Is that pattern of mould indication of poor insulation in the attic?

andre_xs

Dear All,
(apologies for another mould / humidity thread  )
We have just noticed mould at the ceiling in the first floor (below the attic). It's in two rooms, just lining the outside wall, like in the picture below.
The attic is insulated, but the insulation is old and crumbly... Could it be that at the "corners" where the ceiling meets the wall, are not properly covered and cold spots just happen along the outside wall? I presume fitting proper insulation would then fix the problem?

Or are there other explanations worthwhile exploring? The 'strange' thing is that we didn't do anything in the attic in the last couple of years and it never was a problem before. So it looks as if something has changed quite a bit...

Many thanks &
Kind Regards,

Andre

grumbler

The problem is that when insulating the loft floor you don't want to block the eaves and block loft ventilation. As a result, the top part of the wall is exposed to cold both from the side and the top. So, IMO, it's always a compromise between insulation and ventilation, especially for roofs with shallow pitch.

jacko220

Thermal camera image of corner blue low temperature greater risk of condensation, breeder of black mould growth,

andre_xs

Thanks! What's the best solution?

Just trying to get rockwool or similar as far into the eaves without blocking air flow? (I presume the air needs to flow below the felt? I.e., one must be able to "reach" through to the overhanging part, right?). Or are other materials better for those confined spaces?

I just realised, I may be able to get a thermal imaging camera from work.

But I'm still not sure why it wasn't a problem for the last couple of years?

I'll go onto the attic tomorrow. Any tips what I should look out for? I would just check whether the insulation is missing back there, but maybe there's more which would need repair...

Edit: Would it be advisable to invite a roofer so that they can check what the problem might be?

grumbler

Yes, below the felt. If pushing insulation deep into the eaves I'd put short pieces of rectangular plastic ducting along the felt for ventilation. One per a metre (?).

IMO, rockwool or similar is best 'for those confined spaces'. And current norms say that it has to be about 27cm (!) thick that is impossible to achieve in the eaves.