Green Building Forum - Rubble stone parapet, DPC, flashing help please

Rubble stone parapet, DPC, flashing help please

kebabman — Wed, 20 Jun 2012 11:08:19 +0100

I have parapets to the rubble stone gable walls of my house with coping stones. The pitched roof of my house needs to be raised so obviously I need to raise the parapets too. At the moment the coping stones overhang the slates and the underside of the coping stone is about 70mm above them. Mortar is then just filled in above the slates to the underside of the coping stone.
I will probably have to raise the roof at least 150mm so I am keen to know what dpc and flashing detailing options I should be considering. Presumably I should have a dpc directly under the coping stones, if so of what material. Also should there be another DPC at the level of the current top of the parapet?
I am thinking of a warm roof construction possibly with insulation over the rafters so should I be insulating the inside face of the parapet in any way?
Any help would be very gratefuly received. Thanks

Rubble stone parapet, DPC, flashing help please

tony — Wed, 20 Jun 2012 12:02:28 +0100

Could you not get rid of the parapets now, they are nothing but trouble arent they? simply sail over them with the new roof coverings and sell the parapet stones?

Rubble stone parapet, DPC, flashing help please

kebabman — Wed, 20 Jun 2012 12:26:49 +0100

I have hazy recollections that they are a pet hate of yours!
Yes they are a complete pain but the building is listed unfortunately. So I am keen to minimise their inherent problems.

Rubble stone parapet, DPC, flashing help please

tony — Wed, 20 Jun 2012 13:42:47 +0100

OK then, internal or external insulation to walls?

Rubble stone parapet, DPC, flashing help please

kebabman — Wed, 20 Jun 2012 14:26:23 +0100

Posted By: tonyOK then, internal or external insulation to walls?

Sorry if I am being a bit dense but if you are asking am I insulating my main walls then the answer is no I can't.
What I was wondering was that if I have a warm roof construction with some insulation over the rafters (as well as inbetween) should I be linking this to some insulation run up the parapet and run under the coping stones. I'm not sure if this is a good idea or not!

Rubble stone parapet, DPC, flashing help please

tony — Wed, 20 Jun 2012 15:25:33 +0100

Flat ceilings or rooms in the roof etc?

Rubble stone parapet, DPC, flashing help please

kebabman — Wed, 20 Jun 2012 18:11:51 +0100

Rooms in the roof.

Rubble stone parapet, DPC, flashing help please

tony — Wed, 20 Jun 2012 19:05:02 +0100

OK then raise the parapets, it pains me say this because they are horrid leaky things, and thermal bridges,

I would insulate the inside of the gable walls and join this up with the roof insulation, talk to the listed buildings people about EWI

Then where the roof coverings meet the parapet add a secret gutter even in sections or less preferably soakers ideally with tilters too, then a cover flashing that tucks in under the caping stones.

If it were mine the lead flashing would wrap right up and over the parapet wall and turn down 20mm on the outside face, the bottom coping stone would be mechanically restrained, stainless steel cramp then all rest set on eml with parge,

now no possible chance of ingress of water ever.

Rubble stone parapet, DPC, flashing help please

Mike (Up North) — Thu, 21 Jun 2012 14:24:55 +0100

Hi,
Agree a right potential problem area we did as per Tony suggests. Different design from what you describe but we did have that leaking problem. Original builder did everything as cheap as possible and tried to patch and patch. Finally we bit the bullet and had someone else do it. Lead goes from a tilted fillet running down under last slates then up inside face and over and tucked in on the out side face. Pins (and sealant) to stop coping sliding down.

Seems even without complications some get it right others donâ€™t.

Problem areas were
1) At the horizontal table i.e. where lead is folded round on the sides can make a funnel and send the water back in.

2) We had the horizontal and first angled piece cast as a single item so there is no joint at the base of the slope. This was one area that leaked a lot.

3) Use a large over hang with a decent rain groove in the underside. Originally we had what looked like garden type paving with a mere scratch as a drip grove which filled up with render anyway.

When installed make sure the groove is clear of mortar snots particularly where each piece butts up to the next.

Cheers, Mike up North

Rubble stone parapet, DPC, flashing help please

kebabman — Fri, 22 Jun 2012 12:23:21 +0100

Tony and Mike, very many thanks for the info. I knew it would be worth running it past you guys.
Cheers!