Infill Walls: Types, Materials and How to Choose the Right System

Infill walls are one of the most fundamental decisions in the external envelope of any steel or concrete frame building. The wall panel built between the floors of the structural frame determines thermal performance, programme duration, usable floor area, and coordination complexity across the entire project.

Yet in practice, the choice of infill wall system is often made by default. And the default choice frequently costs developers floor area, costs contractors programme time, and creates liability gaps that only become visible when something goes wrong.

This article covers the main infill wall system types, how they compare, and what to consider when specifying one for a commercial or multi-storey residential project.

What Is an Infill Wall?

An infill wall is a non-load-bearing external wall panel built between the floor slabs of a structural frame building. The primary frame, whether steel or reinforced concrete, carries all vertical and lateral structural loads. The infill wall closes the building envelope: separating interior from exterior, providing thermal insulation, managing moisture, and carrying the external cladding.

The term specifically refers to the wall panel filling the space between floors. The insulation, air barrier, and structural wall build-up between the slab edges is the infill wall. The cladding system applied over it is separate.

Light Gauge Steel (SFS) Infill Walls

Light gauge steel framing, commonly referred to as SFS (Steel Frame System), is the modern standard for infill wall construction in commercial and multi-storey residential buildings across the Nordic and Baltic markets.

Cold-formed steel C-sections are fixed between head and sill tracks at the floor edges, forming a structural stud wall between the slabs. Insulation, typically mineral wool, is placed between and over the studs. An air barrier membrane is applied to the external face, and a subframe system carries the external cladding panels over the top.

Advantages:

• Thin wall assembly, significantly thinner total build-up than masonry, recovering usable floor area at every storey

• Lightweight, substantially lower structural load on the frame and foundations compared to masonry

• Dry construction, no curing time, works can proceed immediately after installation

• Accommodates any external cladding type: fibre cement, metal cassettes, terracotta, HPL

• Consistent thermal performance when correctly detailed

The coordination challenge:

In traditional SFS procurement, a complete wall assembly involves four to eight separate suppliers. Framing from one manufacturer. Insulation from another. The air barrier membrane from a third. The cladding subframe from a fourth. Cladding panels from a fifth. Window reveal detailing improvised on site by the installing subcontractor.

Each interface between these components is a potential point of failure. When something goes wrong, whether a thermal bridge, moisture ingress, or a detailing error at a window reveal, establishing which supplier is liable becomes a project in itself. Specialist SFS subcontractors are typically required, adding another trade to coordinate and another contract to manage.

Masonry Infill Walls

Masonry infill, brick or concrete block construction between the structural frame, is the traditional form of infill wall across most of Europe. It remains in widespread use, particularly in Eastern Europe and the Baltics, where it is familiar to contractors and requires no specialist trades beyond standard bricklayers.

How it works: 

Courses of brick or concrete block are laid between the floor slabs. Insulation is applied separately to the internal or external face. An external cladding, render, or facade system is then applied over the completed masonry.

Advantages:

• Familiar to the market, widely understood by contractors and subcontractors

• Good acoustic performance due to mass

• Durable under impact

Limitations:

• Slow, wet trade requiring curing time before subsequent works can proceed

• Heavy, crane-dependent material handling, significant structural load on the frame and foundations

• Thick, a fully insulated masonry infill assembly typically reaches 400-500mm total thickness, consuming usable floor area at every storey

• Multiple separate trades: bricklayers, insulators, and cladding subcontractors are all typically separate

• Thermal bridging at mortar joints requires careful detailing to achieve modern energy standards

The floor area impact of wall thickness is the most commercially significant factor for developers. In a 6-storey commercial building with a 300-metre perimeter floor plate, switching from masonry to a modern thin-wall system recovers 0.3 m² of usable floor area per linear metre of wall, 90 m² per floor, 540 m² across the building. At a sale price of €2,500/m², that is €1,350,000 in additional property value from the wall system specification alone, without changing the building footprint or planning consent.

What Comes After Infill: Complete External Wall Systems

Both SFS and masonry infill walls share a fundamental characteristic: they are assembled from multiple components, supplied by multiple manufacturers, coordinated by the contractor on site. The wall build-up, the cladding system, and the window interface are all separate procurement exercises.

Modern continuous non-load-bearing external wall systems have changed this.

DogWall Ultra by SIMPLEX Technologies delivers all the performance benefits of SFS infill, thin build-up, lightweight, dry construction, full design freedom in cladding finish, without the construction complexity traditionally associated with it.

The complete wall arrives as a factory-configured, flat-pack kit: SFS frame, mineral wool insulation, air barrier membrane, cladding subframe, cladding panels, and pre-engineered window interface boxes, all in one delivery, from one manufacturer. No cranes required for material handling. No specialist SFS subcontractors. No coordination between multiple suppliers. One company is responsible for the complete wall and cladding, and provides a single warranty covering the entire system.

For projects where programme speed, floor area efficiency, and supply chain simplicity matter, this approach replaces the traditional infill wall model entirely.

SIMPLEX Technologies: External Wall and Facade Specialists

SIMPLEX Technologies are specialists in non-load-bearing external wall systems and ventilated facade solutions, with over 300 completed projects across the Baltics, Scandinavia, and the UK.

If you have a project where the external wall system is under consideration, we are happy to advise on the right approach and prepare a technical proposal.

📧 simplex@simplex.lv 📞 +371 28603704 🌐 simplex.lv