Reducing sound transmission is often thought to be a ‘dark art’ because the performance of sound insulation cannot be calculated in a similar way to thermal insulation, and the commonly held rules of thumb that are logical for heat transmission, do not hold true for sound. This creates a risk in design because the performance criteria for Part E in the Building Regulations depend on results obtained from pre-completion testing. That is to say, you won’t know if the Building Regulations have been met until the work is already done.
• Read more about the sound performance standards in Sound Insulation for Floors 101
Some examples of separating wall and floor constructions are given in Approved Document E. However, these examples are not guaranteed; and although the risk of failing is less, a poor sound test result could have costly consequences as remedial work will have to be carried out.
Robust Details offer a more pragmatic approach: prescriptive wall and floor constructions that satisfy Part E requirements without pre-completion testing. No pre-completion testing, no depending on test results, no risk. However, any deviation from the Robust Detail will mean that Regulation 41 no longer applies; so how ‘robust’ are Robust Details?
How Robust Details work
Robust Details are a private limited company who oversee the approved ‘Robust Details’ referenced in Regulation 41 of the Building Regulations (SI 2010 / 2214). These details are listed in the Robust Detail Handbook, freely available for download from www.robustdetails.com.
The construction details are examples of floor and wall constructions using specific proprietary products that have already undergone on-site testing and continue to satisfy Robust Details’ quality assurance requirements. Therefore, building to a registered Robust Detail means that pre-completion testing does not need to be carried out, saving time and money during construction.
Although a site doesn’t have to be registered with Robust Details to use Thermal Economics’ IsoRubber sound insulation products, many are; and Robust Detail E-FC-4 remains the most often used detail, featuring IsoRubber Base underneath a screed on precast concrete planks. As IsoRubber Base is a specified proprietary component listed as the resilient layer in E FC 4, any substitution for another product would invalidate the registration and require pre-completion testing.
Getting it wrong
Unfortunately, Thermal Economics has become aware that in some isolated cases, IsoRubber Base is not being installed on sites registered as Robust Detail E FC 4, and cheaper products have been installed instead. This means that the requirements of the Robust Detail haven’t been met, and therefore the floor construction no longer satisfies the Building Regulations without pre-completion testing.
However, this also raises an interesting question of liability. Who should pay for the pre-completion testing, and who will pay for any remedial work to be carried out?
Is there vicarious liability?
One could argue that the site manager has vicarious liability because the error occurred in the course of employment. Vicarious liability means that a person is also liable for damage caused by the negligence of those in that person’s service, as long as the negligent act was carried out whilst in the person’s commission.
However, when the contractor knows that the plot is registered as a Robust Detail and has been informed of the requirements of the Robust Details scheme, then the resilient layer is a proprietary product. The contractor making any amendments to the design or specification of the building element (such as product substitution) would be doing so on a frolic of his own, and the contractor would be wholly liable for any and all costs incurred.
Avoiding mistakes
The most important action for the site manager is to ensure that the contractor is fully aware that a Robust Detail has been specified, and what the requirements of that Robust Detail are. Thermal Economics products are specified in six proprietary Robust Details, and one semi-proprietary Robust Detail for separating floors; and provide free on-site training to site managers and contractors apropos correct installation and the requirements of the Robust Detail for Regulation 41 to apply.
• Read more on Thermal Economics Robust Details
• Read more on Thermal Economics site training
Guidance on Robust Details specifying Thermal Economics products can also be obtained from our Technical Department on 01582 544255, by e-mail to [email protected] or by using the Live Chat facility on our website.
Booking training
Whenever a site is registered with a Thermal Economics proprietary Robust Detail, Robust Details will advise us, and we will contact the site manager to arrange for one of our site trainers to give a free ‘toolbox talk’ to the contractors and the site manager. Depending on the complexity of the detail, this normally takes between 30 and 60 minutes.
You can also telephone our Sales Office on 01582 429305 to arrange or e-mail [email protected] to arrange a time convenient for you.