How to Build a Deck Around a Tree: Everything You Need to Know

Prep for Building a Deck Around a Tree

You’ll need to evaluate if building around the tree in your yard makes sense and, if it does, make some essential project decisions before starting the work. Consider the following prep steps to avoid barking up the wrong tree. 

Roots

If you have a large, mature tree, erecting a deck by digging supporting footing holes could compromise the sprawling root system. Serious damage could kill off the specimen, and you could compromise your future deck structure.

Instead, if you’re building a freestanding deck, use cement blocks for the base to avoid damaging tree roots. For attached decks built around a tree, hire a local arborist to evaluate your tree’s root structure and the deck plans to determine the best way to work around the underlying root structure.

Pest Infestations

Trees can be home to crawling critters like termites and other wood-eating pests. The last thing you want is for your snazzy new deck to come under attack from these hard-to-banish bugs. They can burrow under the surface and cause irreversible structural damage before you even realize it.

It’s worth your while to have the tree inspected by a local pest control company to ensure it isn’t awash with insects, and don’t forget to apply an insect-resistant coat to the deck timber.

Tree Numbers

Do you have more than one treasured tree in your yard? Integrating them all into the deck design will make things more tricky, and you might have less functional floor space. Consider revising your deck plans to include as few trees as possible.

Tree Type

Is your tree a fast-growing maple or willow? You’ll need to account for tree traits when planning your deck building measurements. Research your tree type to determine any characteristics that could prove tricky to work around, such as those that drop sap or emit an unpleasant smell.

Also, if you have a tree that sheds a lot of leaves or messy fruit, you’ll want to use a more slip-resistant decking material, like composite wood. But don’t forget, there’s no truly slip-proof deck materials, so you’ll need to keep up a deck maintenance regime to minimize the chance of someone taking a tumble.

Building Permits

Whether you’re constructing your deck around a tree or not, you’ll need to check if you need a building permit to erect one in your yard. You’ll often need a building permit if the deck will sit 30 inches or higher off the ground. You can confirm this with your local government planning department.

If you need one, you’ll have to factor in the cost of the building permit (usually between $225 and $500) and the fact that the application process can take weeks (sometimes months) to complete before you can start working.

Draw Up Plans

Take measurements of the area you plan to cover in decking and the tree's circumference. That way, you know how much space to leave for it, with adequate room to grow.

Map out the site layout on paper; include the width, length, and elevation. This step doesn’t just help you create the right design, it also allows you to calculate and budget for the amount of materials you’ll need to buy.

Ready the Site

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Clear the area so you have a relatively level blank canvas ready to map the deck space. Follow the steps below:

1. If you are laying the deck over a grass area, cut the sod out and ensure the soil underneath is relatively level. 

2. Allow for a slight slope away from your home, preventing potential water runoff from heading toward your home.

3. Peg the corners of the planned deck area. Use a rubber mallet or hammer to stake them into harder ground.

4. Tie string between the pegs to mark the perimeter.

5. Mark the spots where you will position the cement blocks using spray paint or chalk.

6. Check the measurements from one corner to the diagonal opposite to ensure they are consistent on both sides.

Position the Concrete Blocks

While wearing gloves, place the concrete blocks used to support the deck joists around the perimeter of the marked area. 

1. Space the concrete blocks about 8 feet apart. 

2. Depending on the deck size, you’ll also need to center support blocks. 

3. Lay the external frame supporting joists (typically 4x4 posts) into the block grooves and use a spirit level to ensure the joists are level. Don’t fix the joists at this point.

4. For uneven levels, you might need to dig out holes or add gravel to place the cement blocks into.

Apply Weed Control

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To ward off weeds that can poke up through the decking, lay and secure a weed control fabric and weigh it down with gravel.

Fashion the Frame

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Start by securing the outer load-bearing rim joists for support and then fit the inner joists and joist hangers (metal fittings that ensure the joist stays secure) to keep your deck structurally sound. During each step, ensure everything is level, flush, and aligned to match the plan. 

You’ll typically secure the joists with a drill and 3-inch wood screws. Pre-drill the holes using a ⅛-inch drill bit.

Inner joists are usually spaced 12, 16, or 24 inches on center, measuring from the center of one joist to the center of another. This distance depends on your deck size and plan instructions, so adjust as needed.

Frame Around the Tree to Allow for Growth

When framing the deck area around the tree, position the joists to allow enough space for about a decade of growth. That’s where your tree type research comes in handy—this space varies depending on the tree’s estimated life span growth. Typically, this is a minimum of 2 feet.

Double-Up the End Joists

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To prevent premature precariousness, add supportive end joists. These short pieces of lumber fit between the outside frame and the first joist on each corner. You’ll also need to add them around the sides of the tree to keep it in place.

Lay the Decking

Install your decking by starting from the outer edge and work your way inwards, securing each board with deck screws that go through the boards into the center of each inner joist. The following tips will help you do a neat and secure job:

• Using pre-cut lumber means you won’t have to trim off excess wood.

• You will probably need to cut some boards to fit around your tree, and it’s easiest to do so with a jigsaw. 

• Wear eye protection and a dust mask when trimming boards.

• Use deck spacers between each board to allow for drainage and even alignment, or leave a ⅛-inch space between boards.

• Attach fascia boards around the edge of the deck if you want a neat finish.

Treat the Deck for Longevity

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To prevent premature rotting or discoloration, seal your deck if the lumber hasn’t already been treated. Apply the sealant coats with a roller on a pole when the wood is completely dry. Wood decks typically need at least two coats, and you’ll need to allow each coat to dry fully before applying the next one.