Condensation? Is this normal?!

[Co1]

Afternoon all. We’ve recently moved into a new house which is a converted bungalow. I happened to be in the eaves and what looks like a fair amount of condensation on the inside of the membrane. There is snow on the roof, so it’s a pretty cold day. 
 

It’s a cold roof, with the ceiling and wall insulated, but it’s not been done well and imagine that there is a lot of heat leaking out. 
 

See pic. How worried should I be?
Thanks

Col

[BotusBuild]

Probably down to a lack of ventilation in the roof space. You may need to draw back some of that rockwool from the edges. Also make a visual check that there is ventilation through the soffits outside.

We had this in our last home, and got some clever plastic thing to "open" the felt to allow airflow across the the roof space. Something like these:

https://www.diy.com/departments/10-x-felt-lap-vents-prevents-loft-roof-condensation-attic-space-ventilation/0700425346027_BQ.prd?=&=&=&=&msclkid=d0a4d322cabd1b66400fb45872788afd&gclsrc=ds

[MikeGrahamT21]

What type of felt is it? Plastic coated or breathable?

 

inevitably even the best ventilated loft spaces will get some condensation unless the property has a vapour control layer, also highly unlikely

[Co1]

Thanks both, much appreciated. There are no soffit vents and the rock wool is tightly packed, so I’ll start by pulling that back and seeing if I can detect any airflow. If not I’ll add some vents. 

[makie]

On 05/01/2025 at 17:19, MikeGrahamT21 said:

What type of felt is it? Plastic coated or breathable?

 

inevitably even the best ventilated loft spaces will get some condensation unless the property has a vapour control layer, also highly unlikely

It's plastic, called monarflex. It's terrible for condensation.