How to correctly re-bed roof coping stones??

[AD76]

Hi,

In Jan'11 we had the entire roof an old c1830's Victorian farmhouse completely recovered which involved fitting felt, new lathes, guttering, flashing and re-fitting slates (around 25% new). The house is made up of an older 'cottage' part with a newer main part to the front, so the 'cottage' roof abuts to a gable end of the main house, hence there are four gable ends and each has coping stones (see photos below).

The coping stones were removed and re-bedded during the re-roof. However, damp penetration over the stairwell which is below the cottage/main house gable end, and which was evident before the restoration started, has clearly continued and has now penetrated through new plaster and paint (even though the plasterer and decorator said it was dry, grrrr).

I recently also noticed a bad leak in the main roof space around the chimney flashing which made me check every nook and cranny of the roof spaces, particularly the gable ends and the rafters adjacent to the copers.

In addition to the continued damp penetration above the stairwell, I have found water droplets on the inside of the felt next to the outermost rafters under the coping stones, damp and mould on some of these rafters, and also signs of damp on the internal stone directly under one of the gable end apexes. This has made be seriously question whether or not the coping stones have been re-bedded properly.

See photos below which were taken during the roofing work, and which show the solid gable end walls, i.e. no cavity, and the lack of lead work before the copers were relaid. I think the roofer has trimmed the felt, laid the slates up to the gable end walls and then laid the copers on the wall before applying a large fillet of mortar. Is this correct/acceptable practice or have I got a case to go to the original builder with who contracted the roofer? I suspect the copers should have been re-bedded on lead flashing with suitable lead soakers, and doing this now will cost around £10-15k which the builder will no doubt be reluctant to do, meaning I may regrettably be forced to go down the legal route if I have a strong case.

Any professional technical advice would be much appreciated.

Thanks.

 

[chappers]

Yep as you suggest soakers should be fitted at all abuttments

 

[^woody^]

Mortar fillet (instead of lead flashing) is a traditional method and is still used on historic buildings. This will rely on additional measures below the tiles to prevent water ingress.

There is no requirement to fit lead below coping stones as a DPC. This is detrimental as it prevents the coping stones bonding, and liable to be blown off.

It all comes down to whether what was done was suitable, and/or whether it was done negligently if suitable.

But fundamentally, there should be no water penetration. And this would be a latent defect, so don't stand for any "out of guarantee period" nonsense.

 

[AD76]

Thanks both. Woody, you mention mortar fillet is an acceptable method on old period properties if additional measures are taken below the slates. What are these additional measures? Thanks in advance.

 

[^woody^]

Its just the detailing of the felt membrane or a secret gutter.

A mortar fillet is only normally used where aesthetics require it - typically on listed buildings. It's not commonly done, but it is an option that could be argued

 

[chappers]

Its just the detailing of the felt membrane or a secret gutter.

or soakers, in this case probably a solid wall there is as Woody suggests no need to cap under the copping stones.
If I had finished the abutments of this roof I would have used soakers and bent them over the edge of the parapet wall, before bedding the copping stones on.

 

[AD76]

Thanks again both. Your advice is much appreciated and is consistent with other advice I have just got in from a roofing association, i.e. lead flashing under the coping stones is not generally done because of the lack of keying with the solid wall below, but lead soakers are essential instead of the mortar fillet which is not best practice. Thanks again.

 

[chappers]

mortar fillets were still common probably up to the 30's but were just used to cover the unsightly edges of the soakers, before cover flashings became the norm.

 

[catlad]

You could take a look at the lead sheet manual I am sure they will give you some guide to best practices.