We’re thrilled to share the finished built-in bunk beds we added to the tiny bunk room at our beach house. The room is narrow—about 7 feet wide—but by building custom, wall-to-wall platforms we fit two Twin XL mattresses and created a sturdy, space-saving sleep and play area that the kids (and the dog) love.
This project felt a bit more intimidating than ordinary furniture builds because the top platform is essentially floating and must safely support a person. In practice, the design is very solid, straightforward to build, and provides a safe, playful space for kids.
What you’ll find in this post:
Steps For Adding A Built-In Bunk Bed
Below is a condensed overview of the main stages we’ll walk through:
- Building a platform for the bottom bunk
- Securing a floating platform for the top bunk
- Choosing height and spacing for both bunks
- Installing a ladder and safety railing
- Adding trim and molding to create a built-in look
The room measures 81 inches wide, which made it ideal for wall-to-wall Twin XL mattresses (80″ long). Once we realized that during the renovation, the bunk layout became an obvious and fun solution for this small space. Before the build, the room was simply a mattress on the floor, so the transformation added both function and personality.
Ready to see how we built them? Here’s everything we used and how we did it.
Materials & Supplies Needed
The plan is two wall-mounted floating platforms connected by a ladder. Because the space is narrow and the platforms contact three walls, we were able to fasten most framing directly into studs for excellent rigidity without vertical posts.
- 2×4 lumber for framing
- 1/2″ plywood panels for platform tops
- 1/8″ plywood for the underside of the upper platform
- Primed 1×8 boards for facing trim
- 2×2 pine boards for ladder and railing
- Primed lattice strips for finishing edges
- Baseboard (reused where possible)
- 4″ and 5″ structural screws (recommended for securing into studs)
- Miter saw and circular saw
- Power drill
- Nail gun
- Stud finder
- Bar clamps to hold pieces while fastening
- Pocket hole jig (optional but helpful)
- Long levels for layout and squaring
For our build the materials cost was roughly $250, excluding mattresses and bedding.
Step 1: Build The Bottom Bunk Bed Platform
We began by constructing a 2×4 frame sized to fit from wall-to-wall. Initially the plan was to sit the first mattress directly on the floor to maximize headroom, but we later raised the platform slightly to allow baseboard and create a cleaner built-in look. Building the frame in place made fitting precise and avoided maneuvering large assemblies in the tight room.
Cut the 2×4 pieces to fit the space, assemble the back and side members, and add cross-bracing spaced about every 12 inches for support. We used pocket holes to join pieces tightly where needed. Once framed, cover the top with 1/2″ plywood panels trimmed to size and fasten with a nail gun—make sure seams land on cross braces.
After assembling the base, we raised the platform a few inches by adding short 2×4 legs and fastening the frame up into studs slightly higher on the wall. We also attached a 2×2 across the front edge to provide a nailing surface for baseboard and trim.
The final bottom platform is solid and well supported by the three walls and the added internal framing.
Step 3: Choose A Height For Your Top Bunk
With an 8-foot ceiling, choosing bunk heights requires balancing several goals:
- Provide roughly equal headroom for both bunks
- Allow an adult to sit up comfortably on the lower bunk (handy for bedtime stories)
- Keep the top bunk snug enough to discourage standing or rough play
We placed the top platform slightly above the halfway point to improve lower-bunk headroom and reduce the temptation to stand on the top bunk.
Step 4: Build Your Floating Top Bunk
The upper platform follows the same framing approach as the lower, but fastening securely into studs is critical since there are no vertical legs. We used heavy-duty structural screws driven into studs to pull the 2×4 framing tight against the wall.
Bar clamps were invaluable for holding the framing flush while we installed the structural screws. After the frame was secured to the three walls, we added 1/2″ plywood to form the mattress surface and tested the platform’s stiffness and safety.
Once the plywood was in place, we double-checked the sturdiness and moved on to finishing details.
At this point the structural work was complete and the build began to look like finished bunks rather than a framing project.
Step 5: Adding Trim & Molding
To hide exposed framing and create a built-in appearance, we attached primed 1×8 boards across the front of each platform and reinstalled the baseboard along the back wall in front of the bottom bunk. We also added 1/8″ plywood to the underside of the top bunk and framed seams with lattice strips for a neat look, securing everything with nails and wood glue.
These small finishing touches make the whole installation read as built-in furniture rather than a temporary assembly.
Step 6: Build Your Ladder
We drew inspiration from modern, clean-lined bunk designs and used 2×2 pine for the ladder verticals and rungs. Rungs were cut to 18″ wide and spaced 12″ apart (top to top). To keep spacing consistent, we used temporary spacer blocks while attaching each rung and fastened them securely into the verticals with structural screws.
We later added an extra layer across each rung so they felt wider underfoot, and sanded all edges to a comfortable, slightly rounded profile.
Step 7: Attach The Ladder & Build The Railing
We clamped the ladder to determine the optimal placement, then fastened it into the platform frame and wall. The top railing attaches into the ladder and into a small vertical post on the opposite side. A middle rail adds extra protection and is installed with pocket holes from the back so the fasteners aren’t visible from the front.
We considered hiding visible screw heads by screwing from the backside or countersinking and filling with wood putty, but in our case the finished stain made the hardware look intentional and slightly industrial.
Step 8: Stain The Ladder And Railings
We matched the wood tone to our floors with a multi-step staining approach. Our process included a pre-stain conditioner, a lighter coat on raw cut ends to prevent dark blotches, a primary stain wiped off after a short dwell, and finally a light glaze of a slightly warmer color to achieve the exact tone we wanted. Testing on scraps helped dial in the final result.
A careful staining sequence produced a warm, consistent finish that complemented the room’s existing floors and trim.
Step 9: Add Mattresses & Bedding!
With paint and stain dry, we added Twin XL mattresses and bedding. The resulting bunk room is compact, comfortable, and instantly beloved by the kids—and by our dog Burger, who tested the bottom bunk immediately.
A small cube organizer added toy and clothing storage, which is plenty for occasional weekend and summer stays at the beach house.
Final Measurements For Our Built-In Bunk Beds
For reference, here are the final dimensions and clearances we used:
- Platform dimensions: 81.5″ x 40″ to fit an 80″ x 38″ Twin XL mattress
- Bottom bunk: top of platform 10″ off the floor; mattress top 17″ off the floor; 34.5″ of headroom
- Top bunk: top of platform 56″ off the floor; mattress top 63″ off the floor; 32.5″ of headroom
- Ladder: rungs 18″ wide; overall ladder width 21″ edge to edge; rungs spaced 12″ apart (top to top)
- Top railing: 7″ above mattress top (code generally requires at least 5″); 3″ gap between rails
Overall, the project was far less stressful than anticipated and a rewarding way to maximize a small space. We’re so pleased with how durable and attractive the finished bunks are, and we’re already planning similar builds for other projects. If you tackle a similar build, measure carefully, fasten solidly into studs, and test load capacity as you go—especially for floating upper platforms.