Replacing a front entrance is one of the few home projects where the measuring is harder than the installing. Get the numbers wrong and you are either shimming a gap you will feel every January, or waiting three weeks for a re-order. Get them right and the job is a day.
This is the practical version — what actually gets measured, what the spec sheet terms mean, and when in the year to schedule it.
First decide: slab, insert, or full unit
Almost every disappointing entrance replacement traces back to choosing the wrong scope. There are three, and they are not interchangeable.
Slab only
Just the door leaf. It reuses your existing frame, hinges and threshold. This works only when the frame is square, plumb, and free of rot, and when you are matching the existing hinge locations and hardware preps exactly. It is the cheapest option and the one most likely to disappoint, because a new slab in a tired frame still drafts and still binds.
Pre-hung insert
The door comes already hung in a new jamb, with hinges and bore already done. The existing exterior brickmould and interior casing usually stay. This is the standard residential replacement and the right answer in most cases.
Full frame replacement
Everything comes out to the rough opening — jamb, threshold, sill. This is what you need when there is rot at the sill, water damage in the subfloor, or when you are changing the opening size or adding sidelites. It costs more and takes longer, and it is the only option that actually fixes a leaking entrance.
The honest test: press a screwdriver into the bottom 6 inches of the jamb on both sides and into the sill. If it sinks in, you need a full frame, and no slab or insert will save you. This is where a proper site assessment before the entrance door replacement is quoted pays for itself.
How to measure it properly
If you are getting quotes, having accurate numbers ready makes every conversation faster and stops suppliers from quoting different things.
The door slab
Measure width and height of the leaf itself, and its thickness. Standard exterior thickness in Canada is 1 3/4 inches. Common widths are 30, 32, 34 and 36 inches, with 36 being the usual for a main entrance. Height is almost always 80 inches, occasionally 96.
The rough opening
This is the framed hole in the wall, not the door. To find it you need to pull the interior casing on one side. Measure width and height between the framing members, and the wall thickness from interior drywall face to exterior sheathing face — that last number is the jamb depth, and it is the one people forget. Ontario walls run anywhere from 4 9/16 to 6 9/16 inches of jamb depth depending on the age of the house and whether it was ever re-insulated.
Swing direction
Stand outside, facing the door. If the hinges are on your right, it is a right-hand door. This convention gets mixed up constantly, so state it as “hinges on the right as viewed from outside” on any order — it removes all ambiguity.
Square, plumb and level
Measure both diagonals of the opening. If they differ by more than about 1/4 inch, the opening is racked and needs correcting during install. Check the sill for level and both jambs for plumb. An out-of-square opening is not a reason to cancel the job, but it is a reason nobody should quote it sight-unseen.
Spec decisions that matter in a GTA winter
Material
Fibreglass is the default for a reason — it does not swell, warp or rot, it takes a wood-grain finish convincingly, and its insulating core outperforms wood and steel. It is the right choice for a south or west-facing entrance that takes sun and weather.
Steel is the value option and dents. A dent in a steel skin is permanent and cannot be filled convincingly. It is fine for a sheltered entrance or a side door.
Wood looks best and costs the most in maintenance. It needs refinishing on a schedule and it moves with the seasons. Worth it for a heritage-appropriate frontage, not worth it for a door that takes direct weather.
Glazing
Every square inch of glass in the door is a thermal weak point and a security consideration. If you want light, a narrow lite or a transom above the door gives you daylight without putting glass beside the lock. Any glass within arm’s reach of the deadbolt should be laminated, not just double-glazed.
The threshold and sill
This is the part nobody discusses at the quote stage and everyone complains about afterward. An adjustable-height threshold with a composite sill substrate is worth specifying. Wood sill substrates are the single most common rot point on a Toronto entrance, because that is where meltwater sits every March.
Hardware prep
Decide before ordering whether you want a standard bore for a knob plus deadbolt, or a multipoint lock. Multipoint locks — which throw bolts at the top, middle and bottom of the leaf — seal noticeably better and are much harder to force, but the prep has to be done at the factory. It cannot be added later.
Timing the job
The opening is exposed for a few hours during a pre-hung swap, longer for a full frame. Practical scheduling notes for the GTA:
- Best window: late spring through early fall. Sealants and foam cure properly, and an exposed opening for half a day is a non-event.
- Winter installs are possible but need cold-weather sealant and a contractor who will manage the exposure. Plan for it, do not improvise it.
- Order lead time is the real constraint, not install time. Custom sizes, non-standard jamb depths, multipoint hardware and factory finishes all extend it. Order well ahead of when you want it in.
- Do not schedule it the same week as flooring. Interior floor height changes the threshold calculation.
If the current door still latches and locks, there is no urgency — plan it properly. If it does not, that changes things: an entrance that cannot be secured is a same-day problem, and interim residential door repair to make it lockable is usually worth doing while you wait for the replacement to arrive.
Questions worth asking your installer
- Is the old frame coming out, or is this an insert into the existing jamb?
- What is going in behind the brickmould for water management — flashing, sill pan, or just caulk? (Caulk alone is not a water management strategy.)
- Will the opening be shimmed and re-squared, or is the unit going in as-found?
- Who is responsible for the interior casing and the exterior trim reinstatement?
- Is disposal of the old unit included?
The answers separate a proper door installation from a fast one. The flashing question in particular is the difference between a door that is dry in ten years and one that is rotting at the sill in three.
Frequently asked questions
Can I replace just the slab and keep my frame?
Only if the frame is square, plumb and sound, and the new slab matches the existing hinge and bore layout. Check the bottom of both jambs for softness first — that is where it usually fails.
What is jamb depth and why does it keep coming up?
It is the thickness of the frame, matching your wall thickness from interior drywall to exterior sheathing. Order it wrong and the frame either sits proud of the wall or leaves a gap the casing cannot cover.
Is fibreglass really better than steel?
For an exposed main entrance, yes — it will not dent, rust or telegraph thermal bridging, and it holds a finish longer. For a sheltered side entrance the difference matters much less.
How long is the house open during the install?
A pre-hung insert swap is typically a few hours of exposure. A full frame replacement with sill work is longer and is best scheduled for a mild, dry day.
Do I need a permit?
Replacing a door in an existing opening generally does not require one. Changing the size of the opening, or altering structure above it, generally does. Confirm with your municipality before the framing gets cut.
Summary
Measure the slab, the rough opening and the jamb depth. Check the sill for rot before choosing between slab, insert and full frame — that one check determines the whole scope. Specify fibreglass with a composite sill and a multipoint prep if the budget allows, and schedule the install for a mild stretch rather than the coldest week of the year.