Water coming under the garage door

Start with the honest limit

"Although sectional doors provide some protection against water infiltration, it is important to understand that they are not leak proof or watertight."

DASMA Technical Data Sheet #1503

Source: DASMA Technical Data Sheet #1503, Wind-Driven Rain and Sectional Garage Doors: Reasonable Expectations (PDF). Checked 31 August 2026.

DASMA goes further and explains why the expectation shifted. Garage doors were historically for vehicle access to parking and storage, and are now often used as access to living and entertaining space. Those are, in its words, "two entirely different use cases, which often come with entirely different sets of expectations regarding water infiltration". Standardised water-penetration tests exist for windows and entry doors. Building codes traditionally have not included water infiltration requirements for sectional doors, because of the nature and purpose of the product.

That is not an excuse for a leaky door. It is the frame for deciding what to spend.

Work out which of four things is happening

A. Water runs in along the floor during any rain, wind or not

This is a slab and grading problem, not a door problem. The water is arriving at the door line because the driveway or apron slopes towards the garage, and no gasket holds back standing water.

DASMA's answer is at the concrete, not the door: a slightly inclined lip or sill for the door to rest on, sloped 3 to 5 degrees, or a rectangular notch in the lip of the slab below slab grade for the door to close into, at least half an inch deep and sized to accommodate up to a 2-inch-wide garage door track and up to a 2-inch-thick door section so the door can fully close.

Source: DASMA Technical Data Sheet #197, Water Infiltration Under the Bottom of a Sectional Door (PDF), Door Solution and Figures 1 and 2. Checked 31 August 2026.

On an existing garage, cutting a notch or repouring an apron is real construction. The practical middle ground is a bonded threshold seal: a rubber ramp glued to the floor that the door closes against. It works, and it is the right answer for a lot of driveways. Two honest caveats: you drive over a small ramp, and if the apron slopes towards the garage it can hold a puddle on the outside instead of letting it drain. That is why we look at the driveway before recommending one.

B. Water only appears in a driving storm from one direction

This is wind-driven rain, and it is what TDS-1503 is about. DASMA lists three routes: water clinging to the face of the door drips in when the door is opened and the sections articulate; water retained in the section joints of a closed door "runs or wicks its way to the ends of the door, bypassing the perimeter door seal and entering the interior space", which it notes can produce a substantial amount of interior water; and strong wind driving rain through the sides, bottom and between sections, which without the right product and mitigation "can become a continuous stream in the interior space".

What actually helps here, from the same document: sections that overlap the jambs by an inch per side where the building allows it, routine trolley arm and top bracket adjustment, adjustable jamb brackets, enhanced perimeter seals where a manufacturer offers them, seals between sections on doors that offer them, and an aluminium or rubber threshold. It also flags roof drainage: buildings with large doors below sloped roofs with no gutters can get severe infiltration, and overhangs, awnings and rain ledges are worth considering, especially on west-facing openings.

C. Water appears with no rain at all

Then it is condensation or snowmelt off the car, not infiltration. DASMA describes garage door condensation as characteristic of a warm humid garage meeting a cold door surface rather than a product defect, and names a wet or snow-covered car as a source. Its control advice is ventilation to manage humidity, reducing garage air temperature in extreme cold, and tight seals around glazing and sections.

Source: DASMA Technical Data Sheet #195, Garage Doors and Condensation (PDF). Checked 31 August 2026.

D. Water comes in at one end of the door only

Almost always the door is not sitting level, or the slab is low at that end, so the seal is compressed at one end and floating at the other. A thicker gasket does not fix this; levelling the door or building up the low point does. Close the door, turn off the light and look along the bottom: an even line of daylight is a worn seal, and daylight at one end only is a levelling problem.

The five-minute diagnosis

1. When does it happen? Every rain, or only in a storm from one direction, or with no rain at all. That one answer eliminates two of the four causes.
2. Where does the water sit outside? Stand at the closed door in the rain and look at where the apron drains. If a puddle forms against the door, the slab is the problem.
3. Close the door and kill the lights. Look for daylight along the bottom, then up each side, then along the header.
4. Feel the seal. Flexible or hard and cracked? A hard gasket has stopped conforming to the floor.
5. Look at the ends. Is water tracking in at the corners rather than the middle? That is the wicking route DASMA describes, not a bottom-seal failure.

What we will and will not sell you

• Will: a new bottom seal and retainer where the gasket has failed, side and header stripping where daylight shows, door levelling, and a bonded threshold seal where the slab is genuinely the problem and a ramp suits the driveway.
• Will not: a second, thicker bottom seal on a door where the water is arriving because the driveway drains into the garage. It buys you one season and the same phone call next spring.

If the answer really is concrete work or grading, we will say so even though it is not work we do.

Why this corridor gets more of it

Two local factors. Lake-effect precipitation puts more water on the door face than the regional average, and freeze-thaw cycling either side of zero works on both the seal and the slab: water gets into a crack, freezes, opens it, and does it again. A slab lip that drained fine ten years ago can be a few millimetres out today.