Understanding why doors leak

by Adrian Gerard Saldanha and David H. Nicastro, PE
Leaking exterior doors are a common problem affecting building owners and tenants, causing property damage, and requiring expensive repairs. Designers and builders are aware of the issue. Nevertheless, they continually struggle to prevent water infiltration through this fundamental building element.

Figure 1 catalogs the various routes taken by rain infiltrating a doorway. Most of the sources of leaks can be eliminated by better design and construction practices, but there remains an intractable problem that must be addressed by the industry.

This article focuses on accessible exterior swing doors used on office buildings, retail, multi-family residential, and institutional buildings for entrances, emergency exits, terraces, balconies, and patios. (Many of the leak sources outlined in this article would also apply to sliding glass doors. However, these doors’ sill tracks and higher allowed thresholds can provide enough of a step to prevent water entry, so they are not covered in detail in this article.) (The authors gratefully acknowledge the continuing support and leadership of David W. Fowler, PhD, PE—the faculty advisor for the research being performed at the Durability Lab, a testing center at the University of Texas at Austin.)

Causes of door leaks
There are many potential pathways for water to leak in through a door, but the biggest opening is, of course, the doorway itself. It may seem obvious, but a door left open, or one that cannot be closed tightly because of wear and tear, is a significant problem during a storm. Other leak risks are discussed in the following paragraphs.

Flashing
The frame’s perimeter must be integrated into the wall’s water-resistive barrier (WRB) through flexible flashings, or water will migrate around the outside of the door.

Perimeter joints
Proper sealant joint design and installation around the perimeter of a door frame is also essential to the building’s waterproofing. Designers should not solely rely on sealant joints to keep water out, but most buildings have critical sealant joints that must be maintained.

Hardware
Hinges, locks, and handles all present openings through the door and frame. The effectiveness of the hardware resisting water penetration varies with the design quality and fabrication of the door and frame. For example, lock strikes form large holes that must be internally sealed on hollow door frames.

Weatherstripping
Where the operable leaf of a door closes against a frame, the gap must have durable weatherstripping. Again, door manufacturers have varying quality of weatherstripping design and fabrication. Out-swing doors generally resist water penetration better than in-swing doors because their weatherstripping is inside. More importantly, they can be designed to close against a ‘bump’ in the threshold, compressing and baffling the weatherstripping.

In-set glazing
Glazing set into a door often relies on a simplistic perimeter bead of sealant. It should, however, employ robust waterproofing and drainage details similar to those provided on a window.

Threshold
Improperly bedded thresholds also provide a common entry point for water to seep below the door frame. Thresholds should be set in multiple continuous beads of sealant, and the fastener holes should be filled with sealant.

An accessible door threshold exposed to direct impinging rainfall can be a source of water penetration almost as large as an open door. This problem is already common, but quickly growing because codes and standards require nearly all exterior doors to be accessible—that is, a low threshold with no step and a low-slope walking surface. The authors frequently remind their clients that if people do not have to step up to come inside, neither does water. In other words, ‘accessible’ should be considered equally applicable to people and water.