How to build an Arched Arbor (with plans)

Posted in Home Improvement on July 22, 2018

If you want to build an arched garden arbor, here are all the step-by-step instructions you’ll need — including how to avoid the few teensy mistakes that I made.

What’s it take to build?

Have you ever watched a sport like high diving, where the judges rate the dive by its degree of difficulty? Well, if I graded this arbor that way, I‘d have to give it a 5 out of 10 for difficulty, and a 3 out of 10 for size and time.

If you have some familiarity with power tools, this arbor should be fairly easy to build. It isn't large, and it doesn’t require a great deal of precision. There isn't even any concrete to fool around with. However, you do have to be able to use a circular saw, belt sander, and jigsaw. A couple of the parts are best made with either a table or miter saw.

Even experienced carpenters might scratch their heads for a while about how to build the arches on top of this arbor. So I've left nothing to chance, and I’ve described that part of the process in particular detail, including all the measurements you’ll need. You’ll find it the most rewarding — and most fun — part of the entire project.

The materials should cost under $270. And if you have an assistant to help hold the other end of things as you work, the whole project can be built in a weekend.

Choosing what wood to use

The classic arbor, the one that most people would think of if you asked them to imagine one, is painted white.

It's also the toughest to own, because of the scraping, sanding and repainting you have to do to keep the paint looking decent. It's especially hard to do this after your climbing plants have made themselves at home on the arbor.

If you want a white arbor with less maintenance, try using a white semi-transparent house stain. It eliminates sanding and scraping and is easier to apply.

You might also think about other colors besides white. Dark green looks particularly handsome. If you're going to paint or stain, you can build the arbor out of pressure-treated lumber. That’s what I did.

You can also build the arbor out of cedar, redwood, or cypress, which are naturally rot-resistant, and leave the wood unpainted. Left to themselves, these woods will gradually weather to a soft gray color, but by applying a preservative every year or two, you can keep much of the original color intact.

Fig. A – A Garden Arbor

When you’re at the lumberyard, choose the wood for the 2x2 rails (part B) with some care. Since the rails are attached only at the ends, any large knots will seriously weaken them. And you can bet that someday a kid is going to try to climb this arbor, rose thorns or not. I had better luck ripping long hits in half and buying a bit more than I needed. That way I could cut around the knots and pick out the best pieces.

If you're building your arbor out of cedar, some of the boards may be rough-sawn on one side. Don’t worry. You can hide all of those rough surfaces as you build.

Cutting List

KeyPcs.SizeDescription
A44x4 x 96" trated pinePosts
B292x2 x 45" trated pineRails
C161x6 x 5" trated pineTrim
D42x6 x 5-1/2" trated pineCaps
E321x8 x 26-1/2" trated pineArch

Setting the Posts

Setting the posts isn’t hard, but if you've got helpers, now’s the time to call them. The first step is to determine where the arbor will go, by stretching four string lines (Fig. B).

Four string lines mark the corners where the posts will go. Tie the strings to batter boards for easy adjustment, and use the 3-4-5 triangle method to test that the corners are square.

Use mason's twine (available at hardware stores), because it doesn’t stretch. Adjust the strings until they‘re the right distance apart and the corners they form are at 90 degrees.

Now use a posthole digger to dig four holes for the posts. Make sure the bottom of each hole is flat and solid dirt. Set a post in each hole, and tamp 6 to 8 in. of soil around the bottom of the post.

The best way to tamp is to pack down about an inch of dirt at a time, using a piece of pipe or a shovel handle. Start lightly, then as the dirt gets more packed, tamp harder and harder, on all sides of the post. As you tamp, use your level to be sure that the post is plumb (vertical) in both directions, and just touching the string lines on both sides.

When all four posts are tamped in place, trim the tops (Fig. C). Start by marking one of the posts at 76 in. above the ground. If your lawn isn’t flat, mark whichever post is on the highest spot. Then, using a straight board and a level, transfer that mark to the other three posts, so the marks are all on the same level. Trim the posts at that height, using either a circular saw or a handsaw and a couple of cutting guides (Fig C).

Trim the posts so the tops are all at the same level. You can use a circular saw for this, or more lately, o handsaw and a couple of 2x4 cutting guides.

With the posts trimmed, cut the four cap blocks (D), center each one on its post, and screw it on. Use two screws, avoiding the center of the block. Now it's time to build the arches

The fun part: how to build an arbor arch

You can build the arches either outdoors or in the shop. Having done it in the shop, I recommend working outside — there are lots of scraps and sawdust. If you're working with pressure-treated lumber, be sure to wear a dust mask while you cut and sand.

The first step is to make a template for the arches, out of any kind of plywood you‘ve got kicking around (Fig. D) As you're marking the plywood for the arch shape, mark the center line on the top of the pattern.

Cut outside the lines you’ve drawn, so the template doesn’t get smaller than it should be. (I learned this the hard way.)

Make a template for the arches out of scrap plywood. Rotate the wood strip with the pencil in it (the “trammel”) to mark the curves. Cut out the template with a jigsaw.

Next cut the small angled pieces (E) out of your 1x8 lumber. These get butted together to form the rough arch shape.

Lay out four pieces on a flat surface, lay the template on top of them so one end of the template is flush with the end of one of the angled pieces, and mark the arch shape on the four pieces of wood (Fig. E).

Piece together one layer of the arch, and mark all the pieces with your template. Cut them out with a jigsaw or band saw. Each arch has four layers.

Using a jigsaw or band saw, cut the shapes out, cutting on the outside of the lines. Mark all four pieces with a number so they stay together.

Now do another four pieces, only this time make the other end of the template flush with the end of the wood piece. This will ensure that, as you stack up the four layers of wood that make up the arch, the joints will be staggered. This makes the arch stronger.

Continue in this fashion until you’ve cut out all the arch pieces, marking ones from the same layer so they stay together.

Assemble the arches one layer at a time, screwing the layers together as shown in Fig. F.

For extra longevity, especially with cedar or redwood, you can glue the layers together, too. Use a resorcinol glue or construction adhesive. It’s not a big deal, though—the arch is plenty strong with just screws.

Assemble the arch screwing each layer to the next. You can also use a waterproof glue for added longevity. Stagger the joints as shown.

If you have one layer that looks particularly good, place it at the bottom of the stack as you screw the arch together, so you won’t have screw heads showing, This good layer. the “show” side, will face out.

When both arches are assembled and the glue is dry, clamp them together and sand the edges with a belt sander (Fig. G). The outside edges are straightforward, but on the inside, you'll have to sand across the grain so the sander will fit. Sand or cut the ends of the arches while they're both clamped together, so they're exactly the same size. Using your template, mark the center line on each arch.

Sand the completed arches while they’re clamped together, so they’re exactly the same. You can go across the grain with the belt sander to even up the layers.

Cutting the rails

Now cut the rails (B) to length.

A good way to do this is to cut the rails roughly to size with your circular saw, then line them up on top of a pair of sawhorses or a bench.

Clamp the rails together with a pair of pipe clamps, then saw all the ends at once with a circular saw (Fig. H).

Give the ends a touch with the belt sander while you've got them all together.

Since the ends of the rails must be predrilled for the screws that hold them down (Fig. A), you can mark them all for drilling at the same time, too.

When all the rails are cut and drilled, file and sand the sharp edges.

Cut angled ends on the rails by clamping them together and cutting a bunch at the same time. Predrill for screws and screw the rails to the arches and posts.

Attaching the arches to the posts

This is a slick system to make it easy for you to attach the arches to the tops of the posts.

Drill holes, as shown in Fig. A, in the ends of the arches and the center of the blocks on top of the posts.

Drive galvanized pipe nipples (short threaded lengths of pipe) into these holes, and push the arches down on top of the posts (Fig. J).

If the arch doesn’t slide over the nipple easily, you can wiggle the posts (that’s why they’re only partially set), or screw a block to the curved surface of the arch and pound on it.

If these methods fail, just enlarge the hole a bit.

To keep the arch securely in place, drive a pair of screws from below, through the cap block into the arch. Predrill to prevent splitting,

With the arches attached, fill the rest of the postholes with tamped dirt.

Attach the arches to the posts with short pieces of galvanized pipe (called “nipples”) and a couple of screws driven in at an angle from below. Add trim pieces to the bottom of the posts, apply a finish, and you’re done!

Attaching the rails and trim

Screw the first rail to the arches directly over the center lines.

Then measure down from it on either side, marking where the bottom edge of each of the remaining rails should go.

You may find a cloth or narrow metal tape measure the easiest way to work on the curved surface of the arch.

Screw all the remaining rails to the arches and posts.

Finally, add the trim pieces (C) to the base of each post.

Rip the bevel on the top edge of the board first, then cut a couple of test pieces to see how they fit around the post.

Once they’re right, cut the rest of the trim pieces and attach.

Give the arbor whatever finish you’ve decided on, and you’re ready to start setting out some plants!

What plants to grow on it

This arbor is designed mainly for heavier clinging plants like roses, wisteria, ivy, grapes, and honeysuckle.

Lighter plants like clematis and morning glory need more closely-spaced support. This design could easily be modified for such plants by stretching stainless steel or galvanized wires vertically across the rails, or by adding vertical 2x2 pickets on the inside of the rails.

Shopping List

ItemQty.
4x4 x 8' treated pine4
1x8 x 8' treated pine8
3' x 5' plywood or hardboard1
1x6 x 8' treated pine1
2x6 x 8' treated pine1
2x4 x 8' treated pine8
Resorcinol waterproof glue2 pints
3" galvanized deck screws120
1-5/8" galvanized deck screws160
6d galvanized trim nails64
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