How to Stiffen a Bouncy Deck

Weathered Wood 2
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A safe, well-built and attractive outdoor deck adds beauty and value to your home, increases your living space, and provides the perfect spot for entertaining guests.

However, all of this use and exposure to the elements eventually takes its toll, and some older decks begin to feel “bouncy,” meaning the deck’s foundation needs shoring up. Wood planking, a common decking material, expands and contracts in various ways, which can create unsightly gaps and give the deck a spongy, unsteady feeling when you walk across it.

By using a technique called blocking — affixing pieces of wood in between the joists located underneath your deck — you can easily stiffen a bouncy deck.

Tools and Materials

  • Long-sleeved shirt and long pants (optional)
  • Work gloves
  • Work light
  • Drill with screwdriver attachment to remove side panels
  • Chalk line
  • Tape measure
  • Treated lumber the same size as the joists (usually two-by-eights or two-by-10s)
  • Circular saw
  • Hammer or rubber mallet
  • Ladder (optional)
  • 16d galvanized box nails

The Process

  1. Make sure no one is standing on the deck as you do these repairs. Remove all items from the deck, including furniture and flower pots. If you have a raised deck with living space underneath, remove all of the items under the deck.
  2. Suit up before starting work. If you have a low-lying deck, wear a long-sleeved shirt and pants to protect your body while crawling underneath. Wear gloves to protect your hands. You will also need a light attached to a headband to wear under the deck or a work light.
  1. Get under the deck. The sides of some decks are open for easy access underneath; others are covered by latticework or decorative panels. These panels are usually secured with a few screws in the corners. Keep in mind that animals and snakes like to hide in small, dark spaces, so be sure to look around carefully before crawling under the deck. Make loud noises or bang on the deck supports to frighten off animals that may be lurking.
  1. Once you are underneath the deck, check to see whether you have any loose or decaying planks, which will need to be reattached or replaced depending on their condition. There’s no point in trying to firm up joists beneath rotting boards.
  2. Starting near the end of the deck, snap a chalk line perpendicular to the joists. Joists are small beams arranged in a parallel pattern to support an overlying structure. The chalk line should run from one end of the deck to other. Repeat this step every 3 to 4 feet across the deck. You will place the blocking along the chalk lines.
  3. Starting with the first chalk line, measure the space between the first two joists. Make sure the measurements are precise, as you’ll be cutting your blocking to fit snugly between the joists. Blocking will effectively unify the joists so that any weight borne by one joist is partially distributed to those adjacent to it. Just be sure not to install blocking directly beneath the spaces in between the deck boards, as this will form pockets that will catch and hold water, which will only exacerbate your problem
  4. Measure and cut a piece of treated lumber to fit in between the joists. This will serve as your blocking. Using a hammer or rubber mallet, tap the blocking into place — narrow side facing up — using the chalk line as a guide.
  1. Once the blocking is in place, drive three galvanized nails through the joists on each side of the blocking to hold the wood into place. One nail should be at the top of the blocking, one in the middle and one at the bottom.
  2. Repeat this process along the chalk line, staggering the blocking so that you can nail each piece easily. When you finish, every second piece of blocking should be aligned.
  3. Remember, the planking that makes up the surface of your deck is exposed to all sorts of wear and tear from the humans who use it, plus whatever else Mother Nature dishes out. Keeping your deck safe as well as beautiful means doing regular maintenance checks at least once a year. Look for damaged or loose boards, inspect for structural damage to the supports underneath the surface and shore up any weak spots to ensure that you, your family and friends can continue to enjoy the deck without fear of injury or discomfort.