The Deck Professor

Every number here is a working estimate to check with your building authority. Whoever prints this page takes responsibility for what is in it.

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How these answers are made

A deck answer is only worth reading if you can tell where it came from and how sure it is. This page explains both, and the one commercial relationship on the site.

The method

Every answer is built the same way.

  1. Find the written requirement. Not a forum post, not a contractor's habit. The National Building Code Part 9, the Alberta edition as the City of Edmonton applies it, or an industry span guide.
  2. Say which document it came from. Every answer page has a "where this comes from" block at the bottom naming the source and the section.
  3. Say when it is not certain. Code editions change, provinces amend, and municipalities add their own thresholds. Where a number moves between editions or between authorities, the page says so rather than picking one and sounding confident.
  4. Never invent a clause number. If the requirement is clear but the exact clause reference is not, the page describes the requirement and leaves the number out. A wrong clause number is worse than no clause number, because somebody will quote it.
  5. Show it where it can be shown. If a question is about geometry, the page gets a drawing you can change, and the drawing and the numbers are produced from the same configuration.

Sources

Four documents do most of the work on this site.

National Building Code of Canada, Part 9
The model code the provinces adopt and amend. Section 9.8 covers stairs, ramps, landings, handrails and guards. Section 9.12 covers excavation and foundations. Section 9.23 covers wood frame construction. This is the default basis on every demonstration, because it is the common ground under every Canadian answer here.
National Building Code, Alberta Edition, and the City of Edmonton Uncovered Deck Design Guide
The Alberta Edition is what is enforced in Alberta. Edmonton publishes a free Uncovered Deck Design Guide written against it, and it is the single most useful deck document in the province: permit thresholds, foundation practice, post and beam rules, decking, stairs, guards and handrails, all in fifteen pages. The version used here was last updated 22 December 2022. Get the current one from the City before you apply.
Canadian Wood Council, Prescriptive Residential Exterior Wood Deck Span Guide
The joist span and beam selection tables on this site are transcribed from the 2016 edition of this guide, imperial tables, including the separate values for incised lumber. Edmonton states that the spans on its own permit application come from the same guide.
InterNACHI deck inspection material
Inspection practice rather than Canadian code, and this site labels it that way every time. Several of its numbers come from the International Residential Code, which is not in force in Canada, so they are quoted as what a home inspector looks for and not as a requirement. It is the best public material there is on how decks actually fail.

Choosing which rules a lesson follows

Every lesson has an Advanced panel where you choose the rules it follows, and the home page has the same switch. It offers three.

  • Canada (national code): the National Building Code Part 9. The default, and the model code.
  • Alberta and Edmonton: the Alberta edition as the City of Edmonton applies it. Adds the permit and engineering thresholds and the typical {L FOUND.edmontonFrostIn ge} frost depth.
  • Maker's tables: supplier or manufacturer tables, for manufactured guards, composite decking and engineered lumber, where the prescriptive tables stop applying and the evaluation report or an engineer governs.

The switch exists because the honest answer to "which rules" is usually "it depends where you are building", and picking one for you would be worse than letting you pick.

What this site will not do

  • It will not approve anything. The authority having jurisdiction has the final word every time.
  • It will not design your deck. A demonstration is a teaching tool, not a stamped drawing.
  • It will not pretend a number is certain when it is not.
  • It will not cover garages, sunrooms, fences or anything else. Decks only.

The referral link

We are paid a referral fee if you hire a listed builder, such as Edmonton Deck Builder. It costs you nothing and changes no answer. Builders who want to be listed can get in touch through the ask a question page.

Corrections

If a number here is wrong, it should be fixed the same day. Send the page, the number and the source that contradicts it. A correction with a citation attached goes in immediately. Details are on the ask a question page.