Most people treat a lock change like a hardware swap. Unscrew the old one, screw the new one in, done. On a house built in the last fifteen years that is usually how it goes. On a Toronto door that has been through forty winters, a few coats of paint and at least one previous owner with a drill, it goes differently.

The lock is the last part of the job. What decides whether the new hardware works is the hole pattern already in the door, the thickness of the slab, and whether the frame still holds the latch where the manufacturer assumed it would. Get those wrong and you end up with a lock that turns freely but does not actually secure anything.

Why an older door complicates a simple swap

Modern residential locksets are built to a small number of standard dimensions. Older doors were not always drilled to those standards, and many have been modified since. A door that once carried a mortise lock and was later converted to a cylindrical one often has a patched face, an oversized bore, or a latch pocket that was chiselled by hand.

None of that is fatal. It just means the measuring has to happen before anything is bought. Returning hardware because the backset was wrong is the most common wasted trip in this line of work.

The three measurements that decide everything

Backset

Backset is the distance from the edge of the door to the centre of the bore hole. Residential hardware in North America is normally made for 2 3/8 inch or 2 3/4 inch backset, and most retail locksets ship with an adjustable latch that covers both. Older doors, imported slabs and some commercial conversions sit outside that range. If the measurement lands somewhere unusual, the lockset has to be sourced to match rather than forced to fit.

Bore size and cross-bore

The face bore on a standard cylindrical lock is 2 1/8 inches, with a 1 inch cross-bore through the edge for the latch. An old door may have a smaller face bore from earlier hardware, or a larger one that someone opened up. A bore that is too small can be enlarged cleanly with the right hole saw and a jig. A bore that is already too large is the harder problem, and usually calls for a wrap plate or a different lock body rather than filler.

Door thickness

Standard exterior doors run about 1 3/4 inches thick. Interior slabs are closer to 1 3/8. Solid wood doors in older Toronto homes sometimes measure differently, and a lock whose spindle is too short for the slab will feel loose and wear out fast. Check the thickness at the lock position, not at the edge near a hinge, because a warped door will give you two different numbers.

The frame side matters as much as the door

Strike alignment

A new deadbolt that has to be lifted, leaned on or pulled toward you before the key turns is not a lock problem. It is an alignment problem. The bolt is hitting the strike plate off centre, and every turn of the key is grinding metal. Left alone it wears the cylinder and eventually the bolt stops retracting properly.

The fix is usually to reposition the strike, deepen the mortise pocket behind it, or shim the hinge side so the door closes square again. On many older homes this is where the real work is, and it is the part that gets skipped when hardware is installed in a hurry. If the jamb itself has moved, split or softened, the strike will not hold no matter how carefully it is positioned, and the frame needs attention first. That is the point where door frame repair comes before any new hardware goes on.

Screw length

The screws that ship with most deadbolts are short. They bite into the jamb only, not the framing behind it. Replacing them with longer screws that reach the stud is one of the cheapest security improvements available on any door, and it takes about two minutes. A reinforced strike plate with long screws does more against a kick-in than upgrading the cylinder does.

Grades, and what they actually tell you

Residential deadbolts are commonly rated under the ANSI/BHMA grading system, where Grade 1 is the most demanding specification and Grade 3 the least. The grade describes performance in standardized tests for cycles, strength and finish. It does not describe how well the lock was installed, and a Grade 1 deadbolt in a soft, misaligned jamb is weaker in practice than a Grade 2 in a properly reinforced one.

For a front entrance that is used daily, the middle of the range with a reinforced strike is a sensible baseline. For a side or garage entry door that is out of sight from the street, the strike and frame reinforcement matter more than the badge on the box.

Rekeying, keyed-alike sets and smart locks

If the existing hardware is in good condition and the only concern is who holds a key, rekeying the cylinder is usually the faster route. It keeps the hardware that already fits the door and changes what the old keys will open.

Keyed-alike sets make sense when a house has three or four exterior doors and the keyring has become unmanageable. They have to be ordered as a set or rekeyed together afterwards, so the decision is best made before anything is purchased.

Smart locks add a constraint most people discover late: many of them need a specific backset, a minimum door thickness, and enough flat surface on the interior face to mount the body. On a door with decorative moulding or a shallow stile, the interior unit may not sit flat. Measure the clear flat area before ordering, not after.

When it is worth calling someone

A straight like-for-like swap on a door that closes cleanly is a reasonable afternoon project. It stops being that when the bore is oversized, the door has dropped, the jamb is soft, or the existing hardware was a mortise unit. Those jobs need the door to be rehung or the frame rebuilt before hardware goes on, and doing them in the wrong order means paying twice.

If the door has already been forced, or a key snapped in the cylinder, the frame and strike almost always took damage too. That is a full assessment rather than a lock purchase, and it falls under residential door repair rather than a hardware change. For a straightforward replacement where the door is sound, a scheduled lock change in Toronto is quick and predictable.

Frequently asked questions

Can I change a lock without changing the handle?

Usually yes, if the deadbolt and handle are separate units. If they share a single escutcheon or are part of a handleset, both pieces normally have to be replaced together.

Do I need a locksmith or a door company?

A locksmith is the right call when the door and frame are sound and only the hardware is changing. A door company is the better call when the door sticks, the jamb has moved, or the strike no longer lines up, because the hardware is not the fault.

Will a new deadbolt stop a break-in?

It raises the effort required, but the weak point in most forced entries is the jamb, not the bolt. Reinforced strike plates and long screws into the framing do more than a higher-grade cylinder on its own.

How do I measure backset if the old lock is still installed?

Measure from the edge of the door to the centre of the existing bore hole with the lock in place. You do not need to remove anything to get that number.