How to Build a Pergola

This guide covers building a freestanding 10×12-foot pergola over a concrete patio or grade-level deck. The structure consists of four 6×6 posts set in concrete footings, two doubled 2×8 beams spanning between posts, 2×6 rafters at 16-inch spacing, and 2×4 purlins (top runners) at 12-inch spacing. The finished pergola provides partial shade, a framework for climbing plants or string lights, and a defined outdoor room without requiring a full permit in most jurisdictions (verify with your local authority — many require a permit for structures over 200 square feet or over 10 feet tall).

The approach described here is post-in-ground with concrete: 4×4 cardboard tube forms, 60-lb bags of fast-setting concrete, and 6×6 pressure-treated posts rated for ground contact (UC4B or better). A surface-mount post base alternative is noted for situations where digging is impractical (existing concrete slabs with no way to core through them).

Time: 2 weekends. Cost: $800–$2,000 depending on lumber species and hardware. Difficulty: Intermediate to Advanced. Permit: Verify locally; most jurisdictions require a permit for freestanding structures over 200 sq ft.

What You'll Need

Tools

• Post-hole digger or rented gas-powered auger (strongly recommended for clay soils)
• Circular saw and miter saw
• Drill/driver and 3/8-inch impact driver
• Level (48-inch), plumb bob or laser level
• String line and batter boards for layout
• Speed square and framing square
• Wheelbarrow and mixing hoe (for concrete)

Materials — 10×12 Freestanding Pergola

• 4 posts: 6×6 pressure-treated, UC4B, 12 ft long (allows 4 ft in-ground, 8 ft above grade)
• 2 beams: doubled 2×8 pressure-treated, 12 ft long (the 10-foot span direction)
• 7 rafters: 2×6 pressure-treated, 12 ft long (the 12-foot run direction, at 16-in OC)
• 13 purlins: 2×4 cedar or redwood, 10 ft long (across the top at 12-in OC)
• 8 post-to-beam connector brackets (Simpson Strong-Tie ABU66 or equivalent)
• Joist hanger hardware for rafter-to-beam connections
• 8–12 bags 60-lb fast-setting concrete per post (3 bags per hole in most soils)
• Structural screws: 3/8×6-inch hex-head lag screws for beam lamination
• 10d hot-dipped galvanized nails or structural screws for all outdoor connections

Step-by-Step Instructions

Step 1 · Call 811 (dig safe) and pull the permit

Call 811 at least 3 business days before digging. They will mark all underground utilities — gas, electric, water, sewer, cable. A post-hole auger through a gas line is a serious safety event. After 811, pull the building permit if required. The permit inspection for a pergola typically covers footing depth and structural connections.

Step 2 · Establish the layout with batter boards

Set batter boards 2 feet outside the intended post locations. Run string lines to define the four corners. Check square using the 3-4-5 method: if one side is 3 feet and the adjacent side is 4 feet, the diagonal should be exactly 5 feet. For a 10×12 pergola: if one side is 10 feet and the adjacent side is 12 feet, the diagonal should be 15.62 feet (check with a long tape). Adjust batter boards until both diagonals match. Mark the post-hole centers by dropping a plumb bob from the string line intersections.

Step 3 · Dig post holes to frost depth

Frost depth varies by climate: 12 inches in the deep South, 42 inches in northern states, 48–60 inches in Canada and the upper Midwest. Check your local building code for the required depth. The hole diameter should be three times the post width: for a 6×6 post (5.5 inches actual), the minimum hole is 16–18 inches in diameter. In stable soil a standard 12-inch auger bit works; in loose or sandy soil, use a 16-inch bit. Holes must be wider at the bottom than the top (flared base) in frost-heave zones — the bell prevents frost from lifting the post.

Step 4 · Set the posts in concrete

Pour 3–4 inches of gravel in the bottom of each hole for drainage. Set the post, brace it plumb in both directions with 2×4 diagonal braces staked to the ground. Pour fast-setting concrete dry into the hole around the post to within 3 inches of grade — do not premix. Then slowly add water per the bag instructions (about 1 quart per bag). The concrete sets in 20–40 minutes, but wait 4 hours before loading the post. Check plumb again 5 minutes after pouring while the concrete is still plastic; adjust braces. Allow the concrete to cure 24 hours before removing braces and continuing.

Step 5 · Cut posts to uniform height

After the concrete cures, mark a level cut line on all four posts at the desired beam height (typically 8 feet above the finished patio surface). Use a long level or laser level to transfer the mark from one post to all others. Cut with a circular saw, making two passes at 90° to each other on a 6×6 — a single pass will not cut through. A chainsaw on a post is tempting but produces a rough cut that makes beam seating difficult.

Step 6 · Build and install the beams

Each beam is two 2×8s laminated with construction adhesive and 3/8×6-inch lag screws every 16 inches (staggered top and bottom). Cut the beams to overhang the outside post faces by 12–18 inches on each end for proportional look. A 10-foot span with 18-inch overhangs means the beam is 13 feet total. Seat each beam in the post connector brackets and secure with the manufacturer's specified fasteners — do not substitute hardware. Beams must be level across the span; shim the low connector if needed before final fastening.

Step 7 · Install the rafters

Rafters run perpendicular to the beams, spanning the 12-foot direction. Set the outside rafters first, flush with the beam ends. Divide the remaining interior space at 16 inches on center and install intermediate rafters with joist hangers or by toenailing. The standard decorative detail on pergola rafter tails is a notched or curved profile cut — lay out the pattern on one board, cut, trace onto the remaining boards, and cut with a jigsaw before installing. All rafter crowns (slight bow in the lumber) face up.

Step 8 · Install purlins across the top

Purlins are the 2×4 top runners that span across the rafters. They run in the same direction as the beams. Install the two outside purlins first, then divide the remaining space at 12-inch spacing. Toenail or screw from the top through the purlin into the rafter (two screws per crossing). Purlin tails overhang the outside rafters by 6–12 inches for a finished look. The spacing of purlins determines the density of shade — 12-inch spacing is the standard; 8-inch produces dense shade, 16-inch is mostly open.

Step 9 · Install diagonal knee braces (optional but recommended for lateral stability)

A freestanding pergola without knee braces can rack in high winds. Install 45° diagonal knee braces at each post-to-beam connection: cut a 2×4 or 2×6 at 45° on both ends, and fasten with structural lag screws. The brace should be at least 24 inches long measured along its face. Four braces (one per post) on the long axis, plus four on the short axis, provide good lateral resistance. Some designs incorporate decorative curved brackets — these also function as knee braces if properly fastened.

Step 10 · Apply finish coat to all cut ends and raw wood

Pressure-treated lumber is treated at the factory, but cut ends expose untreated wood. Apply a copper-based preservative (available in spray cans) to every cut end before installation. For cedar or redwood components, apply an exterior oil or semi-transparent stain to all six faces before installation. Re-coat annually on cut ends and every 2–3 years on full surfaces. Unfinished cedar turns silver-gray in 18 months — this is natural and not structural decay, but it is irreversible if you later prefer stained cedar.

Step 11 · Final inspection and cleanup

Check all connection hardware is fully tightened. Walk the structure by applying lateral force to each post — there should be no perceptible rack. Call for final inspection if required. Grade the soil away from each post location to direct water away from the footing. Cap the post tops with a beveled cut or metal post cap to shed water and extend post life.

Common Mistakes

• Footings too shallow for frost depth. Frost heave will lift a post 1–2 inches per freeze-thaw cycle. Check local frost depth and add 6 inches below that depth.
• Wrong post treatment rating. Posts in-ground or in contact with concrete must be UC4B rated. UC3B (above-ground) will rot within 5 years in-ground even if it's labeled "pressure-treated."
• Beams not level. An unlevel beam produces rafter cuts that must be shimmed or re-cut. Check level before final fastening at the connector brackets.
• Skipping knee braces. A pergola without diagonal bracing can rack and collapse in a windstorm. The knee braces also improve the visual proportions.
• Undersized hardware. All connections must use hot-dipped galvanized or stainless steel hardware. Zinc-plated (bright) hardware corrodes within 2 years in outdoor conditions, especially with pressure-treated lumber which contains copper that accelerates galvanic corrosion.
• No 811 call before digging. This is a safety and legal requirement, not a suggestion.

When to Call a Pro

Hire a licensed contractor if the pergola is attached to the house (becomes a ledger-attached structure with different load requirements), if the span exceeds 14 feet, if the design includes a full roof (not just purlins), or if the local permit authority requires engineer-stamped drawings. Freestanding pergolas under 200 square feet and under 10 feet tall are typically in DIY territory with a basic permit.

Maintenance

Inspect the post bases annually for rot. Probe the wood at ground level with a screwdriver — if it sinks more than 1/4 inch, the post is rotting and needs sistering or replacement. Check all connection hardware for corrosion. Re-tighten any lag screws that have backed out. Re-coat cedar and redwood components every 2–3 years. Trim any vines that are growing into connection hardware — roots and stems exert significant force on metal fasteners over time.

Related Guides

• How to build planter boxes for the patio
• How to build cornhole boards
• How to build a garden gate
• All build × deck & patio guides
• All build guides

Footing Design and Frost Depth

Pergola post footings must extend below the local frost depth to prevent heaving. Frost depths by region: Pacific Northwest 0–12 inches, Southeast 0–6 inches, Mid-Atlantic 18–30 inches, Midwest 36–48 inches, Northern states and mountain elevations 48–60+ inches. Check with the local building department for the frost depth in your jurisdiction — this is the single most important structural requirement for any in-ground post system.

Footing diameter and depth for a 10×12 freestanding pergola with 6×6 posts: minimum 12-inch diameter tube form (Sonotube or equivalent), minimum depth to frost line plus 6 inches for concrete bearing. For most residential applications, a 12-inch diameter by 36-inch deep footing exceeds minimum requirements in most climate zones. Areas with expansive soils (clay) may require larger footings — consult a geotechnical or structural engineer if the soil is visibly clay-rich.

Concrete mix: use 4,000 psi ready-mix for footings, or mix 80-lb bags of Portland cement concrete (not fence post mix) at 0.45 water-to-cement ratio. Fill the footing form, consolidate concrete by rodding (use a piece of rebar to eliminate voids), and slope the top of the concrete away from the post to shed water. Allow 72-hour minimum cure before loading the post with framing weight.

Post Anchor Selection: Direct Embed vs. Surface Mount

Two post installation methods exist: direct embed (post is set directly in concrete) and surface mount (post hardware is set in concrete, post bolts to hardware above grade). Both are structurally valid; they differ in longevity and future flexibility.

Direct embed: bury the post base 24 to 36 inches below grade (or 1/3 of total post length, whichever is greater). Use UC4A or UC4B pressure-treated lumber rated for ground contact. Direct embed provides maximum lateral stability and is the preferred method for areas with high wind load or seismic exposure. Disadvantage: if the post rots at the soil line (typically 10–20 years even with treated lumber), replacing it requires breaking out the footing.

Surface mount: Simpson Strong-Tie ABU or CBSQ post bases anchor into the wet concrete footing; the post connects to the hardware above grade. This method keeps all wood above grade, extending longevity. The above-grade wood can be any species, not just ground-contact treated. Disadvantage: requires accurate footing placement (post bases are embedded at exact layout positions) and provides slightly less lateral base stiffness than direct embed. For most residential pergolas under 400 square feet, surface-mount hardware provides fully adequate lateral resistance when the frame is properly braced with knee braces.

Beam and Rafter Sizing Reference

Pergola framing carries dead load (its own weight) and wind/snow load depending on region. For an open-top pergola (no roofing, just structure), structural requirements are modest. The following sizing is conservative for spans up to 12 feet with standard 4×6 posts or 6×6 posts:

• Beams: doubled 2×8 or single 4×8 for spans up to 12 feet. For spans 12 to 16 feet, use doubled 2×10 or single 4×10
• Rafters: 2×6 at 24-inch OC for spans up to 10 feet; 2×8 at 24-inch OC for 10 to 14 feet
• Purlins: 2×4 at 24-inch OC are decorative and functional for shade material attachment; structural contribution is minimal for an open pergola
• If adding a shade cloth, polycarbonate panels, or retractable canopy, account for the added dead load — polycarbonate panels can add 0.5–1.0 psf over the roof area

For any pergola intended to support a solid roof (metal panels, shingles), obtain a structural engineer's design. A solid roof transforms the pergola into a patio cover or carport, which typically requires a building permit and engineered drawings in most jurisdictions.

Beam Connection to Post Detail

The beam-to-post connection is the critical load transfer point in pergola framing. Options in ascending strength:

Notched post top: notch the post top to accept the beam, providing a bearing surface and lateral restraint. Notch depth: 1.5 inches (half the 2×8 beam depth) or the depth of the doubled beam. Secure with through-bolts — minimum two 1/2-inch galvanized carriage bolts per beam-to-post connection, staggered vertically to prevent splitting. This is the traditional timber-frame method and looks cleanest from below.

Post cap hardware: Simpson LCE4, AC4, or equivalent post cap hardware bolts to the post top and captures the beam on both sides. All-hardware, no notching. Fastest installation, easiest alignment, code-compliant. Use where notching would weaken an undersized post.

Lag-bolt through-connection: beam laps over post top with lag bolts from the beam side through the post. Provides good shear resistance but less bearing area. Appropriate as a supplement to notching, not as a primary connection in high-load applications.

Knee Brace Function and Installation

Knee braces prevent racking — the tendency of a rectangular post-and-beam frame to shift from a rectangle into a parallelogram under lateral load (wind or seismic). A 10×12 pergola with no knee braces and only the beam-to-post connections for lateral resistance will deflect visibly under moderate wind loading. Knee braces triangulate the frame, converting lateral load to axial compression in the brace, which the post and beam handle efficiently.

Knee brace sizing: 2×4 or 4×4 material, 45-degree angle, with at least 12 inches of bearing along both the post and beam face. A 12-inch dimension on both faces produces a brace approximately 17 inches long. Cut both ends at 45 degrees. Connect with two 3-inch structural screws (GRK RSS or equivalent) at each end, driven through the brace into the post and beam face. For decorative curved braces, cut from 2×6 stock on a jigsaw; the curve does not reduce structural performance because the brace carries only compression.

Wood Species and Finish Selection

Exterior pergola lumber: pressure-treated SYP (southern yellow pine) is the most economical and structurally strongest option; the green color weathers to gray within one to two years, or can be painted or stained after a 6-month weathering period (allow new PT wood to dry before coating). Cedar and redwood are naturally decay-resistant, accept stain readily, and maintain their warm color without chemical treatment — they are typically 2× more expensive than pressure-treated SYP. Ipe, teak, and other tropical hardwoods are dimensionally stable and extremely durable but are 4–6× the cost of PT lumber and require specialized fastening to prevent splitting.

Finish system for PT lumber: after weathering, apply an oil-based penetrating deck stain (Cabot Australian Timber Oil, Ready Seal, or equivalent) to all surfaces. A penetrating stain lasts 2–3 years on horizontal surfaces (rafters and purlins) and 4–6 years on vertical surfaces before recoating is needed. Apply a second coat while the first is still wet (wet-on-wet application) on end-grain cuts, which absorb significantly more finish.

Permit and HOA Considerations

Most jurisdictions require a building permit for a freestanding pergola over 200 square feet and for any pergola regardless of size that uses in-ground footings. The permit process typically requires a plot plan showing the pergola location relative to property lines and setback lines, a framing plan, and a footing detail. Most jurisdictions have a simplified permit path for residential accessory structures under a certain square footage threshold — check locally before starting.

HOA approvals often require submission of a design rendering, a specification sheet, and sometimes a paint/stain color chip that matches the house exterior. Submit to the HOA architectural review committee before purchasing materials — committee review timelines range from 1 week to 60 days depending on the HOA.

Maintenance and Seasonal Care

Annual: inspect all post-to-footing connections for ground-level rot (probe with a screwdriver — sound wood resists; soft or hollow wood is rotting). Tighten any loosened bolts. Reapply penetrating oil finish to all horizontal surfaces after cleaning with a deck cleaner. Clear any debris from rafter and purlin channels where water can pond.

Every 3–5 years: sand or lightly pressure-wash horizontal surfaces to remove gray oxidation before restaining. Inspect beam ends for checking (cracks along the grain) and seal with flexible exterior caulk to prevent water entry. Check that post bases are still flush with footing surfaces — any settlement of adjacent soil can pull post bases partially out of their hardware.

In snow-load regions: remove snow accumulation from the top when depth exceeds 6 inches. An open pergola under light snow load is generally adequate, but drifting snow on the leeward side can pile up to 2× the nominal snowfall depth, significantly exceeding design load assumptions for a residential open-top structure.