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I'm putting together a pergola.

Details of the build:

  • 11x17' roof footprint
  • 8x14' to the outside of 6x6" posts
  • Double beams on the 10' side (although not sistered together); Rafters crossing a ~13' gap
  • Beams will be notched and then the joists will rest in the beam notches and then be secured using rafter clips.

Here's my issue:

  • I was able to find some 2x10x14' cedar boards on the cheap - but could not find any 18' at any sane price.
  • The 14' foot boards go all the way to the outside of the beams, but I would like decorative ends on them.

What are my best options for "stretching" the 14' boards? I'm thinking:

  1. Scarf the 14' boards so that some of the original board can sit on the inner beam. Titebond III the scarf joint. Secure the decorative ends on with 8" headlok screws.

Option 1

  1. Scarf in the other direction and then glue/screw the same way. This way the decorative ends become more structural and support the board in place.

enter image description here

  1. Don't scarf at all. Here the decorative ends get supported via 3/4" dowels and are toe-nailed on:

Option 3

  1. Use half lap joints to join boards and then use construction screws to join the outer rafts to the posts and to join the inner rafters to the beams.

Option 4

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  • 1
    Decorative ends were scarfed onto the rafter tails on my house and nailed into place. Every. Single. One. has come loose. Of course, the house was built in the 1890s and I'm not sure how long they've been loose, but it's been more than 30 years (until I got a chance to fix them over the last 2 summers). They were also just nailed, not glued & screwed, YMMV.
    – FreeMan
    Jun 20, 2023 at 15:12
  • Also, option #2 seems to be the worst of all possible worlds. When that joint comes loose (not if - it's wood & wood will move), you loose the connection between the beam and the post. Based on the shape of the joint, it might not slip directly down, but it will be free to move laterally which will end up in vertical movement, possibly right on someone's head.
    – FreeMan
    Jun 20, 2023 at 15:14

1 Answer 1

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I'd probably forego the challenging* and unnecessary angles and do a basic square half-lap. This allows you to run long screws through both members into the beam, and retains full bearing of the primary members.

It also hides the joint better--parallel grain matching is often less conspicuous than an angle. You might position it inboard of the beam face to conceal the vertical joint a bit and make the extension more robust.

______________________ ___________________________________________
\                :    |
 \               :    |
  \            __:____|       primary beam
   \          |  :
    \         |  :<-- screw
     \________|__:___________________________________
            |    :    |
            |    :    |
            |    :    |
            |         |<-- beam (with blocking, if needed)
            |         |
            |         |
            |         |

Consider doweling the lower vertical joint for positioning support, or run a horizontal screw through that area down low. The vertical screw could be two--one for each of the upper and lower halves--if length is a problem.

* It may seem trivial to match arbitrary angles, but it can be easier said than done. A slight mismatch and your extensions come out of parallel. This could be visually apparent. With square cuts you can use miter and table saws for accuracy and precision, at least for the bulk of the cuts. You'll obviously need to finish inside corners with other saws.

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  • Thanks! Half laps seem to be the way to go. I don't have a single solid beam to attach things to (it's 2 2x10 beams running parallel set into a bearing surface in the 6x6posts), but I think I can get screws long enough to attach the rafters to the beams and then back everything up with rafter clips. I added a picture of this as option 4 above.
    – Gary P
    Jun 21, 2023 at 0:39
  • Rafter clips are fugly and not really needed as there's little uplift potential. I'd avoid them.
    – isherwood
    Jun 21, 2023 at 12:49
  • How else would you attach the rafters to the beams? Currently the rafters will be sitting in slots in the beam.
    – Gary P
    Jun 22, 2023 at 0:13
  • The slots appear to be in the rafters, but that's immaterial to the question. Screws from above, per my diagram, would be plenty good.
    – isherwood
    Jun 22, 2023 at 12:29

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