How to Build Built-in Bookshelves with the Ikea Billy Bookcase

Updated: Jul. 08, 2024

There is nothing complicated about this Billy bookcase hack. Just assemble, add some moldings and components, and paint.

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Learn how to build built-in bookshelves using inexpensive Ikea Billy bookcases and standard trim to create a classic and elegant look.

Tools Required

  • 18-gauge brad nailer
  • Allen wrenches
  • Assorted drill bits
  • Caulk gun
  • Circle cutting jig or Trammel arm
  • Clamps
  • Drill/driver
  • Level
  • Miter saw or box
  • Moulding pry bar
  • Painting supplies
  • Random orbital sander w/ sandpaper
  • Router w/ straight cutting bit
  • Screwdrivers
  • Shop vac
  • Stud finder
  • Table saw
  • Tape measure
  • Track saw

Materials Required

  • 1 - 1/4" x 4' x 8' plywood
  • 1 - 1x4x8'
  • 1 – 3/4” x 4’ x 8’ plywood
  • 1-1/4" brad nails
  • 150 and 220 grit sandpaper
  • 2 - 1x3x8'
  • 2 - 3-1/4" x 8' baseboard
  • 2 - 3-5/8" x 8' crown molding
  • 2 - 3/4" x 18" x 4' edge-glued panel
  • 2 - Ikea Billy Bookcases
  • 2 - Ikea Billy height extension units
  • 4 - 1x2x8'
  • 4 - Ikea Oxberg doors
  • 6 - Ikea joining screws
  • Caulk
  • Construction adhesive
  • Duct tape
  • Paint
  • Primer
  • Shims
  • Tack cloths
  • Wood filler

If you are a social media user, you are likely familiar with Ikea furniture hacks. These hacks range from bread box side tables to Ikea desk hacks, but none are more prevalent than Billy bookcase hacks. They are everywhere. As I scrolled one night, it inspired me to build some built-in Billy bookcases in a room I had planned to refresh with new moldings and fresh paint.

But first, I had to do the math. When I went to design Billy bookcases as built-ins just the way I wanted — with arched tops, crown molding, and baseboards wrapped around them — it quickly became apparent that there were three critical height measurements that needed to be considered.

  • Ceiling height: The height of your ceiling is important since it determines whether you can use the Billy bookcase height extender package available at Ikea or whether you will have to make your own. For this project, I built a soffit down to eight feet, which acts the same as a standard ceiling.
  • Crown molding height: The height of the crown molding should be taken into account. If the crown molding is too tall, it will make the arch lower and the top shelves almost useless. If you choose a crown molding that is too short, it may not cover the gap between the top of the bookcase and the ceiling. In my case, I used this common and readily available 3-5/8-in. crown molding that can be found in some form at most home improvement stores.
  • Baseboard height: If you choose to use doors on your bookcases, this height is crucial to both their aesthetics and functionality. Ikea Oxberg doors are overlay doors. This means they rest on the front edge of the bottom and middle fixed shelves of a standard billy bookcase. Therefore, if you choose to use a tall baseboard, you will need to construct a taller riser in order to maintain the functionality of the doors. I stuck with a 3-1/4 inch tall baseboard that was already in the room and is common in newer homes.

Using these three heights, you can follow a process similar to the one that follows for any ceiling height. If you have taller ceilings, you may need to use a taller baseboard and crown molding. For shorter ceilings, you may have to build your own extension box or omit it altogether. This method will allow you to turn IKEA Billy bookcases into built-ins that look like they have been there for generations.

Project Overview

(Excluding doors and moldings for clarity.)

Build Built In Bookshelves- The Billy Bookcase Hack Project OverviewFamily Handyman

Cutting List for Our Project

Riser 1 1/4″ x 11″ x 63″
Side 2 3/4″ x 11″ x 93-3/8″
Shelf build-up (long) 4 3/4″ x 2-1/2″ x 30″
Shelf build-up (short) 6 3/4″ x 2-1/2″ x 5-1/4″
Plywood shelf 2 3/4″ x 10-1/4″ x 30″
Arch panel 2 3/4″ x 17-3/16″ x 32-1/4″*
Upper stile 3 3/4″ x 1-1/2″ x 33-3/16″
Lower stile 2 3/4″ x 3/4″ x 38-3/8″
Center rail 1 3/4″ x 1-3/8″ x 64-1/2″
Base rail 1 3/4″ x 3-1/4″ x 64-1/2″

* – Cut to this size after routing the arch.
Overall dimensions: 69″w x 96″h x 14″d

Project step-by-step (12)

Step 1

Assemble the bookcases

Assemble the two, 31-1/2-in. wide by 79-1/2-in. tall Billy bookcases and height extension boxes according to the instructions provided by Ikea. I reinforced the back panel seam with duct tape and painted the bookcase backs ahead of time.

When painting Ikea furniture that is laminated, such as these bookcases, it is necessary to sand them with 150-grit sandpaper to provide some bite for the primer to adhere to and apply several coats of paint, anticipating the need to touch it up later.

Build Built In Bookshelves- The Billy Bookcase Hack Assemble the bookcasesTMB Studio

Step 2

Cut and attach the riser

Remove the wood trim baseboards and/or crown molding where you would like your Billy bookcases to be installed. Using the height of the baseboard as your guide, determine how high you need to put a riser under the bookcases to allow you to carry the existing baseboard around the cabinet without having it protrude over the bottom shelf or interfere with the doors if you are using them. The taller the baseboard, the higher the riser will be. The next step is to construct or cut a riser that is exactly the same size (or a little smaller) as the footprint of the combined billy bookcases.

Our baseboards only required me to raise the bookcases around 3/16 inch, so I cut a piece of quarter-inch plywood 11 inches by 63 inches and glued it to the bottom of them using construction adhesive.

Build Built In Bookshelves- The Billy Bookcase Hack Cut and attach the riserTMB Studio

Step 3

Attach the bookcases together

With the construction adhesive on the riser still wet, it’s time to attach the two Billy bookcases together. Here is how to accomplish this:

  • Apply construction adhesive to the sides of the bookcases you wish to join.
  • Hold the bookcases together with clamps, ensuring they are flush at the top, bottom and front.
  • Drill holes through existing shelf pin holes in the sides of the bookcases you are joining to insert the joining screws. To minimize the amount of play, drill your holes just a little larger than the barrel diameter of the joining screws. The joining screws were purchased from Ikea’s “spare parts” section. The screws and barrels are sold separately as parts #100402 and #100644.
  • Push or tap the joining screw into their holes and tighten them down with the appropriate Allen wrench and/or screwdrivers.
  • Drill and insert at least six joining screws along the joined sides. Two at the bottom, top, and middle.
  • Let the construction adhesive cure while the clamps are in place.
  • Once the adhesive has cured, mark the wall studs at the top of the wall and push the joined bookcases against it.

Build Built In Bookshelves- The Billy Bookcase Hack Attach the bookcases togetherTMB Studio

Step 4

Fasten the bookcase to the wall

As soon as the joined bookcases are positioned to your satisfaction, use the L-brackets provided by Ikea to attach them to the wall plumb and level. If the walls are not smooth or square, it may be necessary to use shims and attach a second set of L-brackets to the bottom shelves of the bookcases, connecting them to the wall studs through the back to ensure they are stable.

Build Built In Bookshelves- The Billy Bookcase Hack Fasten the bookcase to the wallTMB Studio

Step 5

Attach the plywood sides

This Billy bookcase hack requires that you cut and install plywood sides that run from the floor to the top of the bookcase to hide the extension box seam and any shims needed to secure it to the back wall. Use construction adhesive and 1-1/4-in. brad nails to attach the plywood sides flush to the front edge of the existing bookcase sides. Ensure that your nail gun is set to the correct depth so that the nail does not blow through the inside of the bookcase while being used. If the back wall is incredibly uneven or many shims were used, cut the side pieces wide and scribe them to the back wall before attaching them.

Build Built In Bookshelves- The Billy Bookcase Hack Attach the plywood sidesTMB Studio

Step 6

Build up the fixed shelf

Because the doors we purchased from IKEA to cover the bottom half of our unit will protrude over most of the center fixed shelf, that shelf will need to be built up by 1-1/2-in. to support the cross-member of the face frame. To do that:

  • Frame the shelf buildup with 1x3s or scrap 3/4-in. plywood pieces. Secure the pieces with construction adhesive and 1-1/4-in. brad nails, making sure there are no gaps between the fixed shelf and build-up pieces.
  • Cut a 3/4-in. plywood shelf the same size as the shelf and attach it to the shelf build-up frame you just attached. Again use construction adhesive and nails to secure it down on top of the shelf build up pieces.

How To Build Built In Bookshelves The Billy Bookcase Hack Build up the fixed shelfTMB StudioTMB Studio

Step 7

Cut the arches

Build Built In Bookshelves- The Billy Bookcase Hack Cut the arches

From the edge-glued poplar boards, cut two arches as follows:

  • Mark the center of the edge-glued panel’s width.
  • Configure your router with a straight cutting bit and a Trammel arm or circle cutting jig so that you can cut a circle 30 inches in diameter.
  • Attach the pivot nail/screw of the circle cutting jig on your mark and as close to the edge of the panel as possible.
  • Rout the arches. Cut them in several 1/4-in. deep passes to prevent tearing out the edges.
  • Cut down the arch panel using a track saw or table saw so one side of the arch has a 1-1/2 inch wide tail and the other has a 3/4-inch wide tail. Make sure the two arch panels remain square.
  • Cut the arches to the correct height. The amount of material you leave between the top of the arch and the top of the cabinet depends on the profile height of the type of crown molding you plan to use. The reveal between the arch’s top and the crown molding’s bottom should be 1-1/2 inch, like the upper stiles of the face frame. Our cabinet with riser measured 93-3/4 inches tall, which left a 2-1/4 inch gap between its top and the eight-foot ceiling in the space. The crown we used had a 2-15/16 inch tall profile. This means that when the crown was installed at a 45° angle, only the bottom 11/16-inch would contact our case. So the amount of material left above the arch should be that 11/16 inch plus the 1-1/2 inches we want as a reveal, or 2-3/16 inches.
  • Glue and nail the arches to the top of the cabinet so that they mirror each other, with the smaller 3/4-in. tails meeting in the middle of the joined cabinets.

Build Built In Bookshelves- The Billy Bookcase Hack Create the archesTMB Studio

Step 8

Assemble the bookcase face frame

Assemble the remaining pieces of the face frame, starting with the horizontal pieces.

  • Cut the base rail to the baseboard height and the total width of the bookcases.  Use construction adhesive and nails to attach it to the bottom of the bookcases.
  • Install the center rail flush with the top edge of the plywood shelves. To provide myself with some wiggle room when I installed and adjusted the doors, I trimmed the rail to 1-3/8 inch wide.
  • Attach the narrow lower stiles with construction adhesive and nails flush to the outside edge of the plywood sides.
  • Secure the three upper stiles using construction adhesive and nails. Both outer stiles should be attached flush to the edge of the outer plywood sides. The middle stile should be centered on the joined Billy bookcase sides, in line with the short tails of the arches. Please note that the upper stiles will vary in length depending on your crown molding size.

Build Built In Bookshelves- The Billy Bookcase Hack Assemble the bookcase face frameTMB Studio

Step 9

Attach the moldings

Install the baseboard so that it wraps around the secured bookcases. Do the same with the crown to cover the gap on top of the bookcases. You can either carry the crown all the way around the room as I did, or you can just let it die into the back wall. Both options are acceptable.

This is one of the most difficult parts of the building process. Take your time. Buy extra molding and make sure your miter saw is correctly set up for these cuts and equipped with a sharp blade. Attach them with brad nails only.

Build Built In Bookshelves- The Billy Bookcase Hack Attach the moldingsTMB Studio

Step 10

Prep, prime and paint

With the bookcases built, it’s time to get them looking great.

  • Fill all nail holes and the seam between the arches with wood filler. Wood filler will shrink a little as it hardens, so it is advisable to overfill these areas slightly.
  • If you didn’t end up with perfect miters on your baseboard and crown moldings, you could use a little paintable caulk to improve their appearance. But I recommend not caulking gaps larger than 1/8 in. If you have open miters larger than that, the molding should be removed and recut.
  • After the wood filler and caulk have dried, sand all components (except the painted backs) with 150-grit sandpaper. Use a random orbital sander in conjunction with hand sanding in the corners and edges to smooth the entire piece and give the primer some tooth to adhere to.
  • Use a shop-vac and tack cloth to remove all sanding dust. Be diligent in your efforts. The cleaner the project is, the better the finish will be.
  • Mask off the surrounding floor, walls, and ceiling and prime everything, including both sides of the unattached doors and adjustable shelves.
  • Once the primer has dried, lightly sand the entire surface with 220-grit sandpaper. Clean up the dust with a shop vac and tack cloth.
  • Paint everything in your chosen color with a quality brush and roller. Expect to apply at least two coats, sanding with 220-grit and dusting between each.

Build Built In Bookshelves- The Billy Bookcase Hack Prep, prime and paintTMB Studio

Step 11

Finishing touches

Having painted everything to your liking, it is now time to attach and adjust the doors according to the Ikea instructions provided. Put pulls on the doors if you wish and begin filling your new built-in bookcases with books and treasures.

Step 12


Can you use a Billy bookcase without backing?
Yes, you can use the Billy bookcase without its thin cardboard backing. But keep in mind that this backing is not only intended to prevent contents from falling through the back of the bookcase, but also to hold it somewhat square.

Do Billy bookcases need to be anchored to the wall?
Yes, it is recommended that Billy’s bookcases (and all bookcases, for that matter) be anchored to the wall, especially when young children and pets are present.

How much weight can a Billy bookcase hold?
Ikea’s website states that a properly constructed and secured Billy bookcase shelf can support a maximum load of 66 pounds.