The making of beautiful Built-in Bookshelves: A DIY Success Story

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Katja Nordkvist is a DIY enthusiast who recently completed an impressive hack of IKEA KNOXHULT cabinets and BILLY bookcases. She transformed these basic pieces into custom built-in bookshelves that showcase her decorative items.

What I love about it is the closed storage cabinets at the base and open shelving at the top. One gorgeous seamless storage solution, even though they are made by combining two IKEA products. I got in touch with Katja to learn more about her project and how she did it.

When I asked how she came up with this idea of merging the IKEA KNOXHULT and BILLY, she said this wasn’t her first time landing on this winning formula. “My husband and I did a similar hack before in our previous home. There was a big, naked wall and really high ceilings and we needed a storage unit that would fill out that space and improve the acoustics in the living room.”

When they moved to a new home, they knew they wanted to make something similar in their new space. Compared to the first version, this IKEA hack is a lot more intricate with more decorative trim and details.

It took Katja and her husband a month to complete, working on it in between work, kids, and life in general. Nevertheless, she believes two people would be able to finish this DIY project over 3 days, without interruption. Though it took some time the result is worth it.

Katja adds, “I love having a place to put all of my vases, coffee table books, and so on. It’s perfect for showcasing decorative items for sure.”

What you need for these DIY built-in bookshelves:

built-in bookshelves from IKEA BILLY and KNOXHULT in all white room setting

IKEA item used:

  • KNOXHULT kitchen cabinets (40cm) or IVAR cabinets (if you live in the US)
  • IKEA BILLY bookcase (The narrow bookcase at 40cm wide / 15 3/4″)

Other materials:

  • 12 mm MDF
  • 6 mm MDF for decorating the cabinet doors
  • MDF for the sides and the platform
  • Moldings for decorating the cabinet doors
  • Crown moldings
  • Fluted moldings
  • Wood adhesive (for the moldings)
  • Short baseboards
  • Chicago screws
  • Regular screws
  • Sand filler
  • Acrylic caulk
  • Sandpaper
  • Primer
  • Paint, medium or high gloss


  • Miter saw
  • Miter box and regular jigsaw
  • Powered screwdriver and different-sized drills
  • Powered jigsaw
  • Handheld edge router
  • Caulking gun
  • Wet wipes

Step-by-step tutorial for DIY built-in bookcase

Briefly, this is a summary of her video guide, if you prefer to read it.

Making the cabinet base

  1. Start by building a platform spanning the wall space. Cut wood to size and join the pieces with angle brackets. If you prefer, you can use MDF or plywood instead, which may be easier if you don’t have access to woodworking tools.
  2. Assemble the IKEA KNOXHULT cabinets and line them on the platform. Clamp and use connector bolts and cap screws to attach the cabinets. Then, secure the cabinets to the wall (if drywall, screw onto wall studs). Lastly, screw them into the wooden platform.
  3. If there is a gap between the built-in shelves and the side wall, now is the time to cover it up. Screw wooden blocks into the cabinet and cut a piece of MDF to cover the front of the gap.
  4. The next step is to cover the top of the cabinets with a cut piece of MDF spanning the whole length. Use an edge router to round up the edge, optional but it makes for a polished finish.

Installing the bookshelves

fluted molding, reeded molding on as bookcase spacer
  1. Assemble the IKEA bookcases. (Katja cut 23 cm off each bookcase to fit her ceiling height.) Make new holes for the shelf pins to ensure that the space between each shelf is the same cube size.
  2. Next, place the bookcase on top of the MDF countertop. Katja’s tip is to use a nail. Hammer the nail halfway through the table top and cut off the nail head. Then, place the BILLY bookcase on top of the nail, piercing into the BILLY particleboard. You don’t need to do this for all the bookcases, just the first and last.
  3. Optional step: Place 3mm spacers between the bookcases. This aligns the BILLY bookcases to the KNOXHULT cabinets. Cover the spacers with a fluted trim.
  4. Fill all the shelf pin holes with wood filler. This step is also optional if you want adjustable shelves. However, this extra step will make the display shelves look so much better.
  5. Then a whole lot of caulking before sanding the entire shelving unit down.
  6. Once you have all the surfaces primed, you’re ready to paint the built-in bookcases.

Adding decorative trim to door cabinets

built-in bookshelves from IKEA BILLY and KNOXHULT in all white room setting
  1. The KNOXHULT cabinet door is a simple plain door. You can add any trim and molding to fit your style. For a classic style, Katja glued trim molding on each door and a rectangle piece in the middle. Cut the molding at a 45-degree angle and attach them with wood glue to the doors. Fill the gaps between the joints and caulk them.
  2. Prime and paint the doors. Katja used a Jotun primer and a Supreme Finish medium gloss paint. Let all the doors dry properly.
  3. Attach the doors. You can use knobs or door handles. They used push openers for a clean finish.
  4. Install baseboards to cover up the wooden base and if you like, you can also add crown molding to the top. (Which Katja has planned for a later date.)

Congratulations, you have now built your built-in bookshelves! All ready for styling with your favorite books and display items.

How much did it cost?

I’m not sure about the cost of this hack, but I believe it’s about 1200-1400 EUR.

What to pay special attention to?

The KNOXHULT cabinets can only work with the IKEA BILLY bookcases if they both measure 40 cm. However, in the US, they don’t (because they’re kitchen cabinets and those have different standard measurements in other countries). Instead, you should go for another IKEA cabinet that has either the same as or double the width of a BILLY bookcase, and here I’d say IVAR is the best option!

Looking back, would you have done it differently?

Yes! I probably would have made the bookcase go all the way over the double door in the middle. But instead, we decided to install an ornament on top of the door at some point later on.

Follow @katjanordkvist on Instagram.

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