These deck plans assume you're building on level ground. But what if your yard is on a hillside? Building a deck on a steep slope is more complicated than building on level ground because of the physical demands of raising the deck frame, and because of the challenge of taking precise measurements before locating footings and cutting posts. The best approach involves modifying standard deck-building sequences.

The general idea when building on a steep slope is to start by building the outside frame and propping it on the ledger using a set of temporary posts, and only then determine the permanent locations for posts and footings. By modifying the conventional deck-building sequence you avoid the risk of digging and pouring footings only to find, after setting up the deck frame, that the footings are slightly off center.

Constructing & Installing a Temporary Support Beam

Once you've determined the size of the deck and attached the ledger, identify the approximate locations for the footings, according to your deck plans. Mark these locations with spray paint or stakes.

Next, position bases for temporary posts at least 2' away from the estimated footing locations, and level and anchor two 2 × 12 scraps on the ground to support the temporary posts.

Prop up the temporary posts using 2 × 4 braces and stakes, and check the posts for plumb. Mark a cutoff line on each post by holding a long, straight 2 × 4 against the bottom of the ledger and the face of the post, and marking the post along the bottom edge of the 2 × 4. Cut off the posts at this height. A handsaw will work, although a reciprocating saw is ideal.

Construct a temporary support beam at least 2' longer than the width of your deck by face-nailing a pair of 2 × 4s together. Center the beam on top of the posts, and toenail it in place.

Building & Installing the Outer Frame

Build the outer frame of your deck according to your construction plans and attach joist hangers to the inside of the frame. With several helpers, lift the frame onto the temporary supports and carefully move it into a position against the ledger.

Endnail the side joists to the ends of the ledger. Then, reinforce the joint by installing angle brackets on the inside corners of the frame.

Make sure the frame is square by measuring the diagonals. If the measurements are not the same, adjust the frame on the temporary beam until it is square. Now, check the frame for level. If necessary, shim between the temporary beam and the side joists to level the frame. Toenail the frame to the temporary beam.

Locating & Pouring Footings

Use a plumb bob suspended from the deck frame to stake the exact locations for post footings on the ground. NOTE: Make sure the footing stakes correspond to the exact center of the posts, as indicated by your deck plans.

Dig and pour footing for each post, and insert J-bolts for post anchors while the concrete is still wet.

Attach post anchors to the footings, then check once more to make sure the deck frame is square and level. Adjust the frame, if necessary.

Measure from the anchors to the bottom edge of the deck beam to determine the length for each post. When calculating the height of the posts, make sure to take into account the post-to-beam attachment method you've chosen.

Cutting Posts & Attaching the Beam

Cut the posts to length and attach them to the post anchors and to the beam.

For extra support and to help prevent sway, your inspector may advise you to brace the posts by attaching 2 × 4s diagonally from the bottom of the post to the inside surface of the deck frame. Toenail the braces to the post and deck frame using 16d galvanized nails.

You're now ready to remove the temporary supports, install the internal joists and complete your deck according to the original construction plan.