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14TH CANAD IAN CONFERENCE ON BU I LD ING S C I ENCE AND T E CHNOLOGY

GUARDS IN BUILDINGS – THE CANADIAN CHALLENGE

G. Hildebrand and P. Vegh

ABSTRACT

Several tempered glass balconies from more than twenty buildings have shattered since the summer of 2011

and incidents of glazed balcony glass breakage continue to be reported. These incidents attracted public and

media attention to the issue of the safety of existing balcony guards. This in turn prompted a high level of

technical scrutiny relating to the design and regulatory requirements for guards. In Ontario the Ministry of

Municipal Affairs and Housing formed a committee of stakeholders to address the issue and recommend

interim revisions to the Ontario Building Code to ensure public safety. The stakeholders comprised

developers, engineers, architects, regulators and building code officials. The new Code amendments were

released and took effect in July 2012 and apply to new construction after July 2012. Concurrently a Canada

wide CSA Committee has been formed and has begun working on the preparation of a new CSA Standard

for guards. This paper, provides background insight regarding the issues associated with building guards

including: guard failure mechanisms, inadequacy of existing regulation relating to their design and

installation, interim measures to mitigate the risks associated with guard failures and, the current approach

and variables being considered by the new CSA A500 “Building Guards: standard.” This paper will outline

the basic structure of the CSA approach, which has identified the key areas such as; Categories and Locations

of Guards, Durability, Safety and Risk Assessment, Design Criteria (e.g., loads), Materials and Component

Requirements, Testing Procedures, Installation and Inspection and Repair and Maintenance, that the standard

will address.

The intent of this paper is to alert architects, engineers, specification writers, developers and building

professionals about some of the problems associated with building guards, educate them regarding the

variables that must be considered in their design and inform them about the potential effects of the expected

changes the new Standard will have on the industry. The authors were members of the Ministry of Municipal

Affairs and Housing expert panel and have spearheaded the development of the CSA A500 Guard Standard,

currently under development.

BACKGROUND

In the not too distant past, most balcony guardrail systems for residential high-rise buildings were not light-

weight assemblies. Early high-rise balcony guardrail systems employed materials such as steel, cast in place

or precast concrete, masonry, or combinations of these materials. In addition, the most common method of

construction was to fully support the entire railing assembly on top of the balcony slab and inboard from its

outer edge. The first versions of “by-pass” guard assemblies, in which the railing assembly is supported

outboard from the balcony slab edge, were mostly constructed of precast concrete panels or steel posts with

steel panels. These were typically secured to the building using cast-in-place anchors and plates. Failure of

any of the guard components was rare, within their useful service life, often governed by corrosion of the

guard assembly itself or corrosion of the embedded anchors and/or reinforcing steel with the resulting

damage of the surrounding concrete. In more recent years, (i.e., ≈ 15 years) the architectural community

has gradually incorporated much lighter guard designs comprising materials such as glass and aluminum

(or dimensionally reduced steel), citing the fact that these lighter-weight designs offer several desirable

characteristics, particularly in the use of glass as a baluster or infill component.

7 CCBST 2014 Proceedings Book_v10 B3 215-254_Layout 1 14-10-17 4:00 PM Page 243

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Initially, for high-rise residential buildings, guardrail systems employing glass infill panels were typically

systems mounted entirely inboard of the edge of the balcony slab. In addition, the glass heights were under

42” and were largely restricted to function as infill panels with either two sides fully captured (i.e., by the

top and bottom rails) or four sides fully captured (i.e., by the top and bottom rails for the horizontal edges

and by stiles, balusters or posts for the vertical edges of the glass). ASTM Standard E2353, “Standard

Specification for the Performance of Glass in Permanent Glass Railing Systems, Guards, and Balustrades”

provides several examples of these types of systems.

FIGURE 1: ASTM E2353 GLASS IN GUARDRAIL CONFIGURATIONS

Around the mid-2000’s it started becoming more common to have guardrail designs that employed larger

glass infill panels, typically mounted outboard of the slab edge in a “by-pass” configuration, often extending

below the bottom of the slab. In some cases the portion that covered the balcony slab edge was made of a

different material, but often integral with the assembly. The glass infill panels were typically supported along

the top and bottom edges only by continuous rails. Often the top rail also served as the handrail. Albeit rare,

the design boundaries were sometimes pushed even further by leaving the top edge of the glass infill panel

completely exposed. While this practice is not a new one, it is usually limited to indoor applications, where

a heavier monolithic tempered or laminated glass is employed in a more controlled environment. Most recent

designs continue to minimize the infill capture with the infill material held in place by linear edge rails and

point fixing schemes of various types such as cleats, clips, spider connections, sealants, etc.. These now

mostly utilize a four-sided capture of the panels.

While not necessarily the best concept for serving its intended purpose as a safety component, these

“transparent guards” do not obstruct a view to the exterior, which adds to the perception of a more spacious

habitat, a desirable attribute in the high-rise residential market.


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GUARD FAILURES

The consequences of these, what some may consider, subtle design changes have been dramatic, with an

increase in guard failures, some catastrophic, recorded over the last few years. The major sources of these

failures include:

1. Anchor failures,

2. Frame assembly component (posts, shoes, rails) failures,

3. Glass retention failure (i.e., whole scale glass exiting the guard assembly) and,

4. Glass breakage (both spontaneous and impact).

ANCHOR FAILURES

Failure of individual anchors securing the railing to the structure can lead to catastrophic events and may go

undetected until an overall failure event occurs. The reasons for the failure can be related to an anchor with

insufficient capacity to resist the anticipated loads as a result of design or installation error, poor material

quality or material flaw, inadequate strength substrates and deterioration or damage of the structure into

which the anchor is embedded. The anchor capacity can also be compromised when it is made of an

inappropriate material that is unable to resist the anticipated environmental conditions (e.g., airborne and

occupant applied pollutants, water, snow and ice) or a material that is incompatible with other mating guard

components (i.e., corrosion or mechanical interaction).

In reviewing some of the recent failures involving anchorage, all of these modes of failure have been

observed and while most of these failure mechanisms can be easily addressed at the design stage, poor

installation is the most difficult to consistently identify and resolve. The complexity of this issue relates to

the fact that, most guardrail installations (primarily from the high-rise residential sector) are post-structure

component additions using post-construction installed anchors. Problems associated with anchors commonly

arising from installation errors are, for example: anchors are too close to the slab edge or to each other,

anchors are not installed perpendicular to the top surface of the slab, anchors without proper embedment,

pre-drilled holes that are too shallow, manufacturer’s instructions for installation are not followed, etc.. Any

of these problems can compromise the in-situ performance of the anchor and also the guard.

GUARD FRAME ASSEMBLY COMPONENT FAILURES (EXCLUDING GLASS)

Guard frame components typically include: post shoes, posts, rails, pickets, panels, cleats, gaskets, shims,

connectors (e.g., bolts, nuts, screws, etc.), coatings and sealants. Failure of these components can vary based

on the design of the assembly as well their quality of manufacture and installation, however, failure of any

component that is part of the main frame of the guard can have very serious consequences as it usually

affects the integrity of the whole guard or of the section of the guard in which the component is located.

Examples of some of the observed failures of these components are summarized below:

• The post shoe is the component of the guard assembly through which all or most of the load acting on

the guard is typically transferred to the base building structure. As such, these components are often

subjected to relatively significant localized stresses and stress concentrations. Certain types of materials

and connections, such as cast aluminum and welds, are sensitive to stress concentrations. Numerous

failures have been observed in cast aluminum shoes and also on some welded shoes (specifically

aluminum shoes with welded aluminum parts). These failures may be attributed to inadequate design

(or testing) or material flaws. Cast aluminum is by nature a very stiff material and voids and fissures

are present within the material. Both are undetectable from a visual review of the finished product.

This has led the authors to conclude that, without a high level of quality control in the manufacturing


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plant and extensive testing of the finished products, cast aluminum components represent a greater

degree of risk, than those made of other materials, such as steel or extruded aluminum, especially

when they are used in critical areas of the guard assembly.

• Bolts and screws, employed to mechanically connect components of the guard assembly together,

work loose from vibration. These can also break or pull through their interfacing components, due to

stress fatigue caused by vibration and repeated loading. The probability of failure is increased when

the fasteners and/or the connected parts are weakened by corrosion.

• Infill panels (usually glass) sometimes exhibit movement (i.e., “walking”) within the guard framing

in-plane of the guard as a consequence of vibrations of the system. This may cause material fatigue

and damage of the glass panels due to impact with other guard materials (e.g., glass-to-metal or glass-

to-glass contact). In some cases, where there is no adjacent construction element that would stop the

movement, the panels can “walk” completely out of the guard and fall to the area below. This issue is

most common where infill panels are not adhesive or mechanically fixed in-place and are only friction-

fit into a top and bottom rail, using a gasket or spline system.

GUARD COMPONENT FAILURES (GLASS)

With respect to the glazing, for the new “transparent guardrail” designs, the infill panels are more exposed

and employ larger, thicker and heavier glass to meet the wind and live load requirements. When breakage

occurs it is usually more “dramatic” as the glass can fall unrestrained to areas below and often quite a large

area of the guard is vacated. As for the type of glass employed for balcony guardrail infill (balustrade) glass,

the most commonly employed safety glazing material in North America, has traditionally been thermally-

strengthened “tempered glass”. This glass is considered a safety glazing material and is chosen based on its

superior strength and its high resistance to impact (i.e., by Standard convention, four times stronger than

annealed and twice as strong as heat strengthened glass). The latter is an important consideration in terms

of the ability of tempered glass to act as a guard against anticipated impact loads. In addition, tempered

glass characteristically breaks up into smaller cubes rather than large shards of glass, which is usually the

case for the other glass types. This characteristic is known as fragmentation and is an important variable in

assessing the suitability of tempered glass as a safety glazing. While slightly more costly than regular or

heat strengthened glass, tempered glass is considerably less expensive than the other forms of safety glazing

such as laminated glass. Laminated glasses are those that are composed of two or more layers of any of the

monolithic glass types (i.e., annealed, heat strengthened and tempered) separated by bonding layers of

another material called an “interlayer”. Interlayers are made of many different materials but the most

common ones are polyvinyl butyral (PVB). With respect to strength, under most conditions (temperatures

< 70˚C and load durations under a minute) laminated glass can be considered as a monolithic glass. For

balcony guardrail infill panels, the principle advantage of employing laminated glass relates to its ability to

remain intact (or mostly) and not fall from the building. The latter point of course is predicated on the notion

that the broken panel will remain constrained in the supporting guardrail assembly. If the guardrail assembly

fails to retain the glass, the laminated glass pane will fall from the unit as a whole. This is considered by

some to be a greater safety concern, particularly for many of the minimalistic guardrail framing (capture)

designs. More importantly than for tempered glass, the top edge of the laminated glass must be protected

from the elements, as ultra-violet radiation and moisture can lead to premature failure of the PVB interlayer.

Notwithstanding caveats regarding changes in glass behaviour brought about by the longer-term effects of;

moisture, biological, chemical and other environmental loads; glass breakage is generally attributable to:

1) Impact, both unintentional (e.g. accidental human collision) or intentional (i.e., an act of

vandalism) and “hard body” impacts from projectiles such as stones or solid objects dropped from


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height. The requirements for impact resistance are given in various codes and standards. In Canada

in the past this is a glass only evaluation and testing is conducted under specific conditions in a

standard frame;

2) Glass-to-metal contact, which is a type of impact related to the interaction of the various guardrail

components (i.e., glass, metal posts, anchor shoes, screws, etc.) under the influence of wind or

occupant loading. This may result in the edge or other surfaces of the glass being damaged and

thereby weakened. Glass-to-metal contact is system related and should be avoided;

3) Uniform or concentrated loads which would primarily involve wind loads or the other

concentrated live loads given in the applicable codes and standards;

4) Thermal loading resulting in breakages attributable to excessive temperature gradients across a

pane of glass. This can be caused by shadows keeping areas of the glass sufficiently cooler than

another area, resulting in thermally-induced stresses. The resistance of the glass to thermal loading

is highly influenced by edge or surface damage;

5) Size, as larger glass panels (i.e., width, height and thickness) are statistically, weaker than smaller

units. This is a consequence of the greater potential number of inherent flaws in the glass and the

higher resultant loads to which the larger panels are subjected;

6) Nickel sulphide inclusions (tempered glass only) for thermally-tempered glass, breakage can also

be attributable to the aforementioned nickel sulphide (NiS) inclusions present within the glass

tension zone (i.e., ≈ 79% of the overall thickness of the glass emanating from the centre of its depth).

NiS is particularly troublesome in that it cannot be practically identified during manufacture or in

the field, it is batch related, and it can result in continued spontaneous breakage over a significant

period of time. The problems with NiS can be mitigated by heat soaking after tempering;

7) Poor quality of glass. This would include glass with voids, contaminates, edge damage, non-

uniform or insufficient thickness, etc..

Although the properties of glass are well known, and most design documents take into consideration the

inherent reductions in theoretical performance, the strength of any glass type can be dramatically reduced

by edge damage exhibited as chips, cracks or abrasions to the edges caused during or after installation. For

tempered glass the edges of the glass are in compression and act as a buffer to inhibit the effect of flaws

(i.e., pre-existing defects) within the glass by moisture or other elements; installation damage, which includes

surface scratching, edge damages, chemical etching or weld splatter burns; poor glazing design including,

insufficient edge support or insufficient clearances to prevent initial or eventual glass to metal contact,

oversized panels, unprotected edges at susceptible locations, poor framing design contributing to thermal

stresses, insufficient glass thickness due to inappropriate consideration of loads; etc.

In addition, owing to their differences in properties and interactivity, the strength of glass is significantly

affected by the application of ceramic inks. Research (Morgan 2010) has indicated that the application of a

ceramic frit can reduce the strength of the glass by 30% to 60%1 depending on which side the film is applied

and the number of layers of ink that are employed. Through conversations with the authors, a senior U.S.

glass expert indicated that his research shows that the reduction in strength is typically 40% for a frit applied

to the strong side (i.e., air side) of the glass. The strength is further impacted if the frit runs onto the edge

of the glass, which is considered bad practice by the industry.

In evaluating glass breakage in the field, it is often difficult to establish the exact cause of failure. This is

especially true for tempered glass (or any of the glass that has been removed from the site) that has, in

whole, or in part fallen out of the opening. In some cases a substantial portion of the glass will remain in


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place and allow some analysis of the potential mechanism of failure. For NiS-induced spontaneous breakage,

it is sometimes possible to recover the crystal in-situ or by subsequently sifting through the recovered glass,

which is an excessively time consuming task.

FIGURE 2: NICKEL SULPHIDE INCLUSION BREAK PATTERN.

CURRENT GUARD STANDARDS

Until the new CSA A500 Standard is published, there is currently no Canadian standard that specifically

deals with the design, material or performance requirements for guards for use in and around buildings.

There are, however, a number of international standards that do specifically address the relevant design and

testing protocols that are considered appropriate for guardrail systems and their components.

In broad terms, these standards can be broken into two categories; standards providing “general requirements

for guards” in buildings and their constituent components and; “specific component standards” that outlined

the requirements for their use in guards. As an example, while in Canada there is as yet no “Guard in

Buildings” standard, the two CGSB glass standards, CAN/CGSB-12.1-M90 and CAN/CGSB-12.20-M89

do provide some mandatory and non-mandatory guidance for the constituent glass when employed in a

guard assembly.

In other jurisdictions around the world, different approaches are employed. For example, the British model,

British Standard BS 6180:2011, “Barriers in and about Buildings - Code of Practice” provides a

comprehensive set of general requirements for guards including; defining types of guards, anticipated loads

(i.e., live, impact and wind), as well as prescriptive materials and design requirements for the guard

components. Within this standard, other British and European standards relating to each of the relevant

variables, not directly given in the document, are referenced with the entire document providing the end

users a non-ambiguous and comprehensive set of instructions related to the application of guards for

buildings.

The British standard also provides specific non-compounding horizontal live loads to be imposed on the

guards based on their application (i.e., intended place of use), while indicating that wind loads are covered

separately under another set of standards, namely BS EN 1991-1-4 “General actions – Wind actions.” In

the current version of BS 6180:2011, horizontal deflection limitations are also provided. Notwithstanding

some isolated items, the requirements set out in these documents are quite similar to that provided in Canada,


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although the British standards (and many others) also prescriptively specify minimum glass thickness for

various glass infill and balustrades, based on the size of the panel or their proximity to their surrounding

building components. Similar to the Canadian references, most of the other standards reviewed, consider

tempered or laminated glasses as “safety glass” and allow either to be used for a balcony railing application.

It is interesting to note that other standards, such as the Australian standard, AS1288 explicitly divide glass

for use in guardrails into two distinct categories; 1) structural balustrade panels; or 2) infill balustradepanels.

This is an important distinction in that, where the glazing is acting as a balustrade, it is considered part of

the main live load bearing assembly and a number of restrictions come into play. These include line loading

and the requirement for a continuous capping and adequate load transfer to adjacent panels. This latter

requirement is also provided for in the Canadian Standard CAN/CGSB 12.20 document.

One exception to the directive allowing either tempered or laminated glass for use on balconies, is the

requirement for laminated glass given in the, “Guidelines on the use of Glass in Buildings – Human Safety”2

published by the Confederation of Construction Products and Services (CCPS). This document is a consensus

document, written by a number of industry and regulatory stakeholders and is intended to be mandated by

code within the various jurisdictions in India. With respect to guardrail glazing, the document offers a lucid

set of prescriptive instructions based on end use, with five classifications given in a table and supported by

pictorial examples to ensure non-ambiguity. For guard glass in residential high-rise buildings, the glass falls

under a, “Case 5; Glass acting as a balustrade, parapet or a railing (Human Impact and risk of fall)”category and laminated safety glass would be required.

This guideline specifically addressed two issues, one relating to the issue of retention of the occupant and

the second, the issue of managing the glass after it is broken. Once again, the only issue associated with this

approach is the fact that, in order to satisfy its safety intent, the broken glass must remain in place and not

fall as a single large piece of broken glass.

LOAD CONSIDERATIONS

With respect to the general issue of loads, supplemental to previous comments, the anticipated loads imposed

on guards and their subject component mainly consist of:

1) Live loads are loads imposed either intentionally or accidentally. Intentional loads are service occupant

loads applied in the course of the service life of the guardrail. Live Accidental loads are unintentional live

loads related to impact. These loads are those associated with objects such as a human striking the glass

infill, either with their body, in the case of an accidental fall or, by throwing or hitting the glass with an

object. Accidental human falls have been extensively studied and resultant safety standards, such as the

American National Standards Institute Inc. (ANSI) Standard Z97.1 – 2004. “American National Standard

for safety glazing materials safety performance specifications and methods of test” provide the appropriate

loads and methods of calculating the additional loads based on a study of accidental falls.

2) Wind loads are the forces exerted on the guardrail glazing from the prevailing winds. Establishing the

actual loads acting on balcony guardrails from wind is quite difficult and whether, determined through a

wind tunnel study, or calculation using the methods provided in the building codes, the actual loads will

vary throughout the building and are largely indeterminate. For this reason, the basic wind loads on cladding

(and guardrail) assemblies are usually subject to a number of safety factors to account for this uncertainty.

The current Canadian building code prescribes that both live and wind loads be combined in a prescribed


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manner in the design of guards. This is contrary to the requirements given in some other Codes and Standards

from other parts of the world. The Australian Standard, AS 1288 for example states in Section 7.2 that in

the design of a guard, wind and live loads need not be combined, rather the most restrictive (worst case)

load must be accommodated. That direction appears to be consistent with the guidance given by several

other applicable standards reviewed.

3) Where appropriate, other loads and effects may need to be considered. These would include loads from

snow, ice and rain, temperature and earthquake.

4) Certain known loads and effects have not yet been clearly quantified and/or defined:

a) This includes the magnitude of the wind load, which acts on a guard in various locations and configurations

of a building. To the author’s knowledge there has not yet been a systematic in-situ study carried out to

verify the actual wind loads on different guard assemblies. Most of the available data comes from wind

tunnel studies that have been performed on relatively small-scale models.

b) The lighter guard assemblies that are being used on today’s high-rise buildings are more susceptible to

wind-induced vibrations than the previous more massive designs. In the absence of a proper understanding

of the actual wind loads on guards, vibration loads and effects are not clearly defined or are missing

altogether.

c) Glazing falling from height should be designed to prevent serious injury to those below. In addition to

(larger) pieces of glass being retained in place (or on the building) after their breakage, the conditions under

which they remain in place and their function during that time need to be clearly defined. As such, the load

(and possibly length of time) that the broken piece should be able to sustain without falling out, needs to be

defined (“post-breakage retention load”).

d) The only effect, not specifically dealt with in any of the documents reviewed, with the exception of the

European (British) standard European Standard EN 14179-1:2005, is related to NiS inclusions. In this case,

EN 14179-1:2005 addresses this issue by limiting the risk of spontaneous breakage due to NiS inclusions

to 1 per 400 tons of heat-soaked glass by mandating the process of post-temper heat soaking the glass. Using

this approach, a designer or regulator would limit the problem by specifying that all of the glass be heat

soaked prior to deployment in a guardrail assembly.

CANADIAN GUARD DESIGN RULES

With respect to the Canadian code requirements, for guards, the 2010 National Building Code (NBC) and

the 2012 Ontario Building Code (OBC), for example, provide a number of prescriptive guidelines for

guardrail assemblies, including for, height requirements, clearances, restrictions on the maximum size of an

object that may pass through the assembly, and the climb-ability of the guard. Part 4 of the NBC and OBC

provides the appropriate guard live loads. The Codes do not give specific guidelines on the wind load for

guards.

The codes also specify that for glass infill panels, the glazing must be designed in conformance with

CAN/CGSB-12.20-M, “Structural Design of Glass for Buildings”. Under the CAN/CGSB-12.20-M89

“Structural Design of Glass for Buildings”, in addition to stating that the glass has to meet all the relevant

material and performance requirements given in the CAN/CGSB-12.1-M90 Tempered or Laminated Safety

Glass, this document does indicate the requirement to consider wind loads acting alone or in combination,

where appropriate. The standard also states among other forces the necessity for the glass to accommodate,

“racking and impact loads due to windborne missiles, human impact and sliding snow.”


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As a final observation regarding the standard requirement for the glass, notwithstanding the other

requirements listed, it is interesting to note that while the CAN/CGSB-12.1-M90 standard requires both

tempered and laminated glass to be permanently labeled as safety glass, there is no mandate to use one over

the other (i.e., monolithic tempered over laminated glass) as a guard or infill glazing material. This would

suggest that at the time both glass types were considered suitable for use in this application. With respect to

impact testing, while the CAN/CGSB-12.1-M90 states the method of test to be employed, neither of the

Canadian glass standards requires that the glass be tested as designed in the actual installed assembly. While

this may not be an issue for safety glazing in other building cladding components, an understanding of its

behaviour as an infill material in a guardrail system under all loading conditions (i.e., full design wind loads

as well as live load, independently or in combination) should be evaluated as the issues of breakage and

post breakage retention are clearly a function of the interaction between the glass and its mating guard

components.

The bottom line regarding the Canadian codes and standards as they relate to guards is that, their

requirements are spread through multiple documents, are difficult to follow, can be easily misinterpreted,

and they fail to account for several of the practical issues associated with many of the guard components.

CODE MODIFICATION - INTERIM MEASURES

In the summer of 2011, there were a high number of incidents of spontaneous breakage of monolithic

tempered safety glass employed in balcony guard infill panels or balustrades. This initiated a thorough

review of the methods of design, manufacture and installation of guards for buildings.

In addition to the obvious material issues associated with the failed glass (i.e. nickel sulphide induced

spontaneous breakage of the tempered glass), the engineering community subsequently determined among

other things that:

1. There was no cohesive guidance regarding the design of balcony guard systems other than the

information given in the building code. (i.e., there is no single applicable reference standard).

2. Designers followed different protocols in the design of guardrail systems. Some considered the

guard loads independently, some considered guard and wind loads separately while some considered

the combination of both.

3. There was no procedure and/or data in the Code for determining the magnitude of wind loads

specifically for guards. Different designers were using different approaches. Where available, wind

loads on guards were being determined from wind tunnel studies. All methods appeared to result

in overly conservative loads.

4. No data relating to actual wind loads acting on guardrail assemblies (i.e., in situ measurements) is

currently available.

5. Several other jurisdictions consider guard and wind loads separately.

6. Other than to mandate the use of tempered or laminated glass for use in balcony guardrail systems,

there was no specific guidance given in existing Codes and Standards regarding the selection of

tempered and laminated safety glass for this purpose (i.e., either could be employed in a balcony

guardrail system).

7. There was no mandated guidance regarding post-breakage retention for glass used in guards.

8. While testing was routinely being done on guards, there were no mandated test procedures to

evaluate a balcony guard system for guard load, wind load and impact testing.

9. There was limited to no guidance regarding the materials and design of balcony guards.


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Based on these initial findings, it was clear that there was a need to develop a Canadian standard for guards

in buildings. In view of the fact that standards development time is usually measured in months or years,

development of some temporary measure was required in the interim. The Ontario Ministry of Municipal

Affairs and Housing (MMAH) formed an “Expert Advisory Panel” to conduct a review and provide advice

to the Ministry on Building Code standards for glass panels in balcony guards. “The Panel’s mandate was

to make recommendations on whether and how the Building Code may be amended to address the problem

of the breakage of balcony glass and its risk to persons nearby. It was not the mandate of the Panel to make

findings of fault or assign blame.”3

This committee, chaired by MMAH, Building and Development Branch staff, consisted of approximately

twenty-five stakeholders including engineering consultants and designers, building code consultants,

developers and contractors, municipal building departments, the insurance sector (Tarion Warranty

Corporation and Pro-Demnity, the insurance provider for Architects), and codes and standards representatives

(National Building Code and the Canadian Standards Association).

Ultimately, the expert committee developed seven recommendations for consideration:

1. “That the Building Code be amended to provide supplementary prescriptive requirements for all

glazing in interior and exterior guards in all buildings, except houses (this excludes: detached

houses, semi-detached houses, duplexes, triplexes, townhouses, and row houses).

2. That consideration be given to clarifying that direct glass contact with any metal or similar hard

elements is to be avoided and to require sufficient allowances for deflection and movement under

loads and temperature changes. This clarification could be included as a note in the Appendix to

the Building Code.

3. Where it is incorporated in a guard, glazing located beyond the edge of a floor, or within 50 mm of

the edge of a floor, shall be heat strengthened laminated glass that is designed, fabricated, and

erected so that, at the time of failure of the glass, the glazing does not dislodge from the support

framing.

4. Where it is incorporated in a guard, glazing located more than 50 mm to 150 mm inward from the

edge of a floor shall be fully heat soaked tempered glass or heat strengthened laminated glass that

is designed, fabricated, and erected so that, at the time of failure of the glass, the laminated glazing

does not dislodge from the support framing.

5. Where it is incorporated in a guard, glazing located more than 150 mm inward from the edge of a

floor shall be heat strengthen laminated glass or heat soaked tempered glass. However, tempered

glass is permitted where the glazing does not exceed 6 mm in thickness. Guards using heat

strengthen laminated glass must be designed, fabricated and erected so that, in the event of failure

of the glass, the glass does not dislodge from the support framing.

6. That the memorandum, dated March 8, 2012, from Cathy Taraschuk, P. Eng., reporting on the

advice of the Task Group on Live Loads Due to Use and Occupancy of the Standing Committee on

Structural Design on the applicability of the load combinations listed in Table 4.1.3.2.A. of Division

B of the 2010 model National Building Code be included as an Appendix to the Building Code.

7. That the Ontario Ministry of Municipal Affairs and Housing:

a) Support the development of the proposed CSA Standard on Balcony Guards; and

b) Consider referencing the CSA Standard on Balcony Guards, once it is published, in the Building

Code.”


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Although all seven recommendations did not receive unanimous support within the expert panel, the

prescriptive elements of the recommendations were incorporated into the 2006 Ontario Building Code in

the form of Supplemental Standard SB-13, “Glass in Guards”, which came into effect on July 1, 2012 (for

reference in Sentence 3.1.20.1.(1) of Division B of the Building Code). In addition to setting out the glass

type requirements with respect to their position relative to the edge of the balcony slab, it also referenced

the European DIN Standard ( DIN EN 14179-1, “Heat-Soaked-Thermally-Toughened Soda Lime Silicate

Safety Glass, September 2005”) for a heat soak process to be carried out for monolithic tempered glass to

reduce the residual risk of spontaneous breakage due to Nickel Sulphide inclusions in the glass. As previously

implied, prior to this reference there was no mandated heat soak requirement in North America, in spite of

the fact that spontaneous glass breakage is well known in the industry and, the procedure is often carried

out by some manufacturers for safety glass used for this type of application.

THE NEW CANADIAN STANDARD – CSA A500 “GUARDS IN AND AROUND BUILDINGS”

Concurrent to the work being carried out by the Ministry’s “expert panel”, the Canadian Standards

Association (CSA) was working with some members of the engineering community to initiate the

development of a new standard that would cover all aspects of building guards. Once sufficient financial

support to initiate the development of the document was procured, technical committee members were

identified and the inaugural meeting of the new CSA A500 “Guards in and around Buildings” Technical

Committee (TC) was held on June 8, 2012. At that meeting the scope of the standard was developed: “This

Standard specifies requirements for the design, installation, alteration, and maintenance of permanent guards

in and about buildings. This Standard applies to all building guards required as protective barriers, with or

without openings, around openings in floors or at the open sides of stairs, landings, balconies, mezzanines,

galleries, raised walkways or other locations to prevent accidental falls from one level to another.”

The TC was initially broken down into a number of task groups that developed technical content for

specifically assigned topics. Most of these task groups have since been amalgamated and at present, a small

“Task group of writers” has been meeting on a regular basis to populate the standard based on the structure

developed by the TC and the information provided by the task groups. At present, the body of the standard

is reaching completion and will soon be ready for committee review.

The TC identified one issue, which unfortunately, remains outstanding. This issue is related to verification

of actual wind loads acting on guards. Members of the TC are of the view that the derivation of wind loads

using the current code protocols is unclear and often results in excessively high peak design wind loads that

likely don’t reflect the real wind spectrum acting on guards. This results in potential overdesign in terms of

strength requirements for the guard components. At the same time the exposure of the guardrail assembly

and its components to low energy, high frequency vibrational loads induced by wind is often overlooked or

not addressed. In an attempt to address these issues part of the “Loads Task Group” prepared a scope of

work for a research project consisting of detailed wind tunnel testing in conjunction with in-situ wind

pressure monitoring to develop and validate a procedure for calculating wind loads on balcony guards in

high rise buildings. This Group, with the help of other members of the TC, attempted to seek additional

funding for this project, but was unsuccessful. As a consequence, the TC will have to reference the current

code protocols to establish wind loads acting on guards for the inaugural version of the CSA A500 standard.

It is hoped, however, that funding for this project will be secured in the near future.


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REFERENCES

1 Tim Morgan CEng MIMechE, Technical Manager, Pilkington Architectural “Aspects of Structural Glass”presentation to the Institute of Structural Engineers, SE Counties Branch, England, 2010Source: GlassAssociation of North America (GANA) Guide to Architectural Glass 2010 Edition2 Confederation of Construction Products and Services (CCPS) (2013), “Guidelines on use of Glass inBuildings - Human Safety” 3 Ontario Ministry of Municipal Affairs and Housing, “Report of the expert panel on glass panels inbalcony guards.”, March 30, 2012, Toronto Ontario.


Documents

GUARDS IN BUILDINGS – THE CANADIAN CHALLENGEobec.on.ca/sites/default/uploads/files/members/CCBST-Oct-2014/B3-3... · GUARDS IN BUILDINGS – THE CANADIAN CHALLENGE ... Several tempered