Building performance is a measure of how effectively a building fulfils its intended functions. This encompasses both the operational performance of the completed building and the performance of the construction process itself. However, in recent times, building performance standards have often been related to energy usage and operational costs.

The performance requirements for any given building are determined by two primary factors: regulatory requirements and specific owner/occupancy needs. In almost every jurisdiction worldwide, building construction must comply with the Building Regulations (Building Code) with the primary objective of safeguarding the health and safety of the users of the building and protecting the environment.

These regulations also address issues like energy conservation, sustainability, and accessibility for persons with disabilities. Approved Documents (ADs) offer practical guidance on fulfilling the Building Regulations’ requirements, encompassing areas such as structural safety and stability, fire safety, energy efficiency, acoustics, etc.

In addition to the Building Regulations, certain building types are subject to further regulatory compliance. For example, buildings like special laboratories, correctional facilities, schools, and medical facilities must adhere to special guidelines outlined in various codes and standards. Hospitals in the UK are required to comply with the NHS Health Technical Memoranda.

Beyond regulatory compliance, building owners may establish their own performance criteria. These requirements can stem from the building’s intended function or considerations related to the client’s brand image. For instance, the construction of green and LEED-certified buildings may not be a regulatory requirement, but some corporate bodies may wish to construct green and LEED-certified offices to represent their brand’s interest and support for environmental conservation and reducing global warming.

Evaluation of Building Performance

The evaluation of the performance of a building can be done across different criteria. For instance, the physical efficiency of a building can be evaluated by assessing a range of performance parameters, including, but not limited to: heat loss, energy consumption, water usage, water tightness, structural integrity, and fire safety performance.

Therefore, contemporary building performance assessment considers a broad spectrum of criteria, including:

• Sustainability: Encompasses material selection (environmental impact), energy efficiency (heating/cooling demands, insulation, glazing performance), and water efficiency (e.g., grey-water recycling).
• Comfort: Focuses on achieving a healthy indoor environment through controlled air temperature, humidity, and ventilation.
• Ecology: Evaluate the building’s impact (positive or negative) on local habitats.
• Acoustics: Assesses noise generation from building activities and its impact on neighbouring buildings/spaces, and vice-versa.
• Running Costs: Considers the operational expenses associated with the building.
• Water Tightness: Evaluates the ability of roofs and openings to prevent water intrusion.
• Layout: Assesses the building’s spatial arrangement in terms of privacy, access to sunlight and views, and occupant circulation.
• Occupant Satisfaction: Gauges user satisfaction with the overall design and functionality.
• Accessibility: Determines ease of use for individuals with disabilities, along with general safety and security.
• Societal Impact: Considers the building’s integration with and contribution to the local community.

The discrepancy between a building’s designed performance and its actual performance post-construction is called the “performance gap.” A significant performance gap can negatively impact occupants, owners, and the environment. In severe cases, it may necessitate costly rework and potentially lead to legal action.

Floor Loading and Structural Safety

The type of occupancy (both present and future) must be considered to ensure appropriate floor load assumptions in the design. EN 1991-1-1 (“Eurocode 1”) provides characteristic values for imposed loads (referred to as “actions” in the Eurocodes), as well as densities and self-weights. Key values are presented below.

Category A: domestic and residential floors: 1.5 to 2.0 kN/m²
Category B: offices: 2.5 to 3.0 kN/m²
Category C: Areas where people may congregate 2.0 to 7.5 kN/m²
Category D: Shopping areas 4.0 kN/m²
Category E: Storage areas 2.0 to 15.0 kN/m²

The higher values in both ranges are ‘recommended’, meaning that they may vary from country to country as stated in the relevant National Annex. Apart from special storage facilities, the highest recommended live load value is 5 kN/m², which applies to public areas subject to large crowds, amongst other things. Other loads (actions) are stated in other parts of Eurocode 1, for instance, EN 1991-1-4 covers wind loading.

However, a potential conflict may arise between minimizing the initial cost of construction and providing for future adaptability and conversion of the usage of the building. Designing floors for the relatively light loading of residential occupancy offers an economical solution but may restrict future conversion of the building for uses with higher floor load requirements.

Furthermore, the required floor stiffness varies depending on the intended use. Floors in specific areas, such as certain sections of hospitals, are a prime example where minimizing the “vibration of floors” is of paramount importance.

Fire Performance

Once a structure is designed to adequately support loads and resist excessive deformation, fire resistance becomes another important consideration. Building codes mandate that structures maintain their integrity for a specified duration (ranging from 30 minutes to 2 hours) in a fire event. This duration is dependent on factors such as building height, occupancy type, and the presence of active fire protection systems.

In steel-framed buildings, fire resistance is typically achieved through two primary methods:

1. Fire Protection: Applying fire-resistant materials to structural elements to limit temperature rise within the steel.
2. Fire Engineering: Designing structural members (columns and beams) to withstand loads even with reduced strength due to elevated temperatures.

See:
Fire Resistance Design of Steel Beams
Fire Resistance Design of Steel Columns

Beyond regulatory compliance, building owners may opt for active fire protection systems, such as sprinklers, to further safeguard the building and its occupants.

Beyond ensuring structural integrity and fire safety, a well-designed building should also prioritize the comfort of the occupants. This encompasses careful consideration of both thermal and acoustic performance. While adequate daylighting is another important factor, it typically falls outside the primary control of the engineer and will not be addressed here.

Thermal Performance

Achieving thermal comfort in buildings requires that designers address both heating requirements during periods of low external temperatures and internal cooling when external temperatures are high. The relative importance of these considerations is clearly dependent on the prevailing external climate, which itself is subject to change over time.

Keeping the internal temperature higher during the winter period is quite well understood in the construction industry. Adopting simple strategies such as insulation of external walls, roof, and ground floor, and achieving airtightness in the building can be very effective. Furthermore, effective control of internal temperatures should be implemented in a manner that minimizes material usage, energy consumption, and associated emissions, thereby promoting the most sustainable building solution.

However, the least understood is how to keep the internal temperature lower during the summer, because traditionally, it has never been deemed an issue of major concern. Some of the strategies are:

• control solar gain
• provide thermal mass
• control ventilation
• insulate and make airtight the envelope
• control internal gains.

Solar gain is the increase in temperature of a building that is caused by solar radiation. Managing solar heat gain is usually an architectural issue, and requires careful consideration of several architectural elements. The orientation of windows is critical, as is the internal layout of rooms, particularly in minimizing excessive solar gain in spaces occupied during daylight hours.

While acknowledging that design choices may be influenced by other constraints, the selection of glazing type and the potential incorporation of brise soleil are also key factors in controlling solar gain.

Thermal mass is the ability of a material to absorb, store and release heat. Thermal mass is a frequently debated topic when comparing the benefits of lightweight steel structures and heavyweight concrete structures. While appropriate thermal mass can offer benefits by acting as a heat sink and absorbing energy during the day, its effectiveness is contingent upon its integration within a comprehensive strategy.

The stored energy must be dissipated during cooler nighttime hours through controlled ventilation, ensuring both security and minimizing uncontrolled air leakage through the building envelope. Excessive thermal mass may hinder responsiveness in residential buildings unoccupied during the day, where rapid heating is required shortly before occupants return home. In such dwellings, the absorption of heat that is subsequently re-radiated into bedrooms at night may also be undesirable. Therefore, careful planning is essential to optimize the use of thermal mass.

Acoustic Performance

Acoustic performance requirements vary depending on the building and room types. The primary concern is typically preventing noise from public areas from negatively impacting the comfort of occupants in residential spaces. However, regulations also exist to ensure minimum noise levels in public areas, such as restaurants, to protect conversational privacy.

When adjacent rooms are separated, sound transmission can occur via two pathways: direct transmission through the separating element itself, or flanking transmission, where sound travels around the separating element through adjacent building components. Sound insulation performance for both pathways is governed by three key characteristics.

• mass
• isolation
• sealing

Direct sound transmission is determined by the properties of the separating wall or floor and can be predicted based on laboratory measurements. Flanking transmission, however, is more complex due to its dependence on the specific details of junctions between building elements and the quality of on-site construction.

In some cases, flanking transmission can actually exceed direct transmission in terms of sound passage. Therefore, proper detailing and construction of junctions between separating elements are crucial for minimizing flanking sound transmission.

The transmission of airborne sound through a solid wall or single-skin partition generally follows the mass law. This principle states that sound insulation increases by approximately 5 dB with each doubling of the element’s mass. However, lightweight framed constructions often achieve significantly higher airborne sound insulation performance than predicted by the mass law. This enhanced performance is attributed to the presence of a cavity, which provides a degree of isolation between the different layers of the construction.

Proper sealing around floors and partitions is important, as even minor gaps can significantly reduce acoustic performance. Joints between walls, and between walls and ceilings, should be sealed with tape or caulking. Where walls meet profiled metal decking or similar elements, mineral wool packing and acoustic sealants may be necessary to fill any voids. Special detailing is often required at movement joints located at wall edges.

Ideally, wall linings should remain free of service penetrations, especially in separating walls between dwellings. When penetrations in sensitive locations are unavoidable, meticulous attention must be paid to the detailing of these openings to maintain acoustic integrity.

Building Sustainability

Sustainability, as defined by the Brundtland Commission, is a comprehensive concept encompassing the pursuit of activities that meet present needs without compromising the capacity of future generations to meet their own needs. It reflects a commitment to resource conservation and the avoidance of detrimental impacts.

The environmental impacts of the building and construction sector are extensive and varied, and the industry’s overall environmental performance has been suboptimal. The construction industry is the largest consumer of non-renewable resources and the largest producer of waste, while the operational phase of buildings accounts for approximately half of the UK’s total carbon dioxide emissions. Consequently, both voluntary and mandatory measures have been implemented in these areas to drive positive change.  

It is important to distinguish between embodied and operational environmental impacts. Embodied impacts encompass those associated with the extraction, processing, transportation, and installation of construction products and materials. Operational impacts, conversely, pertain to those arising from the building’s heating, lighting, cooling, and maintenance.

Achieving sustainable building practices requires a collaborative, integrated approach within the design team, with early and active participation from all stakeholders. Clearly defined sustainability objectives agreed upon with the client at the outset of the design process, are essential. Furthermore, all parties must be fully cognizant of the sustainability implications of their design choices and decisions.

While the structural engineer’s role may appear limited when considering the broader spectrum of sustainability criteria, structural design decisions significantly influence a building’s overall sustainability. Key issues requiring careful consideration and balance by the structural engineer include the following.