wet roof membrane

[-Sal-]

Hello,

I'm putting some new rafters into an edwardian butterfly roof, on the advice of a structural engineer, and when it rains there appears to be large water marks forming on the membrane. No water is getting through, but in the darkest spots, around the valley, it's starting to feel slightly damp. This might be a stupid question, but is this normal, or do I have issues on top of my roof. I have treated all of the existing rafters and valley beam for rot as part of the process anyway. I just don't want to put up the new rafters if this is going to be a problem. The roof is not that old, but having uncovered some of the work I have, I cant trust that it was done properly.

Ive attached pictures.

Thanks

 

[freddiemercurystwin]

It shouldn't be wet at all, got some pics of the outside, what is the pitch, the type of tiles and gauge?

 

[-Sal-]

Not sure how useful these are, the best I could do up a ladder holding my phone over the top

 

[datarebal]

How much insulation have you got

 

[^woody^]

It's not normal for the membrane to be wet, and what is more unusual is that it is evenly wet all over, rather than in patches or runs. it may be an extreme condensation issue from cool rain, limited gap between tiles and membrane and warm roof void, but if so I wonder if it would be a bit damp on the underside of the membrane?

The damp stains on the valley trough definitely need investigating.

 

[-Sal-]

How much insulation have you got

No insulation. There was a Plasterboard ceiling (no insulation) which i took down to replace a rotten wooden lintel above the windows. Having uncovered the rafters, I got a SE in to take a look. I have a plan from him which I'm following, but curious about these water marks. As i said, nothing coming through, no drips

 

[-Sal-]

It's not normal for the membrane to be wet, and what is more unusual is that it is evenly wet all over, rather than in patches or runs. it may be an extreme condensation issue from cool rain, limited gap between tiles and membrane and warm roof void, but if so I wonder if it would be a bit damp on the underside of the membrane?

The damp stains on the valley trough definitely need investigating

It's not damp on the underside. And now the suns come out, you can see it is evaporating away - the colour of the membrane much lighter and uniform. The darker stains around the valley feel damp on the underside when there is a very heavy rain. I can also feel loose debris through the membrane, at these areas, so I'm wondering if water is being prevented from running away at these points. Maybe I can get up there and clear these areas. As I said, no leaks or drips. Once i put in the new rafters, I'm planning on infilling between them, and having that as the ceiling (no dropped ceiling below the rafters). I'm wondering if rather than having to do too much work replacing the roof, I put something absorbant, or silica bags for example, behind the boards I infill the rafters with

 

[Harry Bloomfield]

I'm wondering if rather than having to do too much work replacing the roof, I put something absorbant, or silica bags for example, behind the boards I infill the rafters with

Anything absorbent, will need the moisture drawn back out, before it can be reused. Silica, needs to be placed in an oven, to dry it back out after use.

 

[-Sal-]

Anything absorbent, will need the moisture drawn back out, before it can be reused. Silica, needs to be placed in an oven, to dry it back out after use.

Yeah, I was just thinking that as there is no moisture coming through, these would really be a just in case. When there was a plasterboard ceiling below the rafters, there was no sign of water damage, no sign of water on the walls

 

[Harry Bloomfield]

Yeah, I was just thinking that as there is no moisture coming through, these would really be a just in case. When there was a plasterboard ceiling below the rafters, there was no sign of water damage, no sign of water on the walls

Which suggests to me, condensation of moisture, from below.

No point is having anything hygroscopic there, just in case - they will simply absorb the moisture that is naturally in the air. Silica gel is fine, for absorbing the moisture in a sealed enclosure, yours is not a sealed enclosure and therefore rather pointless.

 

[-Sal-]

Which suggests to me, condensation of moisture, from below.

No point is having anything hygroscopic there, just in case - they will simply absorb the moisture that is naturally in the air. Silica gel is fine, for absorbing the moisture in a sealed enclosure, yours is not a sealed enclosure and therefore rather pointless.

Got you, thanks Harry