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  • Writer's pictureMatt Weber

Pergola Construction 101

Updated: Sep 4, 2023


A pergola can make an impressive visual statement in an outdoor space. The sweeping lines and strong, sturdy frame provide an attractive focal point that provides shade for relaxing and entertaining.


If you’re considering adding a pergola to your property, you can build your own, hire a contractor, or assemble one from any number of widely available kits.


DIY vs. Pro

When assembling your project from a kit, all the cutting and notching has been done for you. All fasteners and materials are shipped directly to your job site. The kits include step-by-step instructions, saving lots of time and planning, and the wood usually comes prefinished from the factory. All you need to do is recruit an assistant, unbox the parts, and start building. Because all the prep work is done, it’s usually a quick job to build a pergola from a prefab kit. Depending on its size, a pergola kit can be assembled in a weekend or less.


Although the kits can occasionally cost more than purchasing the raw materials, by the time you spend the time and fuel to source materials from different suppliers, the potential savings may become negligible. And this assumes you already own the necessary tools for construction.

Pergola kits from Backyard Discovery are shipped to your home complete with all fasteners, hardware, and accessories ready for do-it-yourself assembly.


To build a custom pergola from raw lumber will require much more work, but you can design it to suit your needs and personal aesthetic taste, adding details that make it uniquely your own.


Hiring a contractor is the costliest way to get the job done, yet for countless pergola owners, having the project completed by a professional is well worth the expense.

If budget is not an obstacle, a professional can be enlisted to construct your ideal pergola as you sit back and relax. Homewyse.com estimates labor for a 10x10’ pergola to range from $1,500 to $5,000, depending on where you live.


Lumber

The most economical and widely available material to build a pergola is pressure-treated pine. However, professional pergola contractors often build only with Western Red Cedar, which has a consistent wood grain that resists warping and splitting. The wood also has natural oils that deter insect and moisture damage.


Another sought-after pergola material is redwood lumber. Depending on your location, redwood might be difficult to find and expensive if you find it, but it has similar preservative oils as Western Red Cedar, plus it’s an even stronger species of wood.

The Hawthorne Steel Pergola from Backyard Discovery comes as a kit constructed of galvanized steel with a powder-coat finish to be maintenance-free.


Location

Pergolas are often used to cover a deck or patio, protect an outdoor dining area, provide shade for a pool or hot tub, or adorn a backyard garden. To integrate the pergola into the existing landscape, they’re typically built square to the house or a nearby structure.


Design

Pergolas are built in a wide range of sizes and styles, but most are constructed with four support posts connected at the top with beams (AKA girders), rafters, and smaller cross-members called purlins. Pergolas are fairly simple structures in design but can be embellished with decorative accents.

Visual proportion is the key to designing a pergola. The 6×6 posts will need larger beams and rafters so the top of the pergola will look strong and regal rather than undersized. Also consider allowable span based on the size of the pergola you’re building. For example, a 12-foot span is too long for a 2×6 board, which will not only look small and weak but will sag over time. Most builders use a minimum board size of 2×8 for the upper framing members, and that’s for a small pergola. Common lumber sizes for a large pergola include doubled 2×12 for the beams, 2×10 for the rafters, and 2×4 for a layer of decorative purlins fastened atop the rafters. Explore online building plans or even compare your design to ready-made pergola kits to help determine your project’s size and appropriate proportions.

A common variation is a pergola roof attached to a home with a ledger board, similar to a deck, and supported by two posts.


Apply Preservative

Best practice is to stain and seal the wood with a waterproof finish before assembling the pergola. This will add your choice of color while also protecting the pergola from water and insect damage, and even UV discoloration (with some products). It will be much easier to stain the wood while it’s still on the ground. Plus, you’ll be able to access all sides of the boards, including the areas where the wood will meet at a joint.


Treated lumber should only be coated with a protective finish after it has dried from the treatment process. Although cedar and redwood have natural preservative oils, the wood will turn silver over time if not maintained with a UV-blocking stain/sealer.


Support Posts

Most pergolas are supported by 6x6 posts. For a small pergola, 4×4 support posts will work, but the 6x6 has a beefier look that most homeowners prefer whereas 4x4 posts can appear spindly on large pergola designs. Furthermore, the 6x6 posts can be notched to

support the beams and rafters from below, creating very strong, reliable joints

for the pergola construction. If you’re building with treated lumber, make sure the post material is rated for ground contact.


Pergola construction is not a one-man job. The large, heavy lumber requires assistance lifting and fastening in place. Even setting a tall 6×6 post is a two-man job. One worker plumbs and aligns the post while a second secures the bottom and attaches 2x4 diagonal brace boards that hold the post plumb and square. The braces are nailed to each post on adjacent sides and can be adjusted as the post is moved into plumb position. Once the post is set, the braces can be held in place by staking them to the ground.

Use 2x4 diagonal bracing to help stabilize the posts while you adjust them into plumb and square position.


To ensure the most longevity of your posts, it’s best for them to avoid direct contact with the ground. A metal post-base can be bolted and epoxied on top of a concrete pier to protect the post’s end grain from wicking up moisture from the ground. The post rests on the galvanized metal instead of concrete, and the base is fastened to the sides of the posts. You can then conceal the post base by adding trim boards to the bottoms of the posts.

Best practice to protect the posts from rot and moisture damage is to make sure they avoid direct contact with the ground. A metal base like this one from Simpson Strong-Tie provides a standoff that anchors to a concrete pier and fastens to the sides of the post so the wood doesn’t wick water into the end grain.


Connections

The beams can be fastened to the posts using a number of methods. You can utilize metal brackets or a number of 1/2-in. carriage bolts, but the strongest means of supporting the load is to cut notches in 6x6 posts that carry the roof from below.

Doubled beams made of lumber as large as 2x12 are used to carry the joists.


The rafters (and purlins to follow) should all be evenly spaced and centered over the pergola frame. Spacing 16 to 20 inches apart is common. The easiest way to fasten the rafters is to drive 3-inch screws or ring-shank nails through the boards and into the beams at an angle (called toe-screwing or tow-nailing). An even stronger connection and a sharp-looking aesthetic detail is to notch the rafter bottoms so they fit over the beams with a lap joint.


The rafters can be toe-nailed or toe-screwed to the beams. The following course of purlins

will help keep the tops of the rafters in vertical alignment.


Rafters are commonly spaced 16 to 20 inches apart.


The top layer of purlins (AKA louvers or runners) is installed 90 degrees to the rafters. The purlins are usually made from 2x2, 2x3 or 2x4 boards standing on edge. The taller boards can be toe-screwed, while 2x2 size purlins can be face-nailed from the top.


Corner bracing is typically installed to arrest movement between the posts and beams. The corner bracing strengthens the pergola and maintains squareness of the frame.


Details

The shape and contours of your corner-bracing boards and rafter tails present two opportunities to add some customized character to your pergola. You might prefer angular, geometrical shapes for your rafter tails or softer swoops and curves for a more ornate look. The size and shape of the corner-bracing boards can complement the pergola style in similar fashion.


Skilled carpenters might even challenge themselves by engineering mortise-and-tenon connections to give the post-and-beam connection a timber-frame look. For an all-wood look, you can countersink the metal fasteners and conceal them with stain-matched wood plugs.


On the other hand, you might want to purchase painted decorative hardware that serves as ornate accents to make your pergola more distinct. The aesthetic details that you incorporate into your pergola design is where you can elevate your project to a thing of beauty.

One stylish option is to enhance your pergola with decorative hardware. The new outdoor selections from Simpson Strong-Tie provide secure structural attachments and amazing looks with premium corrosion resistance.



SIDE NOTE: Tail Spin

Many pergola designs have the tails of the horizontal boards cut with a decorative pattern. To put your own spin on the design of your rafter tails, practice sketching a few different trial shapes on paper. The tails give the pergola its signature design and can be cut to a curved, scalloped profile, a more angular design, or anything in between. The only rule of thumb is that the longest edge of the boards should be positioned at the top. The rest is up to you. When you’ve decided on your design, cut out a cardboard template to transfer onto the board.


Cut the board to length, then trace the decorative shape on its end. Make the cut using a combination of a handheld circular saw and jigsaw (for making tight curves and intersecting cuts). Once the first board is cut, use it as a template to cut the tails on each matching board. The beams, rafters and purlins can have different tail patterns, but each type of board should match.



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