Advice on deck roof addition please

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Old 04-20-14, 05:25 PM
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Advice on deck roof addition please

I just finished building a low level deck and now want to build a gabled roof over half of it. The roof will extend out 90 degrees to the house as in the attached pic. The small shed roof over the bay window will be cut out and tied back into the new roof.

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Each of the 2 side beams perpendicular to the house will be supported by 3 posts (ends and midpoints, numbered in the above figure)

A cathedral ceiling requiring no rafter ties will require a ridge "beam" fully supported on each end (a center post [#7] at outside gable and the house wall for the house-side gable). If not for the window header underneath where I would tie the the beam into a pocket in the wall, this is the design I would use. One way around this could be to lag the 2 rafters abutting the house into wall studs across their length, reducing the load at the end of the ridge beam. The alternative is to not use a load bearing ridge beam, but a ridge "board" instead and rafter ties to counter the lateral force. I would like to hear opinions on this.

Next issue - posts. The deck is attached to house with a 2x12 ledger. The opposite end is on 6x6 posts with footings or almost directly on bedrock (lower left corner in pic). Double 2x10 or 2x12 rim joists all around and similar beam across middle 6 ft from house. Question: can that ledger support that end of roof structure, and would the underlying deck beam 6 ft away contribute to that support. It is possible to provide concrete footings under posts 1 and 6, but that's not happening at post 4 for obvious reasons. Can I lag posts 1 and 4 to wall studs also?

Final issue: How important is it to have this structure anchored to the ground. I live in Alabama and we do get some winds during tornado seasons. I can sufficiently anchor corner posts 1 and 6, but not the other corners at posts 3 and 4. The corner under post 3 is sitting almost directly on bedrock, and I'd have to drill and pin a footing there if possible.

Any thoughts are appreciated.

Scott
 
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Old 04-20-14, 08:09 PM
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Too many questions to accurately keep track of, but here are some thoughts:

1. You may well require the services of a professional engineer to properly design the roof structure for you. Most local codes will require stamped plans to be submitted when you apply for the building permit.

2. I don't think I'd trust the existing house's wall, and certainly not a deck ledger, to support any part of the roof structure. Adequately-sized and anchored corner columns would be much better. Your engineer can work out the details for you.

3. The two columns closest to the house could be used to support a transverse carrier beam, which in turn could support a column stub up to the ridge beam.

4. On more than one occasion, I've seen excessive lag-bolting make splinters of conventional 2x wall framing members. Do that enough times in enough locations, and you'll compromise a wall's integrity.
 
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Old 04-20-14, 08:34 PM
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Column stub? Are you referring to something like the red post depicted here:
 
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Old 04-20-14, 08:55 PM
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Yes, and with the carrier beam designed to adequately support it without deflecting substantially.
 
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Old 04-20-14, 09:10 PM
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Perhaps the same could be done at the other end and between the middle posts (2 and 5)?
 
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Old 04-20-14, 09:26 PM
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Properly-designed and constructed members would work at those locations as well. Make sure your engineer designs the roof to resist uplift, too--the last thing you want to see is the entire structure cart-wheeling across your backyard in a heavy wind.
 
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Old 04-20-14, 09:52 PM
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Thanks for the advice. I guess can remove decking around post #4's location a dig a footing underneath.

That still leave the opposite corner under post #3 sitting on rock. Perhaps 3 of 4 corner posts anchored in footings is sufficient? The only other solution I can think of is to drill into the rock at that corner, epoxy rebar into the holes, then pour a concrete pier around the exposed rebar as a footing.
 
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Old 04-21-14, 05:05 AM
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While you can cheat some with decks once you add to the load you have to have a suitable footer down to the frost line to support the load!
 
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Old 06-04-14, 07:15 AM
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I'm back with my final design and want to run a few questions by you guys if you care to offer your wisdom.

I have decided to place the 2 posts nearest the house inside the house wall behind the siding and directly on top of the floor sill and house footings.

1) For the transverse beam/column stub option described by Bridgeman45, I assume that transverse beam would have to rest on top of the perpendicular headers coming out of wall. I'm not sure this would work, as a) the beam height would extend above rafter line and b) transverse beam is not directly over post.

2) Going with the more straightforward design using rafter ties/ridge board, I was planning to use continuous header beam around perimeter on 3 sides, but not next to house. Am I correct that the header across outside gable end counts as the first rafter tie and then conventional rafter ties (2x6s at 1/3 roof height) every 4 ft to house and would the last one need to be tied to final rafter pair abutting house?

3) For the 16ft headers perpendicular to house supporting roofline, 2x2x10 or 2x2x12? 4x4 or 6x6 center post? Would that center post need to extend to bedrock underneath deck or would mounting on deck surface suffice? This will be screened porch.

4) Should I use PT rafter ties? Plan is for PT wood everywhere else.

Thanks
 

Last edited by Squindle; 06-04-14 at 07:50 AM.
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