When Building Envelopes Fail: Identifying the Source of Water Infiltration

Water infiltration is a common issue that affects buildings globally. When water penetrates a building envelope, it can lead to deterioration of structural elements, mold growth, wood-destroying insect infestations, and damage to interior finishes, posing health risks to occupants and requiring significant repair costs. Understanding how building envelopes function and where they commonly fail is essential for preventing water intrusion and ensuring proper building performance.

Building Envelopes

The building envelope is the physical barrier separating the interior of a building from the external environment. The building envelope includes the water-shedding surface, water resistive barrier, air barrier, vapor barrier, and thermal barrier systems within the roofs, walls, windows/doors, and foundation walls. Proper performance requires proper installation and maintenance, as well as continuity between these systems. While building codes provide minimum requirements for building weather protection, direction on proper installation of these systems is more often provided by industry organizations and manufacturers.

Signs of Water Infiltration

Identifying early indicators of water intrusion can help prevent extensive damage. Interior signs of recent/short-term infiltration often include moisture staining on interior finishes, cracking/delamination in finishes, localized mold growth, and active wetting/dripping.  Long-term and repeated infiltration can present as deteriorating finishes, failed ceiling finishes, and decayed sheathing/framing.

Interior damage does not always align directly with the location of the infiltration, especially within roof systems. Water can travel significant distances within roof and wall systems before manifesting on the interior. Because of this travel, accurately identifying the source of water infiltration typically requires a comprehensive investigation.

Roof Systems

When properly designed, installed, and maintained, roofing systems will effectively manage water through shedding and drainage. Roof systems are typically categorized as either steep-slope or low-slope, each with different design approaches for managing water.

Steep-slope roofs (generally defined as having a pitch greater than 4:12) are designed as hydrokinetic systems, meaning they are “water-shedding” systems that rely on an exterior cladding layer that is not watertight with an underlying waterproofing layer for water management. The water shedding components of these roof systems are commonly comprised of asphalt shingles, tiles, wood shakes, or metal panels, while the waterproofing component is comprised of sheet underlayment, such as felt paper. Water infiltration in steep-slope roofs often occurs at vulnerable transition points, such as valleys, rakes/eaves, intersections with vertical walls (elevations, chimneys, etc.), and at penetrations.

Low-slope roof systems (typically less than or equal to a 4:12 pitch) function differently from steep-slope roof systems. These systems are hydrostatic, meaning they are “water-holding” systems that rely on an exterior waterproof layer, such as TPO or EPDM membranes, and drainage to manage water. Similar to steep-slope systems, water infiltration through low-slope roof systems often occurs at vulnerable transition points rather than through the primary roof covering itself, such as at penetrations and interfaces with parapet walls. In addition, since low-slope roofs do not rapidly shed water, they can be sensitive to ponding, which can increase the load on the roof structure and/or accelerate material deterioration, both of which can produce openings at seams and allow water to enter.

Wall Systems

When properly designed, installed, and maintained, wall systems will effectively manage water through deflection and drainage. Three wall systems are typically encountered: mass wall, face-sealed, and drained wall, which are the most common encountered.

Drained wall systems utilize a water-deflecting cladding system that is not watertight with a drainage plane. The drainage plane consists of a Water Resistive Barrier (WRB) and flashings installed between the cladding and moisture-sensitive components of the wall. Water infiltration through drained wall systems typically occurs at discontinuities in the wall, such as window/door openings and penetrations. Proper installation, compatible materials, and maintenance are critical to the functioning of these systems.

Common Causes of Water Infiltration

Multiple potential paths for water infiltration through roof and wall systems exist. The most common paths for water infiltration encountered result from storm damage, installation deficiencies, deterioration/weathering, and deferred maintenance.

Storm damage can result from exposure to wind or hail and produce openings in the cladding systems. Such damage would not be expected to immediately result in infiltration unless the waterproofing layer was breached.

Improper flashing installation produces another path for infiltration. Flashing is intended to seal discontinuities between roof/wall materials and building elements. When flashing is incorrectly installed, water can bypass the building envelope and enter the interior.

Material deterioration and weathering are other frequent contributors to water intrusion. Materials used in roofing systems can dry out, shrink, and crack as they age, which produces openings that can become entry points for water. Additionally, fluctuations in temperature and humidity can result in withdrawn fasteners that can puncture the waterproofing component of roof and wall systems.

Deferred maintenance further increases the risk of infiltration. Debris accumulation, vegetation growth, and blocked roof drains can restrict water flow during heavy rain events and cause water to back up beneath roofing or wall materials.

Investigating Water Infiltration

A systematic investigation is essential for determining the true cause of water infiltration into the interior. The investigation typically begins with discussions with building owners/occupants to establish the history of the water infiltration issue and the background on the building. Additional supplemental interviews with other stakeholders, such as contractors, can produce additional information. These discussions are followed by an inspection of the interior to identify the locations and patterns of moisture damage as well as to establish a potential timeline of development. For roof water infiltration, an inspection of the attic or ceiling cavity is critical in establishing, as near as possible, the point of water infiltration. For water infiltration through walls, the removal of interior finishes can be useful in establishing the precise location of infiltration.

Following the inspection of the interior, an inspection of the exterior is conducted to identify potential water entry points. This inspection looks for openings and paths of infiltration in the exterior cladding, flashings, and waterproofing components. Instances of water infiltration where no clear openings are present can indicate the presence of an underlying flashing deficiency. In such cases, removal of cladding is typically required to confirm the presence and nature of the deficiency.  

Following the completion of the onsite investigation, weather research is commonly conducted to establish if the reported and observed conditions correlate with specific storm events. The gathered information and any additional research required are then compiled to produce conclusions on the cause of the reported water infiltration.

Conclusion

Preventing water infiltration ultimately depends on understanding how roof and wall systems are intended to function to ensure proper installation, long-term maintenance, and to identify potential damage. Even well-constructed roof and wall systems will deteriorate over time due to aging and/or environmental exposure, or can sustain damage, making periodic inspections essential. Early identification of damage and/or deterioration allows building owners to address minor issues before they develop into costly damage. By understanding how roofing and wall systems function and where they commonly fail, building owners and managers can make informed decisions that can maintain the functionality of these systems and mitigate the potential for damage. When water infiltration occurs, a structured forensic investigation can help identify the root cause of the infiltration.