The Best Way to Keep the Top of a Shadow Box Fence Level

Measure, mark and trim a piece of scrap lumber to the same width as the desired spacing between the infill pickets or planks for your fence. This will be the spacing block, used to easily ensure that the pickets or planks are evenly spaced on the fence rails.

Drive a nail into the first fence post at the desired height of the pickets. Hammer the nail only about 3/4 inch into the post so you can easily remove it later. Tie a string around the nail. Pull the string taut, then position it against the second post. Hang a line level on the string. Raise or lower the string until the line is level. Hammer a nail into the second post where the level string crosses it. Tie the string to the nail on the second post.

Working from left to right, position the first infill picket against the first post with the top edge of the picket aligned to the level string. Use a carpenter's level to make sure that the first picket is plumb. Screw the first picket to the fence rails with a drill and driving bit.

Place the spacing block against the right edge of the first installed picket. Place the next picket against the right edge of the spacing block. Align the top of the second picket to the level line. Attach the picket to the top rail with one screw. Move the spacing block to a lower rail, then butt the lower edge of the picket against the block so the second picket will be plumb. Finish attaching the second picket to the rail.

Continue adding consecutive pickets, using the spacing block to ensure uniform spacing and using the level line to ensure that the top of the fence is even and level. Attach the pickets on the opposite side of the rails by aligning them to the first row of pickets.