About half the deck jobs we do are rebuilds of existing decks. Unless the existing joists are very warped or decayed, we try to reuse the frame. Unlike new joists that have intact tight grain, however, old joists are punctured with hundreds of holes from the old decking and often have grain cracks opening up on the tops. To give a deck another 20 or 30 years of life, we always install cap strips over the joists to minimize the chance that water and debris will seep through these openings into the core of the old joists and lead to decay.

There are many joist-cap options, including self-adhering membranes like Grace Vycor Deck Protector, DeckWise Joist Tape, and ProtectoWrap Deck Joist Tape, as well as staple-on joist cap strips like YorkWrap. Another option is to make your own joist caps by cutting 3- to 4-inch-wide strips of #30 tar paper or synthetic roof underlayment and stapling the strips in place.

After we’ve removed the old decking and pulled out any nails or screws and before installing the joist caps, we scrape the top of each joist with a block of hardwood or scrap decking. Cutting a 45-degree bevel on one end of the block makes it easier to knock off any caked-on debris. Since we don’t always find all of the fasteners on our first denailing pass, scraping the tops of the joists with the blocks gives us a second chance to find any nail stubs we missed.

When we’re working on an elevated deck and will be standing directly on the joists, we always use self-adhering joist caps. The membranes bond aggressively to the joists and the surfaces are slip resistant. On grade-level decks, we use economical non-adhesive joist caps and fasten them with hammer-tacker staples every 3 feet or so. Since we’re walking between the joists instead of on top, the staples only have to hold the joist cap strips in place until the decking is installed.