How to Expand an Existing Deck

Important Insights

A deck is a fantastic way to enhance your living area. As an extension of your home, it allows you to enjoy the outdoors while still being close to the comfort of your house. It’s also an excellent space for hosting large gatherings: Not only does it add more room, but it gives your guests the freedom to stay inside or step outside. However, if your deck is small and cramped, it won’t be very useful for entertaining. If you find yourself frustrated by the limited space, it can be even more discouraging to realize how costly and time-consuming it will be to demolish and rebuild it.

The good news is, if the original deck is in solid condition, you might just be able to extend it rather than starting over. But don’t be fooled – this is not a simple DIY project. It requires advanced skills and experience in similar projects. It’s highly recommended to hire a professional contractor for this job.

With the right amount of space, you have a few different options. You can opt to widen or extend the deck at its current level. Many homeowners choose to add multiple levels to their deck, linked by stairs. This is especially useful when you’re concerned that new decking materials may not match the old ones (which is likely if the old deck is weathered). By placing the new deck on a different level, the transition feels more seamless and less noticeable. You don’t have to have a full flight of stairs either – one or two steps will suffice. Multi-level decks are also great for hosting because they create distinct, cozy areas for guests.

What should you consider before extending your deck?

Important Factors to Consider Before Extending an Existing Deck

By now, you’re probably imagining hosting gatherings on your newly extended deck. But before you get too carried away, it’s important to check your local building codes and permit requirements. Do this early in the process to understand any potential restrictions. Local building regulations or your homeowners association may limit the size or location of your new deck (which might explain why your deck is so small to begin with!). You’ll also need to reach out to your utility companies to have them mark any underground lines around your property.

Before expanding or extending your deck, it's essential to verify that the original structure is in good condition: Inspect the framing for any signs of rot, cracks, or other damage. If the deck is attached to the house (not freestanding), ensure that the ledger board is securely fastened to the house’s side. Also, check the posts underneath for signs of having shifted or thawed. Even if you're only adding a new level, and the existing foundation won’t bear the weight of the new section, use this opportunity to update the original deck if necessary.

To plan the layout of your deck, use mason’s string attached to batter boards or wooden stakes. This technique, used by contractors to keep the deck level and square, can also help you visualize the placement during the initial stages. Be mindful of space constraints and consider placing your furniture within the marked area to see how much room you have. Also, take into account how much sun or shade the new deck extension will receive.

Even if you plan to hire a contractor to complete the deck extension, it's helpful to go through these steps yourself so you understand the process. This knowledge will help you be clear and precise when discussing your project and negotiating with the contractor.

Important Terms to Understand When Extending a Deck

Most professionals agree that extending a deck is a complex project, so it's wise to hire a skilled contractor for the job. Ensure that the contractor is licensed, insured, and capable of obtaining any required permits (if the deck is not too close to the ground, a permit may not be needed). It’s a good idea to get quotes from different contractors, providing them with all the specific details of your vision for the extension.

Even if you decide to hire a contractor, it’s helpful to understand the basic deck-building process. Familiarize yourself with key deck components. The ledger is the board used to attach the deck to the house. The vertical posts are buried deep in the ground, typically secured with concrete and gravel. Local building codes will often determine how deep the posts need to be for proper support, usually below the frost line. You’ll likely need to dig new post holes and install additional posts for support. You can either mix concrete yourself or purchase pre-mixed concrete from a supplier.

The posts connect to horizontal beams (or girders). The joists are horizontal support boards placed underneath the decking, perpendicular to it. Local codes may also specify how far apart the joists should be spaced. When extending your deck, be particularly aware of cantilevering regulations. Cantilevering involves extending a beam beyond its support post or a joist beyond a beam, and the further the extension, the less stable it becomes. For proper drainage, make sure your decking boards have slight spacing (roughly the width of a 16d nail) [source: Lowes].

If your deck extension is high off the ground, you'll need to account for additional safety elements like railing posts and balusters (vertical pillars that provide support between posts). If you plan on having access to your lawn from the deck, don’t forget to consider stairs. Building codes may regulate the appropriate rise (height) and run (depth) of each step to ensure safety.

In general, this project will require several days or even weekends of detailed and hard work, with costs potentially reaching over $5,000. However, the result will be a beautiful outdoor living and entertainment area that can serve you for many years to come.