Moisture sealing and extraxter fan into a roof

[john_7]

I am to install an air extractor in a bathroom over a shower. The hole needed to insert the unit will leave a 3-4 mm gap most of the way round. There is no information provided by the extractor makers on how to seal this gap to prevent moisture entering the roof from the bathroom. Indeed looking at a wide range of extractors no one appears to take this into account. Speaking to them have no real idea of what to do and say this hasn’t been asked before.
Given that a the much smaller class 1 lights have seals to comply with regulations I am amazed that class 1 extractors don’t have to comply with the same moisture requirements. Does anyone have ideas how to seal the fan so it can be removed if need be without resorting to a bodge of foam or neoprene tape?

 

[foxhole]

Need more details, make ,model, I have not seen or fitted a fan that left a gap to fill.

 

[john_7]

Its a Airflow Icon 30 Extractor

 

[foxhole]

The unit overlaps the surface [ceiling or wall] all round when fitted leaving no gap.

 

[john_7]

Thanks for reply.
My confusion is the class 1 lights I have also have a smooth finish that should create a close fit to the plasterboard. But to create a seal against moisture and air movement they come with a gasket.
The Ion will have a gap between it and the hole cut to insert it through the cealing of 2-3mm all round. It has to as there is a moulding protruding (you could shape the hole to take it and reduce the 150mm hole accordingly to fit) . Now my confusion is if the class one lights need a gasket to comply with the covering regulations why to creat an equal level of seal doesn’t an air extractor?
In my case the ability to fit the Ion to an uneven ceiling is unlikely to be needed but if it were there would be a gap created which the class one lights tell me to add some silicon to maintain a good seal between the gasket and ceiling. Equally looking at the Ion there really isn’t going to be as good a seal, there can’t be, as made with the class one lights used in the same shower area. If the seal created by the Ion is enough to prevent air/moisture moving between bathroom and roof why do the lights need better ones to do the same?

 

[foxhole]

Lighting seals are to protect lamp and power from moisture, they seal against air movement as part of this but it's not the purpose of the seal. Fan motors/power are sealed against this since they have to move the damp air.
No comparison really as they serve very different purposes.

 

[john_7]

Sorry its not protecting the fan I'm intrested in. But its air/moistuer moving between the bathroom and roof I am looking to prevent, I thought the building and IEE regs say you have to seal any gaps to prevent movment (and fire) of moisture. With laps you can but my concern is with fans you can have a problem doing so around the fan and its hole into the cealing.
I had a lot of problems, old house, no eaves and difficult to get venterlation in the roof. Preventing moisture transfering has worked (it took a lot of work to seal every gap so I'm not keen to introduce any new ones if I can find a workable way to do so.

 

[foxhole]

Sorry don't understand there are no gaps between the fan face plate and the ceiling, it fits tight too it.

 

[^woody^]

There is either a foam gasket or you just silicone the cover plate to the ceiling

Even with out this, the plate goes tight against the ceiling and there are minimal/no gaps

There is no moisture going behind the plate as it it all going up the fan duct!

And whilst fires in a bathroom are very uncommon, if there was one the flame is going straight up the 100mm hole and duct and then the duct will melt in any case. So you have no worries about a few micron gap around the fan plate

 

[john_7]

The idea of a thin silicon layer is a good one I had thought of a silicon seal but the usual one could be difficult to get a ventilator out again but a thin over all over lacks strength.
I thought I had lost the plot but had the below pointed out to me pointing at sealing anything breaking the barrier between, esp. bathroom, the building and roof. I know few building trades are implanting this, as I found after a rewire with no effort to seal there work which was picked up by my surveyor. It would look to me its being ignored by extracter makers as well!

6.12 To avoid excessive moisture transfer to roof voids gaps and penetrations for pipes and electrical wiring should be filled and sealed; this is particularly important in areas of high humidity, e.g. bathrooms and kitchens. An effective draught seal should be provided to loft hatches
to reduce inflow of warm air and moisture.

The Building Regulations 2000

 

[foxhole]

I think you may have lost the plot, as the fan mounting offers no gaps as mention in the regs.