How to Drill Holes in Tongue & Groove Deck Boards for Drainage
Tongue and groove deck boards present a solid surface with none of the gaps found in traditional 5/4-inch decking. While the proper installation pitch should take care of most drainage issues, a deck that collects water can be problematic.
Depending on the type of material your deck is made from, drilling a few well-placed holes may be all it takes to help keep you and your deck dry.
Use a garden hose to soak your deck, or observe the next rainfall, to determine where the water is standing on your deck.
Examine each area where you have puddling using a level to determine where the lowest point in that area is.
Use a broom or mop to dry the area and mark the lowest point with an "X" made with a piece of chalk.
Check underneath the deck to be sure that the spot you have marked is clear of any framing members. If it is not, shift your mark to one side or the other until you are over an open space where the water will be able to drain freely.
Prepare a sharp 1/2-inch paddle or spade bit. For wood and composite decks, use a bit made for wood boring. For vinyl and other plastics, a bit designed for metal will create the cleanest cut. It is best to use a new or freshly sharpened bit.
Wrap a piece of masking tape around the bit at the same distance from the flat of the blade as the thickness of your deck boards. This will serve to indicate when you are close to cutting through.
Place a piece of masking tape over the area to be drilled and mark the "X" on it for vinyl or other high-gloss finishes to prevent scratching the deck around the hole.
Use a 1/8-inch-thick twist bit to drill a pilot hole in the centre of the "X." This will serve to guide the paddle bit and avoid scratching your deck.
Place the tip of the paddle bit in the pilot hole. Make sure that the drill is set to forward and on high. Pull the trigger and let the bit come up to full speed before beginning the cut.
Apply steady pressure to the drill, keeping it as level as possible. As you approach the through mark---the tape you wrapped around the bit---make sure not to push. Slightly lessening the pressure as the bit cuts through the bottom will minimise any breakout the bit may cause on the underside of the deck.
Repeat the process for each of the areas you marked. Use the hose to check your work. If you still have standing water in any of the areas, drill a second hole to help the water drain.