We’re thrilled to share the finished built-in bunk beds we installed in the tiny bunk room at our beach house. The room is only about 7 feet wide, yet we fit two Twin XL mattresses by crafting custom built-ins. They’ve become the kids’ favorite spot—not just for sleeping, but for playing and hanging out too.
This project felt more nerve-racking than building a bookcase or table because the top bunk literally floats and supports a person above another person (or a small dog). Spoiler: the design is very solid, sturdy, and simpler to execute than it might first appear.
Below are the main topics covered in this post.
Steps For Adding A Built-In Bunk Bed
Here’s what we walk through in detail:
- Building a platform for the bottom bunk
- Securing a floating platform for the top bunk
- Choosing height and spacing for the bunks
- Installing a ladder and railing
- Adding trim and molding to make them look built-in
The room is 81 inches wide, which matched perfectly with an 80″ Twin XL mattress. Once we realized that during the renovation, a wall-to-wall bunk configuration made perfect sense. The novelty of built-in bunks won out, even though there are other bedrooms the kids could use. Before the build, the space had just been an 80″ mattress on the floor.
Here’s how we built them.
Materials & Supplies Needed
The plan uses two floating platforms connected by a ladder. Because the room is narrow, three sides of each platform could be secured directly into wall studs, which provides exceptional strength and removes the need for vertical posts.
- 2×4 boards
- 1/2″ plywood panels for platform tops
- 1/8″ plywood panels for the underside of the upper platform
- Primed 1×8 boards
- 2×2 pine boards for the ladder and railing
- Primed lattice strips
- Baseboard (can reuse existing)
- 4″ and 5″ structural screws
- Miter saw
- Circular saw
- Power drill
- Nail gun
- Stud finder
- Bar clamps
- Pocket hole jig (optional)
- Long levels
Our material cost for the platforms and trim was about $250, not including mattresses and bedding.
Step 1: Build The Bottom Bunk Bed Platform
We initially built the bottom platform directly on the floor to maximize headroom, though we later raised it slightly for aesthetics. Building the platform in place ensured a precise fit and avoided wrestling large frames in the tight room.
We constructed a 2×4 frame to fit wall-to-wall, then added cross braces roughly every 12 inches for support. We joined pieces securely using pocket holes and screws, which creates tight joints even without a framing nailer.
After the frame was complete, we cut 1/2″ plywood to size and fastened it to the frame with a nail gun, making sure seams landed on cross braces.
The next day we decided to lift the platform a few inches so baseboard could run across it for a built-in look. We re-secured it higher to the wall, added 2×4 legs underneath, and installed a long 2×2 across the front for attaching the baseboard.
The modifications were straightforward and improved the finished look.
Step 3: Choose A Height For Your Top Bunk
With an 8-foot ceiling, we chose heights based on three goals:
- Keep headroom reasonably balanced between bunks
- Allow an adult to sit up on the bottom bunk without hitting their head
- Make the top bunk a bit cozy to discourage rough play or standing
We set the top bunk slightly higher than the midpoint to satisfy those goals, which also made adjusting the bottom platform easier.
Step 4: Build Your Floating Top Bunk
The upper platform was built the same way as the lower, but required secure attachment to studs so it could float without vertical supports. We used heavy-duty structural screws driven through the 2×4 framing into studs on three sides. Bar clamps were invaluable for holding pieces tight while fastening.
Once the frame was secured, we added 1/2″ plywood on top to create a sturdy mattress platform and tested the structure to ensure it felt solid.
With the structural work done, it was time to refine the look.
Step 5: Adding Trim & Molding
To finish the exposed framing, we nailed pre-primed 1×8 boards across the front of each platform and reinstalled baseboards so the bottom bunk read as built-in. We also covered the underside of the top bunk with 1/8″ plywood and framed seams with lattice for a neat finish, securing details with nails and glue.
All painted to match the room trim, these elements complete the built-in appearance.
Step 6: Build Your Ladder
Inspired by clean, modern railings, we built a ladder and rail system from 2×2 pine. Each rung is 18″ wide and rungs were spaced 12″ from top to top. We used scrap spacing blocks to ensure consistent spacing and reinforced each rung later by adding another 2×2 across the front for more surface underfoot.
We sanded edges to round them slightly for comfort and safety.
Step 7: Attach The Ladder & Build The Railing
We clamped the ladder in place, then secured it to the frame with structural screws. The top rails attach into the ladder and into a small vertical 2×2 on the opposite side. A middle rail sits slightly inset using pocket holes so the fasteners aren’t visible from the front.
We debated hiding visible screw heads, but after staining they read as an intentional industrial detail. For a seamless look you can countersink and fill screw holes.
Step 8: Stain The Ladder And Railings
We tuned the wood tone to match our floors with a four-step staining approach: pre-stain conditioner, a light coat on raw ends, a full coat of a lighter base stain wiped after 15 minutes, and a final quick coat of a slightly warmer color to add a subtle reddish cast. Testing on scrap wood ensured the final result matched the look we wanted.
The layered approach added depth and helped mimic the tone of our existing floors.
Step 9: Add Mattresses & Bedding!
With paint and stain dry, we dressed the bunks with mattresses and bedding and revealed the room to our excited kids—and the dog. The built-ins quickly became the family favorite spot in the house.
We later added a small cube organizer for toy and clothing storage. Since the house is used mainly for weekends and vacations, this lightweight storage solution works perfectly.
Final Measurements For Our Built-In Bunk Beds
Here are the final measurements for reference:
- Both platforms: 81.5″ x 40″ (to fit an 80″ x 38″ Twin XL mattress)
- Bottom bunk: platform top is 10″ off the floor, mattress sits 17″ off the floor, giving 34.5″ of headroom
- Top bunk: platform top is 56″ off the floor, mattress sits 63″ off the floor, with 32.5″ of headroom
- Ladder: 18″ wide rungs, full ladder width is 21″ edge to edge; rungs spaced 12″ top-to-top
- Top railing: 7″ above mattress top (building code minimum is 5″); 3″ gap between rails
In the end, the build was far less stressful than anticipated and very rewarding. We’re already planning a similar setup in another space. If you’re tackling a small-room bunk project, securing three sides into studs makes a floating bunk both safe and elegant.
*This post originally contained product references and recommended fasteners used in our build.*