Chimney Shoulder Detail

[MortarThePoint]

Does anyone have a chimney shoulder detail they can share?

 

My plan so far in the absence of a detail drawing. Below are sections of images from the architect. The chimney sticks out ~600mm and has a cavity wall all round. Left to my own devices, I'd bolt a section of 4x2 to the house side wall and build a frame off it that rests on the inner leaf of the chimney outer face (the outer face being the surface you see here). Battens across the top of the frame. Tile overhand around 35-50mm to chimney return (return = front face, next to drain pipe in diagram below).

 

Two options for how tiles end relative to the brickwork face of the chimney that is visible below:

1. flush - tile side is flush with the face of brickwork and gets cement mortar between brick and tile. The top surface of the battens to come ~10mm above the 45 degree cut of outer leaf bricks. That 10mm is to allow the space for tile lugs and some cement at the verge.
2. overhang - side of tile overhangs face of brickwork (e.g. 35mm). Cloak board placed on top of the cut bricks and mortar between cloak board and tiles. If doing this I should probably have the battens go on top of the cloak board like at a normal verge. That will create a much more visible mortar verge, but do a tidier job.

I am leaning towards option 2.

 

Lead dressed down to tiles on the other two sides. No gutter at end of pitch.

 

What do people think? Hopefully this is roof small enough that I can't go too far wrong ?

 

 

Edited June 23, 2021 by MortarThePoint

[PeterW]

Why use tiles ..? Board over with ply and then lead sheet ..? 

[MortarThePoint]

24 minutes ago, PeterW said:

Why use tiles ..? Board over with ply and then lead sheet ..? 

 

Thanks, but not as keen on how that looks. I know another option is to do in brick instead. I'd prefer tile.

[MortarThePoint]

I'm using Redland tiles for the roof and they have some handy CAD resources where you can select your tile type and what detail you need.

 

As they've drawn it, the timber comes up to a bed joint which is handy. They say 75mm min. for the lead flashing. Checking NHBC confirms 75mm min. , 150mm is for flat roof abutments.

 

I think I have my cavity tray a bit high unfortunately as I think I allowed for 150mm.

 

 

[MortarThePoint]

My cavity tray (shown orange below) is a course higher than ideal, so I end up with the three choices below. In the image below, the red the blocks have DPC cavity trays on their left and bottom sides forming a stepped cavity tray down that side wall.

1. Dress the lead flashing ~180mm up the chimney stack to the DPC cavity tray. Could look a bit silly being so high and being visible from the front of the house. It dresses down the tile too >150mm so would create quite a prominent band. Note as prominent as the photo below and hopefully I'd get it all level as well.
2. Leave a gap of 1 course between the top of the lead flashing and the DPC cavity tray. Minimal water would be able to get into such a gap, but it is like an exposed midriff.
3. Shift the line of the roof up a course, which makes the cavity trays round the red blocks lower than ideal ?Too low?

 

[MortarThePoint]

Depending on whether I shift the roof line by using a counter batten, below is my plan for the eave. Simple 4x2 rafter and a 4x2 on edge for the eave vent to sit on. There won't be any vent at the top of the pitch, but the roof section is so small (approx 1m2) it shouldn't matter. I can either birds mouth the rafter to sit on the flat timber. Funny to be putting effectively a wall plate on the outer leaf but will be fine. It needs to stop at the outer leaf end so the brickwork can come through there.

 

Any reason not to be running the outer rafter in the cavity?

 

[MortarThePoint]

Top tip: check your piece if wall plate isn't twisted ? It was only enough to put the bubble at one mark of the level at one end of the section and at the other mark of the level at the other end. Confused me for a moment though.

[MortarThePoint]

I'll leave space for a piece of plasterboard and plaster at the top of the brickwork of the inner leaf.

 

One reason to not put the outer rafter in the cavity is to allow a second timber for the angled plasterboard to mount to. Crazy, but I may end up with three rafters as I am keen for the Brickies to have a line to follow with their outer leaf brickwork.