Infill wall: an overview

In the context of modern construction, ensuring optimal energy efficiency and high thermal comfort is essential for the sustainability and well-being of building occupants. In this scenario, infill walls play a crucial role, being responsible not only for the structural stability of buildings but also for their thermal performance.

In this article, we will look at the various aspects concerning infill walls by analyzing the key factors that influence thermal performance.

Installation of a brick infill wall

Definition and role of the infill wall

The “infill wall” is a vertical building element that serves to separate an interior space from the exterior and protect it from weather elements such as rain, wind, snow, and sun, thus contributing to the durability and longevity of the building.

It is important to understand that infill walls are non-load-bearing, which means they do not directly support the weight of the building. This implies that infill walls are responsible for filling the empty spaces between the load-bearing structures of the building, acting as a protective barrier and defining the building’s external envelope.

The distinction between infill walls and load-bearing structures is crucial to understand their specific role. While load-bearing structures are designed to support the weight of the building and transfer it to the ground, infill walls are designed to provide structural support and protection without serving a load-bearing function. This means that infill walls must be strong enough to withstand external stresses but do not necessarily have to bear the weight of the entire building structure.

Additionally, infill walls are crucial for controlling the thermal performance of buildings, contributing to thermal insulation and maintaining a comfortable internal temperature.

Main Functions of Infill Walls in the Building Envelope

Infill walls are active and complex components of the building envelope. They should not be considered mere filling elements, as their proper design directly influences seismic safety, habitability, and the energy class of the property. Their main functions can be summarized in these fundamental points:

Protection from Weather Agents and Durability

The primary function is to create a physical barrier against rain, wind, snow, and solar radiation.

An effective infill wall:

• Prevents infiltrations – avoids structural damage and the formation of mold within the insulating layers.
• Ensures longevity – through the use of robust materials and scheduled maintenance, it preserves the integrity of the entire building over time.

Thermal-Acoustic Insulation and Living Comfort

The infill wall is primarily responsible for the thermal-hygrometric well-being of the occupants.

• Thermal insulation – reduces the thermal transmittance value (U), limiting heat loss and lowering heating and cooling bills.
• Thermal inertia – essential in Mediterranean climates, it allows for a delay in the thermal wave, keeping interiors cool in summer even without heavy use of air conditioning.
• Acoustic insulation – acts as a shield against urban noise pollution, ensuring quiet and comfortable indoor environments.

Seismic Safety and Structural Interaction

In seismic areas, the behavior of infill walls is crucial. Even though classified as “non-structural elements,” they:

• Provide stiffness – interact with the frame during an earthquake, absorbing some of the horizontal forces.
• Require design attention – must be appropriately uncoupled or reinforced to avoid the “short column” effect or out-of-plane overturning, phenomena that can compromise the overall stability of the building.

Fire Resistance and Compartmentalization

Infill walls play a crucial role in fire safety. By using fire-resistant materials and high-temperature materials (such as brick or aerated concrete), they serve as compartmentalization, preventing the spread of flames between the outside and inside or between different housing units, ensuring the necessary time for evacuation.

Lightness and Load Optimization

A fundamental modern aspect is the pursuit of lightness. The use of innovative materials, such as autoclaved aerated concrete (AAC) or dry systems, allows for:

• reducing the self-weight that burdens foundations and beams;
• simplifying logistics and installation operations on site;
• maintaining high insulating performance without weighing down the structure.

Infill wall in brickwork

Types of Infill Walls and Their Applications

The choice of the type of infill wall depends not only on aesthetic criteria but is closely linked to the intended use of the building, the climatic zone, and the technical performance required by the project. Today, the market is mainly divided between traditional “wet” systems and innovative “dry” systems.

Brick Infill (Traditional Systems)

This is the most widespread solution in Italy, thanks to its durability and excellent thermal inertia.

• Hollow or cellular brick: ideal for residential buildings where a balance between cost and thermal performance is sought.
• Rectified thermal blocks: thanks to the millimetric precision of the joints, they reduce thermal bridges and improve overall insulation.
• Applications: standard residential construction, high-end renovations, and contexts where a high surface mass is required for summer comfort.

Autoclaved Aerated Concrete (AAC) Infill

An extremely lightweight material with excellent insulating properties due to its cellular structure.

• Characteristics: easy-to-install and shape blocks, with excellent fire resistance.
• Applications: high energy efficiency buildings (NZEB) and situations where it is necessary to reduce the permanent load on the supporting structure.

Dry Infill (Layered Systems)

These systems involve the use of a supporting metal structure to which sheets of various materials (fiberglass, reinforced concrete, exterior drywall) are fixed.

• Characteristics: speed of execution, extreme lightness, and ease of integrating systems into cavities.
• Applications: tertiary buildings, offices, hotel structures, and extensions where construction speed is a critical factor.

Prefabricated Panel Infill

These are pre-assembled elements in the factory that arrive on site ready for installation.

• Characteristics: can be made of reinforced concrete, wood (X-Lam), or metal sandwich panels.
• Applications: industrial warehouses, shopping centers, and large infrastructures where standardization ensures certain times and costs.

It is necessary to make a further distinction regarding the number of layers, identifying single-layer walls and multi-layer walls.

Brick Infill vs. Autoclaved Aerated Concrete Infill

The choice between brick and autoclaved aerated concrete (AAC) represents one of the most common design crossroads in modern construction. Both solutions offer excellent performance but have radically different physical characteristics and installation methods that influence the behavior of the envelope.

Pored Brick: Tradition Evolving

Brick—often in variants such as lightweight brick or insulated hollow brick—remains the reference standard in several countries, including Italy.

• Strengths: very high thermal inertia (heat accumulation capacity), ideal for Mediterranean climates where summer comfort is a priority. It also offers superior mechanical resistance for fixing heavy loads (e.g., cabinets, air conditioners);
• Limits: Higher specific weight compared to lightweight concrete and often the need for multi-layer systems or external cladding to achieve the U transmittance values required by NZEB regulations.

Autoclaved Aerated Concrete (AAC): Efficiency and Lightness

Materials such as autoclaved aerated concrete have revolutionized the concept of single-layer infill:

• Strengths – it is an isotropic material (same properties in every direction) that naturally eliminates many thermal bridges. Its extreme lightness reduces the seismic masses of the building and speeds up installation thanks to large blocks that can be worked with hand tools;
• Limits – lower thermal inertia compared to solid brick (although compensated by low conductivity) and the need for specific finishing cycles (reinforced plasters) to prevent micro-cracking.

Single-Layer vs. Multi-Layer Infill Systems

The configuration of the wall stratigraphy determines the hygrometric and thermal behavior of the building. The choice between a single-layer system (massive wall) and a multi-layer system (composite wall) depends not only on regulatory requirements but also on the climatic conditions of the site and the availability of space on site.

Single-Layer Systems (Monolayer)

Single-layer infill walls are made with a single block that simultaneously fulfills structural (filling) and insulating functions. Typically, hollow brick or autoclaved aerated concrete (AAC) blocks of high thickness (from 30 to 50 cm) are used.

Advantages

Simplification of installation, reduction of construction times, and risks of human error. Being a homogeneous system, it ensures excellent natural breathability of the wall.

Disadvantages

To achieve high energy standards (Class A4, NZEB), thicknesses can become significant, reducing the usable internal surface of the building.

Ideal Application

Residential buildings in areas with temperate climates or where the simplicity of the “all-in-one” construction is preferred.

Multi-Layer Systems (Cassette Walls or with Cladding)

These systems involve the combination of different materials, each with a specific function: an internal massive part (brick), an intermediate insulating layer (EPS, rock wool, cork, etc.), and an external finish (plaster or an additional layer of bricks).

Advantages

They allow for achieving very high thermal insulation performance with more contained overall thicknesses. The continuous insulating layer protects the structure from thermal bridges and external thermal shocks.

Disadvantages

Greater complexity of execution. They require particular attention to the dew point to avoid the formation of interstitial condensation between the different materials.

Ideal Application

Buildings in cold climatic zones or complex architectural projects that require maximum control of thermal dispersions.

Infill wall with insulation

Common Issues: Infill Wall Visible Through Walls or Connection Defects

In post-construction phase or during the renovation of old buildings, it is not uncommon to encounter aesthetic or functional defects related to infill walls. These problems, although often perceived as purely visual, can hide critical issues related to the technical physics of the building or its structural response.

The “Ghosting” Phenomenon: Visible Infill Wall

One of the most frequent problems is the appearance of the masonry pattern (the mortar joints or the profile of the blocks) through the external or internal finish.

The Causes – This effect, known as ghosting, is due to the difference in thermal transmittance between the infill wall block and the mortar joint. The joint acts as a thermal bridge, creating colder areas on the surface where air moisture condenses more, attracting dust and dirt particles.

The Solution – To prevent the infill wall from being “visible,” it is necessary to ensure a continuous insulating layer (external insulation system) that equalizes the surface temperature of the facade, preventing the underlying pattern from showing through.

Connection Defects Between Infill Wall and Frame

The interface areas between the infill wall and the load-bearing structure (reinforced concrete columns and beams) are the most vulnerable points of the building envelope.

Detachments and perimeter cracks: They often manifest as linear cracks along the perimeter of the wall. They are caused by the different elastic and thermal deformations of the materials (reinforced concrete moves differently than brick).

Lack of Constraints (Overturning) – If the infill wall is not properly anchored or mechanically constrained to the structure through connectors or plaster carrier nets, there is a risk of “out-of-plane” overturning, particularly dangerous during a seismic event.

Air and Water Infiltration – A poorly sealed connection allows drafts to pass through (reducing acoustic and thermal comfort) and, in the worst cases, rainwater infiltration that degrades the internal insulating materials.

How to Prevent These Problems?

To ensure a durable and aesthetically flawless wall, it is necessary to adopt technical measures during installation:

• use of plaster carrier nets, to be placed mandatorily at points of discontinuity between different materials (e.g., between column and brick) to absorb stresses;
• expansion joints, intended as movement spaces where the dimensions of the wall exceed critical limits;
• foams and elastic sealants, used to fill the head joint between the infill wall and the upper beam, allowing the structure to flex without excessively loading the underlying wall.

How Does the Overlap of Infill Walls Affect Thermal Bridges?

The positioning of the infill wall relative to the structural frame (beams and columns) is not just an aesthetic choice, but a technical decision that determines the extent of linear thermal bridges. A correct “overlap” is the only way to ensure the continuity of insulation and prevent localized energy losses.

The Risk of “Internal Flush”

When the infill wall is built flush with the columns, the reinforced concrete structure remains exposed to the outside.

Consequence – Reinforced concrete has a much higher thermal conductivity than brick or AAC. Without an insulating cover, the columns become true “heat highways” that transport cold inside, causing localized condensation and mold in the corners of the rooms.

The “External Flush” or “Stack” Solution

To minimize thermal bridges, the best strategy is to advance the infill wall outward, partially or completely covering the load-bearing structure.

In the external flush infill wall, the wall completely covers the outer face of beams and columns. This allows for the application of an insulating layer (external insulation) continuously, without interruptions at the frame. When this is not possible (and thus cannot be fully protruded), thin elements (brick tiles or specific insulating panels) are used to be placed between the column and the outer face of the wall to equalize the thermal resistance of the facade.

The Importance of the Beam-Column Node

The overlap must be carefully studied not only in plan (columns) but also in vertical section (edge beams).

Vertical Overlap – The wall must “embrace” the floor beam. If the insulating material does not cover the contact point between the floor and the infill wall, a thermal bridge is created that cools the floor or ceiling of the rooms.

Material Continuity – The goal is to minimize the jump in surface temperature. A correct overlap ensures that the isothermal line (the line connecting points at equal temperature within the wall) remains as straight as possible and does not undergo abrupt deviations at the reinforced concrete.

Advantages of Correct Overlap

• Energy Efficiency: Drastic reduction in heating needs.
• Hygiene and Health: Total elimination of the risk of mold formation in corners and behind furniture.
• Thermo-Hygrometric Comfort: Uniform internal surface temperatures throughout the room.

Thermal Performance of Infill Walls and Material Selection

The thermal performance of an infill wall is not limited to its ability to retain heat in winter but includes managing energy transfer throughout the year.

The selection of materials must therefore meet a dual need: insulation (for cold) and inertia (for heat).

Key Parameters for Evaluation

To correctly choose the infill wall material, three fundamental parameters established by current regulations (D.M. Minimum Requirements) must be analyzed:

• Thermal Transmittance (U): Measures the amount of heat that passes through the wall. The lower it is, the greater the insulating power. For NZEB buildings, very low values are targeted, often below 0.25 W/m²K.
• Thermal Phase Shift (Φ): Indicates the time (expressed in hours) required for the heat wave to pass from outside to inside. A good infill wall must have a phase shift of at least 10-12 hours to ensure summer comfort.
• Periodic Thermal Transmittance (Y_ie): Evaluates the wall’s ability to dampen external heat input. It is the parameter that best describes the wall’s behavior under the action of summer sun.

Material Selection Criteria

The choice of material cannot disregard the climatic zone (from A to F) in which the building is located:

Cold Climates (Zones E, F)

The priority is low thermal conductivity (λ). Multi-layer systems with generous thicknesses of low-density insulators (rock wool, EPS, polyurethane) or high-performance aerated concrete blocks are preferred.

Warm and Mediterranean Climates (Zones A, B, C, D)

Here, inertia is king. Thick porous brick is often the best choice because its mass allows it to accumulate heat during the day and release it at night, keeping the interiors cool.

Materials Compared for Thermal Efficiency

In addition to classic bricks and concretes, modern selection includes:

Blocks with Integrated Insulation

Bricks that house polystyrene or rock wool inserts inside the holes. They combine mass and insulation in a single element.

Layered Dry Systems

Use cavities filled with mineral or natural fibers (hemp, wood fiber), excellent for controlling transmittance but with lower thermal inertia compared to massive systems.

The Importance of Hygrometric Calculation

In material selection, it is essential to perform verification with the Glaser diagram (or dynamic regime simulations). Pairing materials with different vapor permeability without criteria can cause interstitial condensation, which over time nullifies the thermal performance of the insulation and degrades the infill wall.

The best materials for insulating infill walls

The choice of insulating material for an infill wall should not be based solely on the thermal conductivity value (λ). A professional approach requires evaluating the chemical-physical compatibility with the substrate, vapor permeability, and mechanical resistance capacity.

Among the most effective solutions in the contemporary construction landscape, rock wool stands out for its mineral nature and versatility. Being an “open” material to vapor diffusion, it allows the infill wall to breathe, drastically reducing the risk of interstitial condensation. Moreover, its high density provides excellent acoustic insulation and superior fire protection, as it is an incombustible material.

Alternatively, for interventions where it is necessary to maximize economic savings or operate in contexts with a high risk of rising humidity, synthetic materials such as expanded polystyrene (EPS) or polyurethane offer excellent insulating performance with reduced thicknesses. However, the use of these materials requires careful design of joints and finishes, as their low vapor permeability can excessively seal the envelope, making a controlled mechanical ventilation (CMV) system essential in indoor environments.

A rapidly growing sector is that of bio-building insulators, such as wood fiber, cork, or hemp. These materials are particularly suitable for infill walls that require an increase in thermal inertia. Thanks to their high specific thermal capacity, these natural insulators significantly contribute to thermal lag, making them the best allies for summer comfort, especially in warmer climatic zones.

Finally, for infill walls with cavities, the blowing of cellulose or mineral granules represents a high-level technical solution that allows filling every air void, eliminating convective movements within the wall without resorting to expensive external cladding. The final choice must therefore stem from a balance between energy objectives, budget, and, above all, the hygrometric behavior of the complete wall package.

FAQ about infill walls

What is the definition and role of infill walls?

An infill wall is a vertical building element that serves to delimit an internal environment from the outside and protect it from weather agents such as rain, wind, snow, and sun, thus contributing to the durability and longevity of the building. It is important to understand that infill walls (both internal and external) are non-load-bearing, meaning they do not directly support the weight of the building. They are responsible for covering the empty spaces between load-bearing structures, acting as a protective barrier and defining the external envelope. The distinction between infill walls and load-bearing structures is crucial: while load-bearing structures transfer weight to the ground, infill walls provide structural support and protection without performing a load-bearing function. Furthermore, they are crucial for controlling the thermal performance of buildings.

What are the main functions of infill walls?

The main functions are: 1. Protection from weather agents and durability: creates a physical barrier, prevents infiltration, and avoids structural damage. 2. Thermal-acoustic insulation and living comfort: reduces thermal transmittance (U), ensures thermal inertia to phase-shift the summer thermal wave, and acts as a shield against noise pollution. 3. Seismic safety and structural interaction: provides rigidity by interacting with the frame and requires attention to avoid the ‘short column’ effect. 4. Fire resistance and compartmentalization: prevents the spread of flames. 5. Lightness and load optimization: the use of materials like CAA reduces weight on foundations and simplifies logistics.

What are the different types of infill walls and their applications?

The main types include: 1. Brick infill walls (Traditional Systems): perforated or hollow for standard residential use and rectified thermal blocks to reduce thermal bridges. 2. Autoclaved aerated concrete (CAA) infill walls: lightweight and insulating, ideal for NZEB buildings. 3. Dry infill walls (Layered Systems): metal structures with plasterboard or drywall panels, ideal for offices and extensions due to fast construction speed. 4. Prefabricated panel infill walls: pre-assembled elements in concrete, wood, or sandwich for warehouses and large infrastructures. They are also distinguished into single-layer and multi-layer walls.

What are the differences between brick infill walls and autoclaved aerated concrete (CAA) walls?

Porous Brick offers very high thermal inertia, ideal for Mediterranean climates, and superior mechanical resistance for heavy loads, but has a greater weight and often requires external cladding. Autoclaved Aerated Concrete (CAA) is an isotropic material that eliminates many thermal bridges, is extremely lightweight, and speeds up installation, but has lower thermal inertia compared to solid brick and requires specific finishing cycles to prevent micro-cracking.

What is the difference between single-layer and multi-layer infill wall systems?

Single-layer systems use a single block (30-50 cm) for structural and insulating functions, simplifying installation and ensuring breathability, but may reduce the usable internal surface due to high thicknesses. Multi-layer systems (cassette walls or with cladding) combine different materials (brick + insulation like EPS or rock wool + finish), allowing high performance with reduced thicknesses but with greater execution complexity and the need for attention to the dew point to avoid interstitial condensation.

What are the common problems of infill walls and how can they be prevented?

Common problems include ‘Ghosting’ (visible masonry pattern due to differences in transmittance between blocks and joints) and connection defects (peripheral cracking, risk of overturning, or infiltration). Prevention requires: the use of a continuous insulating layer (cladding), the application of plaster mesh at points of discontinuity, the creation of expansion joints, and the use of foams or elastic sealants for the head joint between the infill wall and the upper beam.

How does the overlap of infill walls affect thermal bridges?

The positioning relative to the frame is decisive. The ‘internal line’ leaves the columns exposed, creating thermal bridges and mold. The ‘external line’ solution covers the structure allowing for a continuous cladding. If not possible, brick tiles or insulating panels are used between the column and the wall. The beam-column joint with vertical overlap is also crucial to ’embrace’ the beam and ensure the material continuity of the isothermal line, improving energy efficiency, hygiene, and comfort.

What parameters and materials define the thermal performance of infill walls?

The key parameters are Thermal Transmittance (U), Thermal Lag (Φ), and Periodic Thermal Transmittance (Yie). In cold climates, low conductivity is favored (multi-layer systems or CAA), while in hot climates, inertia (porous brick) is prioritized. Modern solutions include blocks with integrated insulation and dry systems. It is essential to perform verification with the Glaser diagram to avoid interstitial condensation due to the juxtaposition of materials with different vapor permeability.

What are the best materials for insulating infill walls?

The choice depends on conductivity (λ), compatibility, and permeability. Rock wool is excellent for breathability, acoustic insulation, and fire resistance. EPS and polyurethane offer high performance with reduced thicknesses but require attention to CMV due to low permeability. Bio-building insulators (wood fiber, cork, hemp) are optimal for thermal inertia in warm climates. For cavities, the blowing of cellulose or mineral granules eliminates convective movements without external cladding.