We’re excited to share the finished built-in bunk beds we installed in the tiny bunk room at our beach house. The room is only about 7ft wide, but by building custom wall-to-wall platforms we fit two Twin XL mattresses perfectly. They’ve already become the kids’ favorite place to sleep, play, and hang out.
I was a bit nervous about this project—after all, it’s a bed that floats, and one person ends up above another. But the structure we designed is very solid, straightforward to build, and uses studs in three walls to eliminate the need for vertical posts.
Quick overview of what this post covers:
Steps For Adding A Built-In Bunk Bed
This project breaks down into a few clear phases:
- Build a sturdy platform for the bottom bunk
- Secure a floating platform for the top bunk to wall studs
- Choose heights and spacing for comfortable headroom
- Install a ladder and protective railing
- Add trim and molding so everything reads as built-in
This particular room is 81″ wide, which makes it ideal for an 80″ Twin XL mattress. During renovation we realized that a wall-to-wall bunk would be a perfect fit. For months the space sat unused with a mattress on the floor, so building built-ins transformed the room into something functional and fun.
Here’s how we built them.
Materials & Supplies Needed
The build creates two floating platforms connected by a ladder. Because the platforms touch three walls, we could anchor most of the frame directly into studs for maximum strength. Main materials and tools included:
- 2×4 lumber for frames and cross braces
- 1/2″ plywood for platform tops
- 1/8″ plywood for underside sheathing of upper platform
- Primed 1×8 boards for facing
- 2×2 pine for ladder and railing
- Primed lattice strips, baseboard
- 4″–5″ structural screws designed for pulling into studs
- Miter saw, circular saw, power drill
- Nail gun, stud finder, bar clamps, long level
- Pocket hole jig (optional)
Our parts and materials cost around $250 for the build, not including mattresses and bedding.
Step 1: Build The Bottom Bunk Platform
We began by creating a robust 2×4 frame that fits wall-to-wall. Short cross braces were added roughly every 12″ to support the plywood decking. We assembled the frame in place to ensure a precise fit in the narrow room and used pocket holes and screws to secure joints tightly.
After leveling the frame, 1/2″ plywood was cut to size and fastened to the joists so the mattress sits on a solid surface. Initially the platform was built on the floor, but we later raised it a few inches and added small legs and a 2×2 across the front so baseboard could be fitted for a clean built-in look.
Step 3: Choose A Height For Your Top Bunk
With an 8ft ceiling, our priorities were balanced headroom between bunks, enough clearance for an adult to sit up on the bottom bunk, and a somewhat cozy top bunk to discourage standing or rough play. We set the top platform slightly higher than halfway up the wall to meet those goals.
Step 4: Build Your Floating Top Bunk
The upper platform used the same frame and decking approach, but every primary 2×4 was pulled tight into studs using heavy-duty structural screws made for that purpose. Bar clamps were invaluable to hold assemblies in place while driving long screws. Once the frame was secured, 1/2″ plywood was installed across the top and tested to verify stiffness and safety.
With both platforms structurally complete, the next step was finishing: trim, ladder, railing, and stain.
Step 5: Adding Trim & Molding
To hide exposed framing, we attached pre-primed 1×8 boards across the front of each platform and reinstalled baseboard in front of the bottom bunk. Thin 1/8″ plywood and lattice were used under the top platform for a neat underside. Everything was glued and nailed for long-term durability before painting to match room trim.
Step 6: Build Your Ladder
We built a modern-looking ladder using 2×2 pine. Rungs were cut 18″ wide and spaced 12″ apart (top-to-top). Temporary spacer blocks and a flat work surface kept all rungs perfectly aligned. After testing the initial ladder we doubled the rungs by attaching an additional 2×2 across each step to make them more comfortable underfoot and stronger overall.
All exposed corners were sanded to a softer, rounded profile for safety and comfort.
Step 7: Attach The Ladder & Build The Railing
The ladder was clamped in place and fastened to the frame with structural screws. Rails for the top bunk were attached from the top side into the ladder and into short vertical posts where needed. A second rail was added mid-height and secured with pocket holes from the backside so the fasteners aren’t visible from the front. If you prefer a cleaner look, countersink and fill screws on exposed faces.
Step 8: Stain The Ladder And Railings
To match the room’s wood tones we tested multiple stains. Our final process was: pre-stain conditioner, a light coat of natural on cut ends to prevent blotching, a coat of Minwax Puritan Pine wiped after about 15 minutes, and a final light coat of Colonial Maple wiped on to add a subtle reddish cast. Testing on scraps helped dial in the look before finishing the ladder and rails.
Step 9: Add Mattresses & Bedding!
With paint and stain dry we added mattresses, bedding, and storage. The bunks quickly became the kids’ favorite spot—and a dog or two agreed. A small cube organizer gives enough storage for weekend stays and summer visits.
Final Measurements For Our Built-In Bunk Beds
Final dimensions we used:
- Platform dimensions: 81.5″ x 40″ to fit an 80″ x 38″ Twin XL mattress
- Bottom bunk platform top: 10″ off the floor; mattress top 17″ off the floor; 34.5″ headroom
- Top bunk platform top: 56″ off the floor; mattress top 63″ off the floor; 32.5″ headroom
- Ladder width: 21″ overall with 18″ rungs; rungs spaced 12″ apart top-to-top
- Top railing sits 7″ above the mattress top (minimum required is 5″) with a 3″ gap between rails
Overall, the build was much less intimidating than anticipated and delivered a sturdy, attractive solution for a very small room. If you plan a similar project, anchor your main members into studs, use heavy-duty structural screws, and test fit everything in place before final fastening.
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