The Big Chair – Building Your Own

I’ve gotten a few emails and comments asking for plans for the giant adirondack chair I built. The trouble is that I prefer building things to documenting them. But because I love you all, I buckled down and made some plans. Don’t get too excited, because these aren’t formal blueprinty plans. To do that right would require building another chair to test everything out, and there’s only room for one of these in my yard. So instead I measured the already-built chair, tried to remember what I’d done (and in some cases what I’d do differently), and rebuilt it in Google Sketchup.

Please note: this description isn’t intended to be a step-by-step guide with every 1/8 of an inch and every angle accounted for.  Read through the entire thing before building. Then read it again. This will get you close, but you’ll need to figure some things out on your own as you go. No guarantees are made as to the accuracy or suitability of it for any purpose, and you’re responsible for what you build and for any damage when it inevitably falls down.

Here’s a materials list for the lumber:

You’ll also need some deck screws (2.5″ or 3″), eight 1/2″ galvanized hex bolts (length depends on how you build it, but I think I used 3″), washers, and nuts.

Seat/Base

Cut your 12-foot 2×10 in half so you’ve got two 6-foot pieces.  These will be the rails along the side that support the seat slats.  Decide what angle your chair will rest at. Mine’s at 20 degrees, and in regular-sized Adirondack chair plans I’ve seen everything from 17 – 22 degrees or so.  Cut this angle across one end of each of these boards, something like this:

The angle you cut will be the back foot that the chair rests on. If you want to round that corner (shown in red), do so now. This would also be the time to cut a contour in the seat (again in red), should you desire. The seat contour shouldn’t be very deep, and should end about 30″ back where the back of the last seat slats will go.

Measure 9 inches from the front of the 2×10 frame rail, along the bottom.  Starting there, draw a line at 90 degrees to the angle you used before. It’ll be 9″ back on the bottom tilting to barely under 6 inches back on the top. It’s illustrated in yellow in the photo below. This line will be where the front edge of the front vertical support goes.  Do it again on the opposite side of the other rail.

Cut a 4-foot piece from the 8-foot 2×10 to connect the two side rails at the front of the seat.

Put the frame rails four feet apart (from outside edge to outside edge) and make sure everything is parallel and square, then attach the 4-foot 2×10 across the front with a few deck screws in each end.

Cut the 8-foot 2×12 into two 42″ long pieces.  These will be the front vertical supports that hold up the seat and the armrest.

With some friends, stand the vertical supports on either side of the base frame you made, then start lifting the front of the base until the line you drew is parallel with the support.  Getting this right will also mean that that the corner you cut at the rear of the rail is now flat on the ground.

Clamp the rails and the supports together firmly so you don’t need to hold it all up by hand, then drill a pair of  half-inch holes all the way through.  You can use a Forstner bit partway through to sink the bolt head (I used half-inch galvanized bolts) out of the way, but that’s not necessary.  Carriage bolts might be another option, so that the outside would be more smooth.

Cut both of the 8-foot 2x8s in half so you have four 4-foot pieces. These will be the slats you sit on.  I used a round-over bit in the router to soften the top edges, but that’s optional depending on your tool set.

Attach the first 4-foot 2×8 across the top with deck screws, overlapping the edge of the 2×10 on the front. Work your way back attaching each slat about half an inch away from the one before.

Backrest

Now it’s time to make the backrest. This part is tricky, but I’ll do my best to describe it. Make a lot of measurements and do a lot of fitting and testing before you cut. Build to the measurements you end up with, and not strictly to mine.

Cut your three 12-foot 2x12s in half so you’ve got six 6-foot boards. You’ll only need five of them for the slats, and the other will be used elsewhere.

The first problem to be overcome is that the boards are each 11-1/4″ across, and you’ll want a half-inch gap between them. Five boards and four gaps equals 58.25″. That’s fine for the top of the backrest, but the bottom needs to fit the 48″ width of the chair base. You’ll need to taper each board down from 11.25″ to 9.2″ (let’s go with 9.25″ for ease of measurement). 9.25″ x 5=46.25.  Add 2″ for the gaps between and you get just a bit over 48″. That’s close enough.

There’s no need to cut 1″ from each side; instead you can take 2″ off of one side, as long as you can round over the board’s edges to match on both sides. How you cut this is going to depend on the tools you’ve got. I used a circular saw and made a guide to ensure a straight cut.

Once all 5 back slats are cut, lay them onto the ground and space them about half an inch apart at top and bottom. This is mostly a check to make sure all the cuts are correct and the spacing is right. The width on the bottom should be just over 48″. If you want to cut an arch across the top of the slats (shown in red on the picture below), draw it on now while all of the boards are lined up, then cut each board individually. If you want the top to be square, snap a chalk line across the top, then cut each board along the line. The bottom edge of the boards will not be even, and you shouldn’t try to make them even yet.

There are two supports for the back slats, one at the bottom and one about halfway up. Let’s do the bottom one first.

You should have one 6-foot piece of 2×12 left. Cut it down to 4 feet long, then measure 7.25 inches in from the edge and draw a line all the way across (red in the diagram below). You’re basically making a 2×8. Next draw a shallow arc from one corner of that 2×8 piece to the other. This will be a rough guide to the contour of the seat back.

Now divide the arc into five 9-3/4″ (or so) straight segments. These segments will let each back slat fit square against the support. If you cut right along the arc, only the corner of each slat would be supported. Cut as neatly as you can along the lines because you’ll use the convex piece later.

There’s another support halfway up the back, and this one really relies on you making your own measurements based on the back slats you’ve got laid out. Measure 4 feet up from the middle of the center slat and mark it. Draw a straight line all the way across the slats at that mark. Measure the width of each board at the line you’ve drawn and write each down. Because of the way they fan out, the width of the outside boards at the line will be more than the center board. Add a little bit to each measurement, since the curve will make that half-inch gap at the front of the board slightly wider at the back.

Cut the remaining 8-foot 2×8 in half, then mark off your measurements from the center of one piece and cut another segmented arc with these measurements, much like you did with the bottom support. The boards on the edge of the backrest won’t be fully supported, so the outside segments of the arc will be shorter than the rest.

To attach the upper back support to the chair, mark your chosen angle 60″ up the 12-foot 2×6. Measure 60″ off the other side of the angle and cut straight across, so you’ve got one support for each side. Keep the scrap piece to use later as an armrest support.

Lay the two vertical supports 45″ apart, get everything square, then attach the upper horizontal support with screws. There will be a 1.5″ overhang on each side.

Attaching this rear support frame takes some attention to detail, because you want the verticals completely, well, vertical. And at the same time, you want it positioned front to back so that the angle between the seat and the back equals 90 degrees. You might have another method, but what I did was to tie a string between the centers of the upper and lower rear slat supports, then move the support frame back and forth until a framing square held against the seat slats showed the string was at a right angle. The picture below illustrates this method. When everything is lined up and square, clamp the support frame to the rails, drill, and bolt just like you did for the front supports.

Now you can attach the vertical slats! I put four screws into each slat (2 top, 2 bottom). You might have to remove a seat slat or two in order to get access for drilling & screwing. Be careful at this stage: without the armrests tying it together, the chair is very unstable.

Because of the way you cut the angle into the back slats, there may be some unevenness along the bottom where it attaches to the support (see image below). You can either ignore this or mark a line on each slat, take it down, cut it, then re-attach. If you do remove your slats, it’s a good idea to mark which is which so everything can fit back where it’s meant to be.

Armrests

The armrests are 60″ 2x12s. Cut two from the 10-foot 2×12 and contour them as you’d like. The back of each armrest is attached by screws to a small block on the the vertical support in the rear of the chair (see the inset detail below). Cut the blocks from a piece of the 2×8 left over from the 8-foot 2×8 you used for the upper back slat support. Screw the block to the vertical support, then screw the armrest to the block.

In the front, cut two 2x6s about 1 foot long (use the scrap piece from the rear vertical supports) and contour as you like, then attach with deck screws to each front vertical support in a T formation. This will give the armrest a wide, stable surface to rest on.

Now for the problem of how to intersect the armrest and the rear vertical slats. Take a close look at the picture above and see where they meet. It’s a compound angle, possibly even extending into dimensions we haven’t discovered yet. The slats lean back and curve inward. I basically cut it in place by fitting the armrest as close as I could against the vertical slat, marking it, cutting, test fitting, cutting some more, and so on. If you’ve got a laser level, that may help you transfer lines where you need them. All I can really say is “good luck,” or maybe build a chair without the fanned back; then you don’t need to worry about it.

Once you’ve got your armrests attached, fill the gap between the vertical slats and the rearmost seat slat. Remember the convex piece from your 2×12? You’re basically putting these two pieces back together with the backrest between them. You might need to trim the straight side of the board to fit. Leave a gap between this board and the back slats for any rain to drain down.

You’re done! Now you’ll probably want to take it all apart in order to paint it and/or move it to its final destination.

If you do end up building a giant chair based on this page, please send pics. I’d love to see your work. I also welcome any ideas to make the project easier; I’ll add them here to help the next builder.

Here’s the materials list again, this time with each type of board color coded. It corresponds with the picture below where each board is colored the same as in the materials list, so you have a better idea which pieces are used where.

And here’s a PDF (61KB) of all the lumber with cuts marked: