Expert: Bruce E. Johnson - 7/6/2010

Question
QUESTION: I am adding a room over my back deck 8x10 and I want to place the roof under the existing gabel which is about 104 inches from floor to bottom of soffit , what pitch should I use to get good run off will 2x4 's placed at 16 inch on center work for rafters .Thank you Carl

ANSWER: Hi carl, I guess it depends more on what kind of head room you want at the outside of the room.  If 104" is your uppermost starting point then you subtract your 2x4 rafters (which is pushing it for an 8' span 2x6 would be preferred) from the 104" and you are down to 100"..A minimum head room height is 7' or 84"..subtract that from the 100" and you get 16".  An eight foot rafter rising 16" is a 2/12 pitch.. which will work for rolled roofing installed at maximum coverage. I hope this information helps, feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: HI thank you for your help,Bruce. I am thinking of using a tin roof or something like that , would this be acceptable and just insulate. And you mentioned 2x6 for rafters , will this give me more strength or if I placed the 2x4s at 16 inch on center will this be strong enough....Thanks   Carl

Answer
Hi again Carl, like I said the two by fours will probably work but may sag over time..The spacing helps a bit but a two by four with an eight foot span will sag under it's own weight after a while.  A two by six installed with the crown up will span the eight feet.  sincerely bruce e johnson