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.
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.
Place a short length of two-by-four lumber on the ground beside the support post as support for the jack.
Position a car jack on the two-by-four or use a bottle jack.
Raise the jack so it contacts the wooden floor joist supporting the decking. Continue raising the jack until the deck is no longer sagging.
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.
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.