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We are building a wall pergola that we want wisteria to grow on top of. The pergola will only come about 3.5-4 ft out from the wall (Edit: the columns themselves are less than 2ft from the wall). I have already placed 2 6x6 columns bolted into concrete on both sides. The beams are 16 ft apart.

Are there any wood (preferably cedar) beams that can span that 16' distance without having to place additional support in between? If so, what kind? Is there a chart somewhere with max distances that beams can span with minimal weight on top?

In the picture below, these beams span pretty far, but they are also very thick and I wonder if beams that thick can be mounted to a 6x6.

image

Edit:

If worried about the weight, see this wall pergola from Lowes. This would bear the weight with or without the long board in between the columns. This is what I am going to buy or build. I also have 6/6 columns on either side for wisteria to wrap around. I may or may not span a board from one column to the other, depending on if it makes sense to do so.

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Dave
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    I started an answer, and the numbers got big. Live Load is 5.33 PSF for Wisteria, and snow load in Woodstock Il. is 25 psf. So we're looking at a total live loading of this roof of nearly 2000 pounds. So I'm not going to finish my answer, as the DANGER WILL ROBINSON flag is waving. This is exactly the sort of project that gets amateurs in trouble. It SEEMS simple enough, and then it becomes really complicated. For a couple hundred dollars, consult an engineer, and get a permit drawing done. You're risking losing your insurance. – Chris Cudmore Apr 04 '16 at 21:05
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    You say you've placed 2 6x6 *beams*, but do you mean *columns*? Beams are horizontal members (perhaps you've cantilevered them out from a building?) but it sounds like you mean placed columns, similar in function to the stone columns in your picture. – Shimon Rura Apr 04 '16 at 21:08
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    @ChrisCudmore I agree with you. Question about the insurance comment - are ill-conceived building projects executed by homeowners routinely cause for cancellation of homeowners insurance policies or denial of claims? I hear this type of statement often but as far as I know the thing that gets you in trouble is malice, not incompetence. – Shimon Rura Apr 04 '16 at 21:22
  • Chris and Simon, You can pick up a wall Pergola from Lowes, so I'm sure it is ok to have a wall pergola. If anyone is concerned about snow weight on the wisteria, then we will move the wisteria up against the wall or cut down the wisteria. But the columns are needed for the wisteria to grow around, either way. I'm just asking if a board will span that far. It does not need to support the weight of the wall pergola. Lastly, if I worried about insurance for everything I did I would have paid other people 100k by now, which I'm sure unions would love, but I would never retire. – Dave Apr 05 '16 at 05:04
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    @Dave - seems like a couple complete strangers are trying to keep you from hurting/killing someone and/or having an insurance claim denied because you did something without the proper research and permits. If you want the simple answer: yes, any 16' board will span 16'. If you want to know how long it's going to last and how much weight it can carry you'll need to provide a lot more info: what dimensions are required (16x?x?), how will it be attached, etc. – Kyle West Apr 05 '16 at 13:05
  • Note the questions are before the question marks. I also asked if there was a calculator online. Funny how if everyone is so smart they can't just provide this link. I found one. I hope the unions don't try to take this site down. http://www.awc.org/codes-standards/calculators-software/spancalc – Dave Apr 05 '16 at 14:03
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    @ShimonRura If the insurance company doesn't want to pay a claim, they can start asking for permits and inspection reports. Then deny everything for unauthorized work. – Chris Cudmore Apr 05 '16 at 16:48
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    People ride speed boats, climb mountains, race dirt bikes, speed in traffic, jaywalk, etc. all the time, I can't believe people are freaking about about a wall pergola. It's like 1/10th the size of the picture above. It's not in a location accessible or even seen by the public, but an enclosed private patio only my wife and I use. Even if there were snow weight (which there will be hardly none) nobody is outside during the winter about here! This is not a question about insurance. Can't there just be a disclaimer then move on? – Dave Apr 06 '16 at 14:13
  • @Dave You're not going to get an answer here. Questions about simple beams are asked all the time here and never get a satisfactory answer. You'll be told the math is too complicated or that wood is unpredictable or some other cop out. – Zach Mierzejewski Apr 06 '16 at 15:57

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Here is the answer to my actual question:

http://awc.org/codes-standards/calculators-software/spancalc

Edit: Sorry if I'm not on the same wavelengths as anyone else. I already know about insurance and inspectors, and that was not at all what I was asking about. I just wanted to know what length of wood would span a certain distance given various criteria. I would have expected an answer to that question, instead of all the "your a dumb homeowner who's going to get in trouble" type replies. I question the idea that there will be 50psf of weight from snow given the fact that it is an almost non-solid top, and saw no real attempt to answer my question, so I had to come up with this. It took me awhile to find, and I hope it helps others.

Dave
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    Link only answers are not useful, especially when the information in the link does not answer the question. – Tester101 Apr 05 '16 at 19:15
  • What values did you put in the calculator? I don't see a way to specify a 16 foot span. – wallyk Apr 05 '16 at 19:23
  • @wally The span is what it gives you. You specify the type of wood and the board size (2x10, 2x12, etc) and other factors such as load, then it gives you the maximum span. – Dave Apr 06 '16 at 13:42
  • Tester, I asked "Is there a chart somewhere with max distances that beams can span with minimal weight on top" and this is a link to a calculator, even better than a table. So it answers my question perfectly. – Dave Apr 06 '16 at 13:44