New Roof over Deck

Hey Everyone,

I'm looking at a big spring project.. I built a pretty obscenely big deck over the last year and a half, and am looking to build a roof over the middle platform to make it more comfortable during the summer heat and other weather. You can see the relatively finished deck project below, with some fun ones as a lead in!

The next image is my CAD model of what I'm envisioning for the gable roof. To start, I am hoping i can get a gut check on my framing materials as i have gotten drastically different numbers from the few sources i have contacted. The next image lays out the major structural elements: Ridge beam, side beams, front beam, and rafters. The designed pitch is 6/12.

What does everything think? Am I drastically overbuilding or under building this thing? I should mention I live in Minneapolis, MN.

Let me know if you need any further information. I have plans to increase footing size and have some other questions but this would be a great start.
Thanks for any guidance!
Gavin

 

One of the main reasons I want the roof is to cover the middle platform which is used for the TV as shown below. We use an indoor tv that we just run between the living room and the deck wall mount, but it gets too sketchy if there is rain on the forecast.

 

You really cannot get the best advice on a project like this from people over the internet. Something like that needs to be engineered, plans need to be submitted to your building department, and inspections made. Free advice isn't going to cut it.

That being said, you have snow loads that will prohibit the type of roof you have drawn. At a minimum, you will likely need scissors trusses to resist the outward thrust. An open concept is possible if you have a ridge beam, but that requires engineering too. And finally, adding this to an existing deck is not straight forward. Some of it will likely need to be torn off and reworked. The connection of the upper structure with the lower structure must be engineered to withstand uplift and sheer forces.

 

I do agree that advice on the internet should be taken with a grain of salt, but as I mentioned, I sat down with 3 different design consultants that gave me vastly different advice. This plan represents the most conservative parts of each plan. I would find it hard to believe someone on the internet has not built a roof of this rough dimension, with similar vaulted gable style. I will be making a formal plan and submitting for permits, along with inspections from the city, similar to my deck project.

Do you have any formal information on the snow load requirements with respect to ridge beam designs? What I have drawn up is in the ridge board configuration, but I have read and heard that if you use metal strapping from rafter to rafter spanning the ridge beam/board, this adequately ties the rafters into the ridge beam. Lastly, the ridge beam is supported on each end, unlike a true ridge board configuration.

With respect to the footings and tying into the existing deck, luckily I ran those two 6x6's straight down the footings. Unfortunately, the footings are not adequately sized for the load of the roof plus deck. The initial plan that the city has verbally signed off on is to put a new footing in about 1.5 ft inward of the two posts on the existing deck beam (2 new footings). Footings are for wind uplift and to prevent frost heave (to my best knowledge), so its not about weight or number of footings, its about the surface area preventing that uplift. In this case, if you take the existing footing surface area, plus the added footing surface areas, it will exceed a single footing of adequate diameter by about 30%.

I should mention I'm a mechanical engineer, but I haven't had to do deform or statics/dynamics since college!

I appreciate any feedback.
Thanks again!

 

Attached is two options I was trying to describe with respect to the ridge beam/rafter attachment. Both represent a ridge beam with strapping over the top. Again, I have not found any information that this configuration would not be adequate for a MN snow load.

 

Yes i understand what your plan is. And i'm sorry, but I will not be wading further into this discussion. If someone else feels qualified to comment, I will leave this thread open.

 

I want to state right off the bat that I'm not a building expert. That said I will still give my opinion. The item you have shown isn't a very good option, straps are better for repairs. They will not be very effective in this application. When using those types of items think how would they work if that was all you used. In your case the strap would not at all prevent the system from collapsing flat (I know you stated the rafters are also tied in at the other end).
In any joint it's best to treat it as if it was the only thing preventing total failure. Using the pictured strap attached to each rafter and going under the ridge board would be stronger but still not very good. They make metal attachment parts for your application though. Here is a link to one type for sale at Home Depot
https://www.homedepot.com/p/Simpson-Strong-Tie-ZMAX-Galvanized-Light-Rafter-Slopeable-U-Hanger-LRU26Z/205694653