A range of innovative methods and materials are now used across the construction industry and particularly when building new homes.
These offer potential savings in time and material costs, and can provide higher standards of quality than conventional construction methods. Off site assembly means quicker erection on site and the ability to achieve a weather-tight construction within a shorter period of time.
We consider how to manage the risks associated with new construction methods and materials in a 60 minute CPD session via building.co.uk.
So what is classed as an innovative method of construction, what are the design considerations and what are the risks involved with using them?
What are innovative methods of construction?
Innovative methods of construction typically fall into the following categories.
1. Volumetric or modular construction
This involves the off site production of three-dimensional units. Modules may be brought to site in a variety of forms, ranging from a basic structural shell to complete rooms with internal and external finishes and services already installed.
2. Panelised systems
This consists of off site production of panel units, which are then assembled on site to produce a three-dimensional structure. The panels may consist of wall, floor or roof units, sometimes referred to as cassettes.
3. Hybrid or semi-volumetric systems
These systems are manufactured off site and combine both panelised and volumetric approaches and typically volumetric units. Examples would be student accommodation or hotel pods.
There is another category of sub-assemblies and components within an otherwise traditionally built structural form. Typical examples would be floor or roof cassettes, precast concrete foundation assemblies and preformed service installations and cladding systems.
4. Site-based structural systems
These systems include insulated concrete formwork and are not considered to be manufactured off site. Site-based structural systems require independent third-party approval to secure a warranty and their acceptance relies heavily on the quality of procedures in place to ensure correct installation on site.
What are the design considerations?
With many newer methods, the construction, design and layout of a typical system is planned in advance and a “design freeze” should be imposed before factory production begins.
Rigorous project management is essential to avoid last-minute changes.
Standardisation is crucial when using innovative methods of construction, and as such they may not be adaptable for complex architectural or planning design requirements.
Additional testing may be necessary to ensure that standards for durability and weather-tightness can be achieved – for example incorporating flat roof drainage outlets through closed panel parapet extensions.
To obtain warranty approval, products or systems must:
- Meet the requirements of relevant British Standards or Codes of Practice, or equivalent European standards current at the time of application.
- Be approved by an independent third-party technical body with suitable accreditation.
- Be subjected to independent third-party testing that recognises UK Building Regulation requirements and additional warranty standards.
- Have CE marking in accordance with the Construction Products Directive.
What are the risks associated with innovative methods of construction?
All innovative construction materials and/or systems are subject to third-party testing in order to secure a warranty. However there are a number of risks associated with third-party testing as outlined below:
- Components are tested individually and rely on other products to perform adequately.
- Additional products may not be compatible or themselves lack third party certification themselves.
- Product testing does not take UK weather conditions and climate into account.
- There are often caveats included within a certification. For example, the building is said to be waterproof if it is bolted together correctly, but there is no reference as to how this should be done.
- Often the design can exceed the original parameters of the test – for example, where a system is approved for the construction of individual dwellings and it is used for a block of flats, or where it is designed for simple structures and the proposed design is more complex.
- It is often difficult to measure the long-term durability of a new or innovative product. Requirements from the Council of Mortgage Lenders expect structural components to have at least a 60-year durability. Individual components and assemblies, not integral to the structure, may have a lesser durability, but not less than 15 years.
Even when products or systems have achieved third-party approval, they will still need to be structurally approved on a site-by-site basis depending on the layout and loading of the component.
Although innovative methods of construction generally involve off site manufacture, there is always an element of on site workmanship.
The quality of the final product will depend on accurate assembly by factory-trained or authorised specialist contractors and any alterations made on site may invalidate a system’s guarantee or affect its performance.
The following risks should therefore be addressed:
- Approved contractors - most manufacturers have a process for approving specialist contractors but project managers should be satisfied this is suitably robust and determine where liability for design and workmanship lies.
- Foundations - there is very little tolerance for error with factory-built systems. Where only the superstructure is to be delivered in this way, the foundations and substructure must be extremely square and level. The approved contractor may have no control over this process on site, so the project manager must ensure that the contractor carrying out these works understands the level of accuracy required.
- Penetrations - all buildings require some form of penetrations to the structure during the installation of building services. In most cases, these trades are outside the scope of an approved contractor.
- Site planning - Many innovative methods, particularly modular systems and large panel systems, will require detailed advance planning of site access, off-loading, installation and possibly storage.
Though innovative methods and materials do present new and unfamiliar risks, this is not to say that warranty providers do not support their use, as long as the risks are appropriately managed.
LABC Warranty considers that such systems are a good option for development when supported by correct, relevant third-party certification and will accept any product or system that meets the requirement of our technical manual.
LABC Warranty also works in partnership with LABC (Local Authority Building Control) to provide an integrated “Registered Details” approval process, which encompasses both building control and structural warranty approvals. This allows a building or product to be accepted by more than 300 local authorities across England and Wales without a separate structural warranty application.
Don’t forget to check out the CPD module on building.co.uk to receive your 60 minutes’ worth of CPD credits.
By Craig Ross