Condensation where flat roof meets pitched

[phatboy]

Hi all,

I've noticed the past week a bit of condensation forming on the back of the layboards. The temperature has been down to about 2degrees, and very wet until today.

The insulation is a bit untidy, but it is continuous, The space between the warm flat roof space and the loft is thoroughly insulated with 200mm Rockwool.

Everything looks fine from on the roof, however some of the top deck ply feels delaminated but no obvious route for water to get in (Continious EDPM, lapped well up behind the slates. Really wish I'd used OSB, lesson learnt)).

Any suggestions on cause and remedy welcome!?

Tim

 

[Wayners]

Put plastic over to test
Water on plastic surface is condensation
Water under is getting in from outside.

 

[noseall]

Hi all,

I've noticed the past week a bit of condensation forming on the back of the layboards. The temperature has been down to about 2degrees, and very wet until today.

The insulation is a bit untidy, but it is continuous, The space between the warm flat roof space and the loft is thoroughly insulated with 200mm Rockwool.

Everything looks fine from on the roof, however some of the top deck ply feels delaminated but no obvious route for water to get in (Continious EDPM, lapped well up behind the slates. Really wish I'd used OSB, lesson learnt)).

Any suggestions on cause and remedy welcome!?

Tim

View attachment 368635View attachment 368636View attachment 368637

Foam fix 50mm PIR onto the underside of the ply layboards, if you can access.

 

[phatboy]

Foam fix 50mm PIR onto the underside of the ply layboards, if you can access.

Access is fairly awkward. Would 100mm of Rockwool do the job? That would be easier, I could roll it longways, and slice into it where each rafter is, and fit around?

 

[datarebal]

Insulation is rubbish

 

[phatboy]

Insulation is rubbish

Could you elaborate....?

 

[phatboy]

Any further thoughts appreciated?

 

[catlad]

Looks like you have a warm roof with a very poorly insulated junction with the pitched roof.

 

[phatboy]

Looks like you have a warm roof with a very poorly insulated junction with the pitched roof.

I packed 200mm Rockwool between every rafter from the flat roof side before the ceiling was fitted. I cut it around obstacles to ensure a full fit, and looked from the loft side for any light leaking.
I did try to do a good job of it - thought certainly went in.

What would be a standard detail for this?

 

[catlad]

Insulation has to be continuous across that junction.
Have you checked its not condensation running down the membrane until it has nowhere else to go?

 

[phatboy]

Insulation has to be continuous across that junction.
Have you checked its not condensation running down the membrane until it has nowhere else to go?

There is some condernsation higher up, but very localised.

This is only happening between 2 or 3 pairs of rafters, so I wonder if it is a weakness in my insulation on those, and I just need to get in there and re-pack those 3 areas. The rest, and there is 18metres of connection between the roofs, looks completely dry.