How To Build an Expandable Bench
"This bench slides apart so you can expand your seat to fit a friend."
Today’s DIY came about while I was building the DIY Wood Bench. It occurred to me that the slats of the seat boards could be made to slide apart and extend the seat, so I gave it a whirl. While the sliding idea itself is pretty simple, it took me a few more mock-ups than usual to get the design just right. I found out the hard way that the boards wouldn’t slide apart if screwed too tightly together, so I used screws with mushroom heads to build in a little space between each board. The final product is a modern bench that can expand for extra seating or contract for easy storage.
And with that, let’s get building!
Step 1: Cut wood to size
For this bench, we chose to use cedar two-by-fours, but you can use whatever type of wood you prefer. Cut the lumber to eight pieces 30” long and 16 pieces 15” long. Cut as precisely as possible so like boards are the same length. After you’re done cutting, sand the cut ends smooth.
Step 2: Pre-stain wood if desired
The cedar boards we used will weather naturally outside and we’re fine with that. However, if you’d like to stain your boards, now is the best time to do it, as it will be harder when the bench is assembled. A good rule to follow when staining is to apply the finish to all sides of the board (the four sides and also the two ends).
Step 3: Assemble the left side
On a flat surface, lay a 15” piece and a 30” piece in an “L” shape that measures 30” on the long leg and 18 1/2” on the short side. Now lay another 15” piece on top of the first one, but staggered to align with the top of the 30” piece. Square up all the edges—particularly at the corner—and drive 2 1/2” screws through the top piece into the two pieces below. A speed square can help you keep things flush and at a right angle. We used two screws at the corner and two screws in the lower short piece, too.
Note: We chose screws with a mushroom head that stick up above the board. This means as you screw the layers together, the protruding head will create a slight gap with the adjacent board. That’s intentional; the screw heads create this little bit of space so the boards don’t fit too tightly together, giving them room to slide back and forth later on. If you drive the screws too hard, the heads will become flush with the board and your bench will bind, and won’t slide apart—so stop driving the screws when the heads meet the board.
Step 4: Assemble the right side
Now build the right “L.” It’s a lot like the left one, but the 30” pieces are on different layers, so they will lay on top of one another.
Start with a 15” piece on your work table and then lay a 30” piece on top of and perpendicular to it. Add another 15” piece on top of the other one (it will stick out at the bottom). Square up your corner and edges and then screw into place with four or five screws.
Step 5: Continue adding layers
Now add another 15” piece and 30” piece to the left side. Square up the edges and screw into place. Next, do the same on the right side. Add on to the left and right sides until you’ve used up the pieces.
Step 6: Screw bottom braces into place
With the bench turned upside down (like a “U”), slide the two sides apart slightly. Measure and cut a length of two-by-three the depth of the left-hand boards and one for the right-hand boards as well. Pre-drill and fasten in place.
Step 7: Screw top braces into place
Now turn the bench on its side. Measuring the full width of the bench, cut two two-by-threes at that length. These will screw into the ends of the 30" pieces. Pre-drill and screw one piece into the ends of the four right-hand boards, the other into the ends of the left-hand boards.
Now, you have a simple sliding bench built for one or two! If you enjoyed this project, be sure to check out how to build a lounge chair and our inexpensive outdoor side table tutorial.
