Scarf Joint With A Wedge

Scarf Joint with a Wedge

Nothing beats the look and strength of an undersquinted scarf joint with a wedge. In this detail, we illustrate three types of methods to connect the two beams and joints together.  Please note that the preferred method for scarf joint placement is over a knee brace, not over a post.

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This example uses a piece of all-thread secured with nuts and washers, a large false peg can be used to hide the nut and washer after installation.  Using this method allows you to adjust the joint after the raising as the timber dries.

A good structural screw made by GRK or ASSY can take a beating and will perform well over the life of a frame.  If they are spaced evenly and pre-drilled, the installation will be easy and will result in reduced stress on the screws during assembly.  Shown with the scarf joint centered in the knee brace.

While not as common now in engineered frames, a few 1″ pegs could be used or simply using the wedge will do.  While this is an easier and cheaper way to handle this connection,  this method does not perform as well in holding the joint together as the other two methods. It also does not allow any ability for adjustment in the future.

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11 thoughts on “Scarf Joint With A Wedge”

  1. Brice
    Would a longer joint be stronger what do you recommend it seems to me that it would change where the brace meets the joint will this be an issue if the joint was say 36″ long?

  2. I brought it down to 16” end to end of the undersquint. Looks good to me, but I am not an engineer

  3. Brice.
    The timbers I purchased were not custom cut to my specs, I found a deal and bought on craigslist. They’re 8 x 10’s but are only 16′ in length. The king post plan 12×16, has a ridge beam and 2 top plates that are designed to extend to 20′. Can I scarf joint all three of these timbers on their corresponding knee braces?
    Would I be better off doing something like switching to a tongue and fork rafter plan or just buying 20 footers? Forgive me if I have asked this form of question before.

  4. Another use for a scarf joint: I’m using this joint to straighten a 4×12 ledger that is 16’ long. It has a belly of an inch in the middle when stood on the narrow edge. I don’t like the looks of that, so I cut a template out of masonite and laid everything out in pencil to see how it’s gonna work – it looks good so far and I’m only losing about 9” in overall length which still leaves me plenty long for what I need.

  5. refer to page 46 of Historic American Timber Joinery and you’ll understand why this joint is Not recommended directly on top of a post

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