IIRC, an 8:1 splice (i.e. 10" tapered or stepped splice for 5/4) will give the same strength as the original wood. If stepped, you want at least 8 steps evenly spaced and of even thickness graduation. This is the normal formula used wooden in boat building. You need to use an adhesive that won't creep, so PRG would be an obvious choice.
Can the person use spliced lumber?
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