Pergola Basics: What Distinguishes a Pergola from a Gazebo or Arbour

The terms are used loosely in residential construction, but a pergola is generally an open overhead structure with a flat or slightly angled roof of spaced rafters — providing partial shade rather than full coverage. A gazebo has a closed, peaked roof. An arbour is smaller, typically freestanding, and used as a garden entry or support for climbing plants.

Cedar works well for all three because it is light enough to handle without heavy equipment, dimensionally stable enough to remain true through seasonal moisture changes, and naturally resistant to the exposed conditions these structures face year-round in Canadian weather.

Post Sizing and Structural Considerations

Post sizing is the most important structural decision in a pergola. Posts carry the combined dead load (the weight of the structure itself) and any live loads — snow accumulation in winter, wind, and the weight of climbing plants and vines that many pergolas are designed to support.

In Canadian climates, snow load is a critical design factor. Ground snow loads vary from roughly 1.0 kPa in parts of southern British Columbia to over 3.0 kPa in many Ontario locations and significantly higher in Quebec, Northern Ontario, and the Prairies. The National Building Code of Canada (NBC) provides climatic data by location, and local building departments can confirm the design snow load for a specific municipality.

General Post Sizing Starting Points

  • 4×4 posts (89×89 mm): Adequate for small pergolas, spans under 2.4 m, and structures where snow accumulation is minimal (open rafter spacing, steeply sloped rafters).
  • 6×6 posts (140×140 mm): Standard for most residential pergolas; provides more visual weight and substantially more structural capacity.
  • 6×8 or 8×8 posts: Used for larger structures, heavier beam loads, or high snow-load locations.

These are starting points only. Structural adequacy depends on span, post height, beam size, and local snow and wind loads. For larger structures, consult an engineer or use the span tables published by the American Wood Council (commonly referenced by Canadian engineers).

Beam and Rafter Sizing

Beams span between posts and carry the rafters. A common approach for residential pergolas is a doubled 2×8 or 2×10 beam, which provides good visual proportion and adequate spanning capacity for most residential spans (2.4 m to 4.8 m). Single solid timber beams (4×8, 4×10, or 6×10) are also used and provide a cleaner visual when the beam is exposed.

Rafters span the short dimension across the beams, typically spaced 400 to 600 mm on centre. For visual proportion, rafter ends are often cut with a decorative profile — a simple angle cut, a curved ogee profile, or a notch. These profiles serve no structural function but are a traditional element of pergola design and reduce the visual bulk of the rafter ends.

Post Bases and Footings

Cedar posts should not be set directly in concrete or soil. Even though cedar resists decay, constant moisture contact at the post base — particularly moisture trapped between the post and concrete — creates conditions where decay accelerates at the end grain. Post bases that elevate the wood above grade are the standard approach for exterior structures.

Adjustable galvanised or powder-coated post bases set into concrete footings allow the cedar post to sit above the footing with airflow around the end. This significantly extends post life compared to direct burial, even with naturally durable species like cedar.

Footing depth must be below frost depth. In most of southern Canada, this means a minimum of 1.2 m, though local codes may specify more. Underfrosted footings will heave seasonally, eventually compromising plumb and causing joint failures in the structure above.

Joinery for Outdoor Cedar Structures

The most practical joinery method for residential cedar pergolas is mechanical fastening — structural screws, carriage bolts, and metal connectors from manufacturers such as Simpson Strong-Tie or USP (now MiTek Canada). These connectors are designed for exposed exterior use and carry published load ratings, which is useful if the structure is being permitted.

Traditional timber joinery — mortise-and-tenon, half-lap, or birdsmouth cuts — is used in some handcrafted pergolas and produces a cleaner visual result (no visible metal). However, these joints require precise cutting to develop their rated strength and are more demanding to execute than mechanical fastening.

Common Connection Points

  • Beam to post: Post caps or through-bolting with 12 mm or 16 mm galvanised carriage bolts. Post caps are faster and require no drilling through the post, but may be visible.
  • Rafter to beam: Metal hurricane ties or structural rafter hangers for hidden fastening; toe-screwing with structural screws is also used for lighter rafters.
  • Decorative cut connections: Notched lap joints at rafter-to-beam intersections are structurally sound and visually traditional; they require accurate cutting but no specialised hardware.

Cedar Garden Benches

Cedar garden benches share many considerations with larger structures — post and leg sizing, joinery, and finishing — but are simpler to build and do not require permits in most Canadian municipalities.

A standard cedar garden bench uses 4×4 legs, 2×6 seat boards, and a 2×4 or 2×6 back rail. Seat boards are spaced 6–10 mm apart to drain rain and prevent water pooling on the seat surface. All exposed edges and corners are eased (lightly sanded or routed) to reduce splintering as the wood ages.

Leg bottoms should either sit on paving stones or be fitted with end caps to prevent direct end-grain soil contact, which would accelerate decay regardless of the species. Even cedar end grain in direct soil contact decays faster than face or edge grain in the same conditions.

Finishing Cedar Outdoor Structures

Cedar structures left unfinished will weather to a silver-grey within two to three seasons. This is an accepted aesthetic for many garden structures. If the natural colour is preferred, finishing options include:

  • Penetrating oil finishes: Linseed oil, tung oil, or proprietary outdoor wood oils penetrate the wood rather than forming a film. They require reapplication every one to two years on exposed surfaces, but do not peel or crack. The WRCLA finishing guidelines recommend penetrating finishes for most exterior cedar applications.
  • Semi-transparent stains: Contain pigment and a penetrating carrier; provide more UV protection than clear oils; easier to maintain than solid stains because they do not form a film that can peel.
  • Solid stains or paint: Provide the most UV protection and colour retention but form a film that traps moisture at checks and joints, leading to peeling over time. Generally not recommended for rough-sawn or textured cedar in outdoor conditions.

Permits for Pergolas in Canada

Whether a pergola requires a building permit depends on the municipality and the structure's size. In many Ontario municipalities, accessory structures under 10 m² of roof projection are exempt from building permits, though this threshold varies. Structures attached to a house typically do require permits regardless of size.

It is always advisable to contact the local building department before starting construction. This is particularly true for structures in flood plains, within setback distances of property lines, or in heritage conservation districts where design review may apply.