Gazebo Rafter Span

[Yrok]

I am designing and building a gazebo to cover a ground level deck patio and wondered if I could get some input on the design. Pictures are attached (with some dimensions). Roof pitch is 3/12. Roof sheathing will likely be 1/2" OSB (unless something else is suggested) and roof covering will be architectural shingles. Posts, beams, and braces are 6X6 Treated Pine. Gazebo will be free standing (not attached to the house in any way). The posts will be anchored to concrete pillars. I live outside of Huntsville, AL so snow isn't really a concern (4 inches is basically a blizzard), but we do get strong winds occasionally. I currently have the rafters modeled as 4X6s which is my primary question.

1. Are 4X6s or 2X6s sufficient for the rafters? Would 2X8s be better? I would like to avoid adding additional posts if possible. If the span is too large, can I add another beam to each side and add a brace in the middle for additional support?
2. Any other design thoughts/suggestions?

 

[Eng16080]

Roof sheathing will likely be 1/2" OSB (unless something else is suggested)

I'd suggest 5/8" thick at a minimum. Also, if the OSB will be visible from the bottom, that's probably not very appealing aesthetically (not that that's a structural concern).

I live outside of Huntsville, AL so snow isn't really a concern (4 inches is basically a blizzard), but we do get strong winds occasionally.

In that case, the controlling loads are likely either roof live load or wind load, as calculated from ASCE 7.

I currently have the rafters modeled as 4X6s which is my primary question.

Are 4X6s or 2X6s sufficient for the rafters? Would 2X8s be better?

Once roof loads have been calculated, wood framing would be designed per the NDS code. There are lots of ways to accomplish a code compliant structure using different member sizes, wood species, grades, spacings, etc. For something exposed like this there are often aesthetic considerations in addition to the typical strength/serviceability checks.

Any other design thoughts/suggestions?

I don't see how there's any lateral stability in the direction to/away from the house. Lacking that, this seems like a rather dangerous design.

Definitely hire a local engineer to help with this. This is a big, freestanding wind sail that you don't want collapsing on people.

 

[Yrok]

I'd suggest 5/8" thick at a minimum. Also, if the OSB will be visible from the bottom, that's probably not very appealing aesthetically (not that that's a structural concern).

Thanks for the suggestion, I was already considering using thicker sheathing.I also intend to cover the rafters on the underside with thin planking to improve the look

In that case, the controlling loads are likely either roof live load or wind load, as calculated from ASCE 7.



Once roof loads have been calculated, wood framing would be designed per the NDS code. There are lots of ways to accomplish a code compliant structure using different member sizes, wood species, grades, spacings, etc. For something exposed like this there are often aesthetic considerations in addition to the typical strength/serviceability checks.


I don't see how there's any lateral stability in the direction to/away from the house. Lacking that, this seems like a rather dangerous design.

The beams i suggested for the sides in my original post would remedy this, correct? I thought the rafters and roofing would provide sufficient stability but it sounds like that was a bad assumption.

Definitely hire a local engineer to help with this. This is a big, freestanding wind sail that you don't want collapsing on people.

 

[Eng16080]

The beams i suggested for the sides in my original post would remedy this, correct? I thought the rafters and roofing would provide sufficient stability but it sounds like that was a bad assumption.

I don't think so. I would suggest adding knee braces in the front/back direction. Currently they're only shown left/right.