Re: common ducting
You also can't share ducts at the moment - legislative separations, both vertical and horizontal, make it quite a big hole to lay them all at once (I've just done it for a new build).
There is some logic here as well - you don't really want a gas leak to run along a duct that actually enters a building - so gas ducts terminate externally, with just a pipe entering the building (and a metal pipe by that point, so that a fire doesn't cause the gas main to rupture).
Biting the hand that feeds IT
