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Putting a chimney or flue pipe through a Sedum green roof

What is a Sedum roof?

A Sedum roof is a type of green roof. The roof is designed to be able to take the extra weight of plants, growing medium and water and the plants grow on top of the roof requiring relatively little maintenance. There are about 400 species of Sedums found in the Northern hemisphere. Sedums are a good alternative to grass when making a green roof for a variety of reasons. The plants are often hardier than grass and can survive with less growing medium - so the roof weighs less when wet. They are hardy and suited to the harsh conditions on a roof where there is little growing medium, low water, hot sunshine. A Sedum roof can look very nice indeed and is relatively easy to install.

Putting a flue pipe or chimney through a Sedum roof

Sedum roofs are becoming ever more popular and many customers have come to us wanting to put a twin wall insulated flue pipe through their Sedum roof so that they can install a stove. This is relatively easily done.

Flashings for a Sedum Roof

The flashing for a Sedum roof consists of two parts, the flexible flashing that is sealed or bonded to the waterproof membrane and seals around the pipe and a second rigid cone flashing that allow for a border of pea gravel or pebbles and serves to keep the Sedum away from the flashing and the pipe. Normally the drainage layer and Sedum mats are laid on top of the edge of the cone flashing base and then the pea gravel is used to fill in the gap between the Sedum mat and the flashing cone.

The flexible flashing should always be installed on the diamond, i.e. with one of its corners pointing directly up the roof slope as this stops water pooling against the edge of the flashing. Different waterproof membrane materials require different bonding agents so always tell our technical department the type of membrane being used.

If the waterproof membrane allows it, it can be advantageous to have a raised section where the pipe penetrates the roof so as to keep the water flowing down the roof away from the pipe penetration.

For further technical advice, chimney and flue design and consultancy please contact us on 0800 246 1250

If you would like us to design your flue system then please go to the flue design service section of this site.