Condensation (now frozen!) on breathable membrane

[Chrischecked]

Hi - NEED HELP! [/b]
I have moved into a house with loft conversion (dormer bedroom) and loft bathroom. Outside the dormer and bathroom is the empty roof space where there is the boiler and unvented cylinder with quite a lot of pipes running across the boarded roof floor. Only about a third of the roof (area around boiler) has been insulated with celotex between rafters then plasterboard screwed in. Rest of the roof is not insulated - I see rafters and breathable membrane (concrete interlocking tiles). wool from the floor joists go all way to eaves. There is no ventilation.
PROBLEM: condensation on underside of membrane near the bottom (just above the wool). [/b]. There are water patches on the wool and bottom of rafters as well.
I thought that breathable membrane was supposed to let water vapour pass through to the top side of membrane where it would then flow down the membrane into gutter?
Why is there condensation on the underside which has frozen in the cold weather in past few days.

Please help - any advice much appreciated. Many tha ks

 

[freddiemercurystwin]

You sure its a breathable membrane?

 

[Chrischecked]

Sorry want to clarify the above:
Also even the section where there is celotex between the rafters and plasterboarded - it doesn't go all the way down to the floor and there is a gap between the mineral wool in the floor and the celotex between the rafters. There is wet patches on the wool and bottom of the rafters.

There is a permanent staircase going into the roof, with the dormer bedroom and bathroom.
- Should the outside pitched roof section be a warm roof?
- If so should celotex be put between rafters? And is it correct that I should leave a gap between membrane and celotex even though the membrane is breathable one?
- if I put celotex between the rafters, can I then put a polyethylene sheet on the underside across the bottom of the celotex and rafters? Is there any need to use plasterboard?

Sorry complete novice - so really appreciate the help, as I am really worried about rotting timbers in the roof

Cheers

 

[Chrischecked]

Hi there - yes definitely breathable membrane as its the Rubbershield pro... Can you shed any light? Thanks very much

 

[freddiemercurystwin]

Your set up isn't entirely clear, you got this kinda thing going on?

Untitled

• freddiemercurystwin
• 14 Apr 2010
• 12

 

[Chrischecked]

YES! Exactly freddymercurystwin. That's same as my roof setup.

There is the boiler and hot water cylinder in the outside roof space.
This makes me worry if I should avoid cold air ventilation to try minimize heat losses and freezing from all the pipes, boiler and cylinder.

Thanks again

 

[freddiemercurystwin]

So your boiler is here where the red blob is?

Picture Title

• freddiemercurystwin
• 13 Dec 2012
• 1

 

[gemmabuild]

Yes the boiler and cylinder are a bit further in from the eaves but essentially in the area of the red blob.

 

[bpcroofing]

Hi
Your Breather membrane is a good make, I feel like you should have roof tile vents installed though as there is obviously a problem. We have had to install tile vents on properties before as there were condensation problems with various membranes. These Roof tile vents always solved the problem although all cases were examined beforehand.

 

[gemmabuild]

Hi - how easy/expensive is it to install roof tile vents? And roughly how many are required for roof area 60sq m?
Many thanks

 

[bpcroofing]

Hi
For a 60m2 roof with two pitches I would fix 4 per side.Inline tile vents are shaped just like the roof tile & are approximately £20-£40 each depending on plastic or concrete.We charge generally £40 per vent fitted.
The cheapest ones are plastic and can be picked up from Roofing Merchants