cutting rectangular hole in upvc fascia board

[jackfoley]

Hi,

I am installing an extractor fan in the ceiling void above my bathroom.

I plant to use a rectangular felxible ducting 110mm by 54 as this will fit btw the roof and the inner wall through to the soffit.

I'd like to know what is the best way to cut a rectangular hole in the upvc fascia board, jigsaw or hand saw?
Also the fascia is about 15cm wide. is it ok to cut a hole in it?
Many thanks

 

[cmother1]

I'd use a sharp padsaw blade. Drill 4 holes at the corners and saw gently. You haven't got a lot of spare to play with , but you should be OK. Biggest problem is avoiding roof timbers. If you can't work out where they are from outside drill a small test hole and put a bent probe wire up it.

 

[^woody^]

I was not aware that you could get an external grill for this flat ducting?

 

[jackfoley]

http://www.wickes.co.uk/Hit-and-Miss-Vent/invt/713016

was thinking of using this to cover the duct.

but i still have the backdraft problem. Do any of the extractors have a backdraft shutoff mechanism?

 

[^woody^]

Well that looks like it will impede the airflow from the duct and so limit the extract rate of the fan.

An outlet really needs to be as open as possible to let the air out

You can get in-line anti-backdraught shutters, but again, I don't think they come in flat ducting range, normally they are for the round duct

Some fan units have them built in too

 

[jackfoley]

Woody,

The horizontal fascia is about 15 to 20 cm wide. Would it be structurally safe to drill a 102 mm diameter hole in this? Thats why i though of using the rectangular ducting, it would mean cutting off a smaller size hole in the fascia rather than a circular one.
The horizontal upc fascia slots into the vertical one but i can't figure out how many brackets there are on the length so thats why i though that cutting a big hole in it could make it unstable.
From outside it looks sturdy.

 

[cmother1]

Your soffit (horizontal fascia) sounds as if it's easily wide enough to drill a hole. If you've a sharp 102mm hole saw it should be a piece of cake - just don't go mad with it. I'm not sure what you mean by 'brackets'. If you mean the fixing centres for the soffit then you should be able to see the heads of polypins sticking out of it usually at 40cm intervals. If so aim for the middle of one of these intervals for your hole. Do you know if there's timber beneath the soffit? If there isn't the job should be even easier. Like I say, just don't go mad.