On Sunday, 12 May 2019 12:21:24 UTC+1, George Miles wrote:
I guess there isnt enough ventilation in the roof,
has someone added lots of glass fibre and blocked the vents at the eaves?

I don't think there is any eaves ventilation on these houses; certainly looking at the soffits there's no obvious vent holes and I had always assumed that the breathable felt was the reason why (accepting it only probably works in conjunction with a reasonably ventilated house below).

A humidity controlled fan in kitchen bathroom and laundry room will help.

Funnily enough I am actually in the process of taking advantage of the building work going on to install a whole-house MVHR system; having been planning it for ages - not for any specific problem to solve but just because I like the idea on how it works and stumbled across a nearly-new unit at a bargain price.