Two flat vent channel ductings through one external hole

[kriskross]

Hi All

Is it fine to run two rectangular 204x60 channel ductings (one on top of the other) through a single external hole as shown in the enclosed drawing?
Drilling a second hole is not possible.
The two flat channels each 204x60 would go through single rectangular hole 204x120 and would be covered by one 6" external plate louvre grill on the outside.
On the inside, one ducting would be connected to the bathroom extractor fan and the other to the cooker hood.
This seems a much better option than using Y or T connector with single ducting pipe through the wall.
Do the building regulations say anything about similar solutions?

Thanks
Kriskross

 

[big-all]

6" 153mm ?? hole 210mm??

 

[Deleted member 174758]

Yes. I have done just that sort of thing a number of times. Just make sure you seal around the ducts and provide some extra support for the vent plate as it is nominally smaller than the 204 x 120mm of the combined vents. A 250 x 250mm (or 300 x 300) vent plate with a fly screen would be better, though. Note that you can get back draft dampers for rectangular trunking and with those you don't need a wall grille with gravity flaps

 

[kriskross]

6" 153mm ?? hole 210mm??

Thanks for noticing. I meant 9" (250mm)

 

[kriskross]

Yes. I have done just that sort of thing a number of times. Just make sure you seal around the ducts and provide some extra support for the vent plate as it is nominally smaller than the 204 x 120mm of the combined vents. A 250 x 250mm (or 300 x 300) vent plate with a fly screen would be better, though. Note that you can get back draft dampers for rectangular trunking and with those you don't need a wall grille with gravity flaps

I will need to install the grille to maintain the same appearance as the other vent covers in the building.
Are the back draft dampers necessary or recommended even if a wall grille is installed?

 

[big-all]

Thanks for noticing. I meant 9" (250mm)

ok excellent we all get confused with conversion from metric to imperial i am no exception

 

[Deleted member 174758]

Are the back draft dampers necessary or recommended even if a wall grille is installed?

Unless the outfall vent is in a sheltered area without some form of gravity back draft control (which is normally provided by a standard 150mm cover) you can get wind whistling (actually) through your ventilation ducts causing noise and drafts