Looking to build a treehouse-style fort for your kids but don’t have any trees? We’ve got just the project for you.
This elevated backyard fort is perfect for small yards and sparks endless imagination—think pirate ship, rocket launcher, haunted hideout, or a classic treehouse alternative.
Let’s walk through how we made ours from scratch using basic materials, smart planning, and a touch of creativity.
Why This Plan Works
- Designed specifically for yards without trees
- Built with standard-sized lumber to reduce waste
- Sturdy and weather-resistant with minimal maintenance
- Adaptable design for imaginative play
- Budget-friendly with options to repurpose materials
What You Will Need
- 6 cement blocks with metal post brackets
- 6 pressure-treated 4×4 x 8′ posts
- 6 pressure-treated 2×6 x 8′ boards
- 1 OSB or exterior-grade plywood (4′ x 8′, ¾”)
- ~20 2×4 x 8′ boards
- 4 2×4 x 10′ boards
- 5 corrugated plastic roof panels (26″ x 8′)
- Roofing screws with rubber washers
- 5 lb. box of 3″ exterior screws
- 5 lb. box of 1 ⅝” exterior screws
- 2 bags of sand (50 lb. each)
- Waterproof wood sealer
- Deck restoring paint
- Optional: reclaimed pine boards for walls, extra 2x4s, slide, flag materials
Step 1: Set the Foundation Blocks
Place your 4’x8′ floorboard on the ground where you want the fort to go. Cut out openings where each 4×4 post will pass through and spray paint the ground beneath these areas
. Dig oversized holes for each block, lay a base of sand, and level the blocks using a straight 2×4 and level. Don’t backfill the dirt yet—you’ll do that later.
Step 2: Attach Posts to the Blocks
Secure all six 4×4 posts to the metal brackets in the cement blocks using 3″ screws. Pre-drill near the edges to prevent splitting. Anchor one corner post with angled 2x4s and ground stakes to keep it perfectly plumb. The remaining posts can stand freely unless it’s windy.
Step 3: Build the Floor Frame
Using 2x6s, build the floor frame around the base of the posts. Mount them 24″ off the ground, ensuring everything is level and square.
Attach each board with five screws per post. Then add joists across the middle. We originally included a trap door, but eventually screwed it shut for safety reasons.
Step 4: Install the Floor
Lay the 4’x8′ board over the joists and screw it into place with 1 ⅝” screws through pre-drilled, countersunk holes. If all goes well, it should fit snugly and securely.
Step 5: Frame and Build the Walls
Frame the walls using 2x4s at 36″ above the floor frame. Add angled interior braces between posts to stabilize and square the entire structure.
Once secure, begin attaching reclaimed pine boards or other wall slats with 1 ⅝” screws, keeping them 3″ from the ends for hidden screw coverage. Finally, trim the walls and backfill around the cement blocks.
Step 6: Construct the Roof
Trim 3″ off the rear posts to create a slope. Install 10′ 2×4 beams across the front and back posts.
Reinforce with decorative tapered support boards underneath.
Add rafters (82″ long) every 16″ across the beams and top them with ripped-down 1½” strips for the roof panel base.
Attach 5 trimmed plastic panels with roofing screws.
Step 7: Apply Finishes
Paint the floor using thick deck restore paint, applying two heavy coats. Seal the rest of the wood with a waterproof sealer. This allows the wood to age naturally while being protected from moisture.
Step 8: Add a Slide (Optional)
Install a slide off one side by anchoring support 2x4s at the top rail and bolting the slide in place.
Create a soft landing zone by leveling out dirt and adding sand and paver stones underneath the slide.
Step 9: Fly a Flag (Optional)
For a playful touch, we created a pirate flag by painting a skull and crossbones on scrap canvas and stapling it to the structure. Perfect for imaginative adventures!
Note: Take your time with leveling and squaring early in the process—it saves hours of headaches down the line.
Other Details Display
- Dimensions: Floor is 4′ x 8′; Posts are 8′ tall; Roof spans 10′
- Style: Elevated fort with angled roof
- Materials: Pressure-treated lumber, reclaimed pine, OSB, corrugated roofing
- Decor Add-ons: Slide, pirate flag, trap door (optional)
- Safety Features: Screwed-shut trap door, anchored support post
- Finish: Deck paint and waterproof sealer
Summary
This backyard fort is a creative and sturdy alternative to a treehouse, perfect for small yards without trees.
With standard materials and a bit of planning, we built a durable play structure that will grow with our kids and their imagination.
This “treeless treehouse” is both fun and functional—a backyard upgrade that’s well worth the effort.
This plan is a contribution by [seamster]. Project Via Instructables – Get the PDF Instructions here.
