HST Rebate for Substantial Renovations in Ontario: The 90% Rule Explained

Gut-renovating your Ontario home is one of the biggest financial undertakings a homeowner can take on. What many people don't realize is that a project large enough to qualify as a "substantial renovation" under the Excise Tax Act can trigger both a significant HST exposure and a meaningful rebate — sometimes worth tens of thousands of dollars. Getting the details right matters. The HST rebate for substantial renovation in Ontario operates under rules that are surprisingly similar to those for new construction, and the consequences of missing a filing deadline or misclassifying your project can be costly.

This article breaks down who qualifies, what the 90% test actually means in plain language, what work counts (and what doesn't), and how the rebate claim process works. Because HST is a federal-provincial tax program administered by the Canada Revenue Agency, always verify current rates and thresholds directly with CRA or a qualified accountant — the rules summarized here reflect the law as of writing but are subject to change.

What Is a "Substantial Renovation"?

Plain-language definition (as of writing — verify with CRA and a qualified accountant before relying on this):

Under the Excise Tax Act, a substantial renovation is a renovation so extensive that, when it's complete, all or substantially all of the building's interior has been removed or replaced. CRA's administrative position treats "all or substantially all" as meaning 90% or more of the existing interior of the house (excluding the foundation, exterior walls, interior supporting walls, floors, roof, and staircases). In other words, if you gut everything inside those structural elements — down to the studs and subfloor — and rebuild it, you are likely in substantial renovation territory. A kitchen reno, a bathroom addition, or even a full basement finish almost certainly falls short of the 90% threshold on its own. Only a true gut renovation typically clears the bar.

The threshold is evaluated against the pre-renovation state of the interior. If your home already had certain rooms untouched — say, one bedroom that was left intact — that fact counts against you in reaching the 90% mark. Document everything before, during, and after the project.

What Work Counts Toward the 90% Threshold

When calculating whether a renovation reaches the 90% threshold, CRA looks at the proportion of the interior that was removed or replaced. Work that generally counts includes:

• Removal and replacement of all interior walls (non-structural drywall and partitioning)
• Replacement of all flooring throughout the home
• Full replacement of electrical wiring and panels throughout the interior
• Complete replacement of plumbing rough-in throughout the interior
• New HVAC ductwork and mechanical systems installed throughout
• Replacement of all interior insulation
• New windows and interior doors throughout
• Full replacement of ceilings and interior finishing surfaces
• Kitchen and bathroom gut and rebuild as part of a whole-home project

The key word is throughout. Isolated upgrades to individual rooms or systems are not the same as replacing those elements across the entire dwelling.

What Work Does NOT Count

The Excise Tax Act is explicit that certain elements of the structure are excluded from the 90% calculation entirely. These items are ignored — neither for nor against you:

• The foundation
• Exterior walls (including exterior cladding and windows if the wall itself is structural)
• Interior load-bearing walls
• Floors (the structural floor system — though surface flooring is counted)
• The roof structure
• Staircases (the structural staircase, not just the treads and railings)

Beyond these exclusions, work that is purely cosmetic — repainting rooms, refinishing existing hardwood, replacing fixtures in place — contributes very little to the tally because it does not involve removing or replacing the underlying surface or system. Similarly, adding a new addition to an otherwise untouched house does not automatically make the existing portion "substantially renovated."

The Self-Supply Rule: Why Homeowners Become "Builders"

This is where many Ontario homeowners are caught off guard. Under the Excise Tax Act, if you carry out a substantial renovation of a residential property and then occupy it (or allow a relative to occupy it) as a primary place of residence, you are deemed to be a builder who has made a taxable supply of the property to yourself. This is called the self-supply rule.

What it means practically: the law treats you as if you had sold the home to yourself at fair market value the day you (or your relative) first occupies it after the renovation. You are deemed to have collected HST on that fair market value — and you are liable to remit that HST to CRA. The flip side is that you are also entitled to claim the new residential rental property rebate or the new housing rebate, depending on your situation, to recover a portion of that deemed HST.

The self-supply rule exists because HST is meant to apply to new housing. A gut renovation produces what is economically a new home, so the tax system treats it the same way.

The Rebate: What You Can Claim (as of writing — verify with CRA)

The rebate available after a substantial renovation mirrors the GST/HST New Housing Rebate that applies to newly built homes. As of writing:

• The federal portion of the rebate applies where the fair market value of the property at the time of self-supply is below a certain threshold; the rebate phases out as the value rises above that threshold and disappears entirely at the upper limit.
• Ontario has its own provincial component of the rebate, administered alongside the federal portion.
• The combined federal-provincial rebate can be significant — potentially thousands of dollars depending on the property's value.

Because the rebate is calculated on the property's fair market value (not just the cost of the renovation), a professional appraisal at the time of occupancy is usually worth the expense. Verify all current thresholds, percentages, and phase-out ranges with CRA or an accountant, as these figures change.

Primary Residence Requirement

To claim the new housing rebate in the context of a substantial renovation, the property must be used as the primary place of residence of you or a qualifying relative immediately after the renovation is complete. You cannot claim this rebate if you plan to rent the property to an arm's-length tenant right away — though a different rebate (the new residential rental property rebate) may be available in that scenario. Occupying the home personally, even temporarily, before renting it may affect which rebate applies and when the self-supply clock starts, so take advice before you move in.

Who Applies and When: Filing the Rebate

The person liable under the self-supply rule — typically the homeowner who carried out the renovation — is responsible for filing the rebate application. A few practical points:

• If you hired a general contractor who is a registrant, the contractor may be responsible for collecting and remitting HST on their supply of the construction services to you; however, the self-supply deemed on your occupation is your obligation.
• The rebate application is filed directly with CRA using the appropriate rebate form. It must generally be filed within two years of the day the rebate first became available (tied to the date of occupancy or substantial completion). Missing this deadline forfeits the rebate entirely.
• Keep records: all invoices, permits, contracts, before-and-after photographs, and the appraisal should be retained in case CRA audits your claim.

Frequently asked questions