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Fireplace lintel

Steve Maskery

Old Oak
Joined
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87290 Laplagne, France
Last year we had a new fireplace built. The old one was dangerous (flue installed upside down, chimney breast held up by a bit of 4x2, resting on a brick by just 20mm...). We had to sack the builder half way through the project, so it's taken a while to get it finished.

Just about every house we have been into has got a fireplace with a lintel over it. Sometimes it is stone, but more usually it is a massive oak beam. A friend gave me one such beam, saying it was oak. It was about 1.8m long and 200mm square. It took two of us to lift it. It didn't look very pretty - rot and woodworm:
original beam 1.jpg
original beam 2.jpg

My friend Jeff and I deep-ripped it on my bandsaw, but the coarsest blade I have is 3tpi, much too fine for this job. One cut took over an hour. Once cut I could see that it was not oak, but chestnut. No surprise, really, it grows plentifully here and, presumably, did so 200 years ago, too.

But a slice cut from the centre and cleaned up, it looked lovely.

I needed to work out how to attach it to the wall. My first thought was to insert some threaded rod into the wall, bolt on the lintel and then cover the holes with square iron studs. But then I had another idea.

I routed out a big cavity from the back. I can't remember whan I last used my router, I'd forgotten how to adjust it.

routing cavity.jpg

The ends were chopped out by hand

ends needs doing.jpgchopping.jpg


I then cut a pair of French cleats. For bevel cuts I move my fence to the left, so that nothing can get trapped. But that means I have no support for my SUVA guard, so I used my magnetic stand-alone one instead. Here are two views of the setup.

bevel setup1.JPG
bevel setup2.JPG


One piece was screwed into the cavity, the other to the wall.

cleat on wall.jpg

The oversized holes were so that I had some wiggle room for getting things level.

Then the lintel just dropped on and all was good.

finished.jpg

Chestnut is softer than oak, it was easily dinged by trapped sawdust or the like, but finished (I used BLO) it looks beautiful. I think I may have a new favourite timber.
 
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Rule of thumb is 3 times pipe diameter between pipe and your wood if there is no heat shield. I think about 80mm if the pipe is double skinned. France must have building regs?
 
I think it will be OK, I would not have done it otherwise.
The pipe is not twin-walled.

It's just that the previous fireplace had wooden joists screwed to the brickwork to which was screwed plasterboard to make the "ceiling" of the fireplace. The plasterboard was not fire-rated and the rear support, in total contact with the flue, was burned through. Not just charred, but burnt, a 6" gap where wood once was.
How the house never burned down, or the chimney breast did not fall down, I don't know.
 
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Thank you.
The only reservation I have is its proximity to the stove pipe. I hope it doesn't get too hot.
S
Well you will know if you return home one day and your house has burnt down :ROFLMAO:

Just joking, looks great Steve!
 
Yes neatly done, it’s not just French builders, a friend of mine - uk builder installed a woodburner and just wouldn’t listen when I attempted to tell him about the regs, like yours he lined the fireplace with ordinary plasterboard. It’s his house so I tried again as I don’t particularly want him and his clever wife to die but stubborn or what!
 
Steve, I'm guessing the plexiglass or perspex with the caution markings around the edges is a guard for the table saw blade. If so is it held to the table with magnets?
 
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Yes neatly done, it’s not just French builders, a friend of mine - uk builder installed a woodburner and just wouldn’t listen when I attempted to tell him about the regs, like yours he lined the fireplace with ordinary plasterboard. It’s his house so I tried again as I don’t particularly want him and his clever wife to die but stubborn or what!
Yes....Last year we installed a log burner (large, new eco type in compliance with modern reburn and emissions) and to comply with building regs and get a HETAS certificate I decided to engage a registered installer. He built and fitted a new flu and fitted the fire. I did the work on the walls. Our house is a timber barn and the installer insisted on cement board behind the fire, a fire protection screen through the wall penetration and a metal screen on the exterior around the pipe as well. Fire proof sealants. Everything tested. No argument from me as I had no desire for the house to burn down.
 
The fire is lit for the first time since installation. It's been going a good hour or so, so probably as hot as it is going to get.

I've just felt the underside of the lintel. It is warm to the touch, but not uncomfortably so. It has dried out enough to now feel textured rather than the silky smooth finish it was yesterday, but I'm not concened about the risk of flammability. Phew!
S
 
....The plasterboard was not fire-rated ....

ALL plasterboard is fire-rated. The thicker it is, the better the rating. However, there are some circumstances where a special (usually green) plasterboard is required to deal with a specific fire risk. Personally, I wouldn't be in the slightest bit worried about plasterboard, skimmed, in a fireplace. It's what it's attached to that's the issue. As you say, the wood behind can char away, and aluminium framing can buckle. I've been in the aftermath of a couple of serious housefires, and the plasterboard was undamaged in both...just regular common or garden 9 or 12mm plasterboard. In one of the them, the fire was so fierce that a handbasin exploded, and the triple glazing cracked through, but the stud walls surrounding the room contained the fire with nothing other than smoke damage.
 
So what is the difference between "ordinary" plasterboard and the red stuff that my BCO insisted I used on the ceiling of my workshop when I built it?
S
 
I don't know. For a given thickness, it provides a longer fire-resistance than ordinary plasterboard. It's difficult to see why you needed a fire-resistant ceiling in an outbuilding......but one of the reasons that Fireline is sometimes required is that the joists are too flimsy or far apart to carry the additional weight that would be required to achieve a specific fire-rating using ordinary plasterboard alone.
 
I don't think that there was anything that could reasonably be called "flimsy" about the workshop that I built (well, We, really - Ray played a big part of it as well as significant input from woody friends, some of whom are on this forum, for which I shall be forever grateful).

One day, when the BCO came, he had a look around. We were bracing the trusses at the time, IIRC. He laughed. I asked him what was so funny and he didn't answer. He looked around a bit more. The he turned to me and said, and I quote,

"I go to see houses that are not being built as well as this is".

I'll take that.
S
 
I’m sure what you know to be the reality is correct Mike, but a question to Google tells me that all plasterboard is considered to be a combustible material, and this also is what I was told when I built my faux chimney breast completely out of metal studding and Hardy cement board. Perhaps it depends if the paper surface is skimmed over or not?
 
In Germany, standard gypsum wall board (GWB), or Gipskarton Bauplatte (GKB) in German, is 12.5mm thick and has a fire rating of about 30 minutes when a single cladding installation is used. However, all of the installations I managed used double layers with staggered seams in order to meet the minimum German fire ratings for 90 minutes. Non-load bearing walls used as fire breaks will have two layers on each side of the metal studs, with fire retardant mineral wool insulation between the studs. These walls meet the F90 rating (F for walls, ceilings, etc., and 90 for the time in minutes) specified in DIN EN 13501-1. Depending on the construction requirements, the F90 wall might also require a continuous metal sheet on one side of the metal studs.

The most common GWB available at the big box stores here are the 12.5mm thick sheets that meet the DIN EN 13501-1 A2 S1 requirement for F30 or F90 construction. The A2 means the product will not combust in the presence of combustibles, and the S1 means it produces little to no smoke in the presence of flames (I think it covers temperatures up to 1,000 degrees C).
 
I’m sure what you know to be the reality is correct Mike, but a question to Google tells me that all plasterboard is considered to be a combustible material, and this also is what I was told when I built my faux chimney breast completely out of metal studding and Hardy cement board. Perhaps it depends if the paper surface is skimmed over or not?
Don't rely on search engines for the answer to everything, Ian. Here is the true situation. Any of the usual domestic fire resistance periods (30mins to 120 mins) can be achieved with studwork and a combination of plasterboard (sometimes in multiple layers) and plaster skim. This is to the satisfaction of Building Regulations and British Standards.
 
Interesting info above. You can cook on some log burners so the tops on some models must get pretty hot. I imagine the laws on fire retardancy must take into account the extremes of what might be installed.
 
Just a side note regarding wood stoves, over here there is a manafacturers plate attached on the rear of the stove. Showing proof of the model being certified and tested to comply with safety standards. The plate will also show clearances away from combustibles ie., back wall, side walls, minimum allowance from the top of stove , setbacks or clearances for black stove pipe and required projection for the hearth.
 
Yeah, a similar plate is on the back of my stove as well. Not sure if it offers the same extensive amount of information as yours though.
 
If the plate doesn't show all the critical info I'm sure you can search for the model installation instructions.
 
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