External extractor fan on roof

B

BuildingNovice

We are thinking of buying a ventilation hood for the kitchen extension and ducting it upwards to our (pitched) roof.

The external extractor unit that will sit on the roof is something like 25" wide x 29.5" high with a vertical depth of 10". It's fairly large and I wonder if there may be a planning permission or building regs issue with it.

We have planning permission but the drawings did not show such a unit on the roof.
 
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My experience of cooker extractors is an electric fan unit directly above the hob with ducting to the outside.

I have not the first clue what you are describing regards a large unit sat above the roof tiles.

Why can you not install the bulky unit above the hob as opposed to on the roof tiles? :confused:
 
noseall

What you describe is an internal fan - you can also place the fan in a roof void (inline) or place it on a roof/wall (external).

As far as I can tell, the reason for having external is noise reduction, and I also understand external fans can be more powerful (higher cubic metres per hour), but not sure why.

Externals maybe more common in the US; the hood/fan I am buying is US made.
 
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The profile could be the same as that of a velux window, which do not "normally" require planning permission... unless you're within a conservation area, listed building, etc... However, I seem to remember the planning department saying these type of installations would only require planning permission if they project above the roof pitch more than 150mm.

You may be better off checking and having it confirmed with your planning department.
 

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