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Mortise and Tenon Corner Joint

Timber Frame Corner Joint

Used primarily on plates and floor systems, this corner joint uses a mortise and tenon on one plate (red) and a tusk tenon on the opposing plate (purple).  The opposing plate (purple) gets housed onto the plate for bearing. It is important that the plate bears on the post and not the tenon.  To account for timber shrinkage it is recommended that you oversize the bottom of the mortise of the tusk tenon.  A couple of pegs in each joint  secure them.

To help eliminate joinery conflicts there are two different sizes of knee braces: a 36″ (aqua) and a 32″ (green).  We still had to clip the 32″ brace tenon a little at the bottom.

17 thoughts on “Mortise and Tenon Corner Joint”

  1. Hi Brice,
    Thanks for all the good information. Can a knee brace be installed after the perpendicular plates are put together or does it need to bet assembled at the same time the plates are being installed. Thank you!


  2. Stephen Giddings

    If the blue post is a 12″ x12″ post
    And the red plate is a 12″ x12″ plate what size pegs are needed ?

  3. The standard size is one inch but given the scale of the timber going up to 1 1/4″ would be ok. Check with the engineer on the project as you will take more out meat out of your tenons.

  4. excuse me…may i ask something?? Is a dowel will be use it at the mortise and tenon corner joint?

  5. Mr Peter K Jackson

    Hi, I love your site – so helpful!

    Would this joint work with 150mm x 150mm timber (oak)?


  6. Rick O’Brien

    Hi, great site and drawings! Question about the corner joint. Are the knee braces mandatory for this corner connection since both beams are bearing on the post? Wondering if they be omitted?

  7. hi brice, very nice drawings. would you let me know your thoughts about whether a dovetail joint would be as good, or better for attaching the tie beam (purple) to the main plate (red)?

    separately, do you have a preference for attaching a tie beam to a granite stone wall. here i’m thinking about attaching a short ‘upright’ with tenon, so as to sit the tie beam mortice on top?

  8. Brandon Sullivan

    In regards to a dovetail on a corner, intuitively that seems like a poor choice. A dovetail is only as strong as the cheeks on either side of the tail. Seems like there would not be enough meat on the outside corner of the plate’s dovetail mortise. Considering that wood is weakest along the grain, I could imagine there being some significant issues with this method. See image I sketched to try and illustrate: https://timberframehq.com/wp-content/uploads/2023/02/mortise-and-tenon-corner-woodworking-joint.jpg

  9. how much should the purple plate bear on the post? it doesn’t look like much but I’m wondering if 1″ for 8×8 timber is okay.

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