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Leaking roof after re-slate

I had new roof re-slated last year and it is leaking badly already.
The timbers in the loft are saturated at the back wall on the left where the property joins the other one and where the chimney is.
There is also a drip within the chimney breast.
There are pots with elephant feet on the chimney and these have been cemented in. The lead flashing has been replaced. The chimney that is in use has a cowl. The chimney was repointed 'where necessary'
Now I've been told it might be because different size slates (Spanish) have been used on my side to my neighbours side (Welsh).
Does that sound a possibility or does anybody have any other ideas?

Thanks for replies so far, especially W Hartley Ltd. Not sure it has felt. There is a membrane but I'm in Scotland so slates onto membrane onto sarking board. Would that prevent a bonding gutter being used?
Flaunching has just been done btw but to no avail and all pots have elephant feet and cowl on woodburner pot.

4 Answers from MyBuilder Roofers

Best Answer

I’d recommend checking if you can see light from your loft first of all


Answered 12th Feb 2020

Very difficult to give an accurate answer without having a look at the roof and could be a number of reasons I would suggest testing it with water in each area on a dry day to get to the bottom of the problem,And is there sufficient ventilation in the roof areas, Also would it be better to have a secret valley where both roofs meet.


Answered 12th Feb 2020

You said the timbers are wet at the back where roof meets other roof, slates are waterproof on their own if fitted correctly, you should also have breathable roofing membrane under the slates which prevents condensation and acts as waterproof barrier, the leak is probably around the lead flashing or cement fillet , depending on what was used, the felt maybe not fitted great and because the water is getting in at the edge of roof, the drip in the chimney breast is either a crack in the cement flaunching around pots or through top of a pot,if a proper roofer fitted your roof it doesn’t matter if neighbours slates are different size, I can fit new slate roof along side a concrete tiled roof and it has breathable roofing membrane over the join, run into neighbours roof 500mm, then a fibreglass bonding gutter is fitted down the half way point , half under neighbours tiles half under mine, so it has double waterproof barrier regardless of sizes, hope it helps.
Sarking boards won’t stop you using bonding gutters, best thing will be to go in loft with torch when raining next and pin point the exact point of entry then take it from there


Answered 13th Feb 2020

Sounds like flashings around chimney leaking, rough cast chimney also, mixed sized and different type of slateing not a good idea either? unless properly flashed between two properties.


Answered 13th Feb 2020

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