Shiplap and featheredge cladding
Shiplap and featheredge do the same job by different means. Shiplap is machined with a rebate so that each board locks over the one below and presents a flat face. Featheredge is a plain tapered board, thick at the bottom edge and thin at the top, laid so that each board overlaps the one beneath. Both shed water downwards and outwards; neither is watertight on its own.
Because boards move across their width with the seasons, each one is fixed with a single line of fasteners rather than pinned at both edges. A board nailed top and bottom cannot expand, so it splits instead. Fixings are kept back from the board ends by a comfortable margin for the same reason, and pre-drilling near an end is worth the extra minute.
The bottom board sets the line for the whole wall and should be levelled independently, not measured down from the top. A drip at the bottom edge, formed either by letting the board project past the frame or by a separate batten, keeps water from tracking back underneath and into the floor frame.
Behind the boards, a breather membrane and a batten cavity let any water that does get through run back out, and let the back face of the board dry. Cladding fixed tight against a solid wall with no cavity stays wet on its hidden face for far longer after rain, and that hidden face is where decay starts.
Boards drawn at 125 mm cover
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