How to Extend A Deck | Design & Construction Tips

How to Extend an Existing Deck

If your current wood deck is so short on space that it’s essentially unusable, we feel your pain. Or maybe you have a steep slope that makes enjoying your backyard difficult? The good news is a deck extension may be the perfect solution. Extending a deck over this area is a great way to reclaim valuable outdoor space and create the outdoor oasis you’ve always wanted.

STEP 1- Know Your Limits

Due to the scope of this project most homeowners should leave this type of decking project to the pros. A licensed decking contractor can help you navigate the process from permitting and material selection all the way through the construction process. Expert guidance will ensure your deck is a long-lasting feature you and your family will enjoy for years to come.

STEP 2- Inspect Structural Integrity

Before starting any type of deck extension project, have a licensed contractor inspect your existing deck to make sure the structure itself is still in good shape. A knowledgeable contractor will check the footings, posts, hardware and supporting lumber to ensure everything’s structurally sound and suitable for a deck extension. Any questionable areas should be repaired and/or replaced. When building a deck, never cut corners, especially when it comes to safety.

STEP 3- Material Selection

Softwood lumber is not only strong and durable, it’s also affordable. It’s also easy to work with when it comes to staining. Strength is especially important as a deck is an extremely heavy structure. Any hardware should be heavy-duty and galvanized, so it will hold up to outdoor use.

STEP 4- Designing Your Extension

Once you have sketched out your plans or had a professional do a rendering you’ll have a solid idea on how your deck will look against your home and landscape. Also, don’t let any mature trees get in the way of your deck, just incorporate them into the design. With proper planning, it’s not hard to deck around a tree or section of shrubbery.

STEP 5- Prepare Existing Deck

The construction crew will prepare your existing deck in a variety of ways for the new extension. They may cut back existing shrubbery in the area and remove specific supports to create space for the structural transition into the new extension. This means deck boards, railings and stairs may also need to be removed or disassembled, then reassembled for later use on the finished extension.

STEP 6- A Solid Foundation

With your new deck design in place, a contractor will plot out where the new footers and posts will be installed. Then all the footers will be dug down to the proper depth based on local building codes, your deck’s design, and weight load. A high-strength concrete will then be mixed and poured into the holes and left to cure per manufacturer guidelines. Your particular deck design may also require additional ledger boards be installed along the home’s sill plate. Again, it’s important this foundation work is done to code, as it’s crucial for your deck’s safety and longevity.

STEP 7- Utilizing Temporary Supports

Usually the next step would be to install galvanized post brackets into the footers and add posts, but it’s not the only way to approach a deck build. In an effort to be more efficient, some crews will set up temporary supports using 2x4s and begin the framing process (see next step) while the footers cure. This is a more complex construction process and not recommended for DIYers.

STEP 8- Rim Joists Installation

For this project, using temporary 2×4 supports, the crew set the first rim joist in place. A long 2×8 was placed perpendicular to the existing deck band. It was snugged up under the existing decking and toe- nailed into place using 16-gauge nails.

STEP 9- Support Beams Installation

Then the crew installed several 2×8 support beams that ran parallel to the existing deck. They periodically checked to make sure everything was square and level. Depending on the size of your deck, you may need more than one support beam.

STEP 10 – Floor Joist Installation

With the all the support beams in place, the crew began toe-nailing the perpendicular joists every 16- inches on center, making sure each board was level as they worked. Once all the joists were in place, joist hangers were secured using a palm nailer.

STEP 11- Framing Around the Landscape

Keep in mind, if your deck’s design incorporates trees, the floor system will require extra support posts and additional bracing around any deck openings. You’ll also want to ensure there’s room for growth if the tree is NOT yet mature. NOTE: Upon completion of the deck, you may also want to add wire netting around the opening or some type of safety feature if you have small children or pets.

STEP 12- Placing Permanent Posts

Once the footers have fully cured, pressure treated posts will be installed. For this project we installed galvanized brackets into the cured concrete using a large masonry bit and bolt. Then posts were measured, cut to size and notched to fit snuggly against support beams. The posts were then secured into the bracket with the appropriate hardware and bolted to the support beams (may vary depending on the type of bracket/hardware). With all posts in place, the temporary 2×4 supports were removed.

STEP 13 – Remove Old Decking

If your old, existing decking has seen better days, the crew will pry up the decking. Doing this ensures that the decking across both structures will stain and age in a uniform manner. It may be necessary to add perpendicular joists depending on your old deck’s orientation. This way all the new decking will run in the same direction.

STEP 14– Install New Decking

With your subfloor system complete and all the old decking removed, new decking can be installed. Deck boards will be staggered and installed using 2 1⁄2 inch deck screws loaded into a coil screw gun. This particular deck design incorporated a deck band around the perimeter. At the end of each run, the decking was cut to accommodate this design feature.

STEP 15 – Railings May Be Required

An elevated deck will require a 3-foot railing to keep everyone safe and the deck up to code. When you’re deciding on the railing design, consider your deck’s height and if you have small children or pets as you may want to incorporate more boards into the railing design so there aren’t large gaps.

STEP 16- Staining for a Cohesive Look

Finally, in order to make the new extension blend seamlessly with the old, staining all the boards the same shade is key. Per the earlier mention, new decking across both structures will go a long way towards getting that “brand new deck” look without the steep price tag. Keep in mind you may need to sand the older deck bands and re-stain them to match your new look.

Brian Patrick Flynn
Brian Patrick Flynn

Brian Patrick Flynn is an American television producer turned interior designer. After years writing, producing and directing news programs and home improvement shows, Flynn tried his own hand at residential interiors, quickly earning the respect of his peers and shelter magazine editors. Combining his design and decorating skills with his television production experience, he created FlynnsideOut Productions, a full service production company specializing in lifestyle-related content.