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Building facade failures

Kimball J. BeasleyBEng, MBA, PE, FASCESenior Principal, Wiss, Janney, Elstner Associates, Princeton, NJ, USA

Building facades serve mainly to protect occupants and contents from the elements. Failure of the building envelope (i.e.

walls, roof and windows) to function as intended usually has a significant impact on the serviceability of the building.

Roofs and windows periodically fail and are replaced; however, the building facade is expected to endure the forces of

nature for the service life of the building. The increasing complexity of modern buildings, combined with decreasing

tolerance for undesirable performance of building systems, has resulted in an ever increasing frequency of building

facade failures. This paper addresses common serviceability and performance problems associated with various types of

building facades. Methods and tools useful for investigation of facade failures are discussed. The paper is not intended

to be a comprehensive guide for the forensic investigator, but is offered as an aid to help recognise symptoms and

evaluate conditions that underlie common building facade failures. The types of building facades and investigation

methods discussed in this paper are primarily based on the authors experience within the USA.

1. IntroductionCollapse of building walls usually makes the evening news.

Less dramatic facade failures such as water leaks are less

newsworthy but far more common. Such serviceability failures

are also collectively far more costly than wall collapses.

Physical evidence of building facade failures may often include

cracking, bulging and deterioration of the building walls. These

conditions may result from a wide variety of forces acting on or

within the building walls, or from interactions between the

facade and other building elements. A clear understanding of

the characteristics and vulnerabilities of the facade system is

needed to understand why it failed to perform as intended.

2. Types of facadesEarly buildings often employed massive masonry walls that

carried structural loads to the foundation as well as enclosing

the building. Within the last 150 years, the development of the

skeleton frame structural system has resulted in exterior wall

facades being physically and functionally separated from the

main buildings structural system.

Contemporary cladding systems, such as thin brick, metal, tile

or stone veneers, are much lighter and thinner than traditional

wall systems. These facades must be designed and connected to

the back-up wall or building structure in a manner to support

their own weight and to resist any imposed forces with an

adequate factor of safety. Facade support systems may

incorporate flexible connections that secure the facade to the

structure without inadvertently imposing undesirable restraints

against natural building or facade movements.

Water leakage and condensation management systems vary

depending on the wall and cladding system. Mass masonry

walls are intended to absorb water before it reaches the interior

and allow it to evaporate over time. Contemporary walls may

deflect rainwater at the wall surface (surface barrier) or utilise

an internal cavity and flashing system that provides two lines

of defence against water infiltration. The contemporary rain

screen wall system allows water through open joints in the

facade where it is directed to the exterior by a membrane

within the wall.

3. Forces of nature

Building facades must resist a variety of externally and

internally imposed forces. External forces include lateral loads

from wind or earthquakes and vertical loads from the facades

own weight. Internally imposed forces may result from

expanding elements in the wall (e.g. ice formation or corrosion

scale) or by restrained planar movements between the facade

and the walls substrate or the buildings structural frame (e.g.

thermal expansion or concrete shrinkage).

External loads are usually well understood and the response of

the facade to these forces is predictable. Wind, gravity and

even earthquake loads can be quantified and analysed. The

facade system should be designed to accommodate such forces.

However, internal wall forces are more complex and may vary

substantially from structure to structure and even within the

same structure depending on the materials and component

configurations. Internal wall and facade forces include

restrained thermal expansion and contraction of the facade,

or accumulated moisture expansion of fired-clay facade

materials such as brick or tile following installation.Structural building movements can also impose unexpected

forces on the wall or facades. Deflection of a relatively flexible

steel building frame or creep shrinkage of the buildings

Forensic Engineering

Volume 165 Issue FE1


Beasley

Proceedings of the Institution Civil Engineers

Forensic Engineering 165 February 2012 Issue FE1

Pages 1319 http://dx.doi.org/10.1680/feng.2012.165.1.13

Paper 1100020

Received 07/06/2011 Accepted 08/09/2011

Keywords: brickwork & masonry/buildings, structures &

design/failures

ice | proceedings ICE Publishing: All rights reserved

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structural concrete frame can compress or pinch the facade at

rigid connections or support points. Such internal wall forces

are often overlooked or misunderstood during design and

construction, leading to facades that are susceptible to failure.

Failure can also occur from gradual loss of strength or erosion

of materials used to support the facade. Figure 1 shows a

building wall that collapsed from gradual erosion and

displacement of a load-bearing wall.

Water can be a formidable force of nature. While many

exterior wall systems are designed to manage some water entry,

excessive water penetration through the facade can cause a

variety of problems. Aside from the obvious difficultiesassociated with water leakage to the interior, excessive water

penetration and retention in the wall can lead to corrosion of

embedded ferrous metal, which both reduces the strength of

the metal element and produces corrosion scale that, if

confined, can result in spalls, displacements or cracks in the

surrounding masonry. When saturated with water and

subjected to cyclic freezing and thawing temperatures, certain

absorptive materials (e.g. concrete, mortar, fired-clay masonry)

can deteriorate over time. Furthermore, pockets of water

trapped in the wall can freeze, expand and crack or displace the

adjacent masonry by a phenomenon known as ice lensing.

Water trapped in the wall can deteriorate back-up sheathing

materials and can reduce the effectiveness of fibre insulation.

Figure 2 illustrates spalling of a concrete surface from

expansive corrosion of embedded reinforcing steel.

4. Facade failures

A building facade must perform a wide range of functions. It is

required to control light entry and keep out rain, cold, heat and

noise. It also must resist deterioration, cracking, detachment

and various other mechanisms of distress. Facades also define

a buildings architectural character, so they must retain their

aesthetic qualities for the life of the building. Any facade that

cannot perform all of these functions satisfactorily has failed.

Failure is often a misunderstood term in the context of

building walls. Collapse of a wall is an obvious failure.

However, a facade that appears to be intact but would not be

Figure 1. Building collapse from erosion and displacement of a

load-bearing wall Figure 2. Concrete spalling from corroding reinforcing steel




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able to sustain normal wind loads because of missing or

corroded anchors behind the surface has also failed. In fact,

such latent facade failures can be more insidious because they

are difficult to detect and may cause facades to detach and

collapse without warning. Poor performance of building

facades from water leaks or unsightly cracks is far more

common than failures that result in a catastrophic collapse that

claims life and damages property.

Facades are subjected to a wide variety of forces and exposures

that may lead to failure. Corrosion or deterioration of cladding

or connection materials undermines the ability of the facade to

resist normal loads. External forces of a magnitude ororientation not anticipated in design can damage the facade

or its support system. Defects introduced during construction

or prefabrication of a wall system may also affect the facades

ability to perform as designed.

Since most contemporary facades are considered non-

structural building elements, the initial responsibility for design

of a facade support system may be shared between a design

architect and a structural engineer. Often, a project designer

and project engineer will provide conceptual drawings for the

facade support but rely on the contractors shop drawings to

detail or refine the connections and supporting elements, which

must accommodate wind and seismic loads as well as structural

deflections. The facade attachment design responsibility may

reside with the fabricators engineer who is engaged by the

contractor. This fragmenting of responsibility and the resulting

potential lack of coordination are also frequent indirect

contributors to facade failures.

Failure of a building facade to control water leaks is one of the

most common building facade failures. With traditional

masonry walls, water leakage to the interior is minimised

because the solid masonry mass will absorb water and

gradually expel it as vapour. With cavity wall systems, water

that penetrates the facade must be conveyed to internal

through-wall flashings and weep holes via wall cavities.

Blocked or bridged wall cavities, breached or poorly config-

ured flashings and clogged or incorrectly positioned weep holes

may individually or collectively result in water leakage to the

interior. Certain types of construction or architectural features

create walls that are more vulnerable to water leakage. Walls

that are positioned directly above occupied spaces (i.e. rising

walls) tend to result in immediate water leaks if the through-

wall flashings fail. Increased water exposure from poorly

sloped window sills or from roofs or scuppers that pitch water

onto wall surfaces create a greater potential for water leakage.

Surface-sealed facades lack redundancy to protect againstleakage. The primary water barrier in some rain screen wall

systems is buried beneath the facade and cannot be easily

accessed for maintenance or repair. Inappropriate, low vapour

permeable water-resistive barriers behind the facade may resultin wrong-side vapour barriers that lead to condensation within

the wall or inhibit vapour transmission and facade drying.

5. Investigating facade failuresDetermining why a facade failure occurred requires knowledge

of the facade system and its connection and support elements,

the underlying structural system and the environment and

forces acting on the facade. Information on the conditions

surrounding the failure is gained from documents and research

that describe design requirements, maintenance/repair history

and loads at the time of failure. This information helps to

establish the background circumstances leading to the failure.The type and scope of investigation performed depends on the

nature, severity and consequences of the facade failure. Facade

failure investigations often involve the fundamental steps of

(a) gathering basic information on the circumstances sur-

rounding the failure

(b) conducting initial visual assessments of conditions at the

site

(c) collecting data on site through observations, measure-

ments and testing

(d) analysing data and developing failure hypotheses

(e) reporting facts, methods, findings and opinions of the

failure cause(s).

5.1 Data collection

Acquiring information relevant to a facade failure usually

requires a review of existing published materials and observa-

tion of conditions at the failure site.

5.1.1 Document review

Review of available relevant drawings, specifications, prior

reports, photographs, media coverage, etc. can usually provide

background information on the design of the facade system

and conditions or exposure at the time of the failure. Since as-

built construction often deviates significantly from the designdocuments, confirmation by direct observation is necessary.

5.1.2 Aerial and birds-eye satellite images

Recent advancements in mapping websites such as Bing maps

or Google street view can provide valuable tools for

investigating facade failures. Detailed photographic images

that may have been taken from a few months to several years

ago can show the conditions of building facades and

surrounding buildings prior to a failure or collapse.

5.1.3 Visual inspection and condition surveys

Inspection methods can range from cursory visual andbinocular surveys to detailed examination, probe openings

and testing or monitoring. Inspection may help to identify and

document the severity or nature of existing facade distress in




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order to assess possible causes of the failure. Facade cracking,bulging, delamination or leaking usually occurs with patterns

or features that can offer clues to their causes. Periodic

inspection can also serve to determine the rate of deterioration.

A visual condition survey of building facades usually involves

documenting conditions by annotating observations on build-

ing elevation drawings and high-resolution photographs.

The condition survey objectives often include determining the

location and nature of distress, identifying patterns of

deterioration, establishing potential scope and locations for

repair work, and developing baseline conditions for compar-

ison with subsequent inspections. Binoculars or telephotoequipment are useful to facilitate observation of facade

conditions on tall buildings. The condition survey drawings

offer a valuable method of identifying the nature and location

of facade damage and visualising the overall patterns of

distress and force paths. Conditions identified during a survey

will usually help to determine the need for and type of

additional studies and field or laboratory tests.

5.1.4 Detailed inspection

Close-up visual examination of collapsed and damaged facades

and adjacent areas is essential to gain knowledge of as-built

construction. Safe access for such close-up examination may be

from roof setbacks, balconies, swing or pipe scaffolding,

bucket truck, personnel lift or rappelling. Examination of

subsurface wall elements, facade connections and adjacent

construction requires exploratory probe openings or inspec-

tions via borescope or micro-miniature camera device (see

Section 5.2). Contractor assistance is required for close-up wallaccess and for making and patching probe openings. Various

measurements (dimensions of typical wall panels, masonry

units, joint widths, displacements, crack widths, etc.) need to

be taken in detailed inspections. Such measurements also help

to confirm whether the original construction documents

accurately represent as-built conditions.

5.2 Investigation tools

A wide variety of simple, traditional or advanced new

equipment is available to the investigator. The tools and

equipment required to investigate facade failures vary with the

type of failure being investigated. However, certain simpletools are common to most investigations; these include high-

resolution digital cameras, tape measures, binoculars, flash-

lights, mirrors, sounding hammers, etc. Tools that are more

sophisticated, more accurate or dedicated to a specific purpose

may also be used. These may include three-dimensional (3D)

laser scanning, infrared thermography, strain relief testing, etc.

5.2.1 Measurements

Simple measuring devices include tape measures, calipers,

levels and optical crack comparators. Measurements of move-

ment over time can be made using devices such as reticule

gauges, scratch gauges or electronic displacement transducers.

Figure 3 shows a common movement gauge device. A variety

of devices is also available for temperature and moisture

measurements. More sophisticated devices or systems may be

used to measure precise relative positions of visible building

facade areas relative to a reference point. Newer technologies

Figure 3. Reticule gauge used to measure relative movement




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include global positioning, electronic distance measuring

systems and laser scanning.

5.2.2 Photographic equipment

A high-quality digital camera with an adequate optical zoom

feature is an essential investigation tool; a video camera may be

useful if conditions at the site are changing rapidly. A

professional photography service may be needed for aerial

views or specialised high-quality photography.

5.2.3 Laser scanning

3D laser scanning technology involves scanning the building

facade surface from several vantage points with infrared and/orlaser light. The precise position of discrete points on the facade

surface is determined by combining the scans to produce a grid

of measurements. The resulting high-resolution surface map

is useful for identifying displacements, outlining facade

features or establishing a baseline drawing for future surveys

or comparative measurements.

5.2.4 Infrared thermography

Under certain conditions, infrared thermography can be used

to detect discontinuities or connection failures behind a

building facade. Slight variations in the facade surface

temperature measured via an infrared thermography camera

may signify a decrease or increase in thermal conductivity of

the wall. This variance can result from conductivity interrup-

tions from delamination or dislocated facade attachments, or

from increased conductivity from wet insulation that can cause

thermal short circuits.

5.2.5 Borescope or micro camera

A borescope or a micro-miniature camera can be used to view

conditions behind a facade surface. A borescopes small-

diameter (6 or 8 mm) metal tube or camera head is inserted

through a small hole or joint. The device usually includes a

light source and digital image capture feature.

5.2.6 Metal detection

The location and size of embedded steel reinforcement and steel

support or anchor elements beneath a wall surface may need to

be known to fully evaluate the facade system. A conventional

metal detector can detect the presence of metal and a

pachometer can be used to measure the location, orientation,

size or depth of underlying metal reinforcement or anchors.

5.2.7 Strain relief

Strain relief testing can be used to measure compressive stresses

locked into a masonry facade. Such testing involves adhering

carbon-filament strain gauges to the wall surface (see Figure 4)and then releasing the in situ stress by saw cutting around the

instrumented area of the facade. The strain value is measured

before and after saw cutting and the in situ residual facade

stress is computed by multiplying the modulus of elasticity of

the facade material by the measured strain change. This

technique is particularly useful to determine the potential forcracking or compression buckling failure of a masonry facade.

5.3 Field testing

Testing representative building facade elements in place can

provide an effective means of evaluating the physical char-

acteristics and conditions of building facades.

5.3.1 Load testing

The behaviour of facade or wall elements under controlled load

application often helps to establish their strength, deflection

characteristics or mode of failure. Point or uniform loads can

be applied with hydraulic or pneumatic systems. Strains anddeflections can be measured electronically and computerised

data acquisition systems can collect, store and display load,

stress and deflection data rapidly during a test.

Figure 4. Carbon filament strain gauge adhered to a facade

surface




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5.3.2 Models and mock-upsConstruction and testing of models of the subject wall or

facade system and repair mock-ups can help investigators

understand the behaviour of complex building facade systems

and evaluate the efficacy of repairs. Service loads can be

duplicated while monitoring displacements and strains under

controlled conditions. Loads can be increased to test the mode

of failure. Forces may be focused on connections or facade

components of concern. As an investigative tool, duplicating

an actual failure with a mock-up of the as-built elements can

also provide compelling verification of a failure hypothesis.

5.3.3 Water penetration testing

Accurately identifying, tracking and quantifying water leakage

into and through an exterior building wall requires a careful and

systematic testing approach. Several standards provide controlled

water penetration testing methods for diagnostic tools or proof

testing to assess a facades compliance with project specifications,

standards or codes. Among the standards commonly used for

diagnostic water leak testing and assessment of water penetration

resistance of wall and fenestration system joints, gaskets and

sealant detailing are AAMA 501.2 (AAMA, 2003) and ASTM

E1105 (ASTM, 2000). AAMA 501.2 is intended for testing newly

installed operable windows and doors. AAMA 511-08 is used for

systematically investigating and recreating known water leakage

in a fenestration system (AAMA, 2008).

5.4 Laboratory testing

Many laboratory tests are available to determine the properties

of facade materials, the nature of deterioration and the

effectiveness of remedial measures. The majority of the US

standards cited in the following have similar or equivalent

European standards such as those developed and maintained

by the European Committee for Standardisation (CEN), the

British Standards Institution (BSI) and the German Institute

for Standardisation (DIN).

5.4.1 Physical testing

Physical properties of facade materials can be approximated by

load testing specimens representative of the subject wall in a

controlled laboratory environment. These tests are generally

used to establish strength and mechanical characteristics of the

wall or facade materials. Compression or flexural testing can

be performed on a statistically representative number of

masonry, concrete or other samples removed from the building

or supplied by a manufacturer to establish the potential

strength range of the material.

5.4.2 Petrographic microscopy

Petrography involves a standardised microscopic examination

of stone, concrete, brick or mortar based on the methodsoutlined in ASTM C856 (ASTM, 2004a). The objectives of a

petrographic examination are to gain information about the

composition of the materials and to identify the presence of

microscopic defects, visible indicators of deterioration, evi-dence of unsound or reactive aggregate or other deleterious

components. Petrographic examination is also used to estimate

the watercement ratio, percentage of entrained air or

characteristics of the air void system in concrete. In general,

petrography indicates the overall quality and soundness of

stone, brick, concrete or mortar materials. Petrographic studies

are often used in combination with chemical testing to obtain

additional information about construction materials.

5.4.3 Chloride content

The chloride ion content in concrete or mortar provides

quantitative evidence of the potential for corrosion of

embedded steel elements. Measurement of the chloride profile

(variation in chloride concentration with distance from the

surface) can help to establish if the chloride source is external

(e.g. salt spray) or internal (e.g. accelerating admixture). The

chloride content is determined by methods described in ASTM

C1218 (ASTM, 2008) and ASTM C1152 (ASTM, 2004b).

5.4.4 Freezethaw testing

The durability of masonry and concrete materials, specifically

resistance to cyclic freezing and thawing, is measured by

alternately exposing critically saturated samples to tempera-

tures above and below freezing. The onset of freezethaw

distress is measured by weighing samples periodically during atest to assess weight loss from fragmentation. A dynamic

modulus test measures variations in the samples resonant

frequency as an early detection of internal sample degradation.

Procedures for freezethaw testing of prepared concrete prisms

are provided in ASTM C666 (ASTM, 2003), while ASTM C67

(ASTM, 2007a) provides guidelines for freezethaw testing of

brick samples. The ratio of cold water absorption to boiling

water absorption (or saturation coefficient) is also an indicator

of the potential freezethaw durability of brick. The saturation

coefficient essentially quantifies the free pore space that is

available to accommodate ice formation in a water-saturated

brick body. The method of measuring the saturation coefficient

is described in ASTM C67 and the criteria for evaluating brick

performance are described in ASTM C216 (ASTM, 2007b).

5.4.5 WUFI analysis

WUFI (Warme und Feuchtetransport Instationar) analysis

involves the use of a computer software program to assess

multi-layered building enclosure systems (Kuenzel et al., 2001).

This analytical method, which models 1D heat and moisture

transport, is gaining popularity for optimising building

envelope design and as a diagnostic tool for comparing actual

and predicted performance of an enclosure system.

6. Organisation and communication offindingsMost building facade failure investigations require conveying the

findings to the interested parties in a written report. Depending




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on the goal of the investigation, the report may take a variety offorms. However, most investigation reports follow a logical

sequence flowing from acquired information, to factual finding,

to analysis and opinions, and then to recommendations. The

report may start with an introduction and background section.

Observations and factual information gained during the investi-

gation are provided next, followed by analysis and discussion,

which involves assessment and interpretation of verifiable facts.

Finally, opinions and conclusions express the investigators

determination of the cause of the failure based on the referenced

background material and information presented in the report.

Reports also often include recommendations for remediation.

If a preliminary determination and early report are needed

before an investigation is complete, all assumptions and

limitations due to incomplete data that formed the basis of

the report should be described. However, if further investiga-

tions and evaluation of additional data later lead to opinions

that differ substantially from the preliminary report, discre-

pancies must be explained in a subsequent report.

Litigation support cases often require verbal communication of

the investigation findings prior to issuance of a written report.

Depending on the clients needs, graphic presentations or the

development of physical models and court exhibits may also be

required.

7. ConclusionsThe scope and method of facade failure investigation,

diagnosis and remediation will vary depending on the nature

of the failure. The key objective is to collect sufficient reliable

data to determine the underlying cause(s) of the failure. The

tools and methods used for the investigation should be selected

to provide the most useful and accurate information in order to

understand the forces and conditions leading to the failure.

Facade failures can result from a wide variety of circumstances.

However, they occur most often through careless constructionpractices or in facade designs that employ overly complex

features, especially where materials, connections and details

lack redundant facade support mechanisms, fail to accommo-

date movement or lack effective wall drainage systems.

REFERENCES

AAMA (American Architectural Manufacturers Association)(2003)

AAMA 501.2-03: Quality assurance of diagnostic water

leakage field check of installed storefronts, curtain walls, and

sloped glazing systems. AAMA, Schaumburg, IL, USA.

AAMA(2008) AAMA 511-08: Voluntary guidelines for forensic

water penetration testing of fenestration products. AAMA,Schaumburg, IL, USA.

ASTM (2000) ASTM E1105-00: Standard test methods for field

determination of water penetration of installed exterior

windows, skylights, doors, and curtain walls by uniform orcyclic static air pressure difference. ASTM, West

Conshohocken, PA, USA.

ASTM (2003) ASTM C666/C666M-03: Standard test method

for resistance of concrete to rapid freezing and thawing.

ASTM, West Conshohocken, PA, USA.

ASTM (2004a) ASTM C856-04: Standard practice for

petrographic examination of hardened concrete. ASTM,

West Conshohocken, PA, USA.

ASTM (2004b) ASTM C1152-04: Standard test method for

acid-soluble chloride in mortar and concrete. ASTM, West


ASTM(2007a) ASTM C67-07a: Standard test methods forsampling and testing brick and structural clay tile. ASTM,


ASTM (2007b) ASTM C216-07a: Standard specification for

facing brick (solid masonry units made from clay or shale).

ASTM, West Conshohocken, PA, USA.

ASTM(2008) ASTM C1218/C1218M-08: Standard test method

for water-soluble chloride in mortar and concrete. ASTM,


Kuenzel HM, Karagiozis AN and Holm AH (2001) A

hygrothermal design tool for architects and engineers. In

Moisture Analysis and Condensation Control in Building

Envelopes (Trechsel HR (ed.)). ASTM, West


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