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. I know as you skim this, it probably seems like a lot, but to keep it simple, just skim to the sections that apply to you! If you don’t have 9.5-foot ceilings, you should be able to use 2x4s to make up the difference between the bookcase + extender height and your ceiling. Then, add crown molding at the top and 1x2s over each seam to create that built-in look.

But since I have 9.5-foot ceilings, here’s what I did…

Office dimensions for reference: 11’ x 11’ and ceiling height is: 9’5”

Shop the room here: You can find the materials I used on my Lowe’s storefront to build it and everything I used to style it here. 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

These are all linked on my Lowes Storefront:

• (4) 1×2 primed trim
• 1 gallon Zinsser B-I-N Primer
• (2) Pine Cove Moulding
• Barrel Screw (35mm)
• Clamps
• Caulk
• Baseboard Moulding
• Zinnser 123 primer
• Sherwin-Williams Iron Ore Paint (satin)
• (1) Corner Piece
• Caulk
• Painter Tape
• Wood Filler
• 220 grit Sand Paper
• Wood Glue
• Brad Nails
• Liquid Nails
• Miter Saw
• Drill
• Brad Nailer (or hammer)
• Measuring Tape
• Sander (or hand sand it will work too)
• Level
• Stud Finder
• Kreg-Pocket Jig
• Kreg-Crown tool

Hardware and Home Decor

• Extenders that I built I used:
  • 2x2s to create the additional extenders at the top
  • 1/4″ plywood
• Crown Moulding

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

For you, use primed 1×2; I linked it in my storefront for you. I wish I didn’t use the one I did.

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. I primed (MAY SURE YOU PRIME – I made this BIG mistake and trust me don’t skip that step) For the finish, I used Sherwin-Williams Iron Ore in Satin.

Step 6: 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 7: Paint and Add in the Baseboard

I decided at the end 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.

Step 8: Add crown moulding

I technically had an additional step before this because I decided I wanted to add more shelving. I have 9.5-foot ceilings, so instead of adding height at the base during the first few steps, I decided I wanted more shelving at the top. I used 2×2 boards and a Kreg Pocket-Hole Jig to create the look.

If you’re a beginner, you can skip this step and simply add 2x4s to the bottom to get the height you need so you can add crown molding at the top and have it meet the ceiling.

Okay, now for the crown molding! I used the Kreg Crown Tool, which made this part much easier. Unpopular opinion: I skipped measuring the exact angle of the wall and ceiling and simply set the tool to 45°. Place the molding upside down in the tool, then make your 45° cut with a miter saw.

You got this!

– Audra