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Sounds about right.
You need to make sure that there is at least one back draught shutter (non return valve) in the duct line.
I would also strongly recommend that the vent pipe does not not go vertically. The vent pipe will be venting warm, humid air to cold air so condensation is an issue. This is normally not a problem as the condensation will sit where it forms and eventually evaporate, if the duct is vertical gravity will pull it down into the extractor unit which can cause problems. Because of this you are much better off having a horizontal run of ducting in the line.
It is also critical to make sure that the flashing round the cowling that sits on top of your roof is installed properly.
Basically there is no reason why you should not be able to do this but if it's not done properly you could be causing problems for yourself further down the line. These potential pitfalls are the reason why most builders will advise you to have the vent going through a wall or pitched roof rather than a flat roof.
Bobbo-
Excellent advice thank you! I think venting through the roof is the only option on this occasion as there's a rooflight in between the extractor and the external wall. I'll bear that all in mind and work out the best way forward. Thanks again
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Excellent advice thank you! I think venting through the roof is the only option on this occasion as there's a rooflight in between the extractor and the external wall. I'll bear that all in mind and work out the best way forward. Thanks again
Quincy
I imagine that I need:
some vent pipe
flat roof ceiling cone
4" cowl
but then other accessories/finishing bits are a bit of a mystery...you were very helpful regarding a leak at the front of my house a while back. If you have any suggestions/guidance then I'm all ears!