Loft Conversion Condensation

14 Nov 2015
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United Kingdom
Hi hopefully someone can give me some advice in what appears to be a difficult problem to fix.

I have an old bungalow with a converted attic space as a bedroom. When i bought the house the attic room wasn't signed off by building control which i understood and negotiated a price that allowed me to get the necessary work done to get building control to approve it.

The room itself has square walls rather than the walls following the shape of the roof... if that makes sense? This means I have plenty of space behind the room walls and can walk all the way around the room via the roof space.

First thing I done was to put 100mm kingspan around the room to improve the insulation and heating in the room. We then used the room as a bedroom. During winter the 2x velux windows would be soaking/dripping with water which we had to dry each morning. I assume this is condensation that was causing the problem. We tried keeping the trickle vents opened at all times to improve air flow but this did not help.

Now to get the room approved by building control we were told that we had to get roof tile vents all along the roof, which we have done and there is good air flow in the roof space behind the room walls. Next we were told that we required a vapour barrier layer between the plaster and the kingspan. This meant ripping down all the walls and putting the vapour layer in and then the kingspan behind it and finally re-plastering.

After doing all this we are getting worse condenstion problems in the room. All the walls are now showing signs of it. If i go behind the walls in the roof space I can see water built up inside the vapour layer. I presume now that condensation in the room is permeating the plasterboards but building up inside the vapour. My question is why do i need the vapour barrier layer in this type of converstion? Would it not be better to let the warm air get into the roof space where there is good airflow rather than stop it at the vapour layer?

Is there anything else I can do to fix this problem? I have fitted extractor fans downstairs in bathroom and make sure all trickle vents are open on all windows.

Any advice or recommendations would be appreciated.

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The vapour barrier and roof vents are there to ensure that condensation does not form inside the roof space. If that occurs, the end result is the roof timbers rotting and your roof collapsing.

Condensation inside the room is due to excess humidity inside the building. This will condense onto the coldest surfaces in the building, as in the velux windows and poorly insulated walls in your loft room.

While extractors and vents can help, the real solution is to eliminate the sources of the humidity. Typical culprits are drying washing and used towels indoors, using a tumble dryer which does not vent outside, leaving the bathroom door wide open, kitchen having a recirculating device instead of a proper extractor, never opening windows and boiling vegetables etc. in pans with no lid.

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