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Building Homes or Extensions/Tie in patio cover to existing roof

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Expert: - 4/1/2010


Question

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I want to build a patio cover that is 10'x24'.  Struggling to determine if I should do a slant off my existing 8/12 hip roof or if I should do a gable end and have a couple of valleys.  Should I choose to go the slant off route, how high should I go up the roofline to tie in and should I just remove the necessary shingles and sheathing and tie the new rafters into my existing trusses?  Furthermore, will I only need post on the outside edge of the patio along with 2 2x12's as a beam or will I also need posts up close to the home.  Should I go the gable end route, how do I know how long the rafters need to be enable to keep the same slope as I have now?  Thanks

Answer
Tim, let's solve the easy part first.  

To discover the existing pitch - I like to use a 4 foot level.  Put one end on the roof, level with the bubble, measure down to the roof at the other end.  You might do this several times to verify consistency.  It looks like about a 6 in 12, so the tape might read about 24", divide by 4 to give you 6" in each foot.

You have a hip roof.  I would be tempted to extend the patio to the left edge of the house and bring out the patio cover in line with the left edge of the roof which would give you a single valley on the right.  I would suggest doing it with a footing at the perimeter to make it possible to enclose the area some day.  I know you do not intend to do so, but I can't tell you how many questions we get asking about closing in the patio and making it part of the house.

If you still want to cover the existing patio only, I prefer the gable type tie in, but with either a hip or gable end.  Yes, it can sit on the existing roof sheathing.  The single shed gives a difficult flashing condition on each side.  The structure doesn't require columns at the house  side as the loads are transferred to the top of the stud wall.  

Dan Griffin

Expertise

I can answer almost all questions related to the total construction process. My expertise is in commercial construction, though I can field most any residential question. I have hands on experience in concrete, heavy equipment, masonry, all phases of carpentry, interior finishes, and I am fairly strong in mechanical and electrical.

Experience

I have over 20 years experience as a commercial carpenter and commercial construction superintendent. I have another 20 years experience in facility management for a major school district.

Organizations
My favorite hobby for he past 12 years has been singing bass in a The OkChorale men's barbershop chorus and the Mature Moments quartet.

Education/Credentials
I hold a Bachelor's degree in English and Math. I have completed many continuing education hours in the building trades. I hold a Master Carpenter card from the AGC, Associated General Contractors.

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