A legal secondary suite generally has to satisfy several separate sets of requirements, and satisfying one does not satisfy the others.

Zoning. The property must be in a zone where a second unit is permitted, and the suite must meet the conditions attached, which can include parking, unit size and how many units the property may contain.

Building permits. The work itself requires permits and inspections. This is the step most often skipped, and it is the one that cannot be quietly added afterwards.

Fire and building code. Fire separation between units, interconnected smoke alarms, carbon monoxide detection, and a compliant means of egress. Ceiling heights and window sizes for bedrooms are common sticking points in older basements.

Electrical. Work must be inspected and certified by the provincial electrical authority.

Registration. Some municipalities require second units to be registered, which usually involves an inspection. Requirements differ across York Region, so check with yours rather than relying on what a neighbour did.

Costs vary enormously with the starting point. An unfinished basement with adequate ceiling height and an existing separate entrance is a very different project from one that needs underpinning, a new entrance excavated, windows enlarged for egress and the electrical service upgraded.

Beyond construction, budget for design drawings, permit fees, inspections, the electrical authority certificate, and possibly a development charge depending on the municipality and the circumstances. Get a written quote that names each of these rather than a single number.

On return, a legal suite generally adds value and widens your buyer pool at resale, because it appeals to investors, multigenerational families and buyers who need the income to qualify. How much it adds depends on the market, the quality of the work and whether the paperwork exists. An unpermitted suite typically adds much less, and can subtract.

Listings describe basements in a variety of ways, and phrases like "in-law suite", "income potential" and "separate entrance" carry no legal meaning at all. Even "legal" in a listing is a claim, not evidence.

Ask for the permits and the final inspection sign-off, the electrical certificate, and registration documentation if the municipality requires it. Your lawyer can also make enquiries with the municipality about open permits and outstanding orders on the property.

If the income is part of how you are qualifying for the mortgage, confirm with your lender early what they will and will not count, because policies differ and some require the suite to be legal.

And if the unit is tenanted, understand what you are inheriting. Ontario's residential tenancy rules govern what you can and cannot do with an existing tenant, and that is a legal question worth putting to your lawyer before you make an offer, not after.

If your suite is legal, gather the permits, inspection sign-offs, electrical certificate and any registration before the listing goes up. Being able to produce them on request is what turns the claim into value. Without them, buyers discount it and their lawyers raise questions late in the deal.

If it is not legal, do not describe it as legal. Describe what it physically is and let the buyer draw their own conclusions. Misrepresenting a suite creates liability that outlasts the closing, and it is the kind of thing that unravels a deal at the worst moment.

Whether it is worth bringing an unpermitted suite up to standard before selling depends on what it would take. Sometimes it is a modest job. Sometimes it means underpinning a basement. Get a builder's assessment before you decide, and weigh it against simply pricing the home honestly without the claim.

Insurance. Your policy is written on the basis of how the property is used. An undisclosed rental unit can affect coverage, and finding that out after a fire is the worst possible time.

Enforcement. Municipalities act on complaints, and an order to bring the unit into compliance or cease using it is a real outcome. Neighbours complain more often than people expect, usually about parking.

Safety. Fire separation and egress requirements exist for a reason. A basement bedroom without a compliant exit is a genuine risk to whoever sleeps in it, and frequently that is a family member.

Resale. You cannot advertise it as legal, some lenders will not count the income, and informed buyers discount for the uncertainty.

Does my zoning permit a second unit, and what conditions apply?

Is there a parking requirement, and can my driveway satisfy it?

Does my basement have the ceiling height and window sizes the code requires?

What permits are needed, what do they cost and how long do they take?

Is registration required in my municipality, and what does it involve?

Will this trigger a development charge?

And for the contractor: have you completed permitted second units in this municipality, and can I see the sign-offs?