Lead / felt valley detail required

[Fatcat101]

Im having my house reroofed at the moment and have a concern over the way that the roofer has detailed the valleys on my dormers.

The dormer roof ridge is at the same height of the main roof and I was expecting to see a single strip of breathable membrane run down the valley on either side with the lead sat on top of this. The tiles would then sit over the leadwork.

Instead, the breathable membrane sits over the lip of the lead on either side (I am told by the roofer that this is a standard way of doing this detail) with the tiles over the top of this.

Can anyone put my mind at rest over this as I cant see that this is as watertight as what I was expecting to see?

 

[freddiemercurystwin]

Your roofers correct, the membrane should sit on top of the lead, that way any trickles that get under tiles and consequently run down the membrane will drain into the lead valley and not into your loft.

 

[noseall]

grp valleys are sometimes installed on top of the roofing lathes, therefore these do sit above the felt and lathes.

when done this way you would run a piece of felt vertically down the valley first. then you would lap the horizontal layers of felt onto this first layer, giving treble thickness valley felt.

but i concur with above, a lead valley usually sits in a valley tray slightly lower than the lathes with a pair of lath fillets each side to prevent water seeping back into the roof.