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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Cutting notch in roof beam https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1706555220 Message started by DIYme on Jan 29^th, 2024, 7:07pm

Title: Cutting notch in roof beam
Post by DIYme on Jan 29^th, 2024, 7:07pm

Hi all. I'm wanting to install a bathroom extractor and opting to run the duct through my loft space and out through a hole in the soffit with a new cowl on the exit point, directing the steam away from the house. I can just access the inside of the soffit from the loft as shown here (at last, I assume this is the inside of the soffit :-[)...
[gallery]DIYme/1706554355.jpg[/gallery]

[gallery]DIYme/1706554972.jpg[/gallery]

So what I'm wondering is whether I can improve my access into the soffit by cutting a round notch in the horizontal wooden beam so I can get the ducting past it? So I've done two drawings - the first is the current view of the roof, and the second is showing my question of being able to cut a notch in the horizontal beam (please excuse my hastily drawn images!). I wasn't sure if this would affect the integrity of the roof or impact any building regulations etc?

[gallery]DIYme/1706554522.png[/gallery]

[gallery]DIYme/1706554523.png[/gallery]

Hope I've managed to get my question across with the help of these pics but if any more info is needed please let me know.

Many thanks,
Lee

Title: Re: Cutting notch in roof beam
Post by woodsmith on Jan 30^th, 2024, 8:58am

It not exactly clear from your photos but I don’t think your drawings are correct. Typically the ceiling joists and rafters rest on a wooden “wall plate” which runs on top of the internal wall, the outer wall would not normally have any timber on it at all. It’s possible that the wood you can see is the barge board which supports the tiles. If you Google wall plate and bargeboard you should find loads of images showing you the detail. If space is tight you could run the vent in rectangular section plastic ducting rather than risk cutting something you later regret.

Another thing to be wary of is that soffits are often asbestos and can cause a severe health risk if dust is inhaled. It would be wise to find out what it’s made of before you start cutting it and if it is asbestos then get a specialist firm to replace it.

Title: Re: Cutting notch in roof beam
Post by DIYme on Jan 30^th, 2024, 6:28pm

Thanks for your reply Woodsmith. Apologies for the drawing error. It's hard to work out exactly what's going on in the loft from the restricted view I can get of that area. But I think you're right in that it's probably going to be best to have a tile vent rather than potentially disturb any asbestos in the soffit.

Title: Re: Cutting notch in roof beam
Post by woodsmith on Jan 31^st, 2024, 8:07am

Tile vents are great although they are a lot more work than just cutting a hole. One problem people find with them, because they run uphill, is condensation forming in the duct and then it running back into the fan. I put some insulation around the duct to keep it a bit warmer which seems to help. Best of luck with your project.