The Ontario Building Code after the July 17, 2026 amendments.

Anyone pulling a permit in Ontario this fall, including one for a backwater valve or other basement flood work, is working under a building code made of two documents read together. The second of them has carried four different dates since October 2025. The current one is dated July 17, 2026, and it is worth knowing what that version changed and what it left alone.

What the code is made of right now

Section 1 of Ontario Regulation 163/24 says what the code is. The National Building Code of Canada 2020 (First Printing), issued by the Canadian Commission on Building and Fire Codes at the National Research Council, and a Ministry of Municipal Affairs and Housing document titled Ontario Amendments to the National Building Code of Canada 2020, dated July 17, 2026, are together adopted as the building code.

That date comes from O. Reg. 242/26, made on July 22, 2026. It struck out April 21, 2026 and put in July 17, 2026, and it came into force on the day it was filed. So since July 22, 2026, the July 17 document is the one a building department reads a new permit against.

Four dates in under a year

The national code has stayed the same throughout. What moves is the date of the Ontario amendments document named in section 1. Each change was made by a short amending regulation:

• October 21, 2025, set by O. Reg. 247/25, made October 31, 2025.
• April 1, 2026, set by O. Reg. 110/26, made April 17, 2026.
• April 21, 2026, set by O. Reg. 119/26, made April 28, 2026.
• July 17, 2026, set by O. Reg. 242/26, made July 22, 2026.

Why the document date matters to you

The date on the cover of the amendments document is not the day it took effect. The three 2026 amending regulations each came into force on the day they were filed, in each case later than the date printed on the document. The July version, for example, is dated July 17, and the regulation naming it was made on July 22. If a quote, a drawing or an online guide refers to the Ontario amendments, the cover date tells you which version it was written against. A copy dated April 21, 2026 or earlier is out of date.

What the July 17, 2026 version changed

The Ministry's July 22, 2026 announcement described two changes. The first removes design constraints under Part 3 for four-storey non-stacked townhouses. The second widens where cellular core PVC drain-waste-vent pipe may be used, and that one sits in the plumbing part of the code.

Comparing the two documents line by line shows the plumbing change in Division B, Article 7.2.5.16. The April 21 version allowed cellular core PVC pipe only in residential buildings containing 1 or 2 dwelling units and in row houses that do not exceed 3 storeys in height. The July 17 version allows it in a building of residential occupancy permitted to be of combustible construction, which the Ministry's announcement summed up as combustible buildings up to six storeys. The rest of the article reads the same in both versions: the pipe must meet ASTM F3128 and be light grey as specified in CSA B181.2, and its fittings and solvent cements must meet CSA B181.2.

What it left alone: the backwater valve rule

For basement flood work, the article that matters most is Article 7.4.6.4, Protection from Backflow, and its text reads the same in the April 21 and July 17 versions. A backwater valve in a building drain must be a normally open design that meets one of the listed CSA pipe standards, and it may not serve more than one dwelling unit.

The city rebate programs in this guide tie their valve requirements to that same article, and the article is unchanged. The rebate guide has a rule card for each city, and the backwater valve rules page explains why only a normally open mainline valve counts.

Permits from before 2025

The current code took over from Ontario Regulation 332/12 at the start of 2025, and section 2 of O. Reg. 163/24 keeps the older code in force for some projects that were already underway. Those projects are the ones with a permit issued on or before December 31, 2024, or with drawings substantially complete by that date and a permit application made on or before March 31, 2025. The older code only carries over if construction began within six months after the permit was issued. If you have an older permit that stalled, the building department can tell you which code it sits under.

Where to read each part

• The National Building Code of Canada 2020 is free in electronic form through the National Research Council's Publications Archive. Print copies are sold through the NRC Virtual Store.
• Publications Ontario offers a free PDF of the 2024 Building Code Compendium, but its listing says updated to January 16, 2025, and the two free amendment packages it lists stop at that date too. That is useful background, but it predates all four of the amendments documents above.
• The current wording of section 1 of O. Reg. 163/24 on e-Laws is the quickest way to confirm which amendments document is in force on the day you check.