Posted By: denianceI’ve also noticed that since the air sealing and insulation that mould has started to build up below the coving in my bedroom and the other bedroom, but the bathroom that is the wettest has zero mould around the ceiling!

Probably because the bit below the coving is now the cold spot (relatively speaking) so that is where any condensation will settle - and mould grow. Is the coving plaster or EPS? If its is EPS then this will be warmer than the wall beneath. Do you have EWI and is it joined to the loft insulation? If not then again the wall will be the cold bit.
I had mould at the top of the wall after better insulating the loft - it stopped after putting on the EWI

<blockquote><cite>Posted By: Peter_in_Hungary</cite><blockquote><cite>Posted By: deniance</cite>I’ve also noticed that since the air sealing and insulation that mould has started to build up below the coving in my bedroom and the other bedroom, but the bathroom that is the wettest has zero mould around the ceiling!</blockquote>
Probably because the bit below the coving is now the cold spot (relatively speaking) so that is where any condensation will settle - and mould grow. Is the coving plaster or EPS? If its is EPS then this will be warmer than the wall beneath. Do you have EWI and is it joined to the loft insulation? If not then again the wall will be the cold bit.
I had mould at the top of the wall after better insulating the loft - it stopped after putting on the EWI</blockquote>

Yeah I get that bit, it’s plasterboard coving too, just wondering why bedroom 1 and 2 have mould but bathroom doesn’t?
You would think a well used steamy bathroom would be mouldy but nothing and it’s the same build up as the other rooms, external walls solid stone no ewi, plasterboard ceiling etc maybe it’s because we are breathing out in the bedrooms each night? And this causes mould?

Posted By: denianceYeah I get that bit, it’s plasterboard coving too, just wondering why bedroom 1 and 2 have mould but bathroom doesn’t?
You would think a well used steamy bathroom would be mouldy but nothing and it’s the same build up as the other rooms, external walls solid stone no ewi, plasterboard ceiling etc maybe it’s because we are breathing out in the bedrooms each night? And this causes mould?

But you do say that the bathroom has good powered ventilation so this may prevent problems also house orientation may be a factor. I will leave comments about heavy breathing all night in the bedrooms to others

Oh - and if you click the Html button below the comments block then quotes come out in blue. It just makes posts easier to read.

It strikes me from the photo that the outside air coming in between the felt is dry enough to prevent condensation (not all the time probably but alot of the time). My thought would be that increased ventilation in the loft would be what is required - in particular ensuring any eaves ventilation that may be present has not been blocked by the insulation. (The insulation at the eaves seems to be piled up here).

This is a tricky area - you want lots of insulation here, and it's tricky to reach, but any eaves vents need to supply plenty of fresh air from outside - with plenty of ceiling level insulation a draughty loft is what you are looking for. As the insulation levels increase this becomes more important as you haven't got heat from the house keeping the loft warm.

On clear winter nights the roof will be colder than the ambient air and condensation is inevitable - the trick is to create conditions during the following day to dry it all out asap. I agree with Tony in that the plastic needs removing from the insulation - moisture in the form of water drops will be able to get in faster than vapour will be able to get out and so overtime could become waterlogged.

Managed to get a bit more done!

Posted By: tonyIf there is a difference in the partial vapour pressure between that in the air in the house and it in the loft, water vapour will move from the house into the loft, straight through paint and plaster, wood and vapour open insulation.

If is cold in the loft this vapour will condense wherever it finds a surface which is below dew point.

For me this surface will be the underside of the shiny layer on the cold side of the insulation. 🙁

The underside of the insulation is plastic so any vapour coming up from below cannot get into it, only the top silver piece is perforated , but having said that been up there this evening and did find a few cold edges when I was moving insulation , made a hole with finger and yes bits of the insulation were damp!! But don’t know if this is what you said or is it from when the condensation was dripping down on it last week?