HST on Building a Custom Home on Your Own Lot in Ontario

You already own the land. You've hired a contractor — or you're planning to manage the build yourself. Either way, you're about to discover that building a custom home on your own lot in Ontario is not an HST-free exercise.

Many people assume that because they already paid land transfer tax on the lot, and because they're building for their own use rather than to sell, the HST exposure is minimal. That assumption is wrong. The federal Excise Tax Act contains a rule called the self-supply rule that deems you to have sold — and repurchased — your own home the moment you move in, triggering HST on the fair market value of the completed property. Understanding this rule, what rebates offset it, and what records you need is essential before you break ground. All figures and thresholds mentioned below were accurate as of writing — verify current amounts with CRA or a qualified accountant before filing.

Why Building on Your Own Lot Isn't HST-Free

When a developer builds and sells a new home, the HST is embedded in the purchase price and the developer remits it. When you build on your own lot, there is no sale, so CRA created the self-supply rule to ensure new housing is taxed consistently regardless of who builds it. The rule treats you as both the builder and the buyer. The result: you owe HST on the fair market value of the home (and the land underneath it) as a completed unit — even though you never wrote a cheque to yourself.

The Self-Supply Rule: How It Works Step by Step

1. You become a "builder" under the Excise Tax Act. The Act defines builder broadly. If you hire a general contractor to construct a residential complex on your land primarily for use as your place of residence, you are a builder for GST/HST purposes — even if you never touch a hammer.

1. The trigger event occurs. The self-supply is triggered when you, a relative, or someone you allow to occupy the home first moves in — whichever comes first, that is the deemed supply date.

1. CRA deems a taxable sale at fair market value. On the trigger date, you are treated as having sold the completed home and land to yourself at fair market value. HST applies to that full fair market value.

1. You calculate the HST owing. Apply the HST rate (13% in Ontario as of writing — confirm with CRA) to the fair market value of the property on the trigger date. This is the gross tax.

1. You subtract available rebates. The New Housing Rebate or the Owner-Built Homes Rebate (see below) reduces the net amount you owe.

1. You file and remit. You must file a GST/HST return and remit the net tax by the deadline. Failure to file on time can result in interest and penalties.

Hiring a GC vs. Acting as Your Own General Contractor

How you structure the build affects your HST exposure at the construction stage — though both models trigger the self-supply rule at move-in.

Model A: Hiring a General Contractor

• The GC is a registrant; they charge you HST on their invoices (labour and materials they supply).
• You pay HST on every progress draw.
• Because you are a builder-registrant yourself, you can claim input tax credits (ITCs) on those payments — meaning you recover the HST you paid to the GC as a credit against what you ultimately owe under the self-supply rule.
• Your HST liability crystallizes at the fair market value of the finished home, offset by ITCs and the applicable rebate.
• Record-keeping is simpler because one entity (the GC) is accountable for most invoices.

Model B: You Are the General Contractor

• You hire subtrades directly (framing, electrical, plumbing, HVAC, etc.).
• Each registered subtrade charges you HST; you claim ITCs on each invoice.
• You also pay HST on materials you purchase directly.
• You have maximum control over cost but significantly more invoices to track and more exposure if a subtrade fails to properly charge HST or you miss an ITC.
• Your self-supply liability is the same in principle, but the ITC puzzle is more complex to assemble at filing time.

HST on Labour and Materials: What's Taxable

HST applies to substantially all costs in a residential construction project:

• Labour — all invoices from registered subtrades and the GC carry HST.
• Materials — lumber, drywall, windows, doors, fixtures, appliances (most), flooring, and finishes are all taxable supplies.
• Professional fees — architect, engineer, and designer fees are taxable.
• Notable zero-rated or exempt items are rare in residential construction; do not assume any line item is HST-free without confirming with your accountant.

As a builder-registrant you claim ITCs on all legitimate construction inputs. Keep every invoice.

The Owner-Built Homes Rebate vs. The New Housing Rebate

Two rebate streams are available; which one applies depends on fair market value thresholds (confirm current thresholds with CRA):

New Housing Rebate (NHR): Available to owner-builders below a certain fair market value threshold. The rebate phases out as fair market value increases above that threshold, and disappears entirely above the upper limit. The NHR is claimed on CRA Form GST191.

Owner-Built Homes Rebate (OBHR): This is the specific rebate stream for individuals who build on their own lot (as opposed to purchasing a newly built home from a developer). It uses Form GST191 and Schedule GST191-WS. The calculation requires you to enter the fair market value of the land separately from the value of the building — an important distinction discussed below.

If you intend to use the home as your primary place of residence, you are generally eligible to apply. If you build for rental or resale, different rules apply and the rebate may not be available.

How Land Value Affects the Rebate

The rebate is calculated against the full fair market value of the property — land included. If you paid $300,000 for the lot several years ago and it has since appreciated, its current value on move-in day is what matters, not your historical cost. A high land value can push total fair market value above rebate thresholds even if the build itself was modest, reducing or eliminating the rebate. Get a proper appraisal on or close to move-in day and keep it on file.

Records You Must Keep

CRA can audit your self-supply filing years after the fact. Maintain organized records of:

• All contractor and subtrade invoices showing HST registration numbers and amounts
• Materials receipts for any supplies you purchased directly
• Your building permit and occupancy permit
• A timeline of construction milestones and the date of first occupancy
• The appraisal or other evidence of fair market value on the trigger date
• All ITC claims and the GST/HST returns filed
• Proof of your intent to use the home as a primary residence

The Filing Deadline

The self-supply return must be filed within two years of the end of the month in which the trigger event (first occupancy) occurs. Missing this window forfeits the rebate — CRA will not extend it in most circumstances. Set a calendar reminder well before the two-year mark and engage your accountant or lawyer early.

Frequently asked questions