What should the base be for a hot tub pad in Kanata?

We found no specification in the 2024 Ontario Building Code for the base beneath a free-standing concrete pad, and no City of Ottawa rule that sets a gravel depth or base type for a hot tub pad specifically. The base depth and composition come from the contractor's written specification, and you should ask for those details in writing before work starts.

That said, a few Code provisions are relevant context. Section 9.16.2.1 of the 2024 Ontario Building Code requires not less than 100 mm of coarse clean granular material beneath floors-on-ground, though that section applies to floors inside buildings. Section 9.16.2.2 says material susceptible to volume changes from freezing shall not be used as fill beneath floors-on-ground that will be subjected to freezing temperatures. Ask the contractor what depth and gradation of granular fill they are specifying, and why.

On concrete strength, the 2024 Ontario Building Code sets 32 MPa as the standard for exterior flatwork. That is the benchmark to ask about. We found no Code requirement for mesh, rebar or a vapour barrier under an exterior pad, so ask the contractor whether reinforcement is included and what their reasoning is.

A few other things to sort out before work starts:

• Locates: anyone who digs is an excavator under the Ontario Underground Infrastructure Notification System Act, 2012. A locate request goes through Ontario Dig Authority at least five business days before digging. Ask who will submit the request, and ask separately who will mark any private lines running to the pad area.
• Permit: the City's patio page sets out conditions under which a patio may be exempt from a building permit, including that it is supported directly on the ground and does not adversely affect exiting or accessibility. We found no City statement on a permit for the pad under a hot tub specifically; ask the City's Building Code Services before work begins.
• Hardscaping licence: the City of Ottawa's Hardscaping Contractor Licence has been required since March 1, 2026 for businesses that install concrete pads on private property. Ask the contractor to show their licence and check the City's published list yourself. The City's March 2026 guidance also says a licensed contractor will provide a written contract and give you a copy of the City's Landscaping Education Guide.
• Zoning: both Zoning By-law 2008-250 and Zoning By-law 2026-50 apply to applications deemed complete on or after March 11, 2026, with the most restrictive provisions from each applying. Soft-landscaping minimums for the rear yard may affect how much hard surface you can add. Confirm the rules for your lot with the City.

Get it on paper first: a written contract that sets out the scope, the base specification, the concrete strength, removal and disposal of any existing material, and the total price, along with any required permit and a copy of the City's Landscaping Education Guide from the contractor.