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Deck Beam Span in Ontario: Using the Part 9 Span Tables

How deck beam and joist spans work under Ontario's 2024 Building Code: which span tables apply, the snow load check, supported length, posts and bearing.
our example: 3-ply 38 × 184 SPF beam, 2.4 m supported
3.07 m
our example: 3-ply 38 × 184 SPF beam, 2.4 m supported
min deck load, or roof snow load if greater
1.9 kPa
min deck load, or roof snow load if greater
min square wood post, unless calculated
140 mm
min square wood post, unless calculated
end bearing, most built-up beams in Table -H
76 mm
end bearing, most built-up beams in Table -H

Last updated

The Ontario Building Code has no separate deck span table. Under the 2024 Code, deck beams are read from the built-up and glued-laminated floor beam tables, Span Tables 9.23.4.2.-H to -K, and deck joists from Span Tables 9.23.4.2.-A and -B (OBC Div. B 9.23.4.2.OBC Div. B 9.23.4.2. Spans for Joists, Rafters and Beams(1) Except as required in Sentence (2) and Article 9.23.14.10., spans for wood joists and rafters shall conform to the spans shown in Span Tables 9.23.4.2.-A to 9.23.4.2-G for the uniform live loads shown in the Tables. (See Article 9.4.2.2.) (2) Spans for floor joists that are not selected from Span Tables…). For example, a three-ply 38 × 184 mm spruce-pine-fir No. 1 or No. 2 beam with a supported length of 2.4 m can clear-span 3.07 m between posts (Table 9.23.4.2.-HOBC Div. B Table 9.23.4.2-H. Maximum Spans for Built-up Floor Beams Supporting Not More than One Floor – 38 × 184 mm MembersTable 9.23.4.2.-H — Maximum Spans for Built-up Floor Beams Supporting Not More than One Floor – 38 × 184 mm Members Forming Part of Sentences 9.23.2.8.(1), 9.23.4.2.(3), 9.23.4.4.(3) and 9.23.8.1.(1) Commercial Designation | Grade | Supported Length, m | Size of Beam: 3 – 38 × 184 mm | Size of Beam: 4 – 38 × 184 mm |…), as long as the deck load stays within what the tables assume.

That last condition matters most for decks. This page explains the load check, how to read the beam table for a deck, and the post and footing rules that go with it. It does not reproduce the tables. For the full method behind every table, see Ontario Building Code span tables. Confirm your design with your building department before you build.

Deck framing at a glance

You are sizing Where to look Article
Design load greater of roof snow load or 1.9 kPa 9.4.2.3.(1)
Do the tables apply? residential-level live load only 9.23.4.1.
Joists Span Tables 9.23.4.2.-A and -B 9.23.4.2.(1)
Built-up or glulam beams Span Tables 9.23.4.2.-H to -K 9.23.4.2.(3)
Building the beam plies, joints, nailing or bolting 9.23.8.3.
Beam bearing 89 mm, or as the table notes say 9.23.8.1.
Posts 140 × 140 mm or 184 mm round minimum 9.17.4.1.
Post scope limits 2 deck levels, joists up to 5 m, 4.8 kPa 9.17.1.1.(1)(b)
Post anchorage uplift and lateral movement 9.23.6.2.
Footing depth Table 9.12.2.2., small deck exemption 9.12.2.2.

This is our own index, not a copy of any code table.

Step 1: the load check

A deck serving a single dwelling unit must carry the specified roof snow load or 1.9 kPa, whichever is greater (9.4.2.3.(1)OBC Div. B 9.4.2.3. Platforms Subject to Snow and Occupancy Loads(1) Balconies, decks and other accessible exterior platforms intended for an occupancy and subject to snow loads shall be designed to carry the specified roof snow load or 1.9 kPa, whichever is greater, where the platform, or each segregated area of the platform, serves a single dwelling unit. (See Note A-9.4.2.3.(1))). The specified snow load comes from the formula in 9.4.2.2.OBC Div. B 9.4.2.2. Specified Snow Loads(1) Except as provided in Sentences (2) and (4), specified snow loads shall be not less than those calculated using the following formula: S = C_bS_s + S_r where S = specified snow load, C_b = basic snow load roof factor, which is 0.45 where the entire width of a roof does not exceed 4.3 m and 0.55 for all other…, using SB-1 climate data for your location. Our snow load guide walks through it.

The floor joist and beam spans apply only where the uniformly distributed live load does not exceed the value for residential areas in Table 4.1.5.3. (9.23.4.1.OBC Div. B 9.23.4.1. Application(1) Spans provided in this Subsection for joists, beams and lintels supporting floors shall apply only where (a) the floors serve residential areas as described in Table 4.1.5.3., or (b) the uniformly distributed live load on the floors does not exceed that specified for residential areas as described in Table…), which is 1.9 kPa (Table 4.1.5.3.OBC Div. B Table 4.1.5.3. Specified Uniformly Distributed Live Loads on an Area of Floor or RoofTable 4.1.5.3. — Specified Uniformly Distributed Live Loads on an Area of Floor or Roof Forming Part of Sentence 4.1.5.3.(1) Use of Area of Floor or Roof | Minimum Specified Load, kPa (a) Assembly Areas Arenas[1] (areas without fixed seats that have backs) | 4.8 (a) Assembly Areas Auditoria | 4.8 (a) Assembly Areas…). The notes to the beam tables repeat that limit (Table 9.23.4.2.-HOBC Div. B Table 9.23.4.2-H. Maximum Spans for Built-up Floor Beams Supporting Not More than One Floor – 38 × 184 mm MembersTable 9.23.4.2.-H — Maximum Spans for Built-up Floor Beams Supporting Not More than One Floor – 38 × 184 mm Members Forming Part of Sentences 9.23.2.8.(1), 9.23.4.2.(3), 9.23.4.4.(3) and 9.23.8.1.(1) Commercial Designation | Grade | Supported Length, m | Size of Beam: 3 – 38 × 184 mm | Size of Beam: 4 – 38 × 184 mm |…). So:

  • Snow load at or below 1.9 kPa. The deck design load is 1.9 kPa, the residential value, and the span tables can be used.
  • Snow load above 1.9 kPa. The deck load is higher than the tables assume. Spans for floors carrying more than the residential load are determined under Subsection 4.1.3. (9.23.4.1.(2)OBC Div. B 9.23.4.1. Application(1) Spans provided in this Subsection for joists, beams and lintels supporting floors shall apply only where (a) the floors serve residential areas as described in Table 4.1.5.3., or (b) the uniformly distributed live load on the floors does not exceed that specified for residential areas as described in Table…), or the framing can be designed using good engineering practice such as the CWC Engineering Guide for Wood Frame Construction, or Part 4 (9.4.1.1.OBC Div. B 9.4.1.1. General(1) Subject to the application limitations defined elsewhere in this Part, structural members and their connections shall (a) conform to requirements provided elsewhere in this Part, (b) be designed according to good engineering practice such as provided in the CWC 2014, "Engineering Guide for Wood Frame…).

Do this check first. A correct table lookup is still wrong if the table does not apply to your site.

Step 2: size the joists

Deck joists are floor joists, so they come from Table 9.23.4.2.-AOBC Div. B Table 9.23.4.2-A. Maximum Spans for Floor Joists – General Cases with Strapping[2]Table 9.23.4.2.-A — Maximum Spans for Floor Joists – General Cases with Strapping[2] Forming Part of Sentences 9.23.2.8.(1), 9.23.4.2.(1) and (2), 9.23.4.4.(1) and 9.23.9.4.(1) to (3) Commercial Designation | Grade | Joist Size, mm | Joist Spacing, 300 mm | Joist Spacing, 400 mm | Joist Spacing, 600 mm Douglas Fir –… (or -B for its special cases). Read it by species group, grade, joist size and spacing, in the section that matches what you install: strapping, bridging, or both. Most decks have no ceiling under the joists, so the panel ceiling alternative to strapping usually does not apply. Strapping is at least 19 × 64 mm nailed to the underside of the joists in rows not more than 2,100 mm apart, and bridging is 19 × 64 mm or 38 × 38 mm cross bridging at the same spacing (9.23.9.4.OBC Div. B 9.23.9.4. Strapping, Bridging, Furring and Ceilings in Span Tables 9.23.4.2.-A and 9.23.4.2.-B)(1) Except as permitted by Sentence (5), where strapping is specified in Span Table 9.23.4.2.-A, it shall be (a) not less than 19 mm by 64 mm, nailed to the underside of floor joists, (b) located not more than 2,100 mm from each support or other rows of strapping, and (c) fastened at each end to a sill or header. (2)…).

Joists need at least 38 mm of end bearing (9.23.9.1.OBC Div. B 9.23.9.1. End Bearing for Joists(1) Except when supported on ribbon boards, floor joists shall have not less than 38 mm length of end bearing. (2) Ribbon boards referred to in Sentence (1) shall be not less than 19 mm by 89 mm lumber let into the studs.). Where they frame into the side of a wood beam, use joist hangers or ledger strips of the sizes in 9.23.9.2.OBC Div. B 9.23.9.2. Joists Supported by Beams(1) Floor joists may be supported on the tops of beams or may be framed into the sides of beams. (2) When framed into the side of a wood beam, joists referred to in Sentence (1) shall be supported on (a) joist hangers or other acceptable mechanical connectors, or (b) not less than 38 mm by 64 mm ledger strips nailed….

If you plan to build the guard to SB-7, note that SB-7 also sets minimum floor elements for that deck: joists of at least 38 × 184 mm, and decking of 25 × 140 mm or 38 × 89 mm with the nailing it specifies (SB-7 Table 2.1.3.OBC SB-7 Table 2.1.3. Minimum Size of Floor ElementsTable 2.1.3. — Minimum Size of Floor Elements Floor Element | Minimum Size, mm (in) Dimension Lumber Decking | 25 x 140 (⁵/₄" x 6" nominal), when each plank is fastened with 2 - 63 mm (2½") nails Dimension Lumber Decking | 38 x 89 (2" x 4" nominal), when each plank is fastened with 2 - 76 mm (3") nails Dimension…).

Step 3: read the beam table

A deck beam supports one level, so Table 9.23.4.2.-H (not more than one floor) is normally the one to open. Glued-laminated beams use Table -K. Read the beam table by:

  1. Member depth. Table -H has sections for 38 × 184, 38 × 235 and 38 × 286 mm plies.
  2. Species group and grade. Use what is stamped on the lumber. The notes list which species fall in each group, such as Spruce, Jack Pine, Lodgepole Pine, Balsam Fir and Alpine Fir in spruce-pine-fir.
  3. Supported length. Half the sum of the joist spans on both sides of the beam. Straight interpolation is allowed for other supported lengths.
  4. Number of plies. 3, 4 or 5.

The result is a clear span between supports. Add two bearing lengths to get the member length. In Table -H, bearing is 76 mm for most beams and 114 mm for 3-ply beams with a supported length over 4.2 m (Table 9.23.4.2.-HOBC Div. B Table 9.23.4.2-H. Maximum Spans for Built-up Floor Beams Supporting Not More than One Floor – 38 × 184 mm MembersTable 9.23.4.2.-H — Maximum Spans for Built-up Floor Beams Supporting Not More than One Floor – 38 × 184 mm Members Forming Part of Sentences 9.23.2.8.(1), 9.23.4.2.(3), 9.23.4.4.(3) and 9.23.8.1.(1) Commercial Designation | Grade | Supported Length, m | Size of Beam: 3 – 38 × 184 mm | Size of Beam: 4 – 38 × 184 mm |…), which takes precedence over the general 89 mm in 9.23.8.1.OBC Div. B 9.23.8.1. Bearing for Beams(1) Beams shall have even and level bearing and the bearing at end supports shall be not less than 89 mm long, except as stated in the notes to Span Tables 9.23.4.2.-H to 9.23.4.2.-K. ..

Worked example

A deck projects 4.8 m from the house. Joists run from a ledger at the house to a middle beam at 2.4 m, then to an outer beam at 4.8 m. The site's specified snow load is below 1.9 kPa, so the tables apply. The middle beam is three plies of 38 × 184 mm SPF No. 1 or No. 2.

  • Supported length of the middle beam: (2.4 + 2.4) / 2 = 2.4 m.
  • Table: 9.23.4.2.-H, 38 × 184 mm section, Spruce-Pine-Fir, No. 1 and No. 2, 2.40 m row, 3-ply column.
  • Maximum clear span: 3.07 m between posts.
  • Bearing: 76 mm at each end.

If you want posts farther apart, try the 38 × 235 mm section of the same table, or add plies, and read the same row again. The outer beam carries only half of one bay, a supported length of 1.2 m, which is below the shortest row in the table. Ask your building department how it wants that beam checked rather than assuming a value.

Step 4: build the beam

Built-up beams use 38 mm or thicker members on edge (9.23.8.3.OBC Div. B 9.23.8.3. Built-up Wood Beams(1) Where a beam is made up of individual pieces of lumber that are nailed together, the individual members shall be 38 mm or greater in thickness and installed on edge. (2) Except as permitted in Sentence (3), where individual members of a built-up beam are butted together to form a joint, the joint shall occur over…). Butt joints fall over supports, or for a beam continuous over more than one span, at or within 150 mm of the permitted quarter points, with no more than one joint per member in a span. The plies are nailed with a double row of nails at least 89 mm long, rows not more than 450 mm apart, or bolted with 12.7 mm bolts with washers at not more than 1.2 m on centre.

Cantilevers. The only cantilever limit in Subsection 9.23.9. is for floor joists that support roof loads: 400 mm for 38 × 184 mm joists and 600 mm for 38 × 235 mm or larger (9.23.9.9.OBC Div. B 9.23.9.9. Cantilevered Floor Joists(1) Floor joists supporting roof loads shall not be cantilevered more than 400 mm beyond their supports where 38 mm by 184 mm joists are used and not more than 600 mm beyond their supports where 38 mm by 235 mm or larger joists are used. (2) The cantilevered portions referred to in Sentence (1) shall not support floor…). The beam tables give clear spans between supports, so an overhang past the last post is not something they size. Discuss joist or beam overhangs with your building department or a designer.

Step 5: posts and footings

Scope. Section 9.17 covers columns under beams carrying not more than 2 levels of wood-frame decks (or 1 level plus a roof), where the joists bearing on the beam are not more than 5 m long, the snow plus occupancy load does not exceed 4.8 kPa, and the deck serves a single residential suite (9.17.1.1.OBC Div. B 9.17.1.1. Application(1) This Section applies to columns used to support (a) beams carrying loads from not more than 2 wood-frame floors where (i) the supported length of joists bearing on such beams does not exceed 5 m, and (ii) the live load on any floor does not exceed 2.4 kPa, (See Table 4.1.5.3.) (b) beams or header joists carrying…). Outside those limits, the columns are designed under Part 4.

Size. A wood column must be at least as wide as the member it supports, and at least 140 × 140 mm (or 184 mm round) unless calculations show a smaller size is adequate (9.17.4.1.OBC Div. B 9.17.4.1. Column Sizes(1) The width or diameter of a wood column shall be not less than the width of the supported member. (2) Except as provided in Article 9.35.4.2., columns shall be not less than 184 mm for round columns and 140 mm by 140 mm for rectangular columns, unless calculations are provided to show that lesser sizes are adequate.). A 4-ply beam of 38 mm members is 152 mm wide, so a 140 mm post is too narrow for it. Built-up columns use full-length 38 mm members bolted or nailed together at set spacings (9.17.4.2.OBC Div. B 9.17.4.2. Materials(1) Wood columns shall be either solid, glued-laminated or built-up. (2) Built-up columns shall consist of not less than 38 mm thick full-length members (a) bolted together with not less than 9.52 mm diam bolts spaced not more than 450 mm o.c., or (b) nailed together with not less than 76 mm nails spaced not more than…), and wood columns are separated from concrete in contact with the ground by polyethylene film or Type S roll roofing (9.17.4.3.OBC Div. B 9.17.4.3. Columns in Contact With Concrete(1) Wood columns shall be separated from concrete in contact with the ground by 0.05 mm polyethylene film or Type S roll roofing.).

Bracing and anchorage. Columns are fastened to what they support and braced against racking, except posts not more than 600 mm long under a deck with no superstructure (9.17.2.2.OBC Div. B 9.17.2.2. Lateral Support(1) Columns shall be securely fastened to the supported member to reduce the likelihood of lateral differential movement between the column and the supported member. (See also Article 9.23.6.2.) (2) Except as permitted by Sentence (3), columns shall be laterally supported to resist racking (a) directly, or (b) by…). Exterior posts are anchored against uplift and lateral movement, with an exemption for a small freestanding deck (9.23.6.2.OBC Div. B 9.23.6.2. Anchorage of Columns and Posts(1) Except as provided in Sentences (2) and (3), exterior columns and posts shall be anchored to resist uplift and lateral movement. (2) Except as provided in Sentence (3), where columns or posts support balconies, decks, verandas and other exterior platforms, and the distance from finished ground to the underside of…).

Footings. Depth follows Table 9.12.2.2.OBC Div. B Table 9.12.2.2. Minimum Depths of Foundations — Forming Part of Sentence 9.12.2.2.(1)Table 9.12.2.2 — Minimum Depths of Foundations — Forming Part of Sentence 9.12.2.2.(1) Forming Part of Sentence 9.12.2.2.(1) Type of Soil | Min Depth of Foundation Containing Heated Basement or Crawl Space[1] With Good Soil Drainage | Min Depth of Foundation Containing Heated Basement or Crawl Space[1] With Poor Soil…, unless the deck is not more than 1 storey and 55 m², has joists not more than 600 mm above ground, carries no roof and is not attached to another structure (with one exception) (9.12.2.2.OBC Div. B 9.12.2.2. Minimum Depth of Foundations(1) Except as provided in Sentences (4) to (7), the minimum depth of foundations below finished ground level shall conform to Table 9.12.2.2. (2) Where a foundation is insulated in a manner that will reduce the heat flow to the soil beneath the footings, the foundation depth shall conform to that required for…). Column footing areas are in 9.15.3.4.OBC Div. B 9.15.3.4. Basic Footing Widths and Areas(1) Except as provided in Sentences (2) and (3) and in Articles 9.15.3.5. to 9.15.3.7., the minimum footing width or area shall comply with Table 9.15.3.4. (2) Where the supported joist span exceeds 4.9 m in buildings with light wood-frame walls, floors and roofs, strip footing widths shall be determined according to…. The deck building code guide covers these in more detail.

SB-7 is for guards, not spans

Supplementary Standard SB-7 contains details for the construction of wood guards (SB-7 1.1.1.OBC SB-7 1.1.1. Scope (See Appendix A.)(1) This Supplementary Standard includes details for the construction of wood guards. (2) Guards located on the exterior of a building, where they may be subject to deterioration, shall be constructed in accordance with Section 2 of this Supplementary Standard. (See Appendix A.) (3) Guards located inside a building…). It does not give joist or beam spans. Its Table 2.1.3. only sets minimum joist and decking sizes for a deck that uses its guard details. Guard height and baluster rules are in deck railing height in Ontario.

Common mistakes

  1. Skipping the snow load check and using the floor tables where the deck load is above 1.9 kPa.
  2. Using supported length as the post spacing. Supported length comes from the joists; the table result is the post spacing.
  3. Reading the two-floor table (-I) for a single-level deck, or the wrong member depth section.
  4. A post narrower than the beam, such as a 140 mm post under a 4-ply beam.
  5. Butt joints between posts that are not at the permitted quarter points.
  6. Treating SB-7 as a framing standard.

How to look it up yourself

In Division B, Part 9 of the 2024 Compendium, search for:

  • "decks and other accessible exterior platforms" (9.4.2.3., 9.12.2.2., 9.17.1.1.)
  • "Maximum Spans for Built-up Floor Beams"
  • "Supported length means"
  • "Built-up Wood Beams" (9.23.8.3.)
  • "Column Sizes" (9.17.4.1.)

Open 9.23.4.2. in the code viewer to jump to each table, and try more lookups with the joist, rafter and beam span method in our Calculation Lab.

Span lookups appear on the House exam. Read the free House chapter on wood-frame and steel stud construction and practise on the House exam page.

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

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Frequently asked questions

Is there a deck beam span table in the Ontario Building Code?
There is no deck-only table. Wood beams are sized from Span Tables 9.23.4.2.-H to -K for built-up and glued-laminated floor beams, and joists from Span Tables 9.23.4.2.-A and -B (Division B, Article 9.23.4.2.). Those tables apply only to floors at residential-level live loads (Article 9.23.4.1.).
What load is a deck designed for in Ontario?
A deck serving a single dwelling unit must carry the specified roof snow load or 1.9 kPa, whichever is greater (Division B, Sentence 9.4.2.3.(1)). Residential areas in Table 4.1.5.3. are 1.9 kPa, so where the snow load governs, the floor tables alone may not cover the deck and design under Part 4 may be needed (Article 9.23.4.1.).
How do I find the supported length of a deck beam?
Supported length is half the sum of the joist spans on both sides of the beam (Note 3 to Span Table 9.23.4.2.-H). A middle beam with 2.4 m joists on each side has a supported length of 2.4 m.
How big do deck posts have to be?
Unless calculations show a smaller size is adequate, wood columns must be at least 140 mm by 140 mm, or 184 mm round, and never narrower than the member they support (Division B, Article 9.17.4.1.).
Does SB-7 give deck beam spans?
No. SB-7 covers the construction of wood guards (SB-7, Article 1.1.1.). It does set minimum floor joist and decking sizes for a deck that uses its guard details (SB-7, Table 2.1.3.), but beam and joist spans come from Subsection 9.23.4. of Division B.