We're building a pergola on a 18' x 24' patio and I can't figure out what we need for a 18' span with essentially no load. Looking to make something like this:
Here's the question - we want the cross beams to run 18' across the patio perpindicular to the house. Ideally I'd like to use treated 2x6's but I can't find a tool/table to verify that will work. I'm concerned about both sag and warpage.
Anybody know this stuff to offer an opinion or point me in the right direction to figure it out?
Mine is 12 X 12ft. wrapped in plastic, no worries. The link says 53 lbs per linear foot. I put a 16ft. beam through my living room and sistered two 2X6s, glued & screwed with plywood between; only because I wanted the 2nd floor to stay up there. For more load, an Engineer told me not to mate them together but make them taller, 2X8 or 2X10 as the bottom of the board takes the strain. Load bearing of a 2 X 6.
Not finished here.
Look into Toja Grid. They look more modern than most pergolas, but they go up in a hurry and can have 6x6 beams. That's what I built on my own deck a few years ago. It's a 12' span, IIRC. I'm not sure what the limits of a 6x6 span are offhand.
The only thing I'd do differently next time would be to buy unfinished lumber and plane it to size. The sockets are built for dimensional lumber but DIY planing would allow for a nice tight fit. The Harbor Freight 12" planer would probably cost less than the savings in lumber.
That's cool.
What's a "cross beam". Do you mean the beam that supports the rafters, or the rafters?
18' is much too long a span for a 2x6 rafter. It will definitely warp and sag.
For reference, your picture appears to show 2x6 rafters (but they are spanning less than 8') and a beam that may be a 3x12 (with a 2x6 trim board added above)
Your support beam should have a post in the middle, so it's span is either 12' or 9' (depending on the direction). For a beam spanning that far, I'd use a double 2x10. If the rafter span is really 18', you are gonna pay a premium for oversized lengths. Consider making it 16' so the material is readily available. If you use 2x8 rafters, I'd still add blocking every 6' to prevent the twisting.
Good luck!
Side note...
I love the look of that woven fabric, but it sure is gonna get loaded with a lot of leaves and crap, and be very difficult to clean.
This thread is going to cost me money.
Thanks for nothing.
If you were comfortable having a post in the center, you could run a beam parallel to the house like a spine that was 2 12' boards end to end. Then, you could span from the house to the spine beam in 9ft lengths, and the spine beam to the outer beam at the edge of the patio in other 9ft lengths.
It might not be as visually appealing as a clear span, but it would be plenty strong and you'd be able to get smaller lumber "off the shelf" instead of expensive boards that you'd likely have to order and wait for.
I looked at a few of my structure resource books... 18' span with wood is not going to happen and it still look like a pergola. Each span would have to be a large chunk of wood than would have to be specially milled. You won't find 18' lumber even at most high end lumber yards. It would be special order. And then it probably would still warp. You need a beam in the middle to split than span, then you could use something like a 2x8.
Recently I had a high end client that wanted an 18' (non structural) cypress 12" x 12" beam installed in his great room. You could build many Challenge cars for the cost of the wood alone without delivery. OBTW, It looks super.
Curious if 18' material is readily available. I know it is in some states from ordinary lumber yards.
Here is a resource on spans
https://awc.org/publications/tutorial-for-understanding-loads-and-using-span-tables/
SV reX said:That's cool.
What's a "cross beam". Do you mean the beam that supports the rafters, or the rafters?
18' is much too long a span for a 2x6 rafter. It will definitely warp and sag.
Your support beam should have a post in the middle, so it's span is either 12' or 9' (depending on the direction). For a beam spanning that far, I'd use a double 2x10. If the rafter span is really 18', you are gonna pay a premium for oversized lengths. Consider making it 16' so the material is readily available. If you use 2x8 rafters, I'd still add blocking every 6' to prevent the twisting.
By cross beam, I mean the boards running from the house to the end of the patio, used only for the canvas sails, and spaced every 4'. Double 2x10s are going to look funny. They are going to support no load, and the canvas will come off every fall so there will be no snow load, etc.. The perimeter frame can be 2x10, or paired 2x8, whatever.
My builder/handyman guy suggested a couple of support posts in the middle of the patio - I'm trying to avoid that. Maybe 2" black pipe for the cross beams? (Just for canvas support.) Or ???
Had not considered whether 18' lumber was available, that probably kills the single span plan right off.
@Keith - That looks really good, and is pretty much what I'm trying to do with a little more spacing between beams and a canvas weave. I did look at Toja Grid and the brackets look great, but there's nothing there in kits over 12' so I'm pretty sure I'm on my own at 18'.
I did find a pergola maker in Illinois that will do a 18' x 25' aluminum lattice topped pergola for about $7K. (without center support posts) Looks good but I prefer the canvas weave if we can figure out a way to make the span.
In reply to jwagner (Forum Supporter) :
The Toja Grid parts are just the junctions. You put your own lumber in between so the dimensions are whatever you want within the limitations of the material. Same with with joist hangers, you can use whatever spacing you want. Black parts are from Toja, the wood was sourced locally and trimmed to fit my ideal dimensions.
How about the Toja brackets with a 4x4 steel beam on the 12' section? Or a 6x6 aluminum one. Then everything else is wood and you can do your weave.
In reply to jwagner (Forum Supporter) :
How about a steel I beam sandwiched between two 1x6s with the wood just being aesthetic?
Edit or boxing the I beam in wood for that matter.
In reply to jwagner (Forum Supporter) :
Your descriptions keep REDUCING the amount of wood. What we are all trying to tel you is that you can't. You need to INCREASE the amount of wood.
You can't span 18' with 2x6's 4' on center. It's not possible. No matter whose kit it is.
You are gonna have to rethink the design.
In reply to Stampie :
Yes, it could be done with steel. For triple the cost.
In reply to jwagner (Forum Supporter) :
The scale of a structure that is 18'x24' won't look like a pergola.
That would be like a 2 door sedan with a 300" wheelbase.
How about a deck that size with about half of it covered with a pergola?
In reply to jwagner (Forum Supporter) :
I'm sorry but some people always go off script. Cost wasn't mentioned in your post. Is the question how to do a 18x24 pergola as pictured or how much it would cost to do it right?
If you live near a Menards, they sell 2x12x18 pressure treated lumber. They're $76/board according to the website. If you're doing 24' width that would be 12 boards with 24" spacing or 18 boards with 16" spacing. So you'd have over $900 into just the "joists". Plus the 24' beam that they'd rest on, the 24' ledger board or beam on the house side, posts, and hardware.
Alternatively, these people offer a customizable kit for 18'x24'. It's all cedar, and includes hardware, finished ends, etc but the cheapest that I could option it was over $10k. Not sure what size "joists" they'd use for a 18' x 24', but they're using 2x8 for the "joists" of a 12'x16' pergola.
There are also kits like the one that Keith used for around $2k (no lumber). They're basically two adjacent 9x24 pergolas with posts in the center. It looks like that would allow you to use smaller, less expensive and more easily available dimensional lumber, but it's not clear span:
In reply to Stampie :
True. Steel was definitely off script, but I think it was a good suggestion. It is worth considering.
What size steel would you recommend for an 18' span?
What am I looking at here? Is the weight of the joist only being supported by the little tab?
That does not look right to me at all.
In reply to dean1484 :
That is what you're looking at. It only has to support half the weight of a 12' 2x6. Those are cedar, so according to Google it's about 16 lbs for the wood or 8 lbs for each 2"x2" steel tab, and they're considerably thicker than typical joist hangers.
It's a pergola, not a deck. This is not load bearing. Ever considered how little steel is holding up a joist like this if you toe nail it?
In reply to Keith Tanner :
It's still subject to wind loads.
I don't doubt the engineering, I haven't used them. But it sure looks sketchy. What happens if the screw rusts?
Maybe it's a mute point. Might just be the picture. You said they are 2"x2" tabs, which would be fine. The picture looks like they might be #12 screws in a 1/2" tab...
They look awesome.
FYI, it's never really ok to hang a joist off a toe nail. They are supported by ledger strips or joist hangers.
Stainless screws :)
It's definitely more than a 1/2" tab, the tabs are square and there's a dimensional 2x6 socketed into those hangers to give a sense of scale. 2x2 might be a little large, but 1/5x1.5 at least because that tab is at least as wide as the wood. I need to recoat the wood so I'll see if I can grab a measurement of the thickness of the steel. It's so easy to forget how strong steel is compared to wood construction. I see what you mean about potential twist in very high wind situations, I wonder what the maximum wind load on those joists are?
The steel parts for these aren't cheap, but the pergola goes up so fast that it would save a whole lot of labor cost if you were building these for customers. I personally chose it because I like the clean look, the quick erection was a bonus.
@SV reX - I pretty much abandoned the idea of 2x6 18' spans early in the conversation. Hadn't considered the "scale" of the thing - need to walk back in the yard and imagine what it will look like on the back of the house. I did want to create an enclosed feel on the patio and cover the hot tub in one corner and the table/chairs in the opposite corner, with light strings and speakers around above.
I don't think steel is out of the conversation so long as it looks/feels compatible. I did scope out some 18' aluminum beams that looked like they'd work. $676 each X qty 8 - never mind.
The kit @STM317 found would actually work, and the posts in the center really aren't in bad places so that's a reasonable option. It does look pretty large and "heavy".
The original thought was one of these traditional pergolas, which would cost about $8K. Might be more compatible with the house and yard, but I wanted the shade of the canvas sails and to put a retractable shade on the west end of things which would look odd on this type of structure. (I think).
Keith Tanner said:the quick erection was a bonus.
You'll need to log in to post.
