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Old 08-14-2009, 05:42 PM   #1
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Make a beam


O.K. guys, I need some advice here for a project. A "pergola(?)" that was built two years ago and some of the lumber was not even PT. A beam made of multiple pieces of 2 x 8 with a total span of 17 ft. has now rotted to the point that some of the 2 x 6 lumber which was placed on top is falling through this beam. The 2 x 8, non PT, no staggered joints, nailed together, has to be replaced. My first thought was LVL or gluelam, BUT-this is certainly exposed to the elements. I'm wondering if I use 2 x 10's x 20 ft. long (I can't get 18 ft.), trim to length, use three (3) pieces, use an appropriate construction adhesive between them, and lag screws to hold them together, would this be sufficient? Overkill, would be fine with me. The customer has stated they DO NOT want to hear "tear it all down and start over". They really got burnt on the original job. Any suggestions, please? Thanks, David

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Old 08-14-2009, 09:34 PM   #2
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Make a beam


LVL isn't an option for weather exposed applications. Gluelam is, but you'd have to get treated gluelams. Treated PSL is available in most markets but it is ugly as heck.

You'd be better off making a built-up beam from treated 2x10's or whatever dimension is needed for the span. In an outdoor application the glue's probably a waste of time. Don't use lags! You need to use hot-dipped galvanized bolts. Carriage bolts with nuts and washers are appropriate. A common bolting pattern is to put the bolts about 16-24" o.c., with a row on top and a row on bottom, staggered. If this is just a pergola with minimal or no roof load on it you can get away with less bolts.

As for span, I'm hoping you're not spanning 18' if this is an actual load-bearing beam. If so, a post is going to need to be added mid-span. If it is just for looks then go for it.

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Old 08-14-2009, 11:39 PM   #3
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Make a beam


No option to go solid with a 4x or 6x? Those pergolas look disproportionate to my eye when the spans are so long, beams so inadequate, and sagging has occurred. Does the owner expect you to levitate the cross members above thin-air and place a replacement beam atop the posts? In my view you will be taking it down and starting over only reusing the posts and cross-members. You could do piece by piece replacement of the layers of 2x8, but that would be tedious. I concur with placing a mid-span post if you're not going to up-size the beam. Consult a span table, then make a recommendation to your guy given the published data. If you purchase a few dozen hex-cap screws(bolts), pre-drill and impact them on, etc... That would be less attractive to me than paying a couple hundred bucks for a ready-to-install byoo-teaful solid beam. In his position, he's going to pay for your labor OR pay for a better beam.

This advice might be worth less than what you paid for it...
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Old 08-15-2009, 09:46 AM   #4
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Make a beam


As I sat writing the first posting I could "see" what I had and where I was going with it, but missed details in writing my request. kc--all fasteners used in this project will be hot-dipped galvanized, Thanks for the reminder. As far as "Load Bearing", that is one reason I posted here, of course there is the load of the (what do we call those) 2 x 6's which will come from the house out to this beam. These will be 14 ft. long, on 6" center with the rebuild (per the previous build). There are now six (6) 4 x 4 post holding up this gosh-awful 17 ft. pseudo beam which has started separating bad. The HO wants to remove all 4 x 4's they can and still support the Pergola. I'm replacing the two end post with 6 x 6, the beam will sit on top of these (and be attached to), then the "joist" (?) will sit on the beam. I'm looking at using three (3) runs of the 2x10's on this 17 ft. span. The HO wants 1 x 1's placed perpendicular to the joist on top for additional shading, so the 2 x 6's, and the 1 x 1's will be the load. How much shade can you get from 1x1's? NailedIt--the current Pergola is coming completely down as all joints have started to pull apart anyway. This project would be easier if I could talk them into letting me tear it down completely and start all over, placing the current lumber at the side of the road with a "FREE" sign on it. Span tables I have access to do not show using 6x6 across this span as an option, I like the LVL but exposure ruled it out, I'm going to call about treated gluelam Monday as I also have used and like those. Thanks, guys, David
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Old 08-15-2009, 06:29 PM   #5
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Make a beam


I was referring to pressure treated solid timber 6x12 or 4x12 beams, not posts. They are commonly available in my Texas hometown, though I'd probably have to have them special ordered here in Indiana.

Attached is photo, on the far right you see a 6x beam. These particular beams are for sale on Craigs list for $100 each.

I've built that same kind of structure using 1x2 spaced 1-1/2", 2x2 spaced 1-1/2", 2x4 spaced 3-1/2". I like the 2x4 best because they hold up better and take larger sized fasteners. BTW... when I build decks they're built like brick xxxxhouses. I like to use sonotube formed concrete piers on footings or 6x, 8x, 10x posts with 1 or 2 size larger beams/joists than called for. This necessarily drives the material costs up, but I try to allow for that in labor if that's an issue with the customer. The 8-year-old 1.3MP digital pic of the "pergola" I've attached was built with the intention of perhaps adding a translucent poly panel atop or some other roofing in the future.

I hope your project goes well for you and your customer appreciates your efforts.



[IMG]file:///C:/Users/ccity/AppData/Local/Temp/moz-screenshot.jpg[/IMG]

Last edited by NailedIt; 10-27-2009 at 12:01 AM.
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