The Concrete Centre has welcomed a new standard covering the performance of innovative housing. Particularly so as concrete looks set to match the criteria with ease.
Although the term “off-site construction” has been replaced by“modern methods of construction” to acknowledge that innovation is possible on and off-site, there has been confusion over the performance levels that these new systems will have to meet. This confusion should be lifted with the publication later this year of the Loss Prevention Standard for Innovative Dwellings
The LPS 2020 standard was developed by BRE Certification, at the request of insurers, mortgage lenders, regulators and manufacturers, to provide a single and consistent method of assessing the performance and design of methods of construction that do not have a track record in the UK. As such, it will provide a route for the certification of innovative building systems, sub-assemblies and elements used for domestic construction.
BRE Certification plans to launch the standard later this year after a calibration stage that will involve trialling a set of higher performance levels. These will cover floor resilience, fire resistance, security, energy efficiency and environmental impact.
Although the performance levels are yet to be determined, the concrete industry is confident that its construction systems will surpass them. Not only does concrete provide benefits well in excess of Building Regulations, but the long-term benefits are such that the whole-life cost of a concrete home should be calculated for minimum 120-year life time rather than the 60 years used in current comparisons.
One of the main problems of the high density building being advocated by government, and one that modern methods of construction must address, is noise from neighbouring properties. Here, the considerable mass of modern concrete walls and floors provide improved sound insulation compared with more lightweight construction techniques.
There is a wide range of concrete construction options available and all are able to meet the standards for sound transmission as specified by the revised Part E of the Building Regulations. New separating/party wall minimum values for airborne sound insulation are 45 dB for purpose-built dwellings and 40 dB for internal partitions within all house types including detached properties. The robust standard details developed for concrete blockwork separating walls are designed to exceed these levels and so ensure compliance with Building Regulations – and avoid pre-completion testing. A similar range of concrete systems have robust details for separating floors for airborne and impact sound requirements. This is good news for new home owners and housebuilders.
Further good news is provided by the speed of modern domestic concrete construction. One recent development is thin-joint mortar, which allows the depth of mortar to be reduced from 10 mm to 2 mm. Speed trials have shown that a wall of blocks with thin-joint mortar can be laid twice as fast as one built with traditional mortar. Construction speed can be increased by another 13.5% by using large-format concrete blocks, which have a face size equivalent to two traditional concrete blocks.
As well as offering good sound insulation, the density and mass of concrete provide high levels of thermal performance. Concrete’s thermal mass slows down the passage of heat through a wall, which means that, all things being equal, a concrete home is warmer in the winter and cooler in the summer than alternative systems.
A concrete wall is also airtight. Air leakage accounts for a significant percentage of energy loss in the home and is certain to become an important issue with the new revisions to Part L of the Building Regulations later this year.
Invariably, high-density housing raises concerns over fire. Concrete homes well exceed regulatory requirements because concrete does not burn and has an inherent fire resistance of up to four hours. Therefore, a concrete home would be more structurally sound after a fire and could be efficiently repaired.
New methods of concrete construction promise the increase these benefits still further. Insulating concrete formwork (ICF) offers extremely high thermal performance. The system consists of twin-walled, expanded polystyrene panels or blocks that are built up to create formwork for the walls of a building. This formwork is then filled with ready-mixed concrete to create a robust structure with the panels or blocks remaining as part of the finished structure Typically, U-values in the range of 0.11-0.30 W/m2K can be achieved. At the same time, the concrete core provides good sound insulation.
The system is also fast. An experienced team of four can erect and concrete the walls of a three-bedroom bungalow in just one day. ICF ticks other boxes too. There is minimal waste during construction and its thermal mass means it can save at least 20% of space heating energy. Assuming a market share increase of just 1% a year, this could equate to a reduction of carbon dioxide emissions of 40,000 tonnes over the next five years.
Another concrete system that should easily meet the higher performance levels of LPS 2020 is tunnel form. This is well suited to repetitive cellular projects such as apartment blocks.
It works by pouring concrete into a steel formwork “tunnel” to make the floor and walls. After 24 hours, the formwork is moved horizontally so that another tunnel can be formed. When a storey has been completed, the process is repeated on the next floor. A strong, monolithic structure is constructed that can be as many as 40 storeys high. The cells created can range from 2.4 m to 6.6 m wide, and these can be easily subdivided to create smaller rooms.
The speed of construction was underlined by recent accommodation blocks for Queen Mary and Westfield College, University of London. There, the superstructure for a 175-bedroom block was built in only 32 days. The acoustic performance of the system is underlined by testing carried out on a new student block at the University of East Anglia. The tests confirmed that the building exceeded the requirements of the new Part E of the Building Regulations for both airborne and impact sound by more than 5dB.
Concrete construction is likely to out-perform the levels in LPS 2020. Systems such as ICF and tunnel form are tried and tested in continental Europe. Reducing the number of certification and approval processes to just one agreed overall standard will encourage the greater use of innovative concrete systems.
Ian Cox, chief executive of The Concrete Centre