What is meant by exterior wall system?

An exterior wall system is a major concept in building design and building construction that creates an envelope around the concrete or the masonry structure to protect from environmental influences. It is a building enclosure that provides shelter, which was the primary concern in earlier days, but due to the growth of technology and human demands, building enclosures require the use of advanced approaches and materials for their constructions. Exterior wall systems act as barriers that shield the inside from the environment as well as human influences. The increase in human-induced environmental consequences such as weather change, global warming, harsh pollutants suspended in the air, increases the chance of many health hazards. Thus, there is a major need to create a building enclosure, which can block these facts and safeguard its occupants.

Wall systems form the major area in construction. It mainly fills the gap between the columns to form a hollow enclosure, which forms a source of shelter for the individuals. Resistance from heat, wind forces, rainwater penetration, moisture absorption, and so on forms the major area of concern in constructing an exterior wall system. Some of the modern builds make use of advanced engineered materials that block and shield sun rays and provide thermal insulation. This aids in regulating the interior temperature of the building.

Terms used in the design of exterior wall systems

In this section, a brief outline has been provided about the design and building of exterior wall systems. Some of the terms and definitions are discussed below.

Exterior cladding

Exterior cladding acts as a protective layer to the wall systems or the building enclosures. The cladding of a building can be naturally occurring materials or man-made materials. In the present generation, lab-engineered materials are extensively used as cladding materials. These cladding materials are manufactured, developed, quarried and their properties are altered and rendered to suit the application and the purpose they are engineered to fulfill. The base of these lab-manufactured cladding materials is primarily derived from natural sources. Vinyl and composites are some of the examples in this category.

Drainage plane

Drainage planes are the components that are exposed to external weather conditions. The materials for the drainage plane are primarily selected to bear harshness imposed on the building provided by weather. The materials of the drainage plane are intended to provide waterproofing, vapor impermeability, water resistance, and moisture resistance. These materials also have the property to shed rainwater and condensation deposits downwards.

Cavity walls

Cavity walls are concrete structures or wall systems that consist of two wall layers separated by a hollow cavity in between. Cavity walls are the masonry constructions separated by some distance, the space between them is intentionally kept void. One of the main functions of the cavity wall is to provide thermal insulation and maintain normal temperatures inside the wall barrier. As air has an extremely low convective heat transfer coefficient, the space between the walls which remains occupied by air blocks most of the exterior heat. Another use of the cavity wall system is that it aids as a carrier of rainwater which is absorbed by the wall during heavy monsoons. Rainwater ripples and flows through channels constructed in the cavity during the building pre-construction.

Air barrier

Air barriers are masonry or concrete constructions. They are a part of the wall system that block and shield the interiors of the building against wind forces. To make the air barrier effective and efficient, it should fulfill the following conditions in the design aspects:

• A proper masonry or concrete mixture must be made that should provide superior strength after setting and hydration.
• The air barrier construction should be within the exterior wall system.
• It should be three-dimensional and run from the roof to the foundation of the building.
• Should be made of high strength and stiffness materials
• Should be durable and sufficiently strong enough to withstand aerodynamic forces generated by wind flow

The placement of the air barrier should be decided by the engineers and should be such that after its installation, there should be a difference in the air pressures between the interior and exterior of the wall system.

Insulation element

An insulation element is used to prevent heat loss from the interior of the building. These wall types are also responsible for providing insulation and they block the heat from the ambient. The term thermal insulation refers to the blocking of heat fluxes from penetrating the wall type. The material of the wall blocks both heat transfer through convection, conduction, and radiation by providing thermal resistance. Besides thermal insulation, the wall system also provides water insulations. The concrete and the masonry materials keep the interiors insulated. Other materials that are excessively used in structural constructions include mineral wood, glass fiber, plaster, cork, and refractory bricks. Refractory bricks act as an excellent fire-resistant material that keeps the building insulated from fire. Based on their applications, there are different fire-resistant bricks to choose from.

Role of bricks in exterior wall systems

Bricks form the basis of wall systems including concrete and plaster. Bricks also form a part of the cladding of the wall which is laid in courses and patterns known as bonds. This is majorly known as brickwork carried out by masonry professionals. Bricks are stacked on top of one another with concrete in between for bonding between them. A combination of stacked bricks with mortar forms a single structural unit.

Bricks are stacked between the space between the columns, which provide structural integrity to the building. Bricks do not act as load-bearing elements in a building but only act as a protective enclosure that keeps the building insulated from exterior factors. Refractory bricks safeguard the building from fire and extreme heat.

Mass walls and wall assembly

Wall assembly is a combination of sub-components that accounts for the control, support, and finish of the building exterior. There are different types of wall assemblies, some of them are exterior sheathing membrane, exterior sheathing, structural components such as studs, rafters, and joists, vapor barrier, and interior sheathing.

Mass walls on the other hand are built with special materials, that rather than keeping the building interior insulated, store up energy during the daytime and release the stored energy during the night. This can aid in the release of heat energy during colder winter seasons and maintain warm interior temperatures. These walls release energy through energy exchange.

Context and Applications

This topic is extensively taught in many undergraduate and postgraduate degree courses of:

• Bachelors of Technology in Civil Engineering
• Masters of Technology in Civil Engineering
• Masters of Technology in Building and Construction Management
• Masters of Technology in Materials and Engineering

Practice Problems

1. Which of the following materials forms fire-resistant bricks?

1. Refractory materials
2. Wood siding
3. Glass fibers
4. All of these

Answer: Option a

Explanation: Fire-resistant bricks are made up of fire-resistant or refractory materials.

2. Which of the following forms the structural components of a building?

1. Tilt-ups
2. Spandrel
3. Rafters and joists
4. All of these

Answer: Option c

Explanation: Rafters and joists are the structural and load-bearing components of a building.

3. What is the purpose of a cavity wall?

1. To keep the building insulated from heat
2. To keep the building insulated from rainwater
3. To keep the building insulated from heat and rainwater
4. To keep the building insulated from wind

Answer: Option b

Explanation: The purpose of a cavity wall is to keep the building insulated from both heat and rainwater.

4. Which of the following acts as fire insulation elements?

1. Mineral wood
2. Cork
3. Glass
4. Both a and c

Answer: Option d

Explanation: Both mineral wood and glass act as building fire insulation elements.

5. Which of the following is considered in the placement of an air barrier?

1. Wind direction
2. Wind force
3. R-values
4. Both a and b

Answer: Option d

Explanation: Both wind direction and wind force decide the placement of air barriers.