This reader wants to know what a shiplap joint is, and when is it used – besides for building ships, of course?
Michael Dresdner: Most joints make wood come together to make angles, or to make the wood wider. Shiplap joints make the wood longer by cleaving one piece to the end of another. Some musical instrument makers also use shiplap joints, and I am sure there are many other uses outside my sphere of experience.
Ian Kirby: A shiplap joint is used for wooden sheathing where the boards are rabbeted so the edges of the adjacent board overlap to make a flush joint. You may find it is used incorrectly on houses where the planks have overlapping clapboards. These houses are known as ‘clinker built’ and also known as “lap strake” or “lapstreak.” We suffer from mixed up terms from place to place.
At it’s worst, I’ve heard shiplap used to describe the joint used to join boards end to end. There are a variety of design details for the joint-from tapering each end to form a glue surface to a half lap joint with wedges – but they are all scarf joints also used in shipbuilding. That may be the cause of the confusion.