If you have ever come home after a long Toronto rain and found a dark line on the floor just inside the front door, the door itself is probably fine. What has failed is the narrow strip of hardware at the bottom of the opening, and sometimes the part of the frame that strip is fastened to.

Water at a door bottom is one of those faults that looks cosmetic for a season or two and then quietly turns into a carpentry bill. The jamb swells, the paint lifts, the latch stops lining up with the strike, and eventually the bottom few inches of the frame go soft enough to push a screwdriver through. Catching it while it is still a sweep-and-threshold job is the whole trick.

Work out where the water is actually getting in

There are three different leaks that all show up as a wet floor inside the entry, and they need three different repairs. Before anyone buys parts, it is worth spending ten minutes figuring out which one you have.

Under the slab: the sweep and the threshold

The sweep is the flexible strip screwed or slotted into the bottom edge of the door. It rides on the threshold, the metal or hardwood bar that crosses the opening at floor level. Most thresholds also carry a rubber or vinyl insert that the sweep presses against.

When the sweep stiffens, tears or wears a flat spot, and when that insert flattens out from years of foot traffic, there is nothing left to stop wind-driven rain from being pushed uphill into the house. The giveaway is a thin, fairly even line of water right at the doorway, worst during storms blowing from whichever direction the door faces. On a dry day, close the door and look along the bottom from inside with the hall light off. Daylight along the bottom edge means water during the next storm.

Around the slab: weatherstripping and the jamb

If the water shows up higher, on the hinge side or running down from the head, the compression weatherstripping in the jamb is the likelier culprit rather than anything at floor level. The paper test sorts this out quickly. Close the door on a sheet of paper and pull it out. If it slides free with no drag, the door is not compressing the seal at that point, and the fix is weatherstripping plus hinge and strike adjustment so the slab sits square in the opening again.

Under the threshold: the sill and the subfloor

This is the one people find last and the one that costs the most. The threshold is bedded on a sill, and that sill is supposed to be sealed and flashed so water runs out rather than in. When the caulk joint fails, or when the sill was never flashed into the sheathing properly, water bypasses the whole weatherstripping conversation and goes straight into the subfloor.

The signs are not subtle once you know them. The floor feels springy in the doorway. There is staining on the basement ceiling below the entry. On a warm day the hallway has a faintly earthy smell that nobody can place. At that point you are looking at door frame repair rather than a parts swap, because the rot has to come out before anything new is fastened down.

The parts people mix up on the phone

Sweep, door bottom, threshold

These three get used interchangeably and they are not the same thing. The sweep attaches to the door. The door bottom is a channel-style sweep that wraps the lower edge. The threshold is fixed to the floor and does not move with the door. Knowing which one you mean saves a trip, because a technician carrying thresholds and a technician carrying sweeps are not carrying the same van stock.

The sill pan nobody sees

Newer entry installations often sit on a moulded sill pan, a shallow tray under the whole door unit that catches anything getting past the threshold and drains it back outside. Older Toronto houses frequently have nothing there at all. If your door is original to a pre-war build, assume no pan until someone looks.

What a Toronto winter does to the same assembly

Rain is the obvious test, but winter is harder on the bottom of a door than any summer storm. Snow gets shovelled against the slab and sits there melting. Meltwater refreezes under the threshold overnight and lifts it a fraction each time. Road salt tracked in on boots chews at aluminum thresholds and at the steel skin on the lower rail of the door itself.

That freeze-thaw cycle is also why a door that sealed fine in November can be leaking by March without anyone touching it. The fasteners holding the threshold work loose, the joint between threshold and jamb opens up, and the first spring rain finds it.

What the repair usually involves

Scope climbs in steps, and an honest assessment should tell you which step you are on rather than starting at the top:

• Replace the sweep and the threshold insert. Cheapest outcome, and genuinely enough when the frame is sound.
• Replace the threshold itself, reseal the joint at both jambs, and re-bed it.
• Adjust hinges and the strike so the slab closes square and compresses the seal evenly along its length.
• Cut out and rebuild the bottom of the jamb where the wood has gone soft, then reinstall the hardware on sound material.
• Replace the door unit, which is where it lands if the bottom rail of the slab itself has rotted through.

Most calls that come in as a leaking entry end up in the first three steps. Houses where the leak was ignored for a few seasons are the ones that end up in the last two, which is the practical argument for booking door repair in Toronto while it still looks like a small problem.

When the door is not the problem at all

Sometimes the hardware is fine and the house is working against it. A porch that pitches back toward the threshold instead of away from it will beat any weatherstripping ever made. So will a downspout discharging a metre from the step, or a landing that has settled below the surrounding grade so it holds water like a tray.

Before replacing anything, stand outside during a rain and watch where the water goes. If it is running toward the door rather than away, that is the first thing to fix, and no amount of residential door repair will substitute for it.

Frequently asked questions

Can I just add a second sweep to stop the leak?

You can, and it occasionally works as a stopgap. More often the extra drag makes the door harder to close, people start slamming it, and the latch and hinges take the punishment instead. Fix the gap properly rather than padding it.

Why does my door leak only in heavy wind?

Because wind-driven rain is being pushed sideways and upward rather than falling straight down. A sweep that is adequate for vertical rain can be overwhelmed by pressure from the wrong direction. It is a normal pattern and it points at the bottom seal rather than the frame.

The threshold has adjustment screws. Should I raise it myself?

Raising an adjustable threshold is reasonable if the door still closes without force afterward. Go up a little at a time and keep testing the latch. If you have to lean on the door to get it to catch, you have gone too far and you are now wearing out the latch to solve a water problem.

How do I tell rot from water staining?

Press firmly into the suspect area with a screwdriver tip. Sound wood resists. Rot gives way, and once it does, sealing over it only traps moisture against the rest of the frame.

A wet floor inside the entry is early warning, not an emergency. It is also the cheapest moment in the whole lifecycle of that problem to deal with it.