Pergola Questions

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  #1  
Old 02-19-12, 07:21 PM
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Pergola Questions

Hello,

I am going to take on building a pergola this Spring. It is going to be 25' x 20'. The slats will run north/south and be about 20 feet long. They will attach to a ledger that is lagged into the house and then out to a double ledger attached to 6 x 6 posts.


A few questions: The double ledger will have to span roughly 12.5' (I am planning on doing (3) 6x6 posts), will a 2 x 10 (treated) be able to handle that span without sagging?

Also, the slats are going to be 2 x 10 x 20'. I think these would sag over time (there will be minimal load on them) but I really don't want to have to put another double ledger halfway through the span. Any suggestions? Also, how far apart do most people put their slats? I know it is subjective to how much shade you want etc...I was thinking 16"...is that too many? not enough?


X------------X-----------X (X= 6x6 post) 12' between posts
| | | | | | | | | |
| | | | | | | | | | | represents the slats. Roughly 20' feet
| | | | | | | | | | long 2 x 10s
| | | | | | | | | |
| | | | | | | | | | H represents my house and the pergola
HHHHHHHHHHHHHHHHHH will attach to it via lags and a ledger



Thanks!
Dan
 
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  #2  
Old 02-20-12, 12:22 AM
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I see several problems with your plan.

The first -- your'e missing a layer. Posts and the beam, the joists -- but what about the lattice running parallel to the ledger and beam??

Second -- what's going to keep the 2X10 joists upright -- prevent them from twisting or simply laying over? Mid-span blocking and blocks at the beam would stop that.

Finally, if you span dimensional lumber 20' with no mid-span support, it's gonna sag. Spacing won't matter, but it will take 2X10's longer to sag (probably several years) than it would 2X6's or 2X4's (probably within the first year).

There are 2 ways to get around the sag.

DIY with dimensional lumber -- put in a mid-span beam with supporting posts.

The other is to use roll-formed aluminum components, rather than dimensional lumber. (Search the web for aluminum patio covers, and you'll find wholesalers like Metals USA, Amerimax, Duralum, ...)

You're not gonna like it -- those wholesalers ONLY sell to their authorized installers, and their installers won't sell parts at retail. You could have a great cover, without the mid-span beam, without issues of sag, twist, maintenance (these things come with lifetime warranties on the material AND finish). The part you won't like -- it'll have to be installed by a contractor -- it's NOT DIY.

What do you want it to look like in 5 or 10 years, and how much effort do you want to put into maintaining it??

Your call -- pay to have it done, and your only cost down the road is to clean it; or DIY with whatever you can lay your hands on, and you'll be working at maintaining it for the rest of the days that you own the house.
 
  #3  
Old 02-22-12, 07:43 AM
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Thanks!

Lefty,

Thanks for the advice. I think I am going to stick with a wood pergola but I will take your advice and put a mid-span beam across halfway out. Yea, this will cause a 6x6 post to be in the middle of my patio but my patio is 25 x 20 so I think I can afford the space.

Another question: All of the support posts (6x6) are going to be installed on "piers" that I dig out with an auger on the back of a tractor, except for the one in the middle of the patio. I was hoping I can get away with just using the patio itself to anchor that one. The patio is 4" thick with rebar every 12" both directions. What do you think?

Thanks again,
Dan
 
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Old 02-23-12, 01:31 PM
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I wouldn't set a post on the slab -- I'd put a footing under it. Of course, I'm on the left coast, and every patio cover I've ever built has been subject to wind and snow loads, along with having to survive earthquakes. (No bldg. dept. where I've ever installed a cover would have allowed me to do it w/o a footing under EVERY post anyway, for the above mentioned reasons.)

A decent wind (20 or 30 mph) and a post attached to just the slab would put enough stress on the slab to crack it.

A minor earthquake (3.0 or better) could cause the same thing.

Several inches of wet snow may be enough extra stress to crack the slab. A foot or so may be enough to actually punch the post through the concrete.

Just not worth it to me to run the risk. A footing takes virtually nothing to install.
 
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Old 04-22-12, 12:47 AM
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Question : Beams.




Hey, I was wondering if someone could give me some advice. Im planning on building an 8x8 pergola with 9 intersecting beams(as shown in image if link worked)
Is there a specific way to do this style? like all groves upwards on 4 beams(2x6) and drop beams into groves or.. up/down/up/down/up combinations through the beams?
thank for the help
 
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