which flue option is best? Through the wall, or flat roof

[InTheBeginning2007]

My new combi boiler is going to be installed in an outside cupboard, which has a flat felt roof over wood floorboards. The CORGI guy says to put a longer (1.5m) flue across the cupboard, and out through the 9" brick wall. He also wants to put a plume kit on, although strictly it does not need one.
The other option is straight up through the roof, with a right angle bend outside. He says that the moisture from the plume will cause problems with the flat roof and prefers not to do this, although for appearances and ease of installation this would be the best option.

Which should I do?

 

[simond]

Well, you should not post questions asking technical flue details when we don't know what boiler you are fitting.

As a generalisation, concentric vertical flues through roofs cannot be fitted with 90 degree bends outside.

 

[JohnD]

roofs are for keeping the rain out

making holes in them generally does not improve them.

Especially flat roofs.

 

[gas4you]

Why would you want to put a 90 bend on a vertical flue outside the roof?

The vertical terminal should just fit, strangely enough, vertical on the flat roof