The Purpose of a Roof Flashing

When a flue system passes through the roof of a property, the hole that must be cut in the surface will always be larger than the overall diameter of the flue pipe due to safe clearances to combustible materials. For example, a twin wall pipe with an overall diameter of 200mm will typically require a hole in the roof cut to at least a diameter of 300mm… This is where a Roof Flashing steps in.

A Roof Flashing is designed to provide a weather proof seal at this point by covering the hole with a base plate and providing a water tight seal around the flue with the silicone collar.

Generally, Roof Flashings can be separated into one of two types; suitable for tiled roofs or suitable for every other roof type such as profiled, corrugated, felt, wooden and so on.

Tiled Roof Flashings

These Flashings sit on a malleable, aluminium base, designed to be secured beneath the roof tiles for ultimate weather proofing. The silicone cone upper portion will be pre-set to a 20° angle to accommodate the standard pitch of a residential roof. As all flashings are designed to accommodate a range of pipe diameters, the silicone cone portion is simply then cut away to the desired width for your flue pipe.

Non-Tiled Roof Flashings

This form of Flashing features the same silicone upper cone but set at 90° for flat roofs. The base features an aluminium strip around the edge rather than a base plate to allow the product to contour to any roof type, especially handy when it comes to corrugated roofs. It is through this strip that you can secure the Flashing on top of the roof surface and again, as all flashings are designed to accommodate a range of pipe diameters, the silicone cone portion is simply cut away to the desired width for your flue pipe.

Low or High Temperature Flashing?

Depending on the type of pipe being used and distance from the stove, you may select either low or high temperature resistant Flashing. As the hottest point of any system is the connection to the stove itself, it is the distance from this that we judge which tHigh Temp. Flashingype of Flashing you will need:

  • Is your Flashing going to be within 5m of the stove itself? Then you require a high temperature Flashing

  • If your Flashing going to be over 5m of the stove itself? Then a low temperature Flashing will do.

It is a common misconception that using insulated Twin Wall flue means you only require a low temperature Flashing. This is incorrect and the above should be observed as a rule of thumb.

Tip – If you have a particularly steep pitch to your roof, it is advisable to purchase the next size up Flashing to accommodate this.

Glowing Embers supplies leading brands of Flashings and fixing kits to meet the needs of every install and roof type and a range of sealants such as Envirograf Silicone, perfect for sealing external applications.

6 thoughts on “The Purpose of a Roof Flashing”

  1. Hi, Have you got to use twin wall on the silicon roof flashing? Looking to install in garage at bottom of garden so just need a cheap option. Will the flue get to hot and melt it?

    1. This is a very common enquiry and my answer will always be the same; what you save in money using only single skin pipes (rather than the legally required twin wall insulated flue) you will lose in heat loss, poor draw, under-performing stove, rust and fire risk! The heat transferred from a single skin pipe into the flashing can cause it to melt and melted silicone dripping into your garage will cause a fire. Also, being that this is a garage install, the flue system won’t be particularly long which means it may struggle to achieve a sufficient draw, using only single skin pipe will compound this problem as heat is lost from the system due to lack of insulation.

  2. I am wanting to install a wood burner in a wooden glamping pod with a curved roof covered in felt shingles.
    Does the whole of the flue need to be twin wall or can I convert to twin wall close to where it exits through the roof?
    The reason for asking is I would also like to install a water jacket around the base of the flue for producing small volumes of hot water.
    Thanks for your help.

    1. It would certainly be safer in this type of environment to run twin wall insulated flue directly from the stove but you can use a length of single skin stove pipe first and then convert to the twin wall before passinbg through the roof. You just need to be aware of the distances to combustible materials you must maintain which for single skin pipe is 3 x the internal diameter (i.e. 5″ stove pipe must have a clearance of 15″ to any combustibles).

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