Blockwork (concrete masonry)
Concrete blocks are a cost-effective, and tried and tested means of providing load-bearing and non-load-bearing walls with many other performance and sustainability benefits. There is a well-established supply chain for concrete blocks in the UK, providing a readily-available source for construction. Concrete blocks remain the most common choice of material for the inner, structural leaf of an external cavity wall in contemporary UK housing. They are also commonly used below ground for basement construction or as part of the foundation structure and as part of a beam and block structural floor. External block walls may be fair-faced or rendered as part of a building or commonly as robust boundary and retaining walls in the landscaping.
Types of blocks range from ultra lightweight and lightweight aggregate through to dense aggregate blocks, with a corresponding range of performance properties. Many contain high levels of recycled content and are themselves 100 per cent recyclable. Concrete blocks can be supplied to suit a range of wall finishes including plaster and dry-lining or simply a paint finish. Those designed for building fair-faced walls are available in a variety of colours and textures.
Innovation in this sector includes new systems such as thin joint blockwork but also in ancillary products such low conductivity walls, enabling this established method of wall construction to evolve to meet and exceed current thermal performance requirements for external walls.
Performance benefits of blockwork include:
- Robust and durable: concrete blocks are particularly suitable for situations where low-maintenance is a high priority or simply for additional security.
- Resilience and security: their integrity is unaffected by water and concrete is more resilient to impact than many other internal, and external wall systems.
- Inherent fire resistance for fire safety: providing fire isolation with no spread of flame, concrete block walls often exceed the minimum standards required by building regulations for most building types for fire safety.
- Inherent fire resistance for property protection: the inherent fire resistance of concrete offers further benefits for protecting property in the event of a fire during occupation compared to other building materials.
- Inherent fire resistance during construction: for the development of urban sites this is a significant advantage over most other walling systems since recent HSE guidance to limit fire spread between sites would otherwise likely require costly additional fire prevention precautions.
- Thermal performance: lighter-weight blocks have high thermal insulation properties. Dense aggregate blocks are heavier, less thermally insulating but higher in thermal mass so useful as a fabric energy store in buildings to help heat and cool a building. For more information on the use of thermal mass and thermal performance properties of external wall constructions using an inner leaf of blockwork refer to The Concrete Centre publication Thermal Performance: Part L1A Masonry details with pre-determined thermal bridging Psi-values are available.
- Excellent airtightness: effective and durable airtightness can be provided with a plaster or render coat finish but also using perimeter sealed drylining. A combination of both is also effective, with a thin render coat (or parge coat) under dry lining. For more details see publication How to Achieve Good Levels of Airtightness in Masonry Homes.
- Acoustic insulation: inherent mass, stiffness and damping properties are assets for attenuating and reducing noise levels between buildings and within them. For external walls along noisy roads these properties are difficult to replicate in alternative lighter-weight framed solutions. Masonry products are available designed for single skin internal walls for schools, medical facilities and other applications where additional acoustic insulation is necessary. Acoustic performance can be further improved with different linings.
For more information on acoustics in housing refer to How to Achieve Good Levels of Acoustic Insulation in Masonry Homes.
- Adaptability: blockwork is typically assembled on site, providing flexibility and design adaptability late into the construction programme. Unlike other light-weight framed systems structural support is inherent to a whole block work wall, providing flexibility on site and during occupation for the location of internal fixtures and fittings.
- Material efficiency and cost-effectiveness: the combination of performance benefits (e.g. durability, fire resistance and acoustic separation) in a single leaf of masonry is materially-efficient and cost-effective.
Blockwork external walls
Concrete blocks can be used effectively in a variety of external wall construction systems including solid wall construction, brick and block cavity wall or two layers of block work with a cavity. All offer high levels of thermal performance. A range of available solutions, with associated insulation and thermal mass values is available in Thermal Performance: Part L1A. Detailing guidance for thermal performance can also be found in Building low carbon homes – guides 1 & 2 – Masonry cavity wall construction & Concrete frames.
Masonry infill and non-loadbearing concrete masonry walls
The wide ranging performance benefits of concrete blocks as a structural solution extend to the use of blocks in non-loadbearing situations, such as infill panels in concrete framed structures, or for internal partition walls.
For fire protection a distinction is made between non-loadbearing walls and load bearing walls. Refer to BS EN 1996-1-2: 2005 and manufacturers information for more details on specific performance and associated detailing guidance. (Note: A shear wall, or one designed to withstand wind resistance is defined as a load bearing wall.)
Structural design of infill panels in frames
The two main structural issues to consider with infill panels are differential movement of the block work and reinforced concrete structure and, particularly at the building’s perimeter, lateral resistance (to wind). Vertical differential movement is overcome by soft joints and/or head details to accommodate movement at soffits. Laterally, movement joints at maximum 6-9 metre centres should be used to avoid problems. Lateral resistance to wind can be increased using bed reinforcement but often in commercial multi-storey structures where spans and wind loads are large, vertically spanning wind posts may become necessary.
Solid infill masonry walls can be used as shear walls as long as they are appropriately designed and differential movements are catered for. Further guidance is provided in publication How to Design Masonry Structures using Eurocode 6.