I want to build an extention to my house.height of my house is 7.2m,roof 30 degree,width 9.m house facing xxxx. Q,1 can i build a single storie build at the back of the house with a chimney.Q,2 if yes how far should the chimney be constructed away from the house,what height,so as not to get a backdraft.height of extention roof is xx distance between house ridge and extention ridge xx