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Acoustic Insulation being installed

Robust Details, timber floors and block cavity walls – do they work?

Robust Details claim that they are responsible for design, specification and acoustic performance of the majority of new build residential developments in the UK that include separating constructions such as dividing walls and floors in semi-detached houses, town houses or flats/apartments.

Find out more about Robust Details

Why use Robust Details?

Clients, developers, architects and specifiers want to use Robust Details because they remove the need for acoustic testing, something the majority of the industry doesn’t agree with (if you understand the problems this brings) but is something that we have learned to accept.

Building with timber floors & block cavity walls

There is no getting away from the fact that Robust Details are responsible for the majority of specifications created in new build residential sector and most definitely responsible for the acoustic performances achieved within the new build sector. However, with all this in mind Robust Details do not satisfy the needs of the most commonly used construction type in the UK. This is timber joists and block cavity walls. This is because, although many have tried, the level of acoustic performance that is required to get Robust status is not achievable consistently with this form of construction. Due to this, if you are looking to build with timber floors and block cavity walls then you will need to get the site acoustically tested.

Working with consultants

We have worked with acoustic consultants since the regs last changed in 2003 (England & Wales – Document E) to come up with various details to ensure that this form of construction will pass an acoustic test, but without working with companies such as Hush, it is a minefield for specifiers and designers if they don’t understand the weaknesses in this form of construction. The main issue is flanking noise.

Controlling timber floor acoustics to meet Robust Details

Timber floors with traditional external cavity walls is a typical construction for apartment build, but it is one that will cause acoustic issues if not correctly treated. We can provide a solution for the floors, in fact the Hush System HD1036 is one that is used all the time in this form of construction. However, treating the floors is the easy bit when you install the correct floor to ceiling detail, it is the flanking transmission down the inner leaf of the external cavity block walls that will cause the floors to fail a test if not correctly treated.

Up there with installation, flanking transmission is the biggest cause of acoustic test failures and in particular on this form of construction. Flanking transmission can make the majority of sites fail a test if not correctly treated. This is when noise bypasses the floor construction and travels up and down the inner leaf of continuous block work. The only way of guaranteeing to remove the issue is to specify a wall lining system on the inside of the inner leaf of the external cavity wall. Something like our Hush Wall Liner System HD1041 can be used for this.

We have worked with contractors over the years to come up with colourful ideas to treat flanking transmission. Some include changing the density of the block work within the inner leaf of the cavity wall or adding resilient seating’s within the block work to break up the transmission paths. Others have used wall linings but used them sparingly to ensure that just enough has been done to get through the test. The bottom line is however that something does need to be done on site to remove the flanking noise issue and this is something that Hush can help you with.

Consider separating walls

The other thing to think about on this type of development is the separating walls. We have block cavity walls, timber stud walls and metal stud walls that are available and will perform to the standard required to meet the Building Regulations.


In a nutshell, Robust Details does not cover timber floor and masonry cavity walls as a detail and therefore acoustic testing needs to be done on site to show compliance. Make sure you do not fail an acoustic test by coming to Hush to discuss the detailing and the specification. Call technical on 01519332026.

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