Read this before buying lumber

This is a detailed construction sequence for the pergola shown above, but it is not a site-specific engineered plan. A solid roof turns an open pergola into a structure that must resist wind uplift, racking, rain and—in some regions—snow.

The dimensions below create a repeatable layout and shopping framework. Where loads control the answer, this guide tells you exactly what to verify rather than inventing a universal number.

The build at a glance

The high and low beams run parallel. Rafters cross between them in the direction of the roof slope. Purlins run perpendicular to the rafters and support corrugated roofing. The high side is approximately 12–15 inches above the low side when a 1:12 to 1.5:12 slope is permitted by the selected roofing system.

Baseline framing concept

• Four 6×6 pressure-treated ground-contact posts or naturally durable exterior posts.
• Two built-up beams, each made from two 2×8 boards, subject to local span approval.
• 2×6 rafters, commonly laid out at 24 inches on center only if the approved framing and panel instructions allow it.
• 2×4 purlins at the spacing printed by the panel manufacturer.
• Two knee braces at every post—eight total—to resist movement in both directions.
• Corrugated polycarbonate roof with matched closures, EPDM-washer fasteners, compatible sealant and a low-side gutter.

Permits, utilities and the site

1. Contact the correct jurisdiction

   Ask whether a freestanding 100-square-foot patio cover with a solid roof requires a permit, and request rules for property-line setbacks, height, footing depth, wind exposure and electrical work. City rules may differ from county rules even at the same mailing address.

2. Call 811

   Request a utility locate before choosing the four footing points. Private irrigation, pool lines, low-voltage lighting and owner-installed gas lines may not be marked; inspect plans and probe cautiously only after public utilities are located.

3. Check drainage and clearance

   Place the low roof edge where runoff can be collected without flooding a foundation, neighbor or walking surface. Keep the roof clear of service conductors, trees, fire features and exhaust vents. Do not attach this freestanding design to the house.

4. Assess soil and wind

   Loose fill, expansive soil, slopes and exposed hilltops change foundation and bracing requirements. Stop and obtain professional design if the site has any of these conditions.

Complete materials and hardware list

These categories are routinely stocked by Home Depot or Lowe’s. Brand and exact SKU can vary by region. Buy all structural connectors and their specified fasteners as one compatible system; do not substitute drywall, deck or general-purpose screws in metal connectors.

Lumber starting list

Structural hardware

Concrete and roof system

• Bagged concrete mix—calculate bags only after the footing diameter and depth are approved.
• Cardboard form tubes if required; compactable gravel where the footing detail calls for it.
• Five or more 12-foot corrugated polycarbonate panels for roughly 10 feet of width; actual panel coverage varies by profile.
• Matching horizontal and vertical closure strips.
• Manufacturer-approved screws with bonded EPDM washers.
• Polycarbonate-compatible neutral-cure sealant only where the instructions call for it.
• Low-side drip flashing and a 10-foot gutter/downspout kit.
• End-cut wood preservative, exterior stain/sealer, brushes and corrosion-resistant flashing as required.

Tools—and the safe way to work alone

Make these simple jigs first

• Two beam shelves: screw temporary 2×4 cleats to opposite posts at the beam’s underside elevation. They hold one beam ply while it is clamped and connected.
• Four batter-board pairs: place them outside the work area so layout strings remain intact while holes are dug.
• One rafter spacer: cut scrap to the approved clear spacing. It prevents cumulative measurement errors.
• Two identical brace templates: perfect one knee brace, then use it to mark the remaining seven.

Layout a perfectly square 9×9 post grid

1. Establish the first baseline

   Choose the visually important edge and stretch a mason line past both corners. This is Line A. Measure all setbacks from property lines or structures—not from fences unless the fence is confirmed to be on the boundary.

2. Mark two post centers exactly 9 feet apart

   Transfer the two marks to separate batter boards outside the future holes. Add perpendicular strings at those centers.

3. Create the opposite baseline

   Measure 9 feet perpendicular from each first-line post center and stretch Line B between those two points. You now have a nominal 9×9-foot rectangle.

4. Equalize the diagonals

   A true 9×9 square has a theoretical diagonal of about 12 ft 8¾ in. The exact number matters less than both diagonals matching. Measure corner-center to opposite corner-center; move only Line B sideways until both diagonals are equal within 1/8 inch.

5. Verify the 3-4-5 rule

   From one corner, mark 6 feet on one string and 8 feet on the adjacent string. The marks should be 10 feet apart. Repeat at another corner.

6. Save the centers

   Drop a plumb bob from every string intersection and mark the ground. Photograph measurements, then remove only the crossing strings while digging. Do not move the batter boards.

Option A: build on soil with concrete footings

This is the preferred route for a yard. Do not bury wood directly in dirt or cast the finished post into concrete for this design. Use a concrete pier/footing and a metal base that holds the wood at least one inch above concrete where specified.

1. Obtain the approved footing detail

   Confirm diameter or width, depth, reinforcing steel, concrete strength, anchor type and required projection above grade. The bottom may need to extend below frost depth and into competent native soil. An inspector may need to see the holes before concrete.

2. Dig from the saved centers

   Center each hole under its crossing strings. Keep loose soil out of the bottom and avoid bell-shaped voids unless the approved detail specifies them. Check depth from the laser benchmark, not from uneven grade.

3. Set forms to one plane

   Cut all form tubes using the laser so the finished pier tops are level, unless the approved drainage detail says otherwise. Brace each form so it cannot rise or drift while pouring.

4. Place reinforcement and anchor

   Install rebar with proper concrete cover and the anchor template exactly as approved. Keep anchor threads clean. Recheck the 9×9 grid and both diagonals before concrete hardens.

5. Pour and consolidate

   Mix according to the bag—not by eye. Place continuously, rod or vibrate carefully to remove voids, strike the top flat and slope the exposed shoulder away from the anchor if permitted.

6. Cure before loading

   Protect the concrete and follow the mix/anchor instructions for cure and loading time. “Hard to the touch” does not mean ready for a roof structure.

Option B: build on an existing concrete patio

1. Scan for post-tension cables, rebar and concealed utilities. Never drill a post-tension slab without professional locating and approval.
2. Snap the 9×9 center grid and equalize diagonals exactly as above.
3. Use the post-base manufacturer’s template to mark anchors.
4. Drill with the specified bit diameter and depth; keep the hole perpendicular and clean it exactly as the anchor instructions require.
5. Install the approved mechanical or adhesive anchor. Observe edge distances, spacing, torque and cure time.
6. Level bases with manufacturer-approved methods—never a loose stack of washers or untreated wood shims.

Reference: Simpson Strong-Tie’s ABU standoff post-base installation guide shows the required 1-inch standoff and model-specific fastening conditions.

Set all four posts plumb, square and level

1. Sort and crown

   Reject badly twisted posts. Mark the best face outward and coat every field cut with end-cut preservative appropriate for the treatment.

2. Install bases first

   Set each base loosely, pull strings over the center marks, then adjust. Confirm side lengths and equal diagonals. Tighten/torque anchors only as specified.

3. Raise one post with controlled support

   Place the bottom in the base, use a post level and attach two temporary 2×4 braces at roughly 90 degrees. Secure brace feet to driven stakes or concrete-rated temporary anchors. Do not release the post until both braces are fixed.

4. Plumb in two directions

   Use the long level on two adjacent faces. Adjust braces—not the post-base anchor—to bring the post to plumb. Recheck after every fastener.

5. Transfer a single height datum

   With all posts braced, use the laser to mark the low beam underside on both low-side posts. Mark the high beam underside on the other two posts using the exact rise required for the chosen roof slope.

6. Do not final-cut yet

   Leave posts long until beam elevations, slope and connector geometry are confirmed. Mark all four cuts from the laser, wrap the line around with a square, then cut accurately.

How to raise and install the beams when working solo

A double 2×8 beam is intentionally assembled one board at a time. This is much safer than lifting a built-up beam.

1. Install temporary beam shelves

   Clamp and structurally fasten a short 2×4 cleat to each of the two posts at the exact underside elevation of the first beam ply. Add a second safety block below each cleat.

2. Use a material lift

   Center one straight 2×8 on a rented material lift, strap it to the cradle and raise it just above the shelves. Roll or position it without standing under it. Lower it onto the shelves and clamp it to both posts.

3. Level and center

   Set equal overhang at both ends. Verify the board is level along its length; the two high-side posts already provide the roof rise relative to the low-side beam.

4. Install the approved post-to-beam connection

   Fit caps/straps or drill the approved bolted detail. Follow connector hole and edge-distance rules exactly. The temporary shelf is not a connector.

5. Add the second ply

   Lift the second 2×8, clamp it tightly to the first and fasten the plies with the approved staggered structural-screw or bolt schedule. Avoid placing fasteners where post caps, rafter ties or brace hardware must go.

6. Repeat on the other side

   Build the second beam at its different elevation. Measure between beams at both ends and center; the distance must remain constant.

Knee braces: the part that makes the frame feel solid

Post bases alone generally do not prevent a tall post from rotating. A solid roof also catches wind. Install two braces at every post—one in each direction—before roof panels.

1. Choose the brace length and connector system approved for the design. Longer braces usually control racking better but reduce headroom.
2. Hold one blank against the post and beam, mark the actual 45-degree cuts and create one perfect template.
3. Cut all eight from the template; seal cut ends.
4. Clamp each brace tightly. Predrill only when the connector/structural screw maker requires it.
5. Install every specified fastener. Do not use a decorative plate with generic screws.
6. Recheck post plumb and both diagonals before tightening the full assembly.

Simpson Strong-Tie specifically recommends considering knee bracing when a pergola has a solid roof, is taller than 8 feet, has larger bays or is in high wind. See its Pergola System guidance.

Install rafters and purlins without layout drift

1. Mark both beams together

   Hook the tape from the same end on both beams and mark the approved rafter centers. Put an X on the same side of every line. Do not “walk” a spacer across the whole beam; small errors accumulate.

2. Cut a test rafter

   Measure the actual sloped distance, add approved overhang and cut one. Set it at an end, check square to both beams and confirm fascia alignment.

3. Duplicate the cut

   Use a stop block or the test rafter as a pattern. Crown every rafter upward.

4. Set the two outside rafters first

   Fasten them with approved rafter ties or structural connectors. Stretch a string between their tails; it becomes the alignment reference for every intermediate rafter.

5. Install intermediate rafters

   Place each on its marked center, align the tail to the string, clamp and connect. Recheck beam spacing as you go.

6. Add purlins

   Mark purlin centers on both outside rafters according to the current panel guide. Set the low and high edge purlins first, string between them, then install the remaining rows. Add required blocking for side closure strips.

Install the UV-protective polycarbonate roof

For the photographed look, use a bronze/smoke corrugated polycarbonate panel system sold through a home center. Polycarbonate is lightweight, allows filtered daylight and is more impact resistant than economical corrugated PVC. SUNTUF, for example, is marketed as blocking 99.9% of UV radiation; shade/solar-transmission levels vary by color.

1. Read the instructions printed for your exact profile

   Confirm which face goes toward the sun, prevailing-wind installation direction, minimum slope, panel coverage, side/end laps, closure layout, fastener locations and allowable support spacing.

2. Store panels correctly

   Keep them flat, shaded and ventilated until installation. Stacked translucent panels can build damaging heat in direct sun.

3. Square the first panel

   Begin at the downwind side unless the manufacturer says otherwise. Align the lower edge with a chalk line so runoff enters the gutter. A crooked first sheet makes every lap worse.

4. Predrill for thermal movement

   Use the hole size stated by the manufacturer—often larger than the screw shank. Drill perpendicular through the specified corrugation location. Clear chips.

5. Fasten with EPDM washers

   Drive only until the bonded washer seats. If the panel dimples or crushes, the screw is too tight. Never replace roofing fasteners with deck screws and loose washers.

6. Overlap and seal only as directed

   Use the specified number of corrugations and only polycarbonate-compatible sealant. Some systems require sealant at laps; others rely on profile and closures. Do not use an incompatible silicone that can attack the sheet or void the warranty.

7. Finish the edges

   Install profile-matched closures, side flashing and high/low edge details. Close gaps against wind-driven rain without blocking required ventilation or drainage paths.

8. Add the gutter

   Pitch the low-side gutter toward a downspout and discharge to an approved permeable area or drainage system. Test with a hose from the high side before removing scaffold.

If you prefer a metal roof

The wood frame and bracing sequence stays similar, but the roofing package changes completely. Choose a home-center exposed-fastener metal roofing system and obtain its manufacturer’s installation manual before setting rafter/purlin spacing.

• Confirm minimum pitch; low-slope installations may require a different panel profile or underlayment.
• Use matching metal panels, rake/eave trim, closures, butyl tape and roofing screws with bonded washers.
• Cut with tools approved by the panel maker. Abrasive wheels can burn coatings and leave rusting metal particles.
• Account for condensation beneath the panels; use the manufacturer’s approved condensation-control layer or ventilation detail.
• Do not mix incompatible metals or allow copper runoff onto galvanized/galvalume roofing.
• Wear cut-resistant gloves and secure every loose sheet. A metal panel can become airborne before it is fastened.

Finish, inspect and make it look intentional

1. Remove temporary braces only after the complete permanent bracing and roof frame are connected.
2. Check every connector against its installation sheet: required holes filled, correct fastener heads, no split wood, no missing washers.
3. Confirm posts remain plumb and diagonals remain equal.
4. Seal exposed end grain and apply an exterior finish compatible with pressure-treated lumber moisture levels.
5. Cap post tops and protect horizontal ledges where water can sit.
6. Hose-test roof laps, fasteners, flashing and gutter.
7. Keep furniture and grills clear until final inspection/approval when required.
8. If adding lights or a fan, use outdoor-rated equipment and a code-compliant GFCI circuit installed under the applicable electrical rules. Do not run indoor extension cords as permanent wiring.

Final quality-control checklist

• Footings and anchors match the approved detail.
• Post bases hold wood above standing water.
• All posts are plumb in two directions.
• Opposite sides and diagonals match.
• Beam and brace connections use listed exterior structural hardware.
• Rafter and purlin spacing matches both structure and roof system.
• Roof slope, laps and screw locations match the panel manual.
• Roof screws are snug, not panel-crushing.
• Runoff is controlled at the low side.
• No sharp edges, protruding screws or unsealed cuts remain.

The mistakes that create the most rework

Maintenance that protects the work

• After the first major storm: inspect movement, leaks, loose trim and drainage.
• Every six months: clean gutter, remove leaves, check sealant only where the system uses it, and inspect fastener washers.
• Annually: inspect post bases for trapped debris, concrete cracks, corrosion, wood checks and loose brace/beam connections.
• As the finish requires: clean and reseal wood. Do not pressure-wash aggressively into end grain or connector joints.
• Roof cleaning: use only products and methods approved by the panel manufacturer; avoid abrasive pads and walking directly on unsupported panels.

If the structure shifts, racks, separates at a connector, develops a widening footing crack or suffers storm impact, stop using the area and have it evaluated before tightening random fasteners.

Technical references

Use the latest instructions supplied with the products you actually purchase. Helpful starting points: Simpson Strong-Tie Product Installer’s Guide, connector fastener guidance, SUNTUF product and installation resources, and the Palram corrugated-panel materials calculator.

Editorial note: Product names are examples to help readers recognize compatible home-center systems. Klinbi is not claiming sponsorship or engineering approval from these manufacturers. Availability changes by store and region.