Kit for an External Black Flue for a Garage

The distance from the exit of the stove till the vertical flue outside (usually 5 - 7,5 cm from the wall)

Type of Wall support 

Normally the wall supports with a 50 - 70mm distance wall-to-flue are taken. To pass an overhanging roof, you can choose other distances.

Number of Wall supports

This depends on how many meters the flue goes along the wall. 
We recommend to use a wall support  every 3 meter along the wall.  So for a gardenhouse, normally one wall support is needed (plus one base support bracket).

Flue Height for Sheds or Garden Houses:

1. Minimum Total Height:

   • The flue should ideally be at least 4.5 meters from the appliance to the top of the flue cap for optimal draft.
   • However, in smaller structures like sheds or garden houses, a shorter flue of around 3.5 meters may be sufficient if the flue is well-insulated (e.g., using twin wall flue pipes) and the draft is adequate.

2. Above the Roofline:

   • The flue must extend at least 1 meter above the highest point of the roof to ensure proper smoke dispersion and prevent smoke from re-entering the building.

3. Flat or Felted Roofs:

   • If the shed or garden house has a flat or felted roof, the flue must terminate at least 1.8 meters above the roof surface to maintain safety from combustible materials.

4. Distance from Nearby Structures:

   • If the flue is within 2.3 meters horizontally of a wall or roof, it must terminate at least 1 meter above the highest point of that structure.
   • If the flue is more than 2.3 meters horizontally from any structure, it must terminate at least 600 mm above the roofline.

Additional Considerations for Sheds/Garden Houses:

• External Flues: If the flue runs externally, ensure it is properly supported with wall brackets every 2 meters.
• Draft Issues: Shorter flues in small structures may sometimes struggle with draft. To improve performance, ensure the flue is insulated and avoid excessive bends (keep at least 80% of the flue vertical).

Chimney Heights and Termination

Simple rules

Within 600mm from the ridge
The flue has to end minimum 600mm above the ridge.

More than 600mm from the ridge
The distance between the cowl of the flue and the adjacent roof/wall/structure should be higher than 2.3 mtr. 

For the height on the roof this means:

All the rules

The minimum chimney height recommended for minimum performance of wood burning and multi fuel appliances is 4.5 m from the top of the appliance to the top of the chimney. In practice you 3.5m is often enough.

The distance between the cowl of the flue and the adjacent roof/wall/structure should be higher than 2.3 mtr. 

Within 600mm from the ridge: Flue has to end minimum 600mm above the ridge.

The diagram below, taken from Document J (building regulations), shows the minimum flue discharge heights and positions for all wood burning and multi fuel applications.

In some cases, particularly when chimneys are towards the bottom of a sloping roof or at the eaves, it may be necessary to increase the chimney height above these minimum mandatory requirements. The reason for this is to clear pressure zones created by wind hitting the roof and nearby structures, like trees, which may interfere with the up draught required by the appliance or fire.

The maximum freestanding stack height above the roof for a traditional masonry chimney is 4.5 times the narrowest horizontal part of the chimney.
In the case of stainless steel system chimneys, the manufacturer’s installation instructions should be consulted; however in most cases it will be around 3 metres. This measurement is taken from the last point where the chimney stack passes the through or past the edge of the roof up to the chimney capping or termination. Tall chimneys may need bracing, always consult the manufacturer for advice. 

For buildings with flammable roofs such as felted, thatched, or shingle roofs the flue or chimney the regulations are different. The flue or chimney must terminate at a minimum1800mm above the combustible surface.

There are 2 types of cap to choose from:

Rain cap
Will keep vertical falling rain out of the flue. In case of side winds, rain will enter the flue. In case of a flue outside this is less of a problem, as it will not floote into the house. 

All weather Cowl
Keeps rain out of the flue. Also blocks downwinds from entering your flue. Downwinds come from higher objects in the vicinity (up to 10mtr), and without this Cowl they will blow the smoke back into your house.