Lead flashing on flat roof

[Kent1234]

We recently had a flat fibreglass roof installed and we have had some leaking inside the wall next to one side. The external walls are rendered and the installer has been back and looked a few times and said it is cracks in the render, which he has sealed since. I’ve been on there and had a look and my view is that the lead is not as flush as it probably needs to be against the wall and as it’s only driving rain in a certain direction causing the leaks that it might be that it’s getting under the lead. I’ve included a few photos. It didn’t leak before the work and the water has come through all along the edge in the pics (appreciate that water travels). Any advice on what I can do? Obviously I’m not an expert so any help gratefully received.

 

[Exedon]

How deep was flashing cut into render?
Really don't like the lead seal on vertical joints/corner makes me wonder if there is a proper lap.

 

[Kent1234]

I’m wondering that myself. The render is double skinned so I’d imagine the water is getting in between the 2 layers which shouldn’t happen if the cut was deep enough. From what I can see near the join in two lengths of lead it doesn’t look as flush as it might be to the exterior wall. I’m wondering if that’s where it’s getting in as it was only during driving rain that I got leaks.

 

[tell80]

Its wrong. All the lead will have to come off and the surfaces cleaned up of sealant.
Ignore the render depth, you chase the lead in 20mm to 25mm into the backing bricks.
When the flashing is off post another pic please.

 

[Kent1234]

I plan on using a hose to see if water is getting in under the lead where the lead isn’t flush to the external wall (doesn’t look as close as it could and it only leaks with driving rain in a certain direction). If it is getting under would sealing along the underneath be ok. If not why not?

 

[Exedon]

Lead seal mastic is only intended for use where you would have used sand and cement. It is not intended to stick things together seal joints on the lead or bodge poor workmanship.
Check laps on lead (at least 200 mm) check how much coverage the lead has over fiberglass.
At end of day if it leaks get installer back!

 

[Makie]

Check laps on lead (at least 200 mm)

For cover flashings 100mm is the standard.

 

[Notch7]

Bend the lead up and let’s have a look what’s going on.

The correct detailing is a pre made GRP upstand is fitted against the wall, the flat roof Fibreglassing goes across the flat roof area and up the upstand.

Then lead flashing is dressed down over the upstand.

But in your image the lead dresses down to a flat - what is that, does the fibreglass go up a slope behind.


I wouldn’t assume the leak is the roof, it could be a leak getting in the window above and running down the cavity - there are no weep holes so I guess there’s no cavity trays (assuming it’s not a solid wall).

 

[Kent1234]

Thanks for answers. In regards to the water getting in at the window and travelling down how would this happen if the lead was 20mm min in to the brickwork? For info The external wall is double rendered short surely water would stop where the lead goes in?

 

[oldbutnotdead]

Yeah well that's the question- has that lead actually been chased into the brickwork. Looking at it (and that corner) I reckon it's just been glued on the surface.