Slate roof patch repair - valley?

chaotic_j

Hi,

I had some missing and slipped slates on the front apex of my house - had it repaired, but I think there are 2 areas on the right hand side where the valley is, where there is no slate. It looks like a gap where there's only felt - is this normal or could it cause a leak? I'm not an expert.

The slates you see had to be stripped from underneath the vent downward, some battens replaced along with felt as there was a hole in it, some of the new slates are Spanish, the top capping was added as this was missing - which is probably how the damage was caused in the first place.

Thank you so much in advance.
chaotic_j

FreeBear

The slates should go all the way to the valley and cover the lead. The lead should continue under the slates for some distance (usually around 150mm). The felt then sits on top of the lead, followed by the slates. The problem with angled valleys is you invariably end up having silly little bits of slate cut to fill the gaps. Often, these become dislodged... The answer is to use a wider bit of slate, but this isn't always possible.

As long as you have a decent amount of lead under the slates, leaks shouldn't be an issue. But you need to get someone up there to check.

stuart45

The membrane goes under the lead.

FreeBear

Was using NHBC & the Marley site guide - Both recommend felt over lead. But at the end of the day, as long as there is sufficient overlap and tiling fillets either side, it shouldn't make a difference.

stuart45

With lead the standard method is to first fix a central strip of felt or membrane down the valley. Then fix the felt across from each side of the valley so there are 3 layers over the valley. The battens are then fixed and then the lead is fitted. 
There are special troughs where the membrane can come over them.

chaotic_j

Thanks @FreeBear @stuart45 it sounds as though it should be ok. I've been busy with work so when the tradesperson explained what they'd done it didn't go in very well.

I've actually remembered they specifically mentioned that the valleys had been slated very close - perhaps that's why they've left the bit they've done without the small pieces of slate as mentioned by @FreeBear

stuart45

When they did the valleys it's better that they put the membrane under the lead, as in the winter condensation can form on the underside of the lead. This can get into the roof timbers unless there's a membrane underneath to take it down to the gutter.

chaotic_j

That's interesting @stuart45 and makes sense. I've been up in the roof space and at the top of this valley it's pretty wide, laid on top of wooden boards which looked a bit worse for wear - could see the bare lead so no felt underneath.

The slates in the picture have been relaid up to the left hand side of the valley - they haven't laid the valley itself.

stuart45

If you have the old non breathable roofing felt it will go over the lead on a tilting fillet. As it won't let moisture through there would be no point going under it. It's only the breather membranes that allow moisture through.
In the old days condensation in the roof space wasn't a problem, as the roofs weren't insulated and the space was warm.

chaotic_j

Hmm I think @stuart45 the original roofing felt is Protect A1 which is non breathable, the stuff that's been used in this repair area doesn't look like it has any brand on it? It's not really possible to see if there's a tilting fillet from the pictures I have.

Does this help at all? thank you!

stuart45

If they only did a small area of the roof they couldn't alter the valley details. To get a breather membrane under the lead you need a clear roof. Watch this. How to install roofing membranes – valley details - Tyvek® roofing membranes - YouTube
That does like there could be an upstand/tilting fillet by the lead. If you go in the roof space when it's hammering down is the best time to check.