How to Extend an Existing Deck

At this point, you may be using your imagination and having daydreams about entertaining on your new extended deck. As much as we hate to burst your bubble, we have to recommend that you check on your local building codes and permit requirements. Do this early in the process so that you know what limitations it may pose. The codes from your local building department or homeowners association might limit the size or location of your expanded deck (perhaps that's the reason why it's so small to begin with!). You'll also need to contact your utility companies and ask them to send someone out to your house to mark any underground utility lines.

Before widening or lengthening your deck, it's vital to ensure that the original deck is structurally sound: Check the framing for any signs of rotting, cracking or other degradation. If the deck is attached to the house (not freestanding), make sure the ledger board is properly secured to the side of the house. Also, inspect the posts underneath that support the deck for evidence of having heaved and thawed. Even if you're simply adding a new level to the deck, and the existing foundation won't be used to support the new portion, use this renovation as an opportunity to update the old deck if needed.

When planning your deck layout, use mason string attached to batter boards or wood stakes. Contractors will use this method to keep the deck level and square, but you can use it in the initial planning stage to visualize the placement of the deck. Consider space issues, and set up your desired lawn furniture inside the mason string area. Don't forget about sun exposure and how much sun or shade your deck extension will get.

Even if you plan to hire a contractor to install the deck extension for you, it's a good idea to do all these steps anyway, so that you know what to expect and can be as precise as possible when negotiating and explaining what you want.

Most experts agree that a deck extension project is no easy task, and that it's best to hire an experienced contractor to do the work for you. Make sure the contractor is licensed, has insurance and will obtain any necessary permits (if the deck is close enough to the ground, it may not necessitate a permit). Shop around for a good estimate, giving each contractor specific details on what you have in mind.

Even if you hire a contractor, it's wise to know the basic deck-building process so you understand what's going on. Familiarize yourself with the names of deck components. The ledger is the board that affixes the deck to the house. Vertical posts are set deep into the ground on concrete and secured with gravel. Local codes will likely dictate the minimum depth of post holes for proper support, which will probably be below the frost line. You'll probably need to dig post holes and install new posts for additional support for your extension. You can mix the concrete for the posts on site or get it pre-mixed from a local supplier.

Posts attach to horizontal beams (also called girders). The joists are the horizontal support boards that sit underneath and perpendicular to the surface decking. Codes may also specify the distance between joists. When extending your deck, it's especially important to know the safety rules and regulations about cantilevering. Cantilevering refers to a beam that extends beyond a support post or a joist that extends beyond a beam. The further it extends, the less safe it will be. For proper drainage, make sure the surface decking boards are slightly spaced (about the width of a 16d nail) [source: Lowes].

If the deck extension is far from the ground, safety considerations also include railing posts and balusters (vertical support pillars between posts). And if you want access to the lawn, you'll also need to think about stairs. Codes may dictate the requirements for proper rise (height) and run (depth) of each step.

Overall, the project will take several days (or several weekends) of tough, meticulous work, and costs can reach upwards of $5,000. But in the end, you'll have a lovely outdoor entertaining and living space that could last decades.

For lots more information on construction projects, see the links on the next page.