How to Jack Up a Deck

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Things You'll Need

  • Two-by-four lumber

  • Car jack

  • Wood or masonry (for use as shim under support post)

Raise a sagging deck with a jack to make repairs.

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.


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.


Place a length of four-by-four lumber on top of the jack vertically when raising a deck that is several feet off the ground. Use the lumber piece to span the distance between the jack and floor joist of the deck.



Keith Dooley

Keith Dooley has a degree in outdoor education and sports management. He has worked as an assistant athletic director, head coach and assistant coach in various sports including football, softball and golf. Dooley has worked for various websites in the past, contributing instructional articles on a wide variety of topics.