Installing a flue through a flat roof

Installing a flue through a flat roof step by step

Complete the installation step by step and check each phase before moving on. This sequence ensures optimal draft, waterproofing, and safety.

• Determine the route directly above the stove. Keep it as short and straight as possible, because every bend reduces the draft.

• Choose a double-walled insulated flue pipe with the correct diameter according to your appliance's manual.

• Create the roof opening and install the certified flat roof flashing, neatly waterproofed with a flashing plate or collar.

• Finish the roof penetration with a storm collar above the flashing, preventing rainwater from running down the pipe.

• Extend the flue to the required termination height and fit a suitable rain cap or draft cowl.

• Check the locking bands, the stability and the distance to combustible materials for flue pipes, and then test the draft.

Checklist for a flat roof flue penetration

• Required termination height achieved above the roof surface and nearby obstacles

• Certified flat roof flashing that matches your type of flue

• Waterproof flashing plate or EPDM collar with storm collar installed

• Double-walled insulated flue pipe above the roof

• Sufficient distance from skylights, roof domes, and the roof edge

• Stable mounting to withstand wind and storms

Draft, waterproofing, and insulation in practice

The correct diameter is the foundation of proper operation. Always follow the diameter specified in your stove's manual and do not reduce it. A flue that is too narrow restricts the flue gases and weakens the draft, especially over a longer vertical length.

The draft is created by the difference in height and temperature within the flue. A straight vertical route through a flat roof facilitates this process. Therefore, keep the termination free from high walls, domes, and roof extensions within a few meters.

Waterproofing is the most sensitive point on a flat roof, as water tends to pool on a flat surface. A proper flashing plate or collar with a storm collar keeps everything watertight. In our guide on roof penetration for a flue pipe, you can read how these components work together.

The insulation of a double-walled pipe keeps the flue gases warm, which improves the draft and limits condensation. Above the roof, double-walled pipes are therefore the standard. If you are debating between the roof and the facade, compare the options in flue pipe through the roof or through the wall.

Wind and surroundings play a major role with a flat roof. A termination that sits too low behind a wall ends up in a zone of high and low pressure. This disrupts the draft and can push smoke back down. An anti-downdraft cowl limits this effect.

Distance to roof edges, skylights, and obstacles

Keep the termination at a sufficient distance from roof edges, skylights, domes, and air inlets. Flue gases that exit too close to a window or ventilation opening can be drawn back indoors. A clear position on the roof prevents nuisance and odor complaints.

If there is a taller building, a roof extension, or a parapet nearby, you should raise the termination accordingly. The flue gases must exit above the pressure disturbance zone. This ensures the draft remains stable, even with shifting winds.

Standards in Belgium and the Netherlands

The exact rules vary by country and even by municipality. In Belgium, the NBN standards serve as the practical framework for smoke extraction, and your region or municipality may impose additional conditions. In the Netherlands, national building regulations and the municipality determine the requirements together.

For a pellet stove or wood stove, it is also essential that the flue pipe, the roof penetration, and the termination are compatible. You should never mix a certified system from one brand with loose parts from another. This keeps the warranty and fire safety intact.

When in doubt, check with your municipality and insurer regarding the required termination height and distances for your situation. Also check out installing a flue through a pitched roof if your roof is partially sloped, and the common mistakes with flue pipes to prevent problems beforehand.