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Old 02-15-2010, 12:42 PM   #1
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Gazebo structural support?


Hi everyone:

I have a gazebo in the middle of my back yard. It's been there at least 15 years. The gazebo consists of a 16' x 16í cement pad on the ground (no cracks), a raised deck (three feet high) thatís made up of long 2x2s, and an extremely beefy, fully shingled roof thatís about ten feet off the ground and is supported on each of its four corners by thick 6" x 6" posts that sit in saddles attached to the concrete. The gazebo is not closed in Ė itís open on all four sides.

I am buying a new hot tub and thusly must get rid of the hot tub that's currently enclosed within that deck. And to do that, I have to completely disassemble the deck structure. I've already removed all the 2x2s from the old deck, taking it down to the 2 x 4 "skeleton." But I don't want to remove that skeleton because it acts as bracing for that big roof by butting up to all the corner posts and by having crossbraces that run between three of the posts. Once the new hot tub is in, I'll build a new deck, but it will be much shorter than the original deck (just a few inches above the concrete pad) and will not be able to add support for the roof.

My question: If I construct big, beefy knee braces on all the corners between the posts and the roof, would that add enough structural integrity to the roof to stop it from swaying laterally? The four 6x6 posts are pretty strong by themselves, but I just don't want to take any chances.

I'm going to hire a contractor to do the job because I don't have the skill to do it myself, and I have had two contractors come by already who have both said knee bracing will be enough, but I came here anyway because there are a lot of knowledgeable people here and I wanted a couple more opinions.

I thank in advance anyone who takes the time to respond. I'm also trying to include a pic here of the structure, but am not sure if I'm doing it right. :-)


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Old 02-15-2010, 12:49 PM   #2
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Gazebo structural support?


Okay, finally figured out how to post pics. Yay! So...here's the only one I have. Note that all those 2x2s are now gone, leaving the 2x4 substructure underneath. Note also that the new deck (once the tub has been replaced) will be just above ground level (the same height as the ground level deck you can see around the perimenter in this photo).

Would a pic looking up into the underside of the roof also be helpful?


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Old 02-15-2010, 12:57 PM   #3
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Gazebo structural support?


You don't tell us where you are located.

That might help so we could suggest a Timber Framer in your area.
Visit the Timber Framers Guild site at http://tfguild.com and look for the Business Council link. They have resources to assist finding a Timber Framer in your area.

To do a visit and suggest that the structural integrity of the building can be maintained with a few knee braces is something best left to those knowledgeable in the field of Timber Framing or by an Engineer familiar with TF methods. A Finite Element Analysis may be required. Are you in a heavy snow load area? Have wind loads been considered? Earth quake zones? Is there a 6 x 6 or better timber plates to tie the knee braces to? How will the braces be joined? Is this a job that should be covered by a Permit?

I have some Timber Framing experience with new construction and also from rebuilding structures as re-configured frames. I would love to assist you. Can you post a picture of the Gazebo as it exists today?

Thanks.

*edit*

Yes, post a picture of the roof structure from inside, especially the wall plates.
I guess we were cross-posting...
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Old 02-15-2010, 01:40 PM   #4
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Gazebo structural support?


Thanks for the reply!

I'm in Vancouver, Canada. Weather is similar to Seattle - lots of rain, maybe a few inches of snow every year (none this year so far, and maybe an accumulation of a foot of snow every few years). Yes, we do get some big winds (80-plus MPH) in the early winter.

This is an earthquake zone. Haven't had one of any consequence for decades, but that's not to say there won't be one tomorrow. On the positive side, the area where I live is very solid. Dig down a few inches and it's rock. And a lot of it. Probably the reason the concrete pad is crack-free after all these years.

Three of the five deck builders that have come by so far have said the roof needs NO stabilization - that it's just fine with the four saddled posts. I automatically write those guys off because my common sense tells me they don't know what they're talking about.

I'll go out an grab a few more pics right now.

Thanks again.
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Old 02-15-2010, 01:56 PM   #5
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Old 02-15-2010, 02:29 PM   #6
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Gazebo structural support?


Thanks for the pictures. It helps a lot.

I had the following information typed up in preparation for a reply pending receipt of more pictures as you added your last post, so some of it does not apply. (especially the M&T info since the top timber is not there... only a 2 by 10? or 12?)

Two types of joinery to consider. Well, three, actually.

1. "let-in bracing" - Plough out the wood to allow a brace to sit flush with the exterior face of the existing 6 x 6 posts. Peg/screw it into place. Weakest of the methods, but can be made stronger using a housed half-dovetail.
2. "bolt-on" Knee braces. - Some people would lag bolt a brace to the post and top plate, but I don't trust lags over time. They will lose their grip. Through-bolted complete with Timber washers is better than the let-in method or using lags.
3. "Mortise and Tenon" - The trick here is to get the tenons to fit since it is impossible to place a proper M&T once the structure is in place. The trick would be to use floating (loose) tenons on at least one end t allow placing the tenons and draw boring correctly.
Housing the M&T braces is definitely the strongest/best method, but would take some more time/labour. Any Timber Framer worth their wages is able to calculate the required brace sizes and layout/cut the Mortises/Tenons to suit this task.

Remember that in order for these Braces to do their job properly, they need to be installed in pairs. One is in tension when the other one acts in compression. And vice versa.

Another thing that should be addressed is the racking of the frame at the top. It might be a good idea to have lateral bracing between the plates so the frame is stiffer in a horizontal plane. (I see with the pictures that this issue has been previously addressed. I wont consider adding a few more nails to them.)

Seeing your pictures, I would suggest a modification to your deck to allow for a combination of the 'let-in' brace and a through-bolted brace.

Use a 'let-in' joint at the bottom end with a lapped/bolted connection on top.

Top end: If you lap the top so that the material is let-in about 1 " (1/2 inch each piece) the bottom need to consider that and will be proud of the post the same 1 inch. A let-in Lap joint is stronger than a face only overlap.

Bottom: House the bottom end of the brace and possibly a half-dovetail joint would look good there.
Through bolt the connections at each end using Timber washers.

If you used larger material (3 x 12) for the braces, you could shape them into curves and add a really nice eye-catching feature to the overall look of the gazebo. IMHO.

Replace the existing through bolts at the plate to post connections with double dipped all-thread or bolts complete with Timber washers.

Additionally, the post to deck connections should be looked at to determine their condition. They are now 15 years old? They will act as hinges and it may be necessary to stiffen them up somehow. It might be as simple as having a short wall bracing the posts to the concrete. Not sure. Possibly some angle iron connectors?
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Old 02-16-2010, 01:34 PM   #7
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Gazebo structural support?


Hey jlhaslip, thanks so much for taking the time to write such an *extremely* thorough reply. Great stuff.

Anyone else have any suggestions?

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