DASMA TDS 197 - Water Infiltration Under the Bottom of a Sectional Garage Door

Water coming under the bottom of a garage door is one of the most common homeowner complaints. Many assume the door needs replacement or that the bottom seal failed. DASMA TDS 197 explains the real situation and what actually works.

What this data sheet says

DASMA TDS 197 states a key point that surprises many homeowners: residential sectional garage doors are not designed or tested to prevent water infiltration at the bottom. There is no ANSI/DASMA test standard for water resistance at the floor threshold for residential garage doors. The bottom seal reduces air infiltration and limits light gaps; it is not a watertight barrier.

"Residential sectional garage doors are not designed to prevent water infiltration at the floor. The bottom seal is intended to reduce air infiltration and dirt entry, not to provide a watertight seal."

The TDS identifies the main causes of water entry under the door:

• Floor slope toward the door: a floor that pitches toward the garage opening channels water to the threshold during rain.
• Driveway slope toward the opening: a driveway that runs downhill to the garage funnels water directly to the bottom seal during heavy rain or snowmelt.
• Worn or damaged bottom seal: a bottom seal that has cracked, torn, or lost its compression no longer contacts the floor evenly, leaving gaps.
• Uneven floor surface: a buckled or settled concrete apron leaves low spots that collect water at the threshold.
• Wind-driven rain: rain entering at an angle under the door travels across the floor and appears inside the garage well away from the door.

The TDS recommends threshold seals (rubber or aluminum dam strips bonded to the floor at the threshold) and proper grading as the primary solutions. A threshold seal is the only product that creates an actual barrier between the door bottom and the floor.

When it applies

Water infiltration under garage doors is a frequent complaint in Denver, particularly in spring when snow melt combines with heavy afternoon thunderstorms. Two specific conditions make it more common on the Front Range:

Snowmelt pooling. After a winter storm, snow that accumulates against the garage door face melts and saturates the threshold area over several hours. If the driveway slopes toward the garage, that melt water drains toward the opening rather than away from it.

Hail and heavy convective rain. Colorado's Front Range experiences intense summer thunderstorms that can drop an inch or more of rain in 30 minutes. Wind-driven rain at those intensities can push water under any bottom seal that does not have a threshold dam.

What this means for you

A new door will not fix a water infiltration problem if the cause is floor slope or driveway grade. If the floor or driveway pitches toward the door, water will enter regardless of bottom seal quality or door model. Address the drainage first.

A threshold seal is the most cost-effective fix. A rubber or aluminum threshold strip costs significantly less than a door replacement and addresses the actual cause: the gap between the door bottom and the floor when the door is closed.

Replace the bottom seal if it is worn or cracked. A bottom seal in poor condition lets water in even without directional drainage issues. Replacing the seal is a straightforward repair and costs a small fraction of door replacement.

G Brothers replaces bottom seals and installs threshold seals throughout the Denver metro area and Front Range. We can also assess floor slope and drainage issues during a service call.

Full text and source

Download DASMA TDS 197 from the official TDS index at https://www.dasma.com/technical-data-sheets/.

This entry covers water infiltration at the bottom of residential sectional garage doors. Condensation on door panels (moisture from humidity, not rain) is a separate topic addressed in DASMA TDS 195.