DIY Office Built-Ins: IKEA Billy Bookcase Hack

I transformed my office with a custom built-in storage solution using four IKEA Billy bookcases! To make it even more functional, I added a center section doubling as my husband’s standing desk.

Office dimensions for reference: 11’ x 11’ and ceiling height is: 9’4”

Shop the room here: You can find the materials I used on my Lowe’s storefront. Anything not in my Lowe’s storefront I’ve linked separately below. (Please note that these are affiliate links, and I earn a small commission when you make a purchase through them. Your support is greatly appreciated!)

Materials:

• (2) Tall IKEA Billy Bookcases with Doors
• (2) IKEA Billy Bookcase Extender
• (2) IKEA Bill Booksase Short
• (2) IKEA Oxberg Doors
• (4) 1x2x8ft Select Pine
• 1 gallon Zinsser B-I-N Primer
• (2) 11/16 in. x 11/16 in. Pine Cove Moulding
• Barrel Screw (35mm)
• Clamps
• Caulk
• Baseboard Moulding
• Sherwin Williams Paint (1 gallon of Pure White, Satin)
• 1 quart Benjamin Moore Hale Navy at 75% opacity (if you like it a little lighter like mine)
• Spackle
• 1/2 inch x 4 x 8 Sanded Plywood
• (1) Screen Pine
• (1) Corner Piece
• Caulk
• Painter Tape
• Wood Filler
• 220 grit Sand Paper – 
• Wood Glue
• Hardware
• Brad Nails
• Liquid Nails

Tools:

• Miter Saw
• Drill
• Brad Nailer (or hammer)
• Measuring Tape
• Sander (or hand sand it will work too)
• Level
• Stud Finder

Step 1: Build Your IKEA Bookcases, Extenders + Attach Doors

Building the Bookcases

I recommend priming the shelves outdoors and allowing them to dry completely. Once dry, bring them inside and begin assembling the units. Note: Ensure you’re happy with the shelf placement, as we’ll be adding 1×2 boards later, which will make the shelves fixed and non-adjustable.

Securing Bookcases Together and to the Wall

1. Before securing the bookcases to the wall, use a spring clamp to connect them on the sides.
2. Use the pre-drilled holes to attach the bookcases together with 35 mm barrel screws.
3. Finally, use the included L-brackets to anchor the bookcases to the wall, ensuring you fasten them into a stud for maximum stability.

Filler Boards (If Needed)

After the cabinets are connected, check for any gaps on the sides. If gaps are present, measure the width needed to fill them and attach the filler boards to the wall first.

To attach filler boards to the wall, follow these steps:

1. Measure & Cut: Measure the gap on each side of the bookcase and cut your filler boards to fit.
2. Mark the Wall: Use a level to mark where you’ll position the filler boards on the wall to ensure they’re straight.
3. Drill Holes: Drill small pilot holes in the wall where the filler boards will go. Make sure to drill into the wall studs (the wooden beams inside the wall) for added stability.
4. Optional – Add Glue: For extra hold, apply glue to the back of the filler boards before attaching them to the wall.
5. Attach the Boards: Screw or nail the filler boards to the wall, ensuring they are tight and aligned properly.
6. Check Alignment: Double-check that everything lines up before fully tightening the screws.

Step 2: Add in Plywood

I chose to attach 1/4-inch plywood to the bottoms of the bookcase openings. (Note: I’ll be adding baseboard here later so you probably can skip this step and just add the baseboard in.)

Next, apply liquid nails to two separate pieces of 1/4-inch plywood, then attach them to each side of the Billy bookcases (for example, each side piece will be about 11 inches long, so you’ll have two pieces of that length on each top). Follow this by adding a full-length piece along the bottom inside edges. There will be a small gap at the ends of the bookcase, but don’t worry—this will be covered with a corner guard.

After that, measure and cut a plywood piece for the top, making it slightly wider than necessary. Apply liquid nails to the center of the top and position the plywood. Secure it with brad nails, fastening it to the extenders on both sides.

Step 3: Add Trim

Now for the fun part—let’s transform this into a built-in look! Start by adding 1×2 boards to the cabinet face, then apply cove moulding to the corners, and at the top of the center piece plywood at the top. Add in lattice panel at the back to cover the L-bracket on the shorter bookcases. Next, open the cabinet door and measure the interior. Cut a the corner guard to fit horizontally, then position it so that when the door is closed, it aligns perfectly, giving the cabinet a bit more depth and dimension. For the middle piece place the corner guard at the edge of the plywood.

Step 4: Fill the Adjustable Shelving Holes

Now that the 1×2 boards are in place, it’s time to fill the adjustable shelving holes. Use white spackle to fill them in, and then wipe the area with a damp rag to smooth it out. This will eliminate the need for sanding later.

Step 5: Fill, Sand, Caulk and Paint

If your nail gun (or hammer) didn’t drive the nails in fully, you may need to push them in a bit more and then fill the holes. When you caulk, keep a bowl of water and a rag nearby. Dab the rag in the water and wipe the caulk as you go to keep things neat and minimize cleanup later. For the finish, I used Sherwin Williams Pure White in Satin Sheen for the cabinets, and Benjamin Moore Hale Navy for the center of the built-in. (Here’s a fun tip: it’s a bit of an unpopular choice, but I had to visit two different stores before convincing the paint department to mix Hale Navy at 75% opacity. It’s a softer, more subtle shade, and I absolutely love it!) Oh, and when I went back for paint on a new project, they asked me if I used Hale Navy at that opacity. I just gave them a wink and said, ‘Sure did!

Step 6: Add in Screen Pine

Measure the desired spacing for the trim, then double-check that everything is level. I have very textured walls, so even though I checked the leveling at both the top center and the bottom with the plywood, you never really know for sure. Luckily, everything was level, so I nailed it in place. (You can choose to do this step when installing the rest of the trim, but I preferred to paint the entire back center area first before adding this trim.) Then caulk the sides and paint it.

Step 7: Add in Hardware

We’re in luck because the Oxberg Ikea doors already come with a pre-drilled hole at the back for the hardware. Simply use a drill bit to enlarge the hole if needed, then install the hardware of your choice.

Step 8: Paint and Add in the Baseboard

I deciat the ded last minute to add a baseboard here, but you can easily incorporate this step while adding your trim. I painted the baseboard first, then nailed it in place. Afterward, I filled the nail holes and caulk both the bottom along the floor and the top where it meets the cabinets.

You got this!

– Audra