Exterior vent chimney for extractor hood

[Jilly]

The builder and I are having conflabs:

 

The kitchen extractor fan exits exactly into the cavity wall off the extension (my design fail!).

 

Sooo, we have fashioned a duct with 100mm Manrose ducting to get round the awkward space, and stuffed insulation round it. (I thought the flimsy stuff could tear).

 

However, I don't want it to exit close to the eaves vents of my precious cold roof under the porch overhang (builder and BC didn't mind but it seems counterintuitive to me). 

 

I want a chimney to duct away from the roof vents. However, I can see that we need it to be insulated (builder doesn't think so) as I think we could get condensation in the ducting. 

 

We are struggling to find a suitable 100mm product which looks good (Conservation Area) and doesn't let rain etc in 

 

Any ideas? It will have to have a total of 5 right angles (2 in the wall). 

[Mr Punter]

If you have a duct running upwards in a cold space, there is a good chance that condensation will form and run back down.  The insulation may not stop this.