Every autumn the same call pattern starts across Toronto: a front door that latched fine in September suddenly needs a shoulder, or a door that behaved all winter refuses to shut in July. The slab material is a large part of why — and it is the one decision a homeowner makes once and then lives with for twenty years.

Here is how the three common entry door materials actually behave in a climate that swings from roughly minus twenty to plus thirty, and what tends to go wrong with each one first.

What a Toronto winter actually does to a door

Three forces do most of the damage, and they work together rather than separately.

Thermal movement. Every material expands and contracts with temperature, but not at the same rate. A slab, its frame, its hinges and its glass all move differently, so the gaps between them change through the season. That is why a door can bind in August and rattle in February.

Moisture. Snow melts against the threshold, refreezes overnight, and works into any unsealed edge. Wherever water can sit, it eventually gets in.

Freeze-thaw cycling. Toronto does not simply stay cold — it crosses zero over and over. Water that has soaked into a material expands as it freezes, and each crossing pushes fibres, seams and finishes a little further apart. One deep freeze is survivable. It is the repetition that wears a door out.

Steel doors: hard shell, vulnerable core

A steel entry door is a thin steel skin bonded to an insulated foam core over a wood or composite stile-and-rail frame. It is the most impact-resistant of the three and the most dimensionally stable in heat. Steel does not swell, so a steel door rarely sticks in humid weather.

The weakness is the skin. Steel protects the core only as long as it is unbroken and coated. Scratch through the paint at the bottom edge with a shovel, and rust starts from that point. Because the core is foam, rust does not stay cosmetic for long: moisture gets behind the skin, the foam wicks it sideways, and the bottom few inches delaminate quietly for a couple of winters before anything shows from outside.

Where steel doors fail first

• The bottom edge and bottom corners, where salt and meltwater sit
• Dents that break the paint film — moving furniture, a kicked bottom rail
• Around lock and deadbolt bores, where the cut edge was never sealed after a hardware change
• Thermal bowing on a dark slab in full south or west sun, which shows as a gap at one corner

A dented or rusting steel slab is often repairable rather than a write-off — a bottom rail or a skin section can be dealt with without replacing the whole unit. Working out which side of that line a door falls on is exactly what a residential door repair visit is for.

Fiberglass doors: the stable middle ground

Fiberglass slabs are moulded composite skins over an insulated core. They do not rust, they do not drink water the way wood does, and they move less than either steel or wood across a temperature swing. For most Toronto homes that is the practical answer: the fewest seasonal adjustments, and a finish that tolerates sun better than paint on steel.

They are not maintenance-free. Fiberglass is rigid rather than tough — it resists dents but it can crack, and a crack does not dent back out. An impact at a corner, an over-tightened hardware screw, or a door slammed repeatedly against a stop can start a hairline that spreads.

Where fiberglass doors fail first

• Cracks radiating from hardware holes or from a corner impact
• Failed glazing seals in doors with decorative glass — fogging between the panes is the tell
• Finish wear on woodgrain-textured slabs that were stained rather than painted, especially on an unsheltered west elevation
• Weatherstrip compression set, which is not the door’s fault but reads to the homeowner like a draughty door

Wood doors: best looking, most demanding

A solid wood door is the only one of the three that can be refinished indefinitely, planed to fit, and repaired invisibly. It is also the only one that changes size with humidity rather than just temperature — which is precisely the Toronto problem. Wood takes on moisture in a humid July and gives it back in a dry, heated January, so a door sized perfectly in one season is tight in another.

Wood rewards maintenance and punishes neglect faster than the other two. A film finish that has begun to fail on the bottom rail is not a cosmetic issue. It is an open path into end grain.

Where wood doors fail first

• The bottom rail and the lower few inches of the stiles, where end grain sits in standing water
• Joint separation at the rail-to-stile glue lines, showing as a hairline that opens in winter
• Swelling along the latch edge — the door that needs a push in humid weather
• Paint or stain failure on south and west faces, sometimes within a few seasons

The frame decides more than the slab does

This is the part that gets skipped. Most “the door does not close right” calls are not slab problems at all. The frame has shifted, a hinge screw has lost its bite in soft jamb wood, the strike has moved relative to the latch, or the sill has settled. None of that is fixed by changing slab material, and all of it will make a brand-new door behave like an old one within a season.

So before spending on a new door, it is worth having the opening itself looked at. Rot at the base of a jamb, a spread frame after a forced entry, or a sill that no longer sits flat are their own repair — and door frame repair work often resolves the symptom the homeowner had blamed on the door.

Choosing without guessing

A few honest filters, in the order they actually matter:

How exposed is the opening?

A door under a deep porch on a north wall can be almost anything. A door in full west sun with no overhang narrows the field to fiberglass or a light-coloured steel — and wood only if the owner genuinely intends to maintain it.

How much does appearance matter?

If the answer is “a lot”, that points to wood or to a moulded fiberglass with real depth in the grain. Steel photographs flat, and no finish changes that.

Who uses the door, and how hard?

A door that takes strollers, bikes and deliveries all day benefits more from steel’s dent resistance than from fiberglass’s stability.

Is the frame sound?

If not, deal with that first, regardless of material. And if the current door is failing rather than merely old, a diagnosis beats a replacement quote — a door repair in Toronto assessment will say whether the slab, the frame, the hardware or the weatherstrip is the actual problem.

Frequently asked questions

Does a steel door really insulate better than wood?

An insulated steel or fiberglass slab has a higher centre-of-door R-value than solid wood, yes. But most heat loss at an entry door happens around the slab rather than through it — at the threshold, the weatherstrip and the frame-to-wall gap. A poorly fitted insulated door loses more than a well-fitted wood one.

Why does my door stick only in summer?

Almost always moisture uptake in a wood slab or wood frame, or a hinge that has sagged far enough that the latch edge now contacts the jamb. It is usually adjustable rather than a replacement.

Can a dented steel door be fixed, or does it have to be replaced?

It depends on whether the paint film is broken and whether the core behind it is still dry. A shallow dent with intact coating is cosmetic. A crease that has split the skin near the bottom of the door, where water sits, is a different conversation.

How soon does a new entry door need adjusting?

Expect a first seasonal check within about a year. Hinge screws settle, weatherstrip takes a compression set, and the house itself moves. That first adjustment is normal, not a defect.

Is it worth replacing just the slab and keeping the frame?

Sometimes — if the frame is square and sound and the new slab matches the existing hinge and bore layout. It is cheaper and less invasive. It is the wrong call if the frame is the thing that failed.