Loft Condensation - already well vented

3 Jul 2013
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United Kingdom
I know there are a lot of threads on here regarding loft condensation - I've already read many of them - but despite improving the ventilation I still encountered problems last winter.

The property is a late 80s detached house. A few years back I replaced much of the original loft insulation with Recticel 50mm thick insulation board, double layers. This means the house is now very well insulated but little heat makes it to the loft.

I am satisfied that little or no moisture is making it into the loft from the house. I ran an internet-connected humidity sensor in the loft for a number of weeks. There were no peaks in the humidity, just gradual rises and falls throughout the day caused by temperature changes.

The loft is vented by strip vents under the eaves to the front and rear. The insulation does not block this, especially now it's insulation board with a solid edge. In addition there are felt lap vents all across the loft. Then, last winter, I had 8 vent tiles fitted. There was still condensation after all this...

The condensation was particularly bad when the temperature dropped below zero. To try and avoid moisture getting up there I didn't open the hatch too often, but on one occasion I noticed frost on the underside of the felt. The condensation is particularly bad on the south-western side of the loft.


I suspect the only way I can stop the condensation forming is to remove some insulation to ensure the temperature remains warmer. Given heating costs I really don't want to do this. Are there any other suggestions - anything at all - that may help?

Or, failing this, is there any way I can mitigate the effects of the condensation? I'm most bothered about the water falling onto the chipboard as it won't take long for mould to form on this. I tried putting puppy training pads down to cover the worst affected area but it's not a great solution. But would a tarpaulin sheet work, or cause other problems? And what about painting the chipboard to prevent water soaking in - would that help?

Thanks for any suggestions you can come up with


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