how to use pre-made bookcases to create a custom built-in
First, I built a base for my bookcases. A base elevates the shelves from the floor, and gives the entire piece a feeling of substance. The base is built out of a 2×4 frame, with interior studs to support the plywood top of the base.
Cut a piece of plywood to cover the top of the 2×4 base frame. Any type or thickness of plywood would be suitable to use here, but I used the same plywood that I used for my vertical pieces in the next step. I mentioned this in my tools list, but I used a circular saw to cut all of my larger pieces of wood. Before cutting, I mark my cutting line and my clamping line, then clamped a straight edge so that the circular saw can push against the straight edge, ensuring the blade perfectly cuts the edge of the line.
Mark where the vertical parts of your base unit should be positioned. These marks should exactly match the verticals of the bookcase that you will be stacking on top of it. I measured my bookcase’s spacing, and marked those lines on my plywood base here, using a carpenter’s square to make sure they were perfectly perpendicular with the edge of the base. Once the lines for your verticals are drawn, drill three pilot holes in each section, where you will attach the verticals in the next steps.
Begin screwing your wood screws into the pilot holes that you drilled in step three. Make sure they have gone through the plywood completely, but aren’t sticking out beyond its surface.
Now flip the plywood base to its side so you can attach the vertical pieces using the screws you started in step four. If you have trouble driving the screws into the vertical boards without the verticals pulling away from the plywood base, you may want to clamp the pieces together before screwing. A little muscle holding the pieces together should do the trick.
If your screw heads are stripping as you struggle to drive them into the plywood verticals, you may wish to use self-tapping screws that drive their own pilot holes as you screw them in.
Now that the base is complete and in place, flip the Billy bookcases upside down and position them on top of the base, matching up the verticals. At this point you will want to anchor your bookcases to the wall. If you can, choose a place which will be covered with trim, such as crown moulding. If you can’t find a spot that will be covered by trim, then choose somewhere inconspicuous that will most likely not be visible after filling your bookshelves.
Fill any gaps between walls or bookcases with blocks that help secure the bookshelves to the wall, but also serve as nailing boards for the next step. Use several blocks along the height of your gaps so you’ll have various places to affix the framing pieces.
Frame in the completed Billy bookcases by gluing and nailing wood strips to the front of the bookcases, covering where each bookcase meets each other. I started at the bottom of the unit with a 1×6 that I ripped to fit the exact thickness of the bookcase base (which ended up being just a hair too wide for a standard 1×4 to cover adequately). Then I attached a 1×4 to the top of the bookcase. In between the top and bottom frame pieces I fit 1x2s that were trimmed length-wise to fit very snugly in place. The gap to the right of the bookcase in the corner was covered by a 1×6 nailed to the blocks I put in place during step seven.
I covered the sides of each bookcase with pieces of lauan, which is a very thin and inexpensive plywood material. The reason I added lauan here is to cover the gap between the Billy bookcases on top and the plywood addition I built below them. I also added 1x2s on the sides of the bookcases to give it more of a finished look.
Fill all nail and screw holes with spackling and then sand smooth. At this point you’ll also want to fill any cracks with paintable caulk.
Prime and paint the bookshelves. (See post for more detailed insturction on priming and painting laminated pieces.)