How to Extend an Existing Deck

By: Jane McGrath  | 
Need more space for your patio? Stretch things out a little. Want to learn more? Check out these pictures of must-have power tools!
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Key Takeaways

  • Deck extension is a complex project best handled by an experienced contractor, who should be licensed, insured and capable of obtaining any necessary permits.
  • Understanding basic deck-building components like ledgers, posts, beams, joists, and the importance of spacing for drainage and cantilevering rules is crucial even if you're not doing the work yourself.
  • Safety features, including railings and stairs, must comply with local codes. While the project can be costly and time-consuming, the result is a durable and expanded outdoor living space.

A deck is one of the most pleasant ways to expand a living space. As an extension from your house, it's a way to relish the beautiful outdoors while still enjoying the convenience of being just a step away from your home. It's also one of the most popular ways to entertain a big party: A deck not only increases the available space, but it also gives guests the option of staying inside or enjoying the outside. However, if you're stuck with a house that has a small, cramped deck, it won't help much with entertaining. Finding yourself frustrated with the limitation, it can be all the more distressing to discover how expensive it will be to tear down and rebuild.

However, the good news is that if the original deck is structurally sound, you could consider simply extending the existing deck. Make no mistake: This is not a job for the average do-it-yourself enthusiast. It takes advanced skills and some experience with similar projects. Seriously consider hiring a contractor to do the work for you.


Depending on your available space, you have several options. You could consider widening or lengthening the deck on its current level. Many people like to add new levels to the deck, connected by stairs. This latter method is best when you're worried that the new decking material won't match the old (and if the old deck is weathered at all, it likely won't). By putting the new deck on a different level, it makes the transition less jarring and unsightly. The new level also doesn't have to be separated by a whole flight of stairs -- one or two steps will be enough. A multi-leveled deck is also great for entertaining because it offers multiple intimate spaces.

What should you keep in mind when you're ready to stretch that deck out a little?


Things to Consider Before Extending 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.


Terminology to Know When Extending a Deck

Make sure you understand the importance of cantilevering.
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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.


Frequently Asked Questions

How do I match the materials of my existing deck to ensure a seamless extension?
Choose materials that match or complement your current deck. Consult with suppliers or contractors for the closest matches in wood type, finish and age-related appearance.
What should I consider for deck foundation when extending?
Assess the current foundation's capacity to support additional weight, and plan to reinforce or upgrade it as necessary, following local building codes and regulations for depth and construction methods.

Lots More Information

Related Articles

  • Bianchina, Paul. "Great Ways to Expand Backyard Deck." Inman News. Aug. 31, 2007. (June 8, 2012)
  • Black & Decker. "The Complete Guide to Building Decks." Creative Publishing International. 2001. (June 8, 2012)
  • DIY Network. "How to Build an Extension to Your Deck." DIY Network. (June 8, 2012)
  • Donald, Stevie. "How to Hire a Deck Contractor." (June 8, 2012)
  • Lowes. "How to Build a Deck." Lowes. (June 8, 2012)
  • The Family Handyman. "Comparing Deck Wood: Cedar, Pressure Treated Wood & Composite Decking." The Family Handyman Magazine. July/August 2002. (June 8, 2012)