May 1, 2013
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.
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.
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.
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.
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.
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.
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.
Since the Americans with Disabilities Act (ADA) first passed in 1990, codes and standards have evolved to improve accessibility for the disabled. Compliance with the new 2010 ADA Standards for Accessible Design has been required since March 15, 2012.
For doors along accessible routes, the following requirements pose a challenge for waterproofing:
In addition to the 2010 ADA Standards, accessibility is governed by the International Building Code (IBC), International Residential Code (IRC), the Fair Housing Act, and other national codes and standards, not to mention local amendments and ordinances. (See Building Codes Illustrated by Francis D.K. Ching and Steven R. Winkel, FAIA, PE [John Wiley & Sons, 2012].) These documents generally agree on the dimensional requirements for accessible doors, but they impose different criteria for where exceptions apply. Figure 2 maps the exceptions permitting the installation of a higher threshold or even a step, the latter of which completely solves the water penetration issue.
The American Architectural Manufacturers Association (AAMA) has played a leading role in recognizing the issue of water penetration over accessible door thresholds. The group stated:
The current issue concerning the threshold requirement is that the Department of Justice [DOJ] has issued a Fair Housing Act interpretation that requires doors to a deck or balcony from an apartment to meet the accessibility criteria for a Type B unit …This means thresholds higher than 1/2 or 3/4 inch [12 or 20 mm] above the interior floor level are not permitted, even though a step-down of up to 4 inches [102 mm] is permitted between the interior floor and the walking surface of the exterior deck or balcony … A threshold height of 3/4 inch is only sufficient to resist water infiltration in areas of low wind and exceptionally low rainfall. (For more information, read “AAMA Seeks Code Modification for ADA Threshold Height. AAMA Official Website.”)
AAMA proposed the following code change as a second exception to IBC 1008.1.7, which was approved by the International Code Council (ICC) during a code development hearing in 2012:
In Type B units, where Exception 5 to Section 1008.1.5 permits a 4 inch [102 mm] elevation change at the door, the threshold height on the exterior side of the door shall not exceed 4 3/4 inches [120 mm] in height above the exterior deck, patio or balcony for sliding doors or 4 1/2 inches [114 mm] above the exterior deck, patio or balcony for other doors. (Read “ICC Approves Revisions to IBC Egress Codes” on the Door & Window Manufacturer Magazine.)
This code change would allow another exception for the installation of a higher threshold, but only for a limited number of doors in multi-family construction. For that matter, all the exceptions apply to a small number of exterior doors, and they are often ignored. The authors have observed designers default to requiring accessible exterior doors (with their attendant waterproofing challenges) even where they may not be strictly required. This is rational given the complexity of code requirements, the risk of liability, and changing code interpretations (e.g. the Department of Justice [DOJ] requirement in the aforementioned AAMA citation). In other words, low thresholds are here to stay.
The authors’ research indicates there has yet to be an accurate measurement of how much water accumulates outside a door threshold during rainfall. Neither the average, typical rain nor the thousand-year flood should be the basis of design. However, as the climate warms and intense storms become more frequent, exterior doors should be better designed to resist water and require parameters that are more severe than the current leading standard methods.
Three standards specify a horizontal spray of five gallons of water per square foot per hour, which equates to a vertical rainfall rate of 203 mm (8 in.) hourly:
This amount would be an unprecedented flood if the rain continued for an entire hour, surpassing the roof drainage capacity of even the most stringent codes. However, the peak rainfall intensity over shorter durations is much higher and, of course, leakage at a marginal door threshold is most likely during these peak events. Spraying the water horizontally at a test door may appear to compensate for a lower volume of water, but the testing discussed later in this article shows that is not the most severe spray angle.
Accessible doors are required to have a low-slope walking surface outside, which compounds the leakage problem by creating a slow-draining surface. Two-percent slope is so small it can easily be erased by normal construction tolerances and slab distortion from post-tensioning, resulting in flat spots—or even negative slope toward the threshold.
Further, exterior doors typically are at the bottom of tall walls that increase the collection field for water that eventually cascades over the threshold. Water flows turbulently down walls, resulting in eddies and vortices. (See Turbulent Liquid Flow Down Vertical Walls by H.H. Belkin et al [Carnegie Institute of Technology, 1959].) Wind compounds this problem, pushing water against the door, but even on still days, water can stagnate in front of a door threshold due to the fluid dynamics required to turn the direction of the water flowing down the wall onto the low-slope walking surface.
The authors designed an experiment to simulate rainfall on an accessible door and the resulting ‘pile-up’ of water at the threshold. A 12-mm (½-in.) tall aluminum threshold was installed on a platform to recreate the geometry of a 2010 ADA Standards-compliant door and adjacent walkway. Rather than installing an actual door, clear Plexiglas was sealed to the top of the threshold to facilitate observations. The testing platform was hinged to allow varying the slope. Square-pattern nozzles uniformly sprayed water downward over the platform, simulating idealized vertical rainfall of varying intensity. An additional hinged nozzle simulated the water cascading down the building envelope, as well as angled rainfall.
At a downward spray rate of 203 mm (8 in.) per hour, nothing remarkable happened—the water easily drained off the threshold. In fact, the spray was so light it was difficult to fathom this would surpass the highest sustained rainfall in the United States. Even doubling the downward spray rate (to mimic short duration peak intensity storms) did not cause any accumulation.
Similarly, a horizontal spray equivalent to 203 mm per hour (similar to the standard water test methods) directed at the Plexiglas above the threshold did not cause much accumulation. As the water flowed down the ‘door’ and hit the bottom, the resulting rebound caused minor disturbances to the water flow. The rebound effects compounded the turbulence resulting from the sudden change in direction of the water flow from vertical to horizontal. This led to a momentary stagnation of water at the threshold, and caused the water to begin to accumulate.
However, turning the nozzle to spray the threshold at an angle caused water to accumulate up to 25 mm (1 in.) high, which causes more pressure than standard weatherstripping can withstand. As anyone caught in a downpour has noticed, storms blow rain at an angle, rather than vertically or horizontally. Unfortunately, this natural condition turns out to be the worst case for a marginal threshold. Due to the low slope, the vector of water directed toward the threshold overcame the water trying to flow away from the threshold by gravity. The tests were done with static conditions—introducing wind and wave action on the already submerged threshold would obviously exacerbate the leakage.
Increasing the slope of the platform made no measurable difference (even if this were allowed by code). Eddies were observed very close to the door threshold, caused mainly by the geometry at the interface of the threshold and platform. As the water falling in front of the threshold was already turbulent, this geometry further aggravated conditions. At about 0.3 m (1 ft) from the threshold, laminar flow returned, with very few flow instabilities observed for all experimentation conditions. Of course, this is too far from the threshold to be helpful—the turbulence at the threshold is all that matters to leakage.
Attention to detail in construction of exterior doorways can limit water infiltration through most of the paths previously outlined. Where accessible doors are required by code, high-quality door manufacturing design and fabrication can help with improved pressure resistance, hardware, and weatherstripping, as can selecting out-swing doors with a ‘bump’ threshold. However, accessible doors have an inherent weakness—low threshold and low slope. With only a 12-mm (½-in.) threshold height allowed, it is not reasonable to expect an accessible door to be watertight. Therefore, the authors believe the building design should protect exterior doors from direct impinging rainfall by alcoves, roofs, canopies, awnings, or overhangs.
To remedy leaking doors on buildings where adding protection was deemed aesthetically unacceptable, we have had success installing trench drains across doorways. However, these drains have to be surprisingly large— to be effective, they must instantly drain the water that would otherwise accumulate against the threshold. Just as accessibility requirements govern the threshold’s height and the adjacent walking surface’s slope, they also dictate ‘heel-proof’ grates have small holes instead of the large industrial trench grates that would drain faster.
It may seem obvious to recommend collaboration of all stakeholders to achieve project success, but for exterior doors it is essential. Issues related to waterproofing, accessibility, and aesthetics compete with each other, requiring a comprehensive, balanced approach to achieve
a leak-free, attractive, and code-compliant envelope. Ultimately, it is failure to collaborate that leads to finger-pointing when the doors leak.
Adrian Gerard Saldanha is completing his master’s degree in construction engineering and project management at the University of Texas at Austin (UT). He is a graduate research assistant in The Durability Lab—a testing center at UT established by Building Diagnostics Inc., to study the durability of building components, identifying factors causing premature failure. He can be contacted at firstname.lastname@example.org.
David H. Nicastro, PE, is the founder of Engineering Diagnostics Inc. and Building Diagnostics Inc.—firms specializing in the investigation of problems with existing buildings, designing remedies for those problems, and resolving disputes which arise from them. He is a licensed professional engineer, and leads the research being performed at The Durability Lab. Nicastro has published more than 50 articles on durability of building components. He can be reached by e-mail at email@example.com.
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