On 16/05/2019 16:48, Andrew wrote:
On 14/05/2019 20:07, Mathew Newton wrote:
On Tuesday, 14 May 2019 15:42:12 UTC+1, AndrewÂ* wrote:

Did the builders use foil-backed plasterboard for the
upstairs ceilings (they should have).

No, just paper-backed plasterboard and a skim coat.


well that is part of the problem. Water vapour molecules will
migrate through the ceiling and into the loft space. The
breathable membrane should cope with this but seems not to.

Modern building regs make foil-backed plasterboard
mandatory for upstairs ceilings, for precisely this reason,
but older re-roofed properties probably still need some normal
vents even if breathable membranes are fitted.

Lofts that have 300mm of rockwool are much colder, so
condensation is more of a problem.


snip



If your house was built in 2007 then it should have had foil-backed
plasterboard on all the upstairs ceilings.

I wonder if NHBC or similar did the 'building control' ?. Is this
a house built by one of the large national builders, or a small
local outfit ?.

Look at the pdf called "Re-roofing and Plastering" at Rochdale
council.

http://www.rochdale.gov.uk/planning-...gulations.aspx