Flue Heights

As one of the purposes of your flue system is to remove flue gases and the products of combustion, it stands to reason that your installation must be of a certain length and height to safely distribute these fumes away from your home and up into the atmosphere, not your neighbour’s upstairs window. Building Regulations recommend a flue system of at least 4.5m in length to achieve this.

An added benefit of attaining a certain height with your flue system is the improved draw this will create. As you extend your flue you are extending the pressure difference which can only improve the draw and performance of the chimney and stove. This also ensures the draw is not impeded in any way by adjacent buildings and trees.

Approved Document J of the Building Regulations for England & Wales illustrates the heights you must achieve with your system however, if you find it hard to get your head around the jargon they use (and you are not alone!) then hopefully our own illustrations below will help out.

Flue Height 1

Flue Height 2

The only situations where these distances change are if there are obstacles in the vicinity such as windows in the roof or buildings extremely close by. This needs to be taken into consideration when determining how high to run your flue system:

  • If you have an openable window in your roof and the flue will be within 2300mm either side of it or anywhere below it, then your flue system must rise above the window by 1000mm
  • If a neighbouring building is so close that any part of it comes within 2300mm of your chimney system, your flue must rise above that part of the adjacent building by 600mm

We can even go one further and calculate just how high your flue will extend once through the roof, depending on the pitch:

  • 25 Degree Pitch = 1070mm high.
  • 30 Degree Pitch = 1330mm high.
  • 35 Degree Pitch = 1610mm high.
  • 40 Degree Pitch = 1930mm high.
  • 45 Degree Pitch = 2300mm high.
  • 50 Degree Pitch = 2740mm high.

Should your roof be thatched or made of any other combustible material, then as you can imagine these distances must increase. As illustrated below, if your flue exits through the roof within Section A then you are required to rise at least 1800mm vertically above the roof surface AND at least 600mm above the ridge. Alternatively, if your flue exits within Section B then your vertical distance remains at least 1800mm but your height above the ridge must increase to at least 2300mm:

Thatched Roof Regulations

It is worth noting that the distances highlighted above are minimum distances only and your system may be required to extend beyond these to create a sufficient draw.

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2 thoughts on “Flue Heights”

  1. I think that something is wrong here because 2300mm above the ridge of the roof is completely impractical, and apart from requiring a properly engineered support bracket it will look really strange above a bungalow roof.

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