Scribe a Deck Board to a Wall by Cutting the Scribing Block Wider Than the Board

The Problem

The last deck board against a wall almost never runs parallel to it. Walls bow, render is uneven, and the board has to follow that line while still leaving a gap — decking needs an expansion gap at the perimeter, and a board pushed tight to a wall will lift or split as it moves.

Scribing the board to the wall solves the shape. The gap is the part people then get wrong, because they scribe tight and try to add a gap afterwards by eye.

The Technique

Build the gap into the scribing block, so the line you draw is already the line you cut.

1. Lay the board to be scribed in position, lined up with the previous board and parallel to it, not to the wall.
2. Work out the block width: the board's width plus the gap you want. His boards are 140mm and he cuts the block at 150mm, which gives 5mm at each end of the run.
3. Run the block along the wall with a pencil held against its far edge, tracing the wall's shape onto the board across the whole length.
4. Cut to the line.
5. Drop it in and check the fit against the wall.