Flat Roof/Overhang Building Advice
Hi all,
Looking for some structural advice and suggestions on a future project I’m hoping to possibly tackle this summer or fall. I want to build a flat roof overhang just above the backyard door of my house, which will be double french doors eventually, that would walk out onto the patio. The overhang would serve as some shelter from rain and sun, offer some lighting and of course add some architectural appeal. I am thinking the overhang would come out somewhere from 2′ to 2 1/2′ and the width would span 6′-8′ potentially; just putting ranges for the time being as I haven’t determined the exact depth or width. Planning to use either 2″ x 8″ or 2″ x 10″ lumber for the framing. I would like it to be a flat roof/overhang to have more of a modern look and I don’t want to use any posts on the ends, I ideally want it free hanging.
My question is, is it possible to build this by mounting a ledger to the exterior wall with lag through bolts as your main point of support to the house? The interior framing would be 16″ apart on centre, with the same sized dimensional lumber used on the outer frame (2″x 8″ or 2″ x 10″). For added strength and support, I was thinking to use steel L brackets fastened on the inside of the side framing and screwed with lag bolts into the ledger, and use metal joist hangers for the interior portion. I realize that despite this not being extremely large, relatively speaking, there is still a significant amount of wood being used that will create substantial weight, and additionally having to factor in snow weight during the winter season. I understand the most ideal way of building such would be if it was tied into the existing houses structure/joists but I’m not willing to go to those lengths and destruction to build this, so hoping there is another feasible option. Is this idea at all possible or is it destined too fail? If so, is there another design that anyone might be able to recommend that can be applied to build such? I’ve attached a picture of a roof with this type of look and what I’m hoping to somewhat accomplish, to give you a visual.
I’m merely a DIYer so my experience is certainly limited and looking for some folks here who can shed some expert advice. Sincerely appreciate any input. Thanks!
Pete
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Replies
Yes it's possible, likely with structural screws instead of lag bolts. I had 4' deep by 8' wide window pergolas designed built out of 6x6 timber and 2x6 purlins on edge on top spec'd by my structural engineer and he required screws only. What is the snow load for your area? I'd use a 4x ledger, that ledger screwed into studs, and the rafters fastened to the ledger with screws or screws through the hanger.
Are you going to finish it with a soffit? If it's left exposed you may want to do decorative hardware and better quality lumber.
Good luck,
Got a photo? Having a hard time picturing this if it's a flat overhang being supported only at the ledger as Peter had in mind.
Snow load is definitely an important consideration which can cause failure in some designs which work fine in southern climates.
Tom, I'm sorry I don't. The house was not built as we opted to renovate a mid century home instead. I checked the plans I don't have a detail it was something we discussed after the 2nd revision. We did sit down and hash it out because the garage had posts on each side with 4x8 S4S timber beam spanning, and the 6x6 timbers overhung perpendicular as shading. We wanted some of the window sections to match that detail. It was how I described: 4x8x8' ledger screwed into the studs, 6x6x4' timber fastened perpendicular (I believe the screws were at an angle one from the bottom and one from the top), and 2x6 on top perpendicular to the 6x6 on edge.
Peter I should not have suggested that you do it that way but it is possible.
Thanks for the input Brandon. It's too bad you don't have a photo to see it. As for the snow load, not sure exactly, I will need to calculate that, as it is certainly an important contributing factor.
Your local building department may offer a handout that provides your climate zone, snow load, wind design, frost depth, etc etc. For example where I'm located it's 30lbs per square foot. Maybe check with them? I apologize I really hoped I had more to share.
You'll need some slope on the overhang. Probably easier to build the overhang as flat. Then use tapered sleepers on top of the overhang to achieve the slope.
You can definitely do it with CFS (steel studs but beefier than box store stuff). I've had structural engineer spec essentially a bolt on floor overhang supporting a load bearing wall and roof using it. Might not sound very DIY friendly, but it is pretty easy to work with. Since the joints can easily support tension and moments, you can do some structures that are impossible in wood. Bonus is that it will never rot.
You do need somebody to spec it for you though.
I'm not too familiar with CFS first hand, and would not have come to mind as an option. I did look it up after reading your post and it certainly looks to be highly used in many structural building applications. I will look to connect with a supplier outside of the big box stores as you suggested. Thanks for the suggestion.
Since your not willing to cut into your existing structure what you are proposing is basically a pressure block overhang. Of you keep it at 2’ and the snow load isn’t that much (< 30lbs/SF) I would screw a ledger into the existing framing using Simpson SDS screws 3 staggered at 1’ o.c. Through a 2x10 ledger into (E) framing, then 2x10 perpendicular to the ledger at 16” o.c. With joist hangers installed upside down at the ledger (on top of joist instead of on bottom) and put them on normal at the other side to a 2x10 rim joist (you should support this temporarily at the far end while under construction)then glue and screw a sheet of 5/8” plywood to the top. I would use a piece of tapered insulation on top and do your waterproof membrane on top. Do standard sheetmetal detailing on your fascia with an outlet to allow water and snow melt to run off. You might want to consider talking to an engineer to make sure this is adequate for the loads in your area of wind and snow for both uplift and downward pressures.
Thank you Paul for information and detail you provided. A number of great suggestions here which I will definitely reference as I get closer to approaching the project. Appreciate you taking the time to share that!