How to Build a Platform on a Hillside

Outside Framing

• 1

  Drive in a wooden stake at each of the two top corners of the proposed platform. Use a tape measure to space them properly. Make your stakes a little taller than the height of your platform. Tie a string between the two stakes with a string level on it. Adjust the string to match the height of the platform.

• 2

  Tie strings to each of the stakes, as long as the platform will be out from the top posts. Tie the other end of each string to a second post, to represent the downhill post. Drive the stakes in and use the string level to mark the height of the platform. Measure between the two new downhill stakes for proper spacing.

• 3

  Dig a post hole at least 24 inches deep in place of each stake. Stand a 4-by-4 post in each hole. Cut two pieces of 2-by-8 lumber the length of the platform, using a circular saw. Drill two 5/16-inch holes in each end of each board. Attach one end of each board to the outside face of the uphill posts at the platform height with one 3-inch lag bolt each.

• 4

  Use a level and attach the bottom end of each 2-by-8 to the downhill post at the platform height. Drive the bolts in with an impact driver, and add a second bolt to each end of each board once they are level. Check the posts for level too, and adjust before snugging the second bolt in place.

Finishing Platform

• 5

  Cut two pieces of 2-by-8 to fit the width of the platform from outside to outside of the first two 2-by-8 pieces. Bolt them on the uphill and downhill faces of the posts, as you did with the first two, so that their ends are flush with the outside faces of the original 2-by-8s.

• 6

  Fill each hole with gravel up to 3 inches below grade. Pack dirt in the remainder of the holes and tamp it down tight. Cut your posts off even with the 2-by-8s with a reciprocating saw.

• 7

  Cut one 2-by-8 to fit between the two side 2-by-8s every 12 inches of platform length. Fit one of these joists between the two side framing members every 12 inches, measuring from the center of one board to the center of the next. Drive two 3-inch treated deck screws into the end of each of these pieces, through the side 2-by-8s to anchor them in place.

• 8

  Measure and cut 5/4-inch thick by 6-inch wide decking boards to fit the platform lengthwise, perpendicular to the joists. Fit them to the top of the platform, spacing the boards 1/4 inch apart, starting at one edge and covering the entire surface. Attach the boards with 1 5/8-inch treated deck screws -- two screws through each deck board into every joist.