Can a Mortise & Tenon Brace Be Installed After the Post & Beam Have Been Assembled?

Hi Gerald, thank you for your question.

I do not think it is possible to install a typical M&T brace retroactively in an existing frame, as the square corner prevents the rotation necessary to get the brace into place.

Depending on what is required of the brace addition structurally and the geometry of the joint, there is an alternate option of using pegged mortise and tenon joinery that is cut on one side of the timbers. As long as it is cut preciously it should work similar to a centralized M&T typical brace connection.

That would look something like this:

Hopefully, this answers your question and good luck with your project!

Thank you,
Matthew McGinnis, EIT
Junior Timber Frame Engineer
Vermont Timber Works