leak above Victorian bay window

[redtiles]

I have a Victorian terraced house with a bay window at the front on the ground floor. The bay has a parapet round the top and originally a flat roof inside that. There is now a flat zinc roof across the top of the parapet and a gutter all the way round. The roof meets the house wall about 2 inches below the two first floor windows. There’s a zinc apron that covers the join. If you lift up the apron you can see that the upturn on the roof, which should come up about two inches is about ¾ of an inch so the theory is that rainwater is being blown under there. There is damp underneath both windows inside and with heavy rain recently the water dripped through to the room below. If the upturn was higher this shouldn’t happen. So the options I've been given so far are 1) to run mastick along the join – cheap and not reliable I think. 2) to replace the zinc with a higher turn up – but as the space underneath the window ledge is very tight this is quite fiddly. 3) to remove the roof altogether and repoint the wall – this relies on there being a decent roof underneath and a new downpipe also needs to be fitted.

I'm wondering which is the best option and also why the second roof was put on in the first place. About half the houses in the street have this second roof and others are as they were originally. Does anyone have any experience/advice?

 

[Penners]

I can only say that your solutions to the problem don't seem to be mutually exclusive. Why not try mastic (cheap and quick) and if it doesn't work, then resort to more radical measures?

 

[Lime]

If there is damp underneath both upstairs windows I would suspect that the sills are causing the problem.
The sills should redirect the water from the window to drop away from the wall but sometime the "drip edge" under the front of the sill is damaged or eroded so that water runs back under the sill onto the wall and then drains down it.
While it is possible that the wind is driving water up the zinc next to the wall it is much more likely to be running off the sills and entering somewhere above the bay roof.

 

[redtiles]

The sills were replaced two years ago so I hope that isn't the problem! The roofer who came round checked the level with the spirit level and water does run off but I haven't thought about looking underneath them. How should they look underneath?

 

[Penners]

the "drip edge" under the front of the sill

If you look underneath the sill, you should see either a convex bead or (more usually) a concave groove, running the full length of the sill.

This acts as a "break" to stop water clinging to the underside of the sill and flowing back to soak into the masonry.

 

[Lime]

The underneath of the sill should have either a groove, slot, overhang or even a bar to stop the water running back to the wall.

It is a good idea to get out in the rain to see what is happening or you can simulate rain using a fine-rosed watering can...not so good though.
Drips of water should be falling off the front of the sill but not running back to the wall at all.

Thanks Penners.

 

[redtiles]

thanks for your help - i'll wait for the rain now!

 

[Penners]

thanks for your help - i'll wait for the rain now!

I don't think you'll have to wait long!