How to Fix a Wobbly Deck
Two common causes for a wobbly deck and how to stabilize your space
Wobbly deck got you shaking with every step? There are a few reasons for why your deck may not feel secure, and it’s important to get to the bottom of things so that the shaking doesn’t put undue stress on the deck’s fasteners and connectors. Let’s examine a couple of scenarios and how to fix each problem.
Check the Spacing of Your Joists
One reason for a wobbly deck may be that the floor joists are spanning too great a distance. The easiest way to correct this problem is by installing a support beam and posts under the joists to cut the span in half. Use a 1:1 ratio for sizing the beam and spacing the posts; for example, a 10-foot span would need two 2x10s.
Add More Support to Composite Decking
Another problem could be that you have replacement boards made of a composite decking mixed in with the original wood boards. Composite decking isn’t as stiff as solid wood, and the give between the two kinds of boards could cause the deck to shake.
To stiffen the deck, go underneath and install a row of 2x8 blocks down the center, perpendicular to the joists. Stagger them with enough room to nail or screw them in place through the end grain, then fasten the treated 2x4s to the underside of the joists so they run from corner to corner, forming an X. Where they cross, make a lap joint so that both boards fit flat against the joists.
Attach the 2x4s with 4½-inch flathead HeadLOK screws, which are stronger than standard screws and can resist corrosion. Place one screw in each joist, then go back and add one more screw to every other joist.