What is a construction lien and how does a contractor register one against a property in Ontario?

A construction lien is a security interest that the Construction Act gives to contractors, subcontractors, and suppliers who provide services or materials to an improvement on a property but haven't been paid, letting them register a claim directly against the title of the property itself. It doesn't create a right to payment on its own - it secures your existing claim for what you're owed, so the property can't easily be sold or refinanced free of your claim until it's dealt with.

To register one, a lienholder prepares a claim for lien setting out the amount owed and the nature of the work or materials supplied, then registers it against the property's title within the Construction Act's preservation deadline, which is strict and runs from specific triggering events like the last supply of services or materials, or the publication of a certificate of substantial performance. Missing that window generally ends the lien remedy entirely, even though the underlying contract debt can often still be pursued as an ordinary claim. Because the deadlines are unforgiving and the property description and amount must be accurate, having a lawyer confirm the correct trigger date and prepare the registration is worth doing well before the deadline approaches.