Blocking is the secret step to flattening crowned or wavy joists. Blocking is required within 8 feet of a ledger, ideally centered between the house and the outer beam. But we recommend a distance no greater than every 6 feet to minimize the waves in your joists. After this step, your blocking will force the joists more level. If you have a 16’ deep deck, place 2 rows of blocking equidistant between the house and outer beam, at approximately 5.33’ apart.
In this video, master carpenter Pat blocks a deck with a DOUBLE PICTURE FRAME and a SEAM BOARD running down the center of the deck