We’re thrilled to share the finished built-in bunk beds in the small bunk room at our beach house. The room is only about 7 feet wide, but by building custom wall-to-wall platforms we made room for two Twin XL mattresses. The bunks quickly became the kids’ favorite place to sleep, play, and hang out.
I was more nervous about this project than I am about building a bookcase or table — a bunk bed literally supports one person above another — but the design turned out to be solid, sturdy, and straightforward to build.
What this post covers:
Steps For Adding A Built-In Bunk Bed
Here’s a quick overview of the steps we followed:
- Build a platform for the bottom bunk
- Secure a floating platform for the top bunk
- Choose appropriate height and spacing for each bunk
- Install a ladder and railing
- Add trim and molding to make the bunks look built-in
The room is 81 inches wide, which is an ideal fit for an 80-inch Twin XL mattress. During renovation we realized the space would work perfectly as a small bunk room, and the novelty made the project an easy decision. Before the build, the room basically had a mattress on the floor.
Below I’ll walk through how we built these bunks.
Materials & Supplies Needed
We built two floating platforms tied into wall studs on three sides, which creates exceptional rigidity and eliminates the need for vertical posts. Key materials and tools we used:
- 2×4 boards
- 1/2″ plywood panels (platform tops)
- 1/8″ plywood panels (underside of upper platform)
- Primed 1×8 boards
- 2×2 pine boards (for ladder & railing)
- Primed lattice strips
- Baseboard (reused where possible)
- 4″ and 5″ structural screws
- Miter saw
- Circular saw
- Power drill
- Nail gun
- Stud finder
- Bar clamps
- Pocket hole jig (optional)
- Long levels
For this room our material cost was roughly $250, not counting mattresses and bedding.
Step 1: Build the Bottom Bunk Platform
We initially planned the bottom mattress platform directly on the floor to maximize headroom, but later raised it slightly for aesthetics. Either way, the process of building an in-place platform is the same: construct a 2×4 frame that fits wall-to-wall, add cross braces about every 12 inches, and secure the front piece.
We used pocket holes to join the frame tightly where needed, then covered the frame with 1/2″ plywood to form a solid mattress surface. Make sure plywood seams land on cross braces for strength.
After assembly we raised the bottom platform a few inches so baseboard could run across it. To do this we added short 2×4 legs, re-secured the frame to the wall slightly higher, and attached a 2×2 along the front to support the baseboard.
It looks more complex in photos than it felt in practice.
Step 3: Choose a Height for the Top Bunk
With an 8-foot ceiling, our goals when setting heights were:
- Keep headroom reasonably equal on both bunks
- Allow an adult to sit up on the bottom bunk without bumping their head
- Keep the top bunk low enough to discourage standing or jumping
We set the top platform slightly higher than halfway up to satisfy those needs and to make the later bottom-platform adjustment easier.
Step 4: Build the Floating Top Bunk
The upper platform followed the same framing approach but required strong connections into studs so it would float without vertical supports. We used heavy-duty structural screws driven into studs to pull the 2×4 frame tight to the walls. Bar clamps held pieces in place while we installed the screws.
After securing the frame to the studs on three sides and to the front member, we added 1/2″ plywood to complete the mattress surface and tested the platform’s sturdiness.
Clamps were invaluable during this step to keep everything aligned as screws pulled the frame tight.
Step 5: Add Trim & Molding
To hide exposed framing we attached primed 1×8 boards across the platform fronts and reinstalled baseboard along the back of the bottom bunk. We also added 1/8″ plywood and lattice strips under the top bunk so the underside looks finished from the bottom bunk.
The trim was attached with nails and glue to ensure it stays secure over time, and everything was later painted to match the room trim.
Step 6: Build the Ladder
Inspired by a clean, modern railing, we built the ladder from 2×2 pine boards and cut 18″ rungs in matched groups to keep sizes consistent. Rungs were spaced 12″ apart top-to-top, and we used scrap blocks as spacers during assembly to ensure even spacing.
After hanging the ladder we doubled the rungs by attaching an additional 2×2 across each rung’s front face for added comfort and strength, and we rounded the corners of all ladder pieces for a softer feel.
Step 7: Attach the Ladder & Build the Railing
We clamped the ladder in place and secured it to the frame with structural screws. The top rails were attached into the topside of the ladder and into a vertical 2×2 on the opposite side. We added a middle rail and fastened it with pocket holes from the back so the fasteners aren’t visible from the front.
We could have countersunk screws and filled the holes for a seamless look, but the exposed brass heads ended up looking like a nice industrial detail after staining.
Step 8: Stain the Ladder and Railings
To match the floor tone we developed a four-step staining process on scrap pieces: pre-stain conditioner for even absorption, a light stain on raw ends, a main coat of a natural pine shade wiped off after a short set time, and a final light coat of a slightly redder stain to warm the tone. The result matched our intended color closely.
Step 9: Add Mattresses & Bedding
With paint and stain dry, we added mattresses, bedding, and a few storage pieces for toys and clothes. The kids (and Burger the dog) loved the finished room right away.
Final Measurements for Our Built-In Bunk Beds
Final dimensions for this build:
- Platform dimensions: 81.5″ x 40″ to fit an 80″ x 38″ Twin XL mattress
- Bottom bunk: platform top 10″ off the floor, mattress 17″ off the floor, 34.5″ of headroom
- Top bunk: platform top 56″ off the floor, mattress 63″ off the floor, 32.5″ of headroom
- Ladder: rungs 18″ wide, ladder 21″ overall edge-to-edge, 12″ rung spacing top-to-top
- Top railing: 7″ above mattress top (5″ minimum required) with a 3″ gap between the two rails
Overall the project was far less nerve-wracking than I expected and the finished bunks are both sturdy and charming. We might build more of these for future projects — they’re a great way to maximize a small space.