Chimney stack flush with gable wall

Seeger

I'm building a house at the minute, and want the chimney stack to finish flush with the gable wall. With the requirement now to bring up the cavity wall behind the fireplace how can this be achieved? The norm now seems to be to build the chimney off the internal wall and roof over the cavity and external wall. I want the chimney to look like the first photo, not the second.

Calahonda52

Seeger wrote: »

I'm building a house at the minute, and want the chimney stack to finish flush with the gable wall. With the requirement now to bring up the cavity wall behind the fireplace how can this be achieved? The norm now seems to be to build the chimney off the internal wall and roof over the cavity and external wall. I want the chimney to look like the first photo, not the second.

Where did you find the requirement in bold?
What is on your planning drawings?

Duff 6

I am currently building also. The house is built and roofed with windows and doors in. The house is of a traditional style with the chimney stack built flush with the gable. The chimney was built of the inside wall which maintains the cavity, the chimney was then corbelled/ stepped out onto the outside wall in the attic space. Then the lead tray was put in. However I hadn't flagged it at the time but when it was stepped across the cavity you have an outside block and inside block in contact which is now transferring moisture across - below the lead tray that is. The gables are not yet plastered so I don't know if my detailing for the chimney is incorrect. I had an experienced builder build the house and he hadn't flagged any issues at the time.

Seeger

Hi Duff. Yeah, it's a bit of a nightmare detail. I believe the proper way to do the flush gable chimney is to form the cavity wall on the inside of the chimney breast. I hadn't the foundations set up to do this. I'm not sure I'd want to do this either as the insulation is then on the wrong side of the flue so you lose out on heat from the chimney breast upstairs.
I went with the way the Blocklayers had it set up as they were not willing to bridge the cavity because of the damp. It's also not ideal from a thermal bridging point of view. I only wish the Blockies/contractors had highlighted this to me in the beginning. I'm an architectural technician myself so only have myself to blame really.
I found a pic on the Internet of a potential way of doing it but when I showed the contractor and Blockies they said they reckoned it would still cause problems with damp and or plaster cracking. I'll attach pic. It looks like tray is on the bottom? They made it clear they wouldnt be back to fix it if it did cause trouble so I didn't go with it.
Without wanting to give bad advice to you, maybe acyclic plaster could be used on your house to stop the damp if it is an issue for you? Taking back the chimney doesn't sound like a great option for you as you're so far on! I would seek professional advice on it of course. When the chimney is in use it might keep the area dry anyway.

Seeger

Seeger

Hi calahonda, sorry for late reply. Yes, requirement is the wrong word to use there. I should have said its best practice to insulate behind the chimney?