A deck can be a focal point of outdoor activity or a quiet place of rest for many homeowners. Typically made of pressure-treated lumber, decks can sag slightly in one or more areas over time as the result of the ground settling under a vertical support post. Jacking up the deck and shimming the post can resolve deck sag problems.

Raise a sagging deck with a jack to make repairs.

Step 1

Access the area under the deck. Identify the area of the deck that is sagging and locate the support post that needs to be shimmed.

Step 2

Place a short length of two-by-four lumber on the ground beside the support post as support for the jack.

Step 3

Position a car jack on the two-by-four or use a bottle jack.

Step 4

Raise the jack so it contacts the wooden floor joist supporting the decking. Continue raising the jack until the deck is no longer sagging.

Step 5

Place a wood or masonry shim under the deck support post so it will once again support the deck securely. Use treated wood or thin masonry stepping stones as a shim under the support post.

Step 6

Lower the jack so pressure is once again placed on the support post. Determine if the deck is still sagging and add another shim under the post if necessary.