FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Fine Homebuilding Project Guides

Decks

Guide Home
  • Design & Planning
  • Tools & Materials
  • Footings & Foundations
  • Framing a Deck
  • Installing Decking
  • Installing Railings
  • Deck Stairs
  • Custom Details
  • Finishes, Repairs, and Maintenance
  • Complete Deck Builds
How-To

Online Calculators Help Cover Deck-Load Requirements

Span tables don’t cover your deck load requirements? The American Wood Council has two handy online calculators that can handle a range of specifics.

By Mike Guertin Issue 274 - April/May 2018
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

One shortcoming of the span tables in the International Residential Code and the American Wood Council’s Prescriptive Residential Wood Deck Construction Guide (DCA 6) is that they’re limited to decks with a live load of 40 psf and a dead load of 10 psf. That means they won’t work for areas with heavier snow loads, for decks with heavy decking materials like stone, or in numerous other circumstances.


The American Wood Council’s online Maximum Span Calculator for Wood Joists and Rafters offers solutions. The calculator gives you the maximum span for a selected joist species, lumber grade, exterior exposure, on-center spacing, and live and dead loads. This is great when you are designing decks that fall outside the prescriptive limits of the DCA 6 and IRC tables.

Here’s a rundown of the entries:

  • Species: there are about 30 choices including the primary species used for pressure treating.
  • Size: 2×4 through 2×12
  • Grade: there are numerous choices. The main choices for most decks will be #1 or #2 grades and for SYP there will be differing effective dates and density choices.
  • Member Type: floor joist
  • Deflection Limit: L/360 is the best choice and matches what the code tables are based on
  • Spacing: choices for 12 in., 16 in., 19.2 in., and 24 in. on center.
  • Exterior Exposure (two entries): Wet Service = Yes, Incised lumber = Yes for D-fir, hem-fir, SPF or No for SYP
  • Live Load: 30 lb. to 100 lb. choices in 10 lb. increments
  • Dead Load: 5 lb., 7 lb., 10 lb., 15 lb., and 20 lb.

When you click “Calculate Maximum Horizontal Span” at the bottom of the entries, the system will give you the maximum span for the information you’ve entered. Because the calculator goes beyond the limits of grade, live load, and dead load in the DCA 6 and IRC tables, you can design decks that fall outside the table limits. For instance, if you know the dead load of the deck will be less than the prescriptive 10 lb., then you can select 5 lb. or 7 lb. and eek out a longer span. On the other hand, if you build in a ground-snow load that exceeds 40 psf, then you can enter your snow load in the “Live Load” field to size a joist span to handle heavy snow.


The Span Options Calculator is useful if you already have a span designed and want to know what joist size you can use.

On this calculator, you enter everything the same as with the Maximum Span Calculator, except you include the feet and inch dimension of the deck and don’t enter the joist size or the grade. The result gives you options for lumber grade and joist size (depth). Some lumber yards stock #1 pressure-treated lumber in addition to or instead of #2. You may find it more cost effective to use a 2×10 #1 grade rather than a 2×12 #2 grade for a particular joist span.

You can also toggle between different on-center spacing and recalculate to see what different joist sizes options are available to you.

For more about getting your deck joists right and the joist-span tables in DCA 6 and the 2018 IRC, check out the article “Get Your Deck Joists Right” in FHB #274.

Fine Homebuilding Recommended Products

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

Code Check 10th Edition: An Illustrated Guide to Building a Safe House

It would be great if this book didn’t need to exist, but it's definitely a must-have. It's a one-size-fits-all code book that's easy to understand and will help you sail through your inspections.
Buy at Amazon

N95 Respirator

PPE is a must, especially when cutting and sanding. We recommend you always have a box of respirator masks on the job site.
Buy at Amazon

Metal Connector Nailer

This time-saving tool is the fastest way to install hardware. The tip is designed to locate the hole in the hardware, then all you have to do is pull the trigger.
Buy at Amazon
Previous: Making Sense of Snow Loads When Building Decks Next: How Far Can a Deck Joist Span?

Guide

Decks

Chapter

Design & Planning

Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

View Comments

  1. CynthiaDow | May 14, 2019 07:08am | #1

    fantastic

  2. CT_Yankee | Apr 29, 2021 03:24pm | #2

    Careful with these calculators or tables (coming from a structural engineer).
    Many decks have joists that span from ledger to and over a beam, cantilevering a few feet past the beam. Unless the calculator or table SPECIFICALLY includes input for the cantilever portion, one must assume that it calculates for a simple, single span. Cantilevered joists present a whole new stress condition that the prescriptive tables (or calculators) do not take into account.

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Decks

Decks

Hundreds of articles and videos by top deck-building pros on how to design and build a beautiful, sturdy, and safe deck

View Project Guide

View All Project Guides »

Become a member and get unlimited site access, including the Decks Project Guide.

Start Free Trial

Design & Planning
  • Basic Design Options
  • Generating Plans
  • Calculating Deck Loads
  • Code Compliance
Tools & Materials
  • Deck Building Tools
  • Foundation and Framing Materials
  • Decking Materials
  • Fasteners and Hardware
Footings & Foundations
  • Choosing a Foundation
  • Sizing and Laying Out Footings
  • Excavation
  • Pouring the Foundation
Framing a Deck
  • Framing Overview
  • Installing the Ledger
  • Setting Posts and Beams
  • Installing Joists
Installing Decking
  • Decking Basics
  • Installation Process
  • Adding Fascia and Other Decorative Elements
Installing Railings
  • Installing Deck Railing Posts
  • Building Wood Rails and Balustrades
  • Non-Wood Railing Options
  • Installing Nonwood Balustrades
Deck Stairs
  • Deck Stairs Overview
  • Laying Out, Cutting, and Installing the Stringers
  • Installing Treads, Risers, and Stair Railings
Custom Details
  • Benches, Planters, and Privacy Features
  • Pergolas
  • Lighting
Finishes, Repairs, and Maintenance
  • Deck Finishes
  • Cleaning and Refinishing
  • Inspection and Repair
Complete Deck Builds
  • Grade-Level Decks
  • Raised Decks

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 81%

Subscribe

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data