Water trough in roofing membrane

[WWilts]

New build, roof covering in progress.

Pitch ~18 to 19 degr, but somewhat less at eaves on the most exposed elevation (long story, builder made errors). Roofshield air permeable water resistant membrane. Cambrian slates.

In order to achieve slate overhang of gutter, roofer has introduced short counterbattens over the membrane. Near the eaves. Unfortunately this has resulted in the membrane forming a water trough along the eaves of that elevation. (pics) Not very deep, admittedly, but still enough for water to pool there if it gets under the slates.

Question:

 

How to deal with the water trough, or eliminate it?
Architect suggested water-resistant board under the membrane. Presumably from the inside, under the roof.

 

About 100 slates nailed in on that elevation already. Membrane already nailed down to rafters. 

 

 

[Mr Punter]

I would want that stripped and done correctly.  And battens to BS 5534.  Ask Building Control or your warranty provider to inspect and break the news if you don't fancy it.

[joe90]

7 minutes ago, Mr Punter said:

I would want that stripped and done correctly

+1

46 minutes ago, WWilts said:

long story, builder made errors)

Then make him put it right, there is no way I would accept that, whatever is under that bottom batten needs lowering, water pooling there is unacceptable IMO and a problem waiting to happen (after the builder/roofer has left).

[markc]

Where do they think any water that gets there is going to go?

asking for trouble on a steep pitch roof let alone a shallow pitch. As above, strip and redone properly

[PeterW]

That needs all removing and redoing. The absolute minimum headlap is 75mm at 15° and you’re probably looking at less than that on that edge and that will get driven rain under it. 
 

Whole lot including battens off and I would want membrane replaced too as it will be like a seive and it will leak. 

That is missing a full row or two of tiles - needs to be re-gauged and start again. 

 

[Cpd]

It’s all been said already…. Get it redone properly. 

[WWilts]

On 20/03/2022 at 17:53, PeterW said:

Whole lot including battens off and I would want membrane replaced too as it will be like a seive and it will leak. 

That is missing a full row or two of tiles - needs to be re-gauged and start again. 

Roofers doing exactly this now. Dropped batten gauge to min allowed with Cambrian, 210mm (90mm headlap).
Architect's verdict worked well.