Pythagoras in the roofspace

The heating engineer finally made it up to the house on Friday afternoon, and although he has managed to get the system fixed, it can only be turned back on slowly, room by room, so the heat pump isn’t overloaded.

Which meant with the temperatures outside dropping below freezing, when I arrived late on Friday night, my large stone barn had turned into an enormous fridge. It is slowly coming back to life, but in the meantime I’ve been walking around indoors all weekend wearing coat, scarf, hat, gloves, boots and thermal underwear!

So I’ve decided the priority on my ‘to-do’ list is getting the wood-burning stove installed in the living room.

I’ve already got the (shaped like a coffin) hearth finished. I’ve even bought in a large supply of logs ready for burning. All I’m missing is the stove itself.


In an ideal world you plonk a fire down on its appropriate hearth, and take the flue up through the ceiling and out through the roof in a nice easy straight line.

My barn would never allow anything that simple. A straight line above my hearth takes you up into the snug and out through a glass roof.

I’m sure it is possible, theoretically, to put a flue through a glass roof. But I’m equally sure it would be eye-wateringly expensive.

And even if I could get the flue safely through the glass, building regulations require that a flue either a) clears the ridge of the roof or b) extends for a minimum of 2.3m beyond the point it exits the building. Given the height of my roof relative to the glass, it’s a close call on which of those rules I would have to apply. Either way I would need more guy ropes than a circus tent.

And even then, every time there was a howling gale, (which, let’s face it, is most of the time in Scotland) I would just be sitting there waiting for the crash……

I have come up with a cunning alternative. Take the flue up through the ceiling into the snug. Then angle it, just below the glass roof, through the wall into the loft. Then I can run it below the rafters and out through the roof close to the ridge.

No guy ropes. No glass. No second mortgage required to pay an engineer….

That’s not to say it’s going to be simple. Since I don’t have a chimney in place, I’m going to have to install twin-wall flue. There’s still a whole heap of regulations that need to be adhered to. So I googled it. And came across a very helpful website with a lovely chap who promises he can design a flue for any situations. So I sent him an explanation of my fireplace set up and a very precise drawing to illustrate what I mean….


He’s promised to get back to me soon, but in the meantime asked if I knew what is the angle of the roof?

Apparently modern roofs usually have a pitch of 45 degrees, but the barn’s been around a while, so I don’t know whether the roof can be considered modern. Besides which, it was Mister Incompetent Builder who rebuild the roof, so who knows what kind of angle it pitches at. Only one way to find out….

First I need to get up into the rafters…with a set square and a spirit level.

Now I need to remember my O’level maths days. Pythagoras theorem: the square of the hypotenuse is the sum of the squares of the other two sides….

Right. Got that. So now I can apply the trigonometry bit. With a bit more help from Google I’ve decided my roof pitch is 35 degrees. Which I suspect may cause a few problems. The angles on the twin wall, from what I’ve read, only come in 45 or 30 degrees. I have a nasty feeling that using the 30 degree bend is going to take the pipe right through a load-bearing joist……. (which is why I need an expert to design it.)

So while I’m up here, I might as well take a few more measurements. I’m sure that stove fitter chap will be asking for them….


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