Expert: Bruce E. Johnson - 6/18/2009

Question
QUESTION: From Bruce,

"Hi again Billy, how hig you go up on the existing roof shouldn't be an issue but I don't know how your existing roof is framed so I can't make a qualitative response in that regard.  Also, I'm not sure how you are going to frame the new roof, 2x8?  Mastic, in the context I use it in this answere, is a rubberized roofing cement with fibers in it.  It can be purchased in five gallon buckets and applied with a trowel to seal the flashing to the top of the new roofing and seal the old roofing to the top of the new flashing.  Yes Simpson makes all kinds of clips and hangers for your application, they make a skewed joist hanger that you can adjust to the angle you need.   I hope this information helps, feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com"

Hey Bruce,

    I don't belive I will need to go too far up the roof to get a decent slope maybe 2' past the wall if that.  I was told to use 2x12s for the rafters and put them 12" on center, do you think that might be overkill?  The roof is at an angle so the longest span is 21' and the shortest is 13'.  My existing house was built in 1993 and is two stories.  I'm attaching the patio cover to the roof of the lower story.  Another question I had was when attaching my beam to my 3 columns on the patio cover do you think I should bolt them together or use Simpson SDS screws?  Simpson makes two column caps for 6x6 columns one for bolts and one for their SDS screws.  Sorry if this message is fragmented I don't get allot of time behind a computer and I'm trying to send this to you before I start work.  Thanks again for your time.  If it wasn't for this website I would be stuck waiting for a friend of a friend who is a contractor but pretty flaky.

Billy

ANSWER: Hi Billy, I prefer the bolted buckets but if you are going to enclose the room then the SDS screws will be easier to cover over later down the road.  2x12 is necessary for long spans, in fact it's a little puny for 21'..you will want to add a row of solid bridging between the rafters at mid span.  For your sleeper on the existing roof you need to make sure that the sleeper width is equal to the cut rafter width.  In other words, when you cut an angle on a 2x12 the angle cut is longer than the 11 1/2" rafter height.  So you may need to double up two 2x8s to make the connection solid between the new rafter and the sleeper.  Also you should strap the sleeper to the existing rafter if you have access and then clip the new rafter to the sleeper.  This will guarantee uplift protection during a wind storm. I hope this information helps, feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Bruce,
"2x12 is necessary for long spans, in fact it's a little puny for 21'..you will want to add a row of solid bridging between the rafters at mid span."  Should I use 2x16s?  I have not recieved the 2x12s yet so I could change my order.  I will double check the length tonight to see excatly what it is.  When you say solid bridging between rafters is that like blocking between joists?

Billy

Answer
Hi again Billy, yes the solid bridging or in some cases x bracing between joists keeps them from twisting and gives the structure an internal brace to help keep it from sagging somewhat also.  I hope this information helps, feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com