Opening up a Chimney Breast

[stuart45]

My son made an interesting observation tonight... the jambs don't appear to be tied into the back 200mm of the chimney breast - the courses don't line up. Which to me, suggests the jambs aren't bearing the weight of the stack. Does that sound plausible?

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I thought you already knew that, as we discussed it on Monday when you put that photo on. The back wall was probably built first as the structural wall. It's a totally different method to any chimney I've ever built, or even worked on.
If you know what model of woodburner you're getting, you can work out what clearance you need around it.
You also need to work out how to get a 600mm stove pipe connected to the liner, so extra height would help.

 

[stuart45]

Looking at the method they used to build the chimney, it's actually quite clever, because by putting the flue inside the party wall, they can still have a 9inch brick fire protection each side of the flue, so you only get a 9 inch projection into the rooms.

 

[Ivor Windybottom]

I've seen someone pretty much destroy their home by mucking about with the chimney with half an idea of what they were doing.

There are several tons of masonry directly above - on a very tall, thin structure. Don't mess with physics.

As it was built in the 1990s, it's probably safe to assume that if they could have got away with fewer bricks and saved a few quid then they would have.

ALL internal corners in brickwork have a continuous vertical perp joint - it's just how it is. Get your lego out and build a corner. Even if you bond the corners in alternate directions you'll still have a vertical joint right up the whole thing. Now imagine pointing this corner, you'll end up with exactly what you've shown in your photos.

Keep the width the same, don't even think about widening it. You may be able to deepen it, possibly, subject to lots of investigation - by someone who understands it all in person, not on the internet. If you can't deepen it and really need a deeper opening then you could always extend the sides outwards into the room and put a mantel shelf over your extension, which would look totally normal.

 

[Craig-H]

All of this just to gain a few inches!

It's a relatively modern chimney. I definitely wouldn't entertain what you are wanting to do. Yea, I know, your risk etc. Just saying that's all....

Of course, you could increase the depth of the chimney from the front by building out a false wall. Keeping everything intact behind. You could still fit a wood burner if you used the correct materials etc...

The problem is I need those few inches, because as it stands there isn't enough room to feed the stove flue to the chimney flue, it's too tight.

 

[Craig-H]

Looking at the method they used to build the chimney, it's actually quite clever, because by putting the flue inside the party wall, they can still have a 9inch brick fire protection each side of the flue, so you only get a 9 inch projection into the rooms.

Agreed... it's tidy if all you want is a traditional fireplace. It's a good use of space.

 

[stuart45]

The problem is I need those few inches, because as it stands there isn't enough room to feed the stove flue to the chimney flue, it's too tight.

You will need to break into the chimney breast from the front, as you won't have enough room to connect the stove pipe to the liner and get a vertical 600mm flue to get through the regs. I used to work for a firm that did quite a few stove installations, and I used to do the brickwork for the fitter if it was a complex job. Before HETAS came in it was the bricklayers job to install solid fuel appliances, and was part of the apprenticeship.

 

[Craig-H]

I've seen someone pretty much destroy their home by mucking about with the chimney with half an idea of what they were doing.

There are several tons of masonry directly above - on a very tall, thin structure. Don't mess with physics.

As it was built in the 1990s, it's probably safe to assume that if they could have got away with fewer bricks and saved a few quid then they would have.

ALL internal corners in brickwork have a continuous vertical perp joint - it's just how it is. Get your lego out and build a corner. Even if you bond the corners in alternate directions you'll still have a vertical joint right up the whole thing. Now imagine pointing this corner, you'll end up with exactly what you've shown in your photos.

Keep the width the same, don't even think about widening it. You may be able to deepen it, possibly, subject to lots of investigation - by someone who understands it all in person, not on the internet. If you can't deepen it and really need a deeper opening then you could always extend the sides outwards into the room and put a mantel shelf over your extension, which would look totally normal.

I certainly won't take any chances, which is why when I thought I had an answer and I then had some doubts, that I stopped and sparked up a conversation on here. I am seeking advice wherever I can find it and that includes professional stove installers. Again, if I'm not convinced by their structural knowledge, then I won't proceed just because someone said "It'll be alright..." even if they are protected with public liability insurance.

Perhaps I'm missing something, but if the corners were interlocked or the adjacent walls relied on each other, the top and the bottom of the interlocking bricks would have to be at the same height wouldn't they? They're not in the back corners - the mortar joints on the back wall end up in the middle of some of the bricks in the jamb. If you look at bricks 6 and 7 from the bottom of the jamb, they don't align with the back wall mortar joints. Doesn't that suggest they are not part of the same structural design?

It looks to me like the jamb and the back wall were built at different times and given the previous pictures of other people removing their party wall chimney, it seems to me that the jambs and the ground floor breast were built around the party wall stack (main structure 200mm from the party wall).

 

[Craig-H]

You will need to break into the chimney breast from the front, as you won't have enough room to connect the stove pipe to the liner and get a vertical 600mm flue to get through the regs. I used to work for a firm that did quite a few stove installations, and I used to do the brickwork for the fitter if it was a complex job. Before HETAS came in it was the bricklayers job to install solid fuel appliances, and was part of the apprenticeship.

I think that is good advice and I intend to, I just haven't had a chance yet. I'll share what I find

 

[Craig-H]

I thought you already knew that, as we discussed it on Monday when you put that photo on. The back wall was probably built first as the structural wall. It's a totally different method to any chimney I've ever built, or even worked on.
If you know what model of woodburner you're getting, you can work out what clearance you need around it.
You also need to work out how to get a 600mm stove pipe connected to the liner, so extra height would help.

I did realise when we spoke previously, because it does look like the back wall passes behind the jambs, but my son noticing the horizontal mortar not lining up between the back wall and the jambs was something I hadn't picked up on, but just confirms that earlier conversation I think.

That 600mm stove pipe can be staggered with 45 degree bends though can't it?

 

[Ivor Windybottom]

Ah OK, the misaligned courses says that they don't interlock. But that doesn't mean they're not holding up what's above, or aren't needed just to aid its stability. They could be acting as a buttress.

 

[Ivor Windybottom]

Is the house timber-framed?

 

[stuart45]

The chimney jambs should in theory be built with the party wall, but in practice, especially with subbies, it's quicker to run the party wall up first, and leave out indents every other course to tie the jambs in. Then drop back and build the jambs later. You often found the indents hadn't been plumbed up properly, or the odd one forgotten, so the jambs were not tied in to the book.
However, on your chimney it's obvious there's no tie as it's a butt joint against the back wall.

 

[Craig-H]

Ah OK, the misaligned courses says that they don't interlock. But that doesn't mean they're not holding up what's above, or aren't needed just to aid its stability. They could be acting as a buttress.

Agreed... it's just another part of the puzzle.

 

[Craig-H]

Is the house timber-framed?

No it's stone.

 

[Ivor Windybottom]

Actually, couldn't the courses at the edges continue beyond the back of the fireplace? It may be that the sides are the structure, and the back is infill.