Low pitch roof (20-20 tiles) with rooflights - leaks :(

michaels

Our single story roof has about 2m of roof at 16-17 degrees then 2m of flat roof at the top, it is about 6m wide. In the sloping section are 3 velux style roof lights. The tiles are sandtoft 20-20 interlocking tiles designed for low pitch down to 12.5 degrees.

When it rains hard the roof leaks on the pitched section, luckily only a small damp patch on the plaster but enough to mean we can't decorate.

I suspect the cause is that next to the window flashing kit the tiles do not lie completely flat. With this design of tiles they achieve water proofness by interlocking together rather than via a double overlap (headlap). As the ones on the flashing can not lie flat and thus do not form the correct interlocking water is able to penetrate to the felt which is not keeping all the water out on its own.

Does anyone have any suggestions?

WestonDave

Not entirely clear from your comments whether the leakage is sideways into the vertical joints or water backing up under the overlap.

I guess either way there wouldn't be any harm in a very thin bead of clear silicone sealer just to aid the waterproofing.

The other thing to check is whether there is a moss issue - we had problems with valley tiles where moss in the valley slowed the water running down it such that it backed up enough to go up into the overlap. Clearing the moss increased its capacity to clear water and the problem was resolved (we've subsequently overlaid it with lead to further avoid the issue).

keystone

Moss also has a tendency to introduce lots of nice capilliary action.

The lower the pitch the greater the head overlap needed.

Is this a new job? If so get the builder back.

Cheers

michaels

Dunno exactly where the water is getting in, the damp patch is appearing just above where the ceiling (which is pitched) meets the external wall. This is between two of the veluxs which are about 2 feet apart and about 18 inches below the bottom of the windows. The windows are about 3 whole tiles apart but in this small section they do not lie completely flat as the edges which are over the flashing are slightly raised. I think we got the roofers to double batten.

Builder is being very slow in coming back (surprise, surprise) but it would be useful if we could explain to him what the problem is.