Small Gable Roof - No ties or ridge beams?


I'm going to add on to our storage shed and extend the roof over an 8'x10' patio. The roof has a 6/12 exterior pitch, and an 8 foot span.
We want a vaulted ceiling over the patio, with T&G boards on the underside, and no beams or ceiling joists overhead.
The obvious solution would be to add a ridge beam and take out the ceiling joists. But, a ridge beam needs a supporting post, and the 8' span of our roof would mean a post every 4 feet. Kind of cluttered. I would also have to devise some method of supporting the ridge beam where it meets the shed. I also want avoid any horizontal beams that could be potential resting spots for birds.
We have an 8' wide pump house I built many years ago that uses metal brackets to build a small gambrel roof. There are no ceiling joists but the roof is still quite strong. But, I haven't seen any brackets like those in years?
I've also briefly looked at storage sheds at the home centers that use simple plywood gussets to accomplish a similar task. Again, no ceiling joists.
So, I'm curious if I can use a similar approach to frame the roof over our patio.
The roof has a 6/12 pitch, which means the peak only rises 2 feet in the middle. I would like the interior ceiling to have the same 6/12 pitch if possible.
I'm willing to use larger rafters (2x6, 2x8, or 2x10) if needed for strength, and can space the rafters closer together if needed as well.
I have not been able to track down any information on the strength of a simple gusseted connection. I have no idea if two rafters gusseted at the peak would be able to resist the outward thrust, or support a 30lb/ft roof load (We can get a foot or two of snow each year).
Has anyone built a roof like this?
Thanks,
Anthony
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HerHusband wrote:

8'x10'
underside,
ceiling
our
have
shed.
resting
but the

those in

use
ceiling
over our

the
if
well.
a
the
roof
Can you build a truss at either end to support a structural ridge?
R
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Rico,

I could, but I'm trying to avoid any obstructions on the gable end as it would block our view of the nearby trees (part of the reason for building the patio where it will be).
I'm also trying to avoid any cross beams that ceiling joists or a truss would introduce. I don't want birds building nests, or worse yet sitting on the beam and leaving droppings all over the patio.
I could use a simple scissor truss, but I need to match up the roof plane with the shed roof.
After a little more research, I think what I'm looking for is called a "rigid frame" structure. But, I haven't been able to find any real details for the design. Basically it's just two rafters connected and reinforced at the top so they can't spread apart.
Anthony
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HerHusband wrote:

it
building
truss
sitting on

plane
a
details
reinforced at

An iron shop could cut/weld whatever you needed. Plywood gussets might work, but without doing calculations I couldn't tell you.
Since it's a small structure you might be able to build the roof as a torsion box, but again, you'd need to crunch some numbers.
R
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A ridge beam is not a "beam". It only serves to butt the ends of structural members and can be a 1x (you select the depth). If anything, it provides lateral support at the member ends.
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In a previous post Steve Kachaylo says...

Steve:
In this case that is not true. The ridge is a true beam. You are thinking of a ridge board which carries no weight and is used a convenient way to butt the ends of rafters.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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A ridge beam is not a "beam". It only serves to butt the ends of structural members and can be a 1x (you select the depth). If anything, it provides lateral support at the member ends.
Only in some designs.
In many designs, it is most definitely a bearing member.
--
Lyle B. Harwood, President
Phoenix Homes, Inc.
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What's going to hold this roof up? Columns at the corners? What's going to do lateral bracing duty?
M9

underside,
shed.
the
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M9,

One end will be supported by the adjoining shed. The other end will be supported by posts at the corners, and another post in the middle on each side.

That has been a concern of mine... The shed will provide a fair amount of stability on one end, but the other end could still flex around rather easily. The usual approach would be to put diagonal corner braces up near the roof, but without a horizontal cross beam, there's really nothing to brace against.
The patio will be surrounded by a "fenced" wall about 4-5 feet high. We want the view of the surrounding trees, but privacy from the neighbors. My plan has been to provide lateral bracing in the lower section of the wall, and leave the upper part of the roof as unobstructed as possible.
If I can't find more information on the gusseted roof system, I'll probably just add another post on the gable end and add a ridge beam. It's the simplest approach I can think of that will accomplish our goals.
Anthony
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In a previous post HerHusband says...

Anthony:
Roofs like this have a tendency to push the supporting walls or beams outward. The connection at the ridge requires engineering and is a little complicated to build -- it's more than a simple plywood gusset. With one end 10 feet away from the main structure you will need some sort of lateral support at the outside edge. This can be accomplished with embedded poles or something similar.
Your small structure has a lot of "not-so-easy" structural issues that are not readily solved by the average homeowner. I suggest you draw up a sketch and take it to a local engineer for review. You might as well do BEFORE the local building inspector sees it and then makes you have it engineered, which will cost more and be difficult to retrofit.
As to my last comment, this comes from the fact that I'm currently working on 3 projects where the homeowner built something without permit. I'm trying to come up with solutions that don't require tearing out large portions of the work already done. The engineering and construction costs will be much higher than if the homeowner had simply done the job correctly in the first place.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Bob,

That's what I figured. It seemed to go against the basic structure principles I'm familiar with.
I'll probably stay with a more traditional design. At this point an extra post and ridge beam seems like it'll be the best approach, but I'm comparing a few other options as well.

Most open structures I have seen like this have diagonal braces up near the roof. I would like to keep the upper section as open as possible.
Since the lower portion of the wall will be enclosed with a fence anyway, I've been planning on placing diagonal bracing in the lower half of the wall, rather than up near the roof. Wouldn't this accomplish the same task?
Thanks for the feedback!
Anthony
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One other option might be to install a top plate to act as a lateral beam that would resist the outward push
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Yeah, I thought of that too... Sort of the principle that keeps a hexagonal gazebo together without ceiling joists. I'll keep it in mind, but again, I haven't been able to find any information on how to calculate loads for a lateral beam.
Anthony
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In a previous post HerHusband says...

Maybe. Depends a great deal on the geometry.
Here's my take on the structure as a whole:
Ridge beam, supported by existing structure on one end, spans 10 feet to simple king post truss at open end. Rafters are supported by beams at eaves and ridge. For a 10-foot span the beam is probably something in the 2-2x10 or 4x10 range depending on snow load. King post truss sits on top corner posts and has knee braces at top of post to provide lateral support. Truss might be 2-2x top & bottom chords with 4x king post.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Bob,

That's kind of what I've been thinking, except I want to avoid the horizontal beam of the king post truss. So, I would probably support the ridge beam with a post running all the way to the footing.

I've been using a 30lb sq/ft load rating for the 8'x10' patio roof, which should be about 600 pounds on each side beam, and about 1200 pounds on the ridge beam. The two side beams will have an additional support midspan, but the ridge beam will span the full 10 feet. The tables I have show a 4x6 should work fine for the ridge beam, but I may use a 4x8 for the ridge.

I'm thinking a similar approach, just flipped upside down. The beams would rest on posts with the knee brace at the bottom of the post (may just use plywood and make the lower half of the wall a shear panel?).
Anthony
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In a previous post HerHusband says...

The design I was proposing uses 2 posts, yours uses 5.
This little building is going to look like a forest with posts at 5' o/c along the sides and at 4' o/c on the ends. I don't think you will be happy with the way it looks, but hey that's just me.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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In a previous post HerHusband says...

You could always put some "birdspikes" on the beam.
http://www.birdguard.com/HTML2/birdguardspikes.html
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Ridge "beams" do not need supporting posts, neither at end nor intermediates. Ridge beams are supported by the rafters, though in some instances, collar ties may be required. The "supporting post" would be used to hold the ridge board (not beam) until the opposing rafters are installed.
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In a previous post Steve Kachaylo says...

Sorry Steve. "Ridge Beams" require posts (or another beam) for permanent support. "Ridge boards" are the usually 1x material between the top ends of rafters that are collar tied by ceiling joists in conventional construction. It is these that are temporarily supported until the rafters are in place. Refer to Architectural Graphic Standards for terminology.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Steve Kachaylo wrote:

But what supports the rafters?
Matt
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