Is this chimney valley still good for purpose? Information, help and tips on many areas of roofing including trusses, tiling, venting, insulation etc....

[groovybug]

Hello everyone,

We have just moved into our new place for a couple of months and spot some leaks. I managed to get on to the roof to check things out and it seems the reason is the valley around one chimney is completely blocked with debris and easily overflown. I have cleared it, however wonder if I should replace the valley.

It is quite an old tin/steel valley that sits under the tile (Please see photo. I moved the tiles up to clear the valley). The chimney runs diagonally that's why they designed it that way I think. Do you think it was properly done and still fit for purpose? My worry is it is quite shallow and can be overflown regardless. I understand the newer design would be a lead valley with mortar sealing the edges between the valley and the tiles. However I feel this design also has some issues, one, the lead and tiles both contract and expand seasonally, so the mortar will break down quite quickly, and two the tiles are not easily replaced.

If there's a way I can keep using it for now, or improve it in some simple way that would be great, as we plan to do a major refurbish once we have lived a while and figured out all that we want to do. However of course it's not fit for purpose then I will get it replaced asap.

Hope to hear your advice. Many thanks.

[stoneyboy]

Hi groovybug
It looks like the tiles, at some time in the past, abutted the chimney and a mortared fillet was used for sealing. The tin valley tray was probably there as a second line of defence against water ingress.
There is a small upstanding on the outer edge of the valley trough and this is not adequate if you are going to move the tiles away from the chimney.
You’ll probably be ok temporarily unless there is heavy rain and strong winds.
Regards S

[groovybug]

@stoneyboy Thank you for your really helpful reply.

The tiles do abut the chimney but they are not sealed in. The mortar you see is to seal the tin valley onto the side of the chimney. And you are right that the valley trough is quite shallow. It was completely blocked before, that explains why it is easily overflown and leak downward. I have cleared it, and it seems to survive yesterday rain, however I do worry if it can hold up in heavier rain.

I'm trying to find a DIY solution so it can hold up for a year or so. One I can think of is prop up the standing edge of the valley, so it can hold more water and two is seal up the edges between the tiles and the chimney (like how you thought it were). The thing is I don't think we can seal it with mortar, as it might block the valley below. I'm thinking using butyl flashing tape. However with the way the chimney runs diagonally to the tiles, the water will keep seeping under the tape and I'm afraid it won't stay sealed for very long.

If you have any more suggestion please let me know. Much appreciate.

[stoneyboy]

Hi groovybug
What about sliding a piece of plastic guttering up above the valley and rest the tiles on its outer edge? You’ll probably have to use 3” mini guttering.
Regards S