Tom Posted October 13, 2022 Share Posted October 13, 2022 Afternoon all There's an outside chance, if the stars align and with a following wind, that work finishing our roof might begin in the next few weeks. I'm now thinking about the opening I need to make in the roof for our woodburner flue. The ceiling is vaulted and the roof make up from outside-in will be: corrugated tin-felt/batten-composite PIR panel (metal clad PIR, 150mm thick)-rockwool(200mm)-plasterboard. Can anyone advise what size hole I need to make in the composite panel to take the flue? Does 300mm sound right? If we are some way off actually installing the flue, what would you suggest we do in terms of preparatory stuff while the roofer is up there? Make the hole in the composite and just felt/batten and put the corrugated over - to be finished at a later date, or actually make the hole proper through the felt and corrugated tin etc? Is there a grommet or something that goes in the hole through which the flue passes and could this go in now? Guess I'm just trying to get an idea of what we can do now to make it simpler/cheaper when we actually come to install the flue. Thanks all! Link to comment Share on other sites More sharing options...
ProDave Posted October 13, 2022 Share Posted October 13, 2022 A 150mm twin wall flue is usually somewhere in the region of 250mm diameter, and then there is the manufacturer specified "distance to combustible material" usually at least 50mm, so it's going to be a very minimum of 350mm. But check with the manufacturer of the flue you intend to use for actual dimensions. 1 Link to comment Share on other sites More sharing options...
Tom Posted October 13, 2022 Author Share Posted October 13, 2022 Thanks Dave, is there a grommet? I'm struggling to see how the penetration is made through the various layers to ensure it is all air tight. Link to comment Share on other sites More sharing options...
ProDave Posted October 13, 2022 Share Posted October 13, 2022 the flue manufacturer will make some sort of flashing kit to suit their pipe and different types for different roofs. Link to comment Share on other sites More sharing options...
Tom Posted October 13, 2022 Author Share Posted October 13, 2022 OK, but where it passes through the internal plasterboard and then the composite panel, if there is a 50mm gap all around is this sealed in some way? Link to comment Share on other sites More sharing options...
ProDave Posted October 13, 2022 Share Posted October 13, 2022 Have a look at something like this https://www.flue-pipes.com/pipe-150-mm.html you will see the typical range of fittings available including flashing kits and various finishing plates to cover the hole in a ceiling etc. 1 Link to comment Share on other sites More sharing options...
Hastings Posted October 13, 2022 Share Posted October 13, 2022 Have a look here https://www.schiedel.com/uk/products/additional-ranges/protect-box/ I have just installed a 150mm thick Ignis Protect by them, for a wood stove flue going through a 150mm insulated stud wall at 45 degrees, but it isn't fully airtight. Good enough for my build (a nearly airtight house conversion). I heard about it from someone else on this forum but then my supplier also came up with it as they supply the Schiedel flues. 1 Link to comment Share on other sites More sharing options...
saveasteading Posted October 13, 2022 Share Posted October 13, 2022 One of these. Needs to be suitable for high temperatures so it is likely to be red, but worth asking for high temp black if possible. They each have a range of diameters they can be cut to. Choose the biggest as that allows more tolerance and best fit on the pipe. On a steepish roof the silicon skirt has to distort from slope to vertical. I have known plumbers make a right mess of installing these, so don't assume the skills are there. Needs roof screws and mastic tape. In answer to how much prep to do...it depends if you think you or the roofer will do the better job. I would us an old fashioned plumb bob to get the hole in the right place, then a vertical pilot hole. NB the circular pipe requires eliptical holes through the roofing materials. .or oversized circles. 2 Link to comment Share on other sites More sharing options...
Tom Posted October 14, 2022 Author Share Posted October 14, 2022 Great, thanks everyone, got a clearer idea of it all now Link to comment Share on other sites More sharing options...
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