Storefront Entrance Leaking at the Sill and Threshold: Where the Water Actually Gets In

Water at the threshold is almost never coming through the glass. It is coming under it, around it, or through a joint that was never sealed to shed water in the first place. That is the first thing to understand about a leaking storefront entrance in Los Angeles. Owners mop the floor inside, stare at the pane, and ask for new glass. The glass is usually fine. The leak lives in the bottom six inches of the system — the sill, the threshold, the door bottom, and the ground right outside the door.

Start outside: slope, drains, and water that has nowhere to go

Before you blame any part of the storefront, look at where the water outside is headed. A sidewalk, landing, or slab that slopes toward the building will deliver every rain — and every morning's hose-down from a neighboring business — straight to your threshold. Storefront systems are built to shed a normal amount of wind-driven rain. They are not built to hold back standing water pooled against the sill for hours.

Check for a clogged drain, a raised mat well, planters draining toward the entrance, and concrete that has settled so a low spot now sits at the door. If the floor inside is wet even when the door has not been opened during the rain, that points to water passing under or through the sill assembly itself. If it is wettest right after customers come and go, the door sweep and the traffic pattern are part of the story. The pattern of the wet floor is evidence. Photograph it before anyone mops it up.

The sill and threshold: bedding matters more than caulk on top

A threshold is supposed to be bedded — set in sealant so there is no open path underneath it — and tied into the sill and jambs so water that reaches it is turned back outside. When a threshold is just screwed down dry, or the bedding has cracked and pulled away after years of foot traffic and carts, water runs under it by capillary action and shows up inside, sometimes several feet from the door, where it has traveled along the slab or under flooring.

The same is true of a storefront sill flashing or sub-sill. Many systems are designed to collect a small amount of water in the sill channel and weep it back outside through weep holes. Block those weeps with dirt, sealant smeared over them during a well-meaning repair, or debris from the street, and the channel fills and spills inward instead. I have seen entrances "fixed" three times with more caulk on the outside while the actual problem was a sealed-over weep and a sill with no end dams at its corners. Adding sealant in the wrong place makes a leaking sill worse, not better.

Frame corners and joints: the quiet path in

Storefront framing is assembled from verticals and horizontals joined at corners. Those joints need to be sealed as the system is built, not just pointed up from outside afterward. At the bottom corners, where a jamb meets the sill, a failed or missing joint seal lets wind-driven rain enter the framing and exit inside at the floor. The stain or puddle appears at the corner post, so people assume the glass above it is leaking. Usually the glazing gasket above is dry and the joint below it is open.

On our storefronts and curtain wall service calls, we trace this with a controlled water test: one area at a time, low to high, with someone watching inside. Spraying the whole entrance with a hose at once tells you nothing — everything gets wet and every suspect looks guilty. Testing the threshold alone, then the corner joints, then the door perimeter, then the glass, in that order, isolates the actual path. Any repair quoted without that kind of tracing is a guess.

The door itself: sweep, gap, and alignment

• Worn or missing door sweep. The sweep at the bottom of the door is a wear part. When it is torn, shortened, or gone, rain and wash water pass straight under the door, and so does air conditioning the rest of the year.
• Excessive bottom gap. A door that has sagged on its pivots or hinges, or a threshold that has worn or been replaced at a different height, can leave a gap no sweep can cover. The fix is alignment and threshold height, not a longer strip of rubber.
• Failed perimeter weatherstripping. Cracked or compressed seals at the head and jambs let wind drive rain around the door leaf, where it runs down and pools at the sill, masquerading as a sill leak.
• All-glass doors. A frameless entrance has no frame to seal against in the same way a framed door does. It will pass more wind-driven water by design. If an all-glass entrance fronts the street and the weather, some of that trade-off was chosen with the look.

None of those parts is expensive on its own. What makes entrance leaks linger is replacing one of them at random, declaring victory, and waiting for the next rain to grade the work.

What a lasting fix actually involves

A proper repair starts with the water test and a look under and behind the threshold, not with a caulk gun. Depending on what that finds, the work is reseating or replacing the threshold on a full bed of sealant, resealing the sill corners and frame joints, clearing or restoring weep paths, replacing the sweep and weatherstripping, and realigning the door so it closes against its seals evenly. Where the outside slope is the root cause, the honest answer includes correcting the drainage or adding a drain at the entrance — no glazing repair can out-perform a slab that funnels water at the door.

One caution on timing: in Los Angeles, long dry months hide these leaks, and the first real rain finds them all at once. If your entrance leaked last winter, it has not healed over the summer. The sealant is older, the sweep is more worn, and the joint is more open. Getting the tracing and repair done in dry weather, when the system can be opened up, resealed properly, and tested on your terms, is far cheaper than an emergency call during a storm with stock and flooring at risk.

If water is coming in, do not start by asking for new glass. Start by asking where, exactly, the water gets in — and expect the person answering to show you the path. That answer decides whether you need a sweep, a threshold reset, joint work, drainage work, or some combination, and it keeps you from paying for the same leak twice.