Sorry for the length of this post.
Normally, I wouldn't consider doing any work on a chimney breast, given the risk, but something made me change my thoughts on this yesterday in our house.
We are looking at having a Rayburn fitted, but the company have recommended we arrange the work to enlarge the fireplace ourself because they have to charge too much to do building work!
The chimney breast currently has a standard builders opening, with a construction hearth formed by two wells made of floorboards filled with concrete, one below the fireplace approx 2" deep, and one, not as deep, below the extending hearth. I'm aware this does not meet current regs, but it did in 1902 when the house was built :) I don't know how high current lintel is.
I need to open the chimney up to approx 4' wide and 6-7' high, which means a new lintel - or RSJ because that is what the suppliers of the Rayburn have spec'd; they use the shape of the RSJ to set a concrete flag in place above the Rayburn.
The chimney is supported from the floor of the cellar by 9" solid walls, but only on the sides, so the chimney breast itself stops at ground floor level - like this:
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I assume this means the load from the chimney is being passed entirely into the sides, so a lintel is taking very little load - is that correct?
I need to do two things:
- Strengthen the floor to take the Rayburn. As it needs a 6' plinth of non combustible material to sit on to meet regs, rather than set this on the floorboards and create a raised plinth which would be a real pain, my plan was to create a 6' deep well and fill this. To do this I was planning to build up the supporting side walls in the cellar forward to the required depth and lay concrete lintels across to form a structural well, then pour the plinth on these. This (I hope) would supply a strong supported base for the Rayburn that was fireproof. Naylor's state a 2 tonne max load on a 2m lintel, and I would have about 10 forming this well.
- Open up the chimney breast using acro's and strongboys to support the chimney during the work. the RSJ would sit on the inner course of the 9' chimney sides, as so:
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So, am I mad to think about doing this myself? Am I on the right track or am I talking complete rubbish?