How to Build a Treehouse

Treehouse

 

Johner Images / Getty Images

Overview
  • Yield: 8-foot by 8-foot treehouse
  • Skill Level: Intermediate

A treehouse is a dream not just of children but of adults alike. Thoughts of lazy days while reading a book or sipping a cold beverage in a private, lofty paradise is heaven on earth. Enjoying a treehouse worry-free, though, is possible only when the treehouse is sturdy and secure.

This open-air platform-style treehouse is safe, basic, and requires only one tree. Difficult and unfamiliar arboreal engineering is kept to a minimum because the weight of the platform is borne entirely by four posts sunk into the ground. Alternately, for a more classic treehouse look, half of the platform can be carried by two trees substituting for two posts. Save time by installing pre-built deck railing or save money by building the railing from scratch.

Some treehouses require unusual materials found only at specialty online treehouse supply stores. This treehouse, though, uses basic building materials, tools, and techniques. All materials can be found at your local home center.

Clear the Legalities

There are few, if any, building codes for safety and zoning laws for placement on the property that apply to these tiny houses in the sky. To be sure, call your local permitting and zoning departments after drawing out your treehouse plans.

Call your local utility company's avoidance hotline to make sure that you do not hit electric, sewer, water, or other vital service lines when digging deep holes for your footers. In addition, speak to any neighbor whose adjacent property may be affected by the treehouse for neighborly etiquette.

What You'll Need

Equipment / Tools

  • Tree branch trimmers
  • Hammer
  • Post-hole digger
  • Laser level or bubble level
  • Circular saw
  • Ladder
  • Cordless drill and drill bits
  • Set of mechanic's ratchet wrenches
  • Carpenter's pencil
  • Miter saw
  • Tape measure

Materials

  • 4 wood stakes
  • 2 bags landscape gravel
  • 4 8-inches diameter by 48-inches long concrete form tubes
  • 8 bags quick-set concrete
  • 4 6-inch by 6-inch galvanized adjustable post bases
  • 4 5/8-inch diameter J-bolts
  • 4 12-foot long 6-by-6-inch posts
  • 8 8-foot long pressure-treated 2-by-4-inch posts
  • 23 8-foot long pressure-treated 2-by10-inch posts
  • 12 2-inch by 10-inch galvanized concealed face mount joist hangers
  • 24 1/2-inch diameter by 6-inches long lag screws with matching washers
  • 3 1/2-inch long 16d nails
  • 1 1/2-inch long 10d nails
  • 4 8-feet long by 3-feet high pre-built deck rails, either wood or powder-coated aluminum, each 8 feet long by 3 feet high, as well as deck railing posts and included hardware
  • Hidden fastener deck system (optional)
  • Rope ladder or extension ladder
  • Bungee cords or metal brackets (optional)

Instructions

  1. Choose a Tree

    Due to their beauty and strength, deciduous hardwoods like oak, maple, beech, apple, and ash have long been used for building treehouses. Evergreens such as Douglas Fir, pine, spruce, and hemlock work well, too. Ensure that the tree is healthy, straight, and as close to vertical as possible.

    Lower branches should be trimmed away to the desired height of the platform. Then, clear another 6 feet of branches above the platform height.

    Tree Diameter

    A rule of thumb: For an average-sized treehouse of 8 feet by 8 feet, choose a tree with a trunk diameter of 12 inches or more.

  2. Mark the Post Locations

    Using the tree as the center point of the treehouse, mark four locations for the post footings in a square shape. Post footings will be 8 feet from each other and equidistant from the tree. Mark these locations by pounding four wood stakes into the ground.

    Measure Outer Dimensions

    Ensure that outer dimensions of this square measure 8 feet by 8 feet, not the on-center dimensions. This is vital because the inner dimensions of the floor frame you will create in a later step will be 8 feet by 8 feet; the posts and the frame must align.

  3. Dig the Post Footer Holes

    With the post-hole digger, dig four holes. Dig to a depth required for your area so that each post extends below the frost line. Bed the bottom of each hole with 3 inches of gravel.

    Then, place a cardboard form tube in each hole. Cut each form tube down so that about 2 inches of the tube extends above ground level.

    Frost Line Info

    To find your area's frost lines, check with your local building department for this information.

  4. Pour the Footers

    Mix the concrete. Fill each form tube until the concrete is level with the top of the tube. Smooth the concrete so that it is flat.

    With the concrete still wet, set a 5/8 inch diameter J-bolt into each concrete footing. The J-bolt should extend 3/4 inch to 1 inch above the concrete.

  5. Mount the Posts

    Install a post base to each of the four footers with the included washer and nut that attach to the embedded J-bolt. Set each piece of 6-by-6-inch lumber atop a post base. Plumb with a level and then nail pieces into place with 16d nails.

    Temporarily secure the post by tacking two 2-by-4-inch pieces of lumber to each post to form a triangle brace with two free arms resting on the ground.

  6. Build the Outer Section of the Floor Frame

    Using four 2-by-10-inch pieces of wood, create a square that will form the outside perimeter (or rim joist) of the floor frame. The frame should be 8 feet long by 8 feet wide.

    Cut two of the 2-by-10-inch boards so that each one is 7 feet by 9 inches long. The other 2-by-10-inch boards remain 8 feet long. Nail the four boards together with 16d nails on end to form the square.

  7. Mount the Floor Frame

    With two people on ladders, raise the floor frame above the level of the tops of the posts. The floor frame should now be wrapped around the four posts. Slide down the floor frame to the desired floor height.

    Temporarily tack the frame into place on each post with 16d nails. The nail heads should stay exposed for easier removal.

    With the cordless drill, make two pilot holes at each post through the 2-by-10-inch frame and into the post. Follow up by screwing the lag bolts and washers into each pilot hole with a ratchet wrench. Remove the temporary 16d nails with the claw end of the hammer.

  8. Install the Knee Braces

    Remove the temporary 2-by-4-inch board braces as these will be used to create permanent cross braces. These can either be short knee braces that extend from one post to the floor frame or they can be longer diagonal braces that extend from one post to an adjacent post.

    To create knee braces, cut four of the 2-by-4-inch boards in half so that you have eight 2-by-4-inch boards that are each 48 inches long. Place a 2-by-4-inch board in the desired position of the knee brace (45-degrees, extending from the rim joist to the post), then mark the cuts from the back with the pencil.

    Cut with the miter saw and test it out on the treehouse. If it works, use this as a template for cutting the remaining three knee braces.

    Drill pilot holes, then attach one knee brace per post with the 1/2-inch lag bolts. To avoid lag bolts from one brace interfering with lag bolts on a post's other brace, the second set of four knee braces should be cut either longer or shorter than the first set. Measure, mark, cut, and attach these braces as you did the other set.

  9. Set the Joists

    With the pencil and tape measure, measure twelve positions on the inside of the floor frame for the joist hangers. There should be six hangers on one side and six on the opposite side. Hangers should be 16 inches apart. You may have to slightly adjust the position of the middle two hangers to accommodate the tree.

    Nail the joist hangers into each position with the 10d nails. Firmly pocket the remaining two-by-tens into the joist hangers. Then attach the boards and the hangers with 10d nails.

    For Extra Strong Joists

    To increase the joists' strength, double up the two sides of the frame that have the joist hangers with two more 2-by-10-inch boards mounted on the outside of the frame. Nail into place with the 2 1/2-inch nails.

  10. Build the Flooring

    The eleven remaining 2-by-10-inch pieces of wood will be used as deck boards.

    Face-nail onto the joists with the 16d nails. Or for a cleaner look, consider purchasing a hidden fastener deck system. Space boards 1/8 inch to 1/4 inch apart. When reaching the tree, cut these boards to length.

  11. Install the Railing and Ladder

    Install the hand railing on the top of the deck following the manufacturer's instructions. Be sure to leave a section about 2 feet wide for access.

    For a ladder, consider the many rope ladders are available online that can be attached to the treehouse. Or, tilt an extension ladder into place for a sturdier solution. As an option, secure the ladder with bungee cords or metal brackets to stay in place.

    Rope Ladder Safety

    Put a pile of soft mulch or wood chips underneath the rope ladder in case someone loses their footing.