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For horizontal boards that don’t exceed 150mm in width, the vertical overlaps for feather edge and square boards should be a minimum of 25mm. This is relevant for dry wood, but if the green wood is used there may be some shrinkage after it is installed so board width and overlap will need to be considered.
when using shiplap or rebated feather-edge horizontal boards for cladding, it is possible to reduce the overlap to 15mm but you should have a 2mm gap to allow for possible extension of the boards. The curve or chamfered shoulder to shiplap boards helps it to effectively drain away water and create a strong shadow line.
Open jointed boards on horizontal cladding should have an 8-15mm gap at the outer face. The top and bottom edges should be chamfered to about 30o, this is so that water runs off the top edge and doesn’t run onto the underside of the boards, these edges also allow for overlapping so that the breather membrane underneath the horizontal boards doesn’t get exposed to direct sunlight.