Call your local code office to speak to a worker there, or go directly to your state’s website for the necessary information. Alternatively, sites like BuildingsGuide have a directory of every state website in the US. Get a building permit for the extension if your local town or homeowner’s association requires one. Bring in a schematic for the extension with dimensions so they can get a clear picture of your plans.
Some building codes may even require your support posts to be buried 12 inches (30 cm) below the frost line. Check local regulations to be sure! If a deck’s support posts aren’t below the frost line, the annual frost-thaw cycle can cause those posts to buckle and deteriorate over time.
A frame is a structure that holds your deck’s floorboards in place. Look underneath your elevated deck for spongy, discolored wood (rot), and consider hiring a professional inspector to ensure the deck is examined properly. Decks attached to your home have a ledger board: a plank of wood connecting the house and deck. The ledger board should be correctly and securely fastened to the house before you continue with the extension. Heaving and thawing cause wood to buckle after cold weather. Ice gets in the cracks of the wood and expands; when the ice thaws in the spring, the wood splinters and breaks.
To make planning easier, consult an architect or use an online deck-designer tool to plan your extension.
Lumber for the floorboards should be pressure-treated, and you can choose between natural wood like cedar or redwood, composite boards (which mix wood and plastic), or plastic PVC decking.
If you have a painted deck, use a handheld screwdriver to remove the paint from the top of the screw before removing it. Similarly, clear wood away from the top of a screw using a Dremel tool if the wood is blocking your screwdriver. Using an impact driver (a type of drill) is more effective than a cordless driver because it has more torque, which is the rotational force that helps you remove screws from the wood.
To remove the fascia, use a hammer and a small pry bar to remove the nails connecting the fascia and pull it away from the wood deck. A fascia board, also called a “deck skirt,” is the trim that makes your deck look polished. It covers the deck’s wood perimeter and serves as added protection against the elements.
If you choose a same-level extension, use one of the existing substructure support beams as the ledger board. Whatever edge of the deck you extend, anchor the new frame to that sideboard—no need to add a ledger board. Add joists to the bottom of the beam if you want a step-down extension. You can still use the sideboard of the existing deck, but all joists (boards that form the deck’s structural base) should be attached to its bottom rather than its top. Attach a new ledger board for a step-up extension. This extension does require a new ledger board; fix the new sideboard on top of the existing substructure’s edge and connect the extension frame to that board.
Ensure the twine is level with the top of the existing deck’s rim joist (a technical term for the boards that make up the sides of your deck’s structural base).
Using a tape measure is the simplest way to calculate each supporting post position.
Concrete typically needs about 24 hours to dry properly, so stop working and return to your deck the next day once the anchor bolts are in place. Use roughly half a bag to fill each hole before mixing in water. Concrete forms are plastic or cardboard tubes that can hold the concrete, and once hardened, the concrete and anchor bolt form the footing on your deck extension. Position post bases over the exposed anchor bolts and fasten them by tightening a washer and nut by hand. Then, attach wood posts by sliding them into the bases and drilling them in place with structural screws (which should be included with the bases).
Attach the joists by inserting 3. 5 inches (8. 9 cm) by 5⁄16 inch (0. 79 cm) bolts into each hole and fastening them with a washer and nut. Once the washers and nuts secure each bolt, you can tighten them with a socket wrench to ensure the joists are firmly attached. As joists are the boards that form your structural base, this new joist makes up the side of the extension attached to the existing deck.
Ensure the rim joists can extend to the outside face of your corner posts, matching up with the older joists on your original deck.
Internal joists are the support beams holding up floorboards inside the deck’s base.
In other words, there should be 2 screws affixed to the deck board every time it meets an inner joist and on either end where the board meets the rim joists. Once again, use your circular saw to cut the planks to your desired length.
If you’re staining the deck (rather than using a sealant), sand the deck’s surface with an orbital sander and 60-grit sandpaper first to help the wood absorb the stain better. Vacuum the deck after you sand it to pick up the dust. Don’t worry about the underside of the deck; it won’t need any stain or sealant, especially if it’s made from pressure-treated wood. Of course, you can add stain or sealant to the deck even if you took the time to cover it with entirely new floorboards.
