I have had a new single story extension built to first fixtures; this includes a new kitchen area. Building Control (UK), will not sign off the extension until an extractor hood is fitted with external ventilation.

To give an overview of the issue, the location of the Cooker hood is to be located on an external load-bearing wall, which is supporting a steel RSJ beam, because of this I am unable to place the ducting straight out of the wall, or out through the ceiling above. Therefore, I plan to use rectangular flat ducting to hide behind the cornice and come out at a different location along the wall.

My main concern is the height of the cabinet means the ducting will come out approximately 20cm (2 bricks), lower from under the eaves and directly centre between the joists.

I would ideally like to have the vent come out higher up the wall so the cabinets can sit higher, it will then mean that it will only be 10cm from the eaves.

I have considered boxing in the ducting so it protrudes further out than the guttering but this will be unsightly.

In the UK, is there a minimum distance the vent can be to the eaves/guttering and joists?

Any guidance or other suggestions would be a great help.

  • Watch out how much ducting you have for kitchen exhaust, there is no good way to clean it, overtime grease buildup will cause fire, or other unexpected issues (grease leak). – Tyson Apr 25 '18 at 11:40
  • Tyson, thanks for the response. Approx a meter in length with two corner joints. This would all be easily replaceable apart from the ducting through the external wall. I was thinking adding a fire stop collar before it enters the wall, as the builders have installed fireboard in the ceiling bellow the RSJ and also down the supporting wall. Do you foresee any issues with the vent being so close to the eaves? – 5202456 Apr 25 '18 at 11:49
  • I don’t know UK building codes, so I have no idea. Moist greasy exhaust will cause greasy buildup to accumulate on the inside of ducts. It can be fuel for fires, it can leak out of the duct if it finds a way, and it can smell bad. The instructions for your hood will include specific do and don’t instructions, be sure to pay attention to those. If the inspector has already denied you once, I’d check your plans for this with that very code enforcement office before you install this. – Tyson Apr 25 '18 at 12:51
  • Nothing mentioned in the instructions about proximity or location of external vents but I will have to ensure the ducting will allow the correct volume of airflow. Inspectors have not yet had any issues with the work carried out so far, just they need to see the venting before they will finally sign the build off. – 5202456 Apr 25 '18 at 13:10

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