Prescriptive Residential Exterior Wood Deck Span Guide - Outdoor Project Series 1 - Design assumptions and span tables

Oct 12, 2026

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Prescriptive guidance for designing residential exterior wood deck framing, covering joist spans, built-up beam sizing, and supporting column sizes. The guide defines key CSA O86-14 and NBC 2015 design assumptions, including specified live and dead loads, allowable deflection limits, lumber grade and species grouping, and wet-service and incised-lumber treatment factors. It provides metric and imperial design tables for decks with joists and beams supporting single or two spans, including cantilever and built-up beam details, plus a worked design example.

LanguageEnglish

CategoryPresentations

FormatPDF

Pages17

Reading Time6 min

AccessFree to download

Contents

Design Assumptions

Figure 1 - Deck Layout

Figure 2 - Built-up Beam details

Table 1 - Species Grouping for Selection Tables

Table 2a-Deck Joist Spans Not Incised

Table 2b-Deck Joist Spans Not Incised

Table 3a-Deck Joist Spans Incised

Table 3b-Deck Joist Spans Incised

Table 4a - Beam Selection Not Incised Supporting Single Span

Table 4b - Beam Selection Not Incised Supporting Single Span

Table 5a - Beam Selection Incised Supporting Single Span

Table 5b - Beam Selection Incised Supporting Single Span

Table 6a - Beam Selection Not Incised Supporting Two Spans

Table 6b - Beam Selection Not Incised Supporting Two Spans

Table 7a - Beam Selection Incised Supporting Two Spans

Table 7b - Beam Selection Incised Supporting Two Spans

Design Example

Figure 3 - Design Example Sketch and Design

Prescriptive Residential Exterior Wood Deck Span Guide OUTDOOR PROJECT SERIES 1 Copyright © 2016 Canadian Wood Council Prescriptive Residential Exterior Wood Deck Span Guide Revision 1 © 2016 copyright Canadian Wood Council Conseil canadien du bois Ottawa, Ontario, Canada Design and production: Canadian Wood Council Ottawa, ON RESIDENTIAL PRESCRIPTIVE EXTERIOR WOOD DECK SPAN GUIDE CONTENTS | Design Assumptions | 4 | | --- | --- | | Figure 1 – Deck Layout | 5 | | Figure 2 – Built-up Beam details | 6 | | Table 1 – Species Grouping for Selection Tables | 6 | | Table 2a-Deck Joist Spans Not Incised (m) | 7 | | Table 2b-Deck Joist Spans Not Incised (ft. -in. ) | 7 | | Table 3a-Deck Joist Spans Incised (m) | 8 | | Table 3b-Deck Joist Spans Incised (ft. -in. ) | 8 | | Table 4a – Beam Selection Not Incised Supporting Single Span (m) | 9 | | Table 4b – Beam Selection Not Incised Supporting Single Span (ft) | 10 | | Table 5a – Beam Selection Incised Supporting Single Span (m) | 11 | | Table 5b – Beam Selection Incised Supporting Single Span (ft) | 12 | | Table 6a – Beam Selection Not Incised Supporting Two Spans (m) | 13 | | Table 6b – Beam Selection Not Incised Supporting Two Spans (ft) | 14 | | Table 7a – Beam Selection Incised Supporting Two Spans (m) | 15 | | Table 7b – Beam Selection Incised Supporting Two Spans (ft) | 16 | | Design Example | 17 | | Figure 3—Design Example Sketch and Design | 17 | DISCLAIMER This document has been developed for information purposes only. Although all possible efforts have been made to ensure that the information in this document is accurate, the CWC cannot under any circumstances guarantee the completeness, accuracy or exactness of the information. Reference should always be made to the appropriate Building Code and/or standard. This document should not be relied upon to substitute for legal or design advice, and the user is responsible of how the document is used or applied. SCOPE The intent of this document is to provide guidance on joist spans, built-up beam sizes, and supporting column sizes for exterior wood decks. The following items which are typically included in an exterior wood deck are not addressed and are beyond the scope of this document. 􀁸 Deck footings 􀁸 Deck railings and guards 􀁸 Attachment of the deck to houses 􀁸 Lateral bracing of a deck Design tables are provided for lumber which is not incised (Tables 2a, 2b, 4a, 4b, 6a and 6b) and lumber which is incised (Tables 3a, 3b, 5a, 5b, 7a and 7b) . Tables are provided in both metric and imperial units. CANADIAN WOOD COUNCIL RESIDENTIAL PRESCRIPTIVE EXTERIOR WOOD DECK SPAN GUIDE DESIGN ASSUMPTIONS Joists and Beams 􀁸 Design based on CSA O86-14 and NBC 2015 􀁸 Live load: 1.9 kPa (40 psf) 􀁸 Dead load: 0.5 kPa (10 psf) 􀁸 Grade: No.2 or better 􀁸 Species: Refer to Table 1 􀁸 Live load deflection limit: L/360 􀁸 Wet service condition factors for all Tables (Ksb = 0 .84, Ksv = 0 .96, KSE = 0 .94) 􀁸 Treatment factors for incised lumber Tables (KT = 0.85 for Bending and Shear, KT = 0.95 for Modulus of Elasticity) Joists only 􀁸 Lateral Support is provided at the top of joists by closely spaced perpendicular or diagonal lumber (KL = 1.0) 􀁸 Case 1 load sharing system (KH = 1. 1) Beams only 􀁸 Lateral Support is provided by the supported joists (KL = 1.0) 􀁸 Case 2 load sharing system for built-up beams with three plies (KH = 1. 1) Spacing Dimensions For the purpose of this document, the following spacing dimensions may be used interchangeably: i) 200 mm and 203 mm ii) 300 mm and 305 mm iii) 400 mm and 406 mm iv) 600 mm and 610 mm CANADIAN WOOD COUNCIL RESIDENTIAL PRESCRIPTIVE EXTERIOR WOOD DECK SPAN GUIDE FIGURE 1 – DECK LAYOUT Notes: 1. Deck joist allowable spans as per Tables 2a, 2b, 3a and 3b. 2. Beam selection for supporting a single span as per Tables 4a, 4b, 5a and 5b. 3. Beam selection for supporting two spans as per Tables 6a, 6b, 7a and 7b. Table

FAQs

What loads and design basis does the guide assume for deck framing?

The design is based on CSA O86-14 and NBC 2015, using a live load of 1.9 kPa (40 psf) and a dead load of 0.5 kPa (10 psf). It also uses a live load deflection limit of L/360.

How does the guide handle treated vs. incised lumber when selecting table values?

Tables are separated into lumber that is not incised and lumber that is incised. For incised lumber tables, treatment factors are provided for bending and shear (KT = 0.85) and modulus of elasticity (KT = 0.95). Wet-service condition factors are also applied across the tables.

Are the provided design tables valid for joists spanning more than two supports?

No. The tables are not valid if joists span continuously over more than two supports. An engineering analysis is required for that situation.

Oct 12, 2026

Upload by Sarah