DIYbanter - View Single Post - Suspended ground floor condensation problem

(xavier) wrote in message . com...
(Alex) wrote in message . com...
I have installed rockwool insulation blankets under the floor and I am
now experiencing some worrying problems with condensation as the

I think you have two problems he

1. There will be a vapour pressure from the living accommodation
which is acting to force warm, moist air down via the permeable
flooring. This is resulting in interstitial condensation and it's
manifesting itself within the rockwool insulation.

2. This is exacerbated by a poor air circulation beneath the rockwool
although even with a dramatic improvement in ventilation, problem 1 is
likely to persist. (I don't understand or recommend your intended
reduction in airspace)

I don't think (as NT says) that rockwool is the ideal insulant here,
probably Kingspan or somnething similar would be more appropriate.

Even if you increase sub floor ventilation, you are still going to
have the potential problem of the interstitial condensation and the
only way you're likely to overcome this is by placing a vapour barrier
(as your friend suggested) directly under the floor decking, between
it and the rockwool. I guess this isn't really an option though (is
it?)

You must ensure that any damp rockwool is either dried out or removed
as quickly as possible. If your joists achieve and retain a moisture
content in excess of 20 percent you could easily develop a fungal
problem.

MY tuppenceworth would be to suggest you remove the rockwool and
replace it with Kinspan or do away with it all together. Although its
marginally 'helping' your fuel efficiency, its also having the
detrimental affect of lowering the sub floor temperature and thus
increasing the relative humidty. This will present you with an
ongoing condensation problem...

at last, someone who understands the issues. The short story is:
remove the rockwool.

NT