Boiler Flue Height Above Roof

Vent caps 12 and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows.

Boiler flue height above roof. From my very limited understanding of building regs part j for where the flue should be positioned i thought that the height of the top of the flue must be a minimum of 2 feet above the ridge. 300 mm above ground roof or balcony level 2000 mm below a velux window for a vertical flue 300 mm above roof pitch or flat roof for a vertical flue note that more powerful boilers might require larger clearances between the flue and the relevant object. 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 and at least 2300mm horizontally from the roof surface.

If the pitch of the roof is 38 degrees or greater the termination point of the flue or chimney will need to be 2300mm horizontally from the roof line and roofing material. Roof pitch rise run in inchesminimum height flat to 7 12 1 0 foot above the roof surface 7 12 to 8 12 1 5 feet above the roof surface 8 12 to 9 12 2 0 feet above the roof surface. Degrees the height of flue or chimney stack will need to be at least 1800mm above the roof when not close to the ridge. So take the top number of your roof pitch and multiply it by 10 then add 24 note example 1.

The amount of flue protruding from the slope of the roof is about 2 feet but the top of the flue is just a bit higher than the ridge of the roof. Back to our example over a run of 10 feet the roof would rise 40 inches. This means that below 38 degree roof pitches that the height of the flue outlet should be at least 1800mm above the roof when not close to the ridge and above 38 degree roof pitches the flue outlet height should be 2300mm horizontally back to the roof flue height figures are given in the table above where the flue is not close to the ridge. Vertical flues the majority of boiler flues exit out of a wall horizontally but if the flue from your boiler comes out at roof level then there are also some regulations that.

The figures above are minimum clearances for typical domestic boilers. This is a bit of an odd measurement and chimney clearance case because the chimney side is actually about 8 away from the roof edge. The height of the chimney above the roof surface measured at the up slope side of the chimney from the roof surface to the chimney top should be at least three feet the green line in our photo. Additionally per our rule we need to add 2 feet or 24 inches giving us a total height of 64 inches.

Homes built on varying terrain have their own set of chimney and flue regulations.