The term limiting distance refers to the minimum required distance between an exposing building face and a property line, the centre line of a street or lane, or another structure. This measurement is critical in urban planning and construction as it ensures compliance with building codes, particularly for fire safety, spatial separation, and emergency access requirements.

Great Fire of Toronto (1904)

Bay Street looking north from just north of Front Street
[ca. 1903]
Photographer: Alexander W. Galbraith
City of Toronto Archives Series 409, Item 61

Bay Street looking north from just north of Front Street
April 1904
Photographer: William James
City of Toronto Archives Fonds 1244, Item 2
Total Loss - $10,387,000.00 in 1904 ($373 million in 2023 dollars)

What is Limiting Distance on Properties?

A more in-depth analysis -

Firestorms were the driving force in the development of early building regulations following disastrous city-wide fires which destroyed Rome in 64 AD, London in 1189 and 1666, the USA in the late 1800's and Canada in the early 1900's.

Two great fire's occurred in Toronto. The Great Fire of Toronto of 1849, April 7, 1849, also known as the Cathedral Fire, was the first major fire in the history of Toronto, Ontario, Canada.

In the heart of Toronto, 55 years and 12 days after The Cathedral Fire, in 1904 the Great Fire of Toronto blazed through the city. The mystery of its origin still lingers, with theories ranging from faulty wiring to a forgotten stove. As the clock struck 8:04 pm on that chilling April night, chaos engulfed the Wellington Street building, marking the beginning of a relentless inferno that swept through the City of Toronto and across neighborhoods.

These fires were characterized by significant building-to-building fire spread primarily driven by radiant heat transfer and ignition by brand spotting (airborne embers). Early regulations required division of a city into "fire limits" and exterior wall construction in certain areas to be of substantial noncombustible construction and firewalls to separate adjoining buildings.

However, these regulations impeded development and were extremely difficult to enforce and maintain.

The St. Lawrence Burn a joint effort between the United Kingdom and Canada in the 1950s, supported by large-scale fire testing, facilitating the development of regulations for the separation of buildings based on the fundamentals of radiant heat transfer.

One key test programme was conducted in 1958 in Aultsville, Ontario a town being flooded as part of the St. Lawrence Seaway Project. The "St. Lawrence" burns involved 6 residential dwellings and two larger assembly occupancies.

View the St Lawrence burn here, from The National Research Council of Canada, produced and archived at The National Film Board of Canada. circa 1958

nfb.ca/film/setting-fires-for-science/

The results were used to develop the spatial separation requirements in the NBCC. (National Building Code of Canada) Even though these requirements have changed, the principles remain the same.

The spatial separation requirements are based on the following test data, observations and associated assumptions from the St. Lawrence burns.

1. Fire Department Intervention: The radiant heat results from later in the fires in St. Lawrence burn tests resulted in "safe" distances that were considered impractical. Therefore, it was assumed that fire department response would occur within the first 10-16 minutes from the start of the fire, and limit the high radiant heat measured during the tests. Thus, lower emissive energy values could be used.
2. Emissive Energy: The radiant heat was measured at several locations away from the burns and back calculated as a function of configuration factor (relative location of the recording locations to the fire source) to determine the emissive energy, which is the energy being emitted from each opening in the dwelling. The emissive energy was calculated to be 178 kW/m2 for low hazard occupancies, and 356 kW/m2 for high hazard occupancies.
3. Grey Radiator: The formula for determining the amount of energy leaving the openings in a building (fire compartment) face and reaching a target was considered to be too complicated to be calculated for each opening. To address this, the spatial separation requirements were based on the assumption of the entire building (fire compartment) face as the radiating source. The actual openings were based on a percentage of the area of the building (fire compartment) face. Thus, the emissive energy is assumed to be emitted from the entire building (fire compartment) face as opposed to the individual openings. This assumption breaks down where building faces are located in close proximity and is the reason why localized clusters of openings are regulated for limiting distances of 2 m or less.
4. Flame Front: Within the early stages of the St. Lawrence burns, the flames were observed to extent approximately 5 to 7 feet from the openings in the buildings. This range was simplified to 6 feet (1.8288 m) for purposes of determining the
5. Target Criteria: It was assumed at the time of development of the spatial separation requirements, that the predominant combustible building material would be wood, which has a piloted ignition heat flux of 12.5 kW/m2. Note that this value can be considered as a quantitative performance criteria that can be used in the development of an alternative solution.
6. Mirror Boundary Condition: The actual "absolute" distance between buildings is not practical for purposes of regulation. Therefore, it was assumed that "the exposing building faces of adjacent buildings are of similar size and configuration, and are equidistant from the shared property line". This assumptions allowed the characterization of the "limiting distance", which is approximately half of the "absolute" distance required between buildings and could be applied such that the design and construction of a building on one property does not affect the design and construction of a building on an adjacent property.

Understanding the Concept

Fire separations establish the minimum distance between buildings, creating barriers that limit the spread of fire from one structure to another.

These distances are calculated based on the height of the buildings, occupancy, construction type of the buildings and the presence of combustible materials. All of these factors influence the required fire separations.

Building codes provide specific guidelines for each scenario, ensuring appropriate safeguards for occupants and property. Fire separations are critical components of fire safety strategies designed to prevent the catastrophic spread of fire within and between buildings. They act as passive fire protection systems such as Fire-Rated Windows tested to ULC Standards UL9, that are labeled (Both Framing and Glazing) to safeguard lives and property.

By containing fires within defined compartments, fire separations minimize structural damage, reduce property loss, and provide critical time for evacuation and firefighting efforts.

Ensuring Safety and Standards

Fire-rated glass is engineered to prevent the spread of flames, smoke, and hot gases to limit the transfer of radiant and conductive heat a process known as compartmentalization in fire safety. While various fire-rated materials offer this protection, only fire-rated glass maintains full visibility, enhancing aesthetics, day-lighting, and security.

Fire-rated glazing is categorized into two types: fire-protective glazing and fire-resistive glazing. Understanding the distinctions between the two material classes is essential, as many products belong to each category, and improper specification can compromise the safety of building occupants.

There are two types of fire-rated glazing, fire-protective glazing and fire-resistive glazing. It is crucial to understand the differences between the two material classes since numerous products fall within each category. Fire-protective glazing is specially designed to help compartmentalize buildings by defending against the spread of flames and smoke for its designated fire rating. It is typically suitable where building codes allow an assembly designated as "opening protective" to enclose a space. (CAN 4 S 106).

Fire-resistive glazing adds further protection by blocking the transfer of radiant and conductive heat (Heat Flux). It is tested to the
stringent fire-resistance test standards for walls (including ASTM E119 and UL 263, CAN 4 S 101), and can therefore exceed 25 percent of the total wall area. It is typically suitable where building codes require an assembly designated "fire resistant" to enclose a space.

Historically, wired fire-rated glass was among the most frequently utilized materials for fire-protective glazing. Nonetheless, its
institutional appearance and potential for human injury due to breakage prompted manufacturers to create wireless alternatives, such as Glass Building Code's in Canada require that all fire rated glazing material must be labeled. No one in Canada has the ability to label wire glass, so it no longer meets code. Therefore it can not be used period. Plus who likes the look of an institution within their own residence.

Currently, fire-rated ceramic glass is a fundamental component of the fire protection market. The material exhibits clarity and
strength, characterized by a crystalline structure that maintains cohesion under elevated temperatures. Upon installation, this
wireless product resembles standard window glass, offering significant design flexibility. The product offers fire ratings ranging from 45 minutes to 60 minutes. Fire-rated ceramic glass may be integrated into insulated glass units (IGUs) to meet energy code
requirements.

Transparent wall panels represent a significant category of contemporary fire-resistive glazing materials. This product features
intumescent interlayers that expand into foam upon heat exposure, effectively blocking radiant and conductive heat transfer for a duration of up to 120 minutes. The material is evaluated based on fire-rated wall standards, successfully meets fire and hose stream tests, and provides up to Category II impact safety ratings and Level III bullet resistance ratings. The material's superior protective qualities render it appropriate for wall-to-ceiling and wall-to-wall applications.

A ten minute conversation with us, could save you hours of research.

Fire-rated windows are a critical component of fire separations, designed to prevent the spread of fire and smoke, thus enhancing building safety in compliance with building codes and regulations. Their performance is crucial in protecting occupants and limiting property damage, especially in high-rise buildings or those with high occupancy levels. The type of fire-rated window selected depends on the building's height, occupancy, and construction type, as outlined in various fire safety standards and codes.

Safety Features & Compliance

Fire-rated windows undergo rigorous testing to ensure they meet specific fire resistance ratings, delaying fire spread and providing valuable time for safe evacuation. These ratings consider factors such as the duration of fire exposure and the level of heat transmission. Regular inspections by building
officials ensure compliance with these standards and maintain
public safety.

Fire-Rated Glazing

Fire-rated glass is engineered to prevent the spread of flames,
smoke, and hot gases to limit the transfer of radiant and conductive heat a process known as compartmentalization in fire safety. While various fire-rated materials offer this protection, only fire-rated glass maintains full visibility, enhancing aesthetics, day-lighting, and security.