Chisel 20mm out of ceiling joist

[blued]

I'm going to be getting a free standing wood burning stove fitted and did some measurements in the loft last night to see where the flue will go. The stove we've ordered has to be 200mm from the wall downstairs. With the flue running straight up and into the loft there will be a clearance of only 30mm to the closest joist. The minimum clearance allowed is 50mm. I can't move the stove back any closer to the wall and moving it forward another 600mm isn't an option either. With that in mind here are my questions...

1. Would it be safe for me to chisel 20mm into this joist, probably 200mm in length and add reinforcement to the other side of the joist?

2. If the answer to 1 is yes, how should I reinforce it? Should I use a length of joist on the other side of the joist I am cutting out of? If so how long should the reinforcement be and how should I fix it to the existing joist?

The only other option I can think of is to have the flue come out of the stove at a slight angle so that it brings the flow back 50mm or so. However I expect that having a twin flue part made up to go up, back at an angle and then straight up again would be rather expensive.

 

[Inky Pete]

Assuming that the 50mm minimum clearance is to avoid the risk of heat from the flue harming the ceiling joists, I'd first ask the stove/flue manufacturer whether it would be acceptable for you to fit a metal plate to the side of the joist nearest the flue - or some other form of insulation/protection between the two.

 

[blued]

Yes the clearance is the minimum distance to combustible material. I think the problem with something like a metal plate is that it would transfer the heat to the joist. With only 30mm to play with I think it will be difficult to get something in there that will sufficiently shield the heat.

 

[TheVictorian]

I had something similar with a downligher and I fixed a ceramic tile to the joist - this worked perfectly.

However, I'm not saying this would be safe/recommended but I would have thought that a tile would be safer than 20mm of extra air.

 

[blued]

Thanks, a ceramic tile may be a an option. I'll run it by the installer when he comes to quote.

I've also spoken to a flue supplier and they can supply 15 or 30 degree bends to offset the flue. They do seem to increase the price of the system by about 20% though and probably wouldn't look as good as a straight up system.

 

[Inky Pete]

A metal plate would conduct heat along its length and radiate it at its ends - effectively "spreading out" the heat from the flue and protecting the joist from a localised high temperature. Ceramic tile conducts heat quite well too, so that'll be doing the same thing.

But maybe a more insulating material such as Fire Board would be more appropriate.

Fire Board

 

[blued]

Thanks, I'll run that by him as well and see what he says. It would only be at the joist and ceiling truss and because the flue is curved it will be a minimal amount passing the wood.

 

[Chri5]

I'd see what the temperature at that point / distance from the burner is likely to be.

Is it really likely to be that hot? Some lead nailed to the joist and shaped a bit like a deflector would seem a reasonable method.

The flu type? Double skinned? Is there a makers site that might have external temp readings against the burner size?

 

[blued]

It is double skinned Selkirk, the installation instructions can be found here.

http://www.selkirkchimney.co.uk/documents/products/STC UK 51000701 080911.pdf

Looking at page 6 you can see at the ceiling support it is effectively boxed in and it says that the air gap MUST be maintained.

It looks like the flue will probably have to be offset with a 15 degree bend if there is no option to adjust the joist.