|A problem that is easy to miss|
Many homes now have bathroom extractors that feed through the loft space and out through vents. This system has some advantages over systems that go straight through walls, but having just been in a house in Penarth there are some disadvantages as well!
The vents are commonly joined together using tape, but this tape is subject to a wide range of pressures and temperatures which can cause some cheap tapes to fail. What sort of tape do you think is used for most joint sealing? High quality tapes designed for high temperature range conditions or standard duct tape?
So this is the problem, What happens if the tubes that are meant to be feeding warm moist air to the eave or roof vent are actually feeding this same air into the cold loft space? Lots of moist air condensing on the cold felt and timbers.
The rafters in the attic I was in were very damp and it felt very muggy, so drastic action to reduce the amount of water in the structure is needed. Having put the extracts back together I also noticed that the well insulated loft space had been done in such a manner to block the eave ventilation. So this had compounded the problem.
Ventilation is often seen as the antithesis of energy efficiency, but actually you need good ventilation to keep buildings and people healthy. There is a balance to be struck. Maintaining good levels of ventilation is as important as creating an insulated fabric, especially in older buildings where the actual breathable fabric may also need its own ventilation to keep dry.
With most housing problems it comes down to maintenance and being aware of how your building works. Neither of these two factors are glamorous, but they are both essential if we are to have a healthy built environment. So check your vents, especially in areas where you rarely go.
One last note – try to fix vents on elevations that are away from the prevailing winds – the wind will just blow the louvres shut and make it ineffective. You might also think about alternatives to the £20 standard vents. How about one with a cover? Or one that is controlled by humidity levels, or potentially the ultimate where you have a room based heat recovery system!