroofing.co.uk

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