New extension - condensation !

[ibirch]

Hi

We have just built a large extention on an old cottage. We are living in the roof space with dorma windows and a few velux windows.

The roof is now entirely new, with 150mm insulation between rafters, with breathable membrane and cavity above, and foil back plasterboard below against rafters to meet building regs.

We are now noticing condensation on the north face of the house roof (mostly in master bedroom) in cold weather. Water is dripping from where the skimmed plasterboard meets the exposed oak perling.

Also the downstairs kitchen (which has a pitched roof above with large velux) also has condensation - but again only in one location in the room (drips where two plasterboard joins meet - not yet skimmed).


We have not yet completely insulated or plasterboarded all of the house so there are still a few cold spots. Also, this is the first winter under the new roof - so maybe there is a dry out period ?

I am told that we do not need roof vents due to breathable felt membrane.

We have not yet fitted extractor fans to bathrooms or kitchen.


Should we complete the works and then reasses the situation ? or do we have a problem ? We dont want to assume that everything will be fine on completeion and then create wmore work or expense for ourselves.


Thanks,

Ian.

 

[PerryOne]

You have no doubt mixed loads of water into the new structure?

A hundred years ago, a home would be left empty for a year after building to dry out, these days people move in as soon as its built.

All this water has to make its way to the surface and evaporate off into the air.
However, the thing with water vapour is that it settles on any nearby cold surface and condenses onto or into the fabric.
The normal point of condensation is a cold window and we have all seen windows running with water in the cold days/night of winter.

You almost certainly have double glazing and probably the standard of insulation for the windows is higher than some other parts of your home.

Plus you have no ventilation to adulterate the moisture and you are adding more water vapour to the property every 24 hours by being there and breathing and sweating and washing etc.

Unless you did the work yourself, you have no idea how well your home was put together, how careful were the builders, how many holes have they left in the insulation? Have you climbed inside the roof and checked their work. You will probably be surprised to learn that even a hole as small as 9mm can strip the heat from a room in a cold windy night.