How mechanic's liens work and how to prevent them
Short answer
A mechanic's lien (called a construction lien in much of Canada) is a legal claim on your property by someone who worked on it or supplied materials and wasn't paid. That can include subcontractors and suppliers, even if you paid your contractor in full. In the US, lien waivers and joint cheques help prevent this. In provinces like Ontario and Alberta, owners usually hold back 10% for a set period to protect against liens.
Liens surprise homeowners because the claim can come from someone they never hired directly. Knowing how it works helps you pay safely.
This guide is educational, not legal advice. Lien deadlines and forms are strict and vary by state and province; talk to a lawyer if a lien is filed.
1. How it happens
You pay the contractor
The contractor is supposed to pay subs and suppliers.
Someone isn't paid
A sub or supplier can file a lien against your property within legal deadlines.
Warning notices
In California, for example, subs and suppliers often send a preliminary notice telling you they could file.
2. US vs Canada
| Tool | Where | How it protects you |
|---|---|---|
| Lien waivers / releases | US | Signed statements that a party was paid, collected with each payment. |
| Joint cheques | US | Pay the contractor and supplier together on one cheque. |
| 10% holdback | Ontario, Alberta and others | Owner keeps 10% of each payment until the lien period ends. |
3. What to say
Before each payment
- 1.“Before I release this payment, please send lien waivers from your subcontractors and suppliers for the work covered.”
- 2.“For the final payment, I'll need final unconditional releases.”
The one thing to remember
Paid down the chain
You are safest when you can show everyone below your contractor has been paid.
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Common questions
Can I get a lien if I paid my contractor?
Yes, in many places, if a sub or supplier wasn't paid. Lien waivers and holdbacks reduce this risk.
How long does a lien last?
It depends on state or province; the claimant usually must act to enforce it within a set time.
What is a holdback?
In provinces like Ontario and Alberta, owners keep 10% of payments until the lien period passes.
Keep reading
Is it normal to pay the full amount before work is completed?
Why full prepayment hands over your leverage, and what a normal payment schedule looks like.
What to do if you think you were overcharged — after you've already paid
Paying doesn't end the conversation. The escalation path that actually gets money back.
How much should a plumber charge?
Flat-rate vs hourly, trip charges, access work, and what a fair quote itemises.
Is this HVAC quote normal?
Tonnage, SEER2, ductwork, line sets — why two AC bids are almost never comparable.
Sources
- CSLB: Mechanics lien — How liens, preliminary notices and releases work in California.
- Ontario: Construction Act — 10% holdback and lien rights in Ontario.
- Alberta: Prompt Payment and Construction Lien Act — 10% holdback and lien rules in Alberta.
- FTC: Hiring a contractor — Ask for lien releases before final payment.
Last reviewed October 2026. This article explains how prices and bills are structured in general terms, and is not a price guarantee, because what's reasonable depends on your location, scope and market. Educational information only — not professional, legal or financial advice. See our disclaimer and browse the full cost guide library.