Green Building Forum - Roof/Stone wall junction

Roof/Stone wall junction

andybw — Tue, 08 Jun 2010 11:27:23 +0100

Hi
Building new extension with lean-to slate tile roof abutting ex gable stone wall. To ensure decent weatherproof junction I have been advised to insert cavity tray within ex lakeland stone wall, length approx 10m.
What are the complications of a builder undertaking this and what alternatives are there without using exposed lead/mortar junction?
Many thanks

Roof/Stone wall junction

davidfreeborough — Tue, 08 Jun 2010 11:51:08 +0100

Do you mean a cavity tray or an abutment flashing? Could you do a simple sketch?

David

Roof/Stone wall junction

andybw — Tue, 08 Jun 2010 13:31:03 +0100

Hi
I mean cavity tray, don't wish to see the abutment detail and concerned about its effectiveness.
see section sketch
cheers

Roof/Stone wall junction

tony — Tue, 08 Jun 2010 15:15:18 +0100

I wouldn't bother with a cavity tray -- there is no cavity anyway.

Go up the wall say 200mm and neatly cut a diamond slot level and sloping 15 uphill into the wall and mastic a flashing into that slot.

Roof/Stone wall junction

James Norton — Tue, 08 Jun 2010 15:22:49 +0100

Whether you wish to see it or not is not really the issue. You can't put a cavity tray inside a solid wall.

Unless what you are trying to do is cut back some of the stone, put in an abutment flashing (a la Tony's post) and then rebuild some stone over the front...?

J

Roof/Stone wall junction

CWatters — Tue, 08 Jun 2010 16:31:59 +0100

Posted By: andybwHi
Building new extension with lean-to slate tile roof abutting ex gable stone wall. To ensure decent weatherproof junction I have been advised to insert cavity tray within ex lakeland stone wall, length approx 10m.
What are the complications of a builder undertaking this and what alternatives are there without using exposed lead/mortar junction? Many thanks

I'm not sure I follow how they propose you use a cavity tray? Are they suggesting you build another wall on the outside to form a cavity or something?

Most people would use a conventional lead flashing inserted in a slot down onto the slate.

One possibility would be to construct an "internal" or "hidden gutter" where the new roof meets the house wall. That could be done in a way that makes it invisible from the ground. These sorts of gutter are prone to leaking unless designed and implemented correctly.

Another possibility would be to build a roof from onduline with conventional lead flashing down onto it. Then put deep battens and slates on top. If the battens are deep enough that would hide the lead flashing. You might have to use tapered counter battens so that at the bottom end the height difference is minimised (eg so water from both the onduline and slates can both discharge into the same gutter). Onduline have an apps note for something like this - it's intended to allow tiles to be used below their rated pitch.

Roof/Stone wall junction

Dominic Cooney — Tue, 08 Jun 2010 22:54:00 +0100

I would have thought a cavity tray unnecessary effort on a solid stone wall.

We are also in a similar position, but with a dual pitched roof (single storey) joining a gable end (2 storey).
Still thinking about the detail for this. Can't decide whether to step the flashing with the stone courses or cut one straight line in line with the new roof? Or maybe straight line then mortar flaunching to hide the lead? Not that I mind the lead so much, its around the chimneys on the main roof (stepped - but the chimneys are brick).

Roof/Stone wall junction

martone — Tue, 19 Aug 2014 19:28:14 +0100

Posted By: Dominic Cooney

We are also in a similar position, but with a dual pitched roof (single storey) joining a gable end (2 storey).
Still thinking about the detail for this. Can't decide whether to step the flashing with the stone courses or cut one straight line in line with the new roof?

Old thread revival sorry, but having exactly this dilemma right now!

Roof/Stone wall junction

tony — Tue, 19 Aug 2014 22:49:02 +0100

Straight cut is technically better, secret gutters are nice too, what roof finish?