Humidity in Attic

Kisk_2

Anyone know what levels the humidity in an attic should be below? I am in a new house, 2 years old, and I first noticed some mould on some items which I stored up there. Also cardboard boxes felt damp so I borrowed some instruments for measuring the levels. In March this year the temp in the attic varied from 3 deg C day to 2 deg night with humidity levels as high as 96% and never dropping below 92%. Measured again last week with day temps of 20 deg and night 12 deg and humidity level up to 78% and never dropping below 54%.

The house builder has been back and the house is constructed with a breathable membrane which is overlaid with the tiles. There are no soffit vents which they say are not required as the membrane gives enough air change. The house is traditional brick and is very well insulated. I have also checked all shower vents which go through the attic for leaks but they are all fine. I have all the data on excell spreadsheets if anyone wants a look.

Any advice gratefully received.

Thanks

Mikeyorks

Is 'attic' ... what I would regard as 'loft'?

Assuming so - that's an awfully damp one! Mine has no soffit vents (shortly to be remedied), no roof vents and no breathable membrane - but runs at a humidity level representative of the rest of the house.

If you've checked the damp bits (extractor vents, soil pipe extension) all safely exit the loft space without breach? Then the only other source of 'steam' is the vent pipe from the boiler? Is that vented into a static cold water tank - and does it vent (hot water and therefore steam) periodically?

Had a (solid fuel) Rayburn several houses ago - and that turned the loft into a sauna every winter. As it vented - with appropriate Vesuvius noises - every 30 mins during the night. Had to encourage the wife into 10 baths a day - just to lose the hot water!

Kisk_2

Mikeyorks wrote:

Is 'attic' ... what I would regard as 'loft'?

Yes Mikey it is a loft and there is nothing else in it apart from the waste and shower vents which have all been checked. The boiler is in the garage and vents out the wall. I think all it needs is a large amount of soffit vents on each side of the building to give a good airflow.

Wig

What was the humidity outside the house? I reckon you you need a few vent tiles put in. Doesn't matter what builder says if there is condensation in winter it needs ventilating!

bcoman

Certainly sounds as if something is not right. If the breathable underlay is of the right permeability there should be no need to ventilate the roof void. Certain measures should be in place to prevent moist air reaching the roof space - a vapour control layer above wet areas (bathroom, en-suite etc) and a sealed loft hatch. Also using the extract fans to eject the moist air when using the wet rooms. Might also be worth checking if the cavities have been closed at the top of the wall.
My suggestion is to find out the manufacturer of the underlay and get them to check for correct specification and installation. If its a new house you probably have an NHBC guarantee, and they will have approved the design and inspected. Write to them and explain your problem. Otherwise the local authority would have been involved, same applies. The Building Research Establishment may also help, they write guides to ensure good practice and here's a link.

http://www.bre.co.uk/service.jsp?id=425

With the data you already have I would expect some useful response.
This is still a relatively new construction method in overall terms, so feedback is essential to monitor effectiveness. Be interested to know the outcome.

alanobrien

Normal levels for humidity are 40 to 70 Rh.

One of these would help you monitor it.

http://www.tlc-direct.co.uk/Products/BGHM.html