Even a small garden arbor can be expensive if you buy it prebuilt or hire a landscape carpenter to build it according to your specifications. But fortunately, this is one of the easiest (and cheapest) do-it-yourself projects for the landscape.
Our design calls for a simple four-post structure, ideal for covering a small patio or providing an overhead shelter for a garden bench. The design is quite simple: four vertical 4x4 posts; two horizontal beams made from pairs of 2x6 lumber sandwiched around each post at the top; a series of 2x4 "rafters" spanning the joists and running perpendicular to them; and finally, 2x2 lattice strips running across the rafters. The result is an overhead screening structure that offers pleasing dappled shade or a base to support a canopy of vines.
The Basics of Arbor Construction
Building this arbor will be simplified if you keep in mind five steps in the construction process:
- Digging holes for four post foundations
- Embedding 4x4 posts into the holes with concrete, aligned so they are perfectly upright (plumb)
- Sandwiching pairs of 2x6 crosspieces to serve as beams around opposite pairs of posts at the top
- Installing 2x4 "rafters" to span across the sandwiched beams
- Installing 2x2 lattice strips as an open roof surface over the rafters, aligned so they are perpendicular to the rafters
The costs of your arbor can vary considerably depending on the size you choose to build and the type of lumber you select. A 6x6-foot arbor built with pressure-treated pine lumber will be considerably cheaper than a 10x10-foot arbor built with top-grade cedar or redwood lumber. If you are building a larger arbor, the size of the structural lumber may need to be increased. For example, a 12x12 arbor or larger may require 6x6 posts, 2x8 or 2x10 beams, and 2x6 rafters.
While the skills required are not particularly difficult, some precision is required to erect the posts so they are perfectly plumb and to secure the beams and rafters in place. This work will be considerably easier if you have two or three helpers to assist you.
Before Getting Started
In our example, we are building a 7- to 8-foot-tall arbor with an open space of 8 feet square between the posts. Over the beams, six 10-foot-long rafters spaced 2 feet apart span across the structure. Finally, over the rafters, there are 11 2x2 lattice strips to form an open grid as a roof.
However, you can adapt this design to your own needs, adjusting the materials list as necessary. Your costs will be less if you choose to build a smaller arbor, such as you might use to cover a narrow walkway.
Make sure to choose lumber that is resistant to decay and insect damage. The least expensive alternative is pressure-treated pine, which has been impregnated with chemicals to hinder decay and insect damage. Pressure-treated lumber can be painted or stained after a short period of drying. Other, more expensive alternatives include cedar or redwood, both of which have a natural resistance to decay.
Equipment / Tools
- Post-hole digger
- Wheelbarrow or mortar mixing tub
- Tape measure
- Saw (power miter saw is recommended, but any saw will work)
- Drill with screwdriver bits and 1/4-inch spade bit
- Jigsaw (optional)
- Safety gear (work gloves and eye protection)
- Bags of concrete mix
- Drainage gravel
- 4 4x4 posts
- 4 2x6 boards for beams
- 6 2x4 boards for rafters
- 11 2x2 boards for lattice
- 8 1/4-inch bolts, 6 inches long, with washers and nuts
- 2 1/2-inch deck screws
Dig Post Holes
The first step is to locate and dig holes for the posts. Spacing can vary, but with this simple design, it's wise to space the posts no more than 8 feet apart. For sturdiness, it's best to embed your posts to at least 2 feet deep. But always check with your local building inspection office to learn if there are requirements on post depth. Follow whatever standard practice calls for in your area.
Stake out the position of the posts on the ground, then use a post-hole digger to bore holes to the desired depth for the post foundations. Place several inches of gravel in the bottom of each hole to assist drainage.
Position the Posts
The most important (and most difficult) step in the project is getting the posts installed correctly so that they are perfectly upright (plumb) and solidly anchored. Take your time on this part of the project. A helper can be very useful at this stage of construction.
If necessary, cut 4x4 lumber to length for the posts, including the portion that will be underground. Most carpenters choose to cut posts a little longer than needed, then trim the tops of the posts to the proper height at a later stage of construction. Position the posts in the footing holes, making sure the spacing is uniform between the posts. The posts should form a perfect square space.
Anchor the Posts
Mix concrete in a wheelbarrow or mortar box. Consistency should be dough-like—not too wet, nor too crumbly. Have a helper hold the post upright (or stake it in place), then shovel wet concrete into the hole up to ground level. As you add concrete, check the post with a level to make sure it remains perfectly upright (plumb). Lightly tap the side of the post with a hammer; this will settle the concrete and eliminate any air pockets.
Once the post is positioned properly, avoid touching it as you proceed to the other post. If the post wobbles or will not stay upright, you can anchor it with diagonal stakes attached with screws.
Proceed to the second post. It is critical that you install it so the front faces of both posts are aligned. A long straightedge board can be used to ensure that the faces of the posts are aligned.
Now proceed to the final two posts, again making sure the spacing is uniform and that all post faces are square to one another. When all posts are installed, allow the concrete to dry overnight. Take care to prevent the posts from being bumped or moved as the concrete dries.
Cut and Attach the Beams
The two cross beams for your arbor will consist of a pair of 2x6s sandwiched around each of the posts near the top. (For small arbors, these beams can be made from pairs of 1x6 lumber if you prefer).
First, cut four 2x6s to the desired width of the arbor "roof." The size is up to you, but it is typical for the beams to overhang each post by about 1 foot. If the posts are spaced 8 feet apart, in other words, the beams should be 10 feet long to allow for a 1-foot overhang on each side.
Next, measure up from the ground along each post, and make a mark indicating the bottom of the joists. This measurement, too, is up to you, but 7 to 8 feet is ideal, as it gives enough room for people to pass beneath.
Position and temporarily screw the beams to the posts, taking pains to make sure they are perfectly level and uniformly aligned with one another. Use a long straightedge and level to ensure that the beams are level from side to side.
When the beam pieces are positioned as you want, drill a pair of 1/4-inch holes through the posts and sandwiched beams, then insert lag bolts through the holes and secure the three layers together with washers and nuts. Each beam pair should be secured to its post with two bolts.
If the posts are extending up beyond the tops of the joists, you can now cut them off flush, using a handsaw, jigsaw, or reciprocating saw.
This arbor design calls for six 2x4 parallel rafters to span across the beams, overhanging slightly on each side. Here again, the exact rafter length is up to you, but generally, the rafters should not overhang the outside of the joists by more than about 1 foot. This design calls for a custom feature in which the rafters are notched to fit down over the joists; this step can also be omitted to simplify construction.
Cut the 2x4 rafters to length. Position the first rafter across the tops of the beams so the overhang is uniform on each end. Outline the location of the sandwiched beams on the edge of the rafter.
Take the rafter down and mark the face for 3/4-inch wide x 1 1/4-inch deep notches at each beam location. Use a handsaw or circular saw to make the depth cuts for each notch, then use a chisel to remove the wood and complete the notch.
Repeat this process with each of the remaining rafters. Position the rafters onto the beams, tapping them down so the beams are fully embedded into the notches. Make sure the rafters are evenly spaced along the joists.
From above, drive 2 1/2-inch deck screws down through the top face of the rafters to secure them to the beams.
Attach Lattice Strips
The final step is to cut and attach the 2x2 lattice strips as the top architectural layer above the rafters, installed so they are perpendicular to the rafters. The spacing and number of strips are up to you, but generally, a gap of 6 to 12 inches is ideal. Our design calls for 12-inch spacing, which requires 11 lattice strips, assuming the first and last strips are flush with the ends of the 10-foot rafters.
Begin by cutting 2x2s to length for the lattice strips. Lay out the position for the lattice strips on the rafters, striving for even spacing. Attach the lattice strips to the rafters with deck screws driven from above.
Finish the Arbor
If you built your arbor from pressure-treated lumber, you should wait at least six months before staining. Because of the wait involved, you won't be able to plant any vines on the arbor for the first summer. If you've built from cedar or redwood, staining isn't needed, and you can plant immediately.