How to Make a Perpendicular Hardwood Floor Flush

Place a carpenter's square against a wall or cabinet against which the flooring boards will abut. Use a pencil to draw a perpendicular line on the subfloor that extends into the space where the floor will extend. The line should be flush with the surface of the wall or cabinet.

Use a chalk line to extend the line across the entire space. Mark it either to the opposite side of a doorway or to a point at which the boards again abut against a wall or cabinet. The line you make should be flush with the surfaces on both sides of the space.

Measure the width of the space. Cut a straight piece of 1-inch-wide lumber that has a length equal to the width you measured. A spare piece of flooring works well, but any straight lumber is suitable. If the edge is irregular, straighten it by running the board through a table saw. Set the saw fence a distance from the blade that is slightly less than the width of the board. Push the board through.

Place the board on the floor and align one edge with the chalk line. If you use a spare flooring board, place it so the grooved side is facing the floor. If you prepared a board with the table saw, put the side you cut facing the floor. Nail the board to the subfloor with several 2-inch finish nails. Allow the heads of the nails to protrude about 1/2 inch so you can pull them out easily when you're done.

Install the floor across the opening. Begin each course of flooring at the brace and work toward the opposite wall. Chop off the end of each flooring board that butts against the brace with a chop saw. When you install the board, tap it against the brace before you nail it to the floor.

Pull out the nails and remove the brace when you have installed the flooring across the opening. The ends of the boards will be straight and flush to the walls or cabinets on either side.