Durability - Acoustic separating flooring

Complaints about noise between dwellings are on the up. Peter Mayer of Building LifePlans looks at the choice of acoustic flooring solutions and analyses their whole-life costs.

Introduction

Noise is a modern paradox: we use more noise-generating products than ever in the home yet we want increased levels of peace and quiet. The 2004 changes to Part E of the Building Regulations, which cover resistance to the passage of sound, have attempted to address this by improving sound insulation for residential buildings.

Part E addresses key areas including separating walls, floors and stairs, internal walls and floors and reverberation in common areas and stipulates minimum performance criteria for airborne sound and impact sound insulation of separating floors. To achieve these standards, housebuilders can either use their own design and subject it to pre-completion sound testing or choose one of six approved separating floor “robust details” solutions, which exceed the minimum standard in Part E by a minimum of 5dB and therefore escape pre-completion sound testing

Separating floors

Separating floors are designed to limit or insulate against airborne sound , such as that from a television; impact sound, such as footsteps; and flanking sound – the indirect transfer of sound through the building fabric, usually through the walls separating dwellings. There are four principles to achieving the required sound insulation:

• Mass The heavier the floor, the less sound is transmitted. Mass is designed into floors by using concrete or adding layers of dense material to the timber or steel floor structure.

• Completeness of the acoustic element Air gaps and non–uniformity in the floor construction can reduce sound insulation performance. A high standard of installation is required to ensure air tightness and uniformity.

• Flexibility Flexible floors generally provide better sound insulation. The problem is a certain stiffness is required for structural reasons, and certain frequencies of sounds can be transmitted because of resonance.

• Isolation The physical separation of a floor reduces the transmission of sound through a structure. The installation of a floating floor, which incorporates resilient layers and uses soft or acoustic floor coverings, is the standard option for achieving separation.

Ceiling treatment in the room under the floor is just as important as the floor structure and floor covering.

Robust details-compliant separating floors

The “robust details” scheme details six principal separating floor solutions for concrete and timber flooring. There are 100 variations of ceiling and floor finishes within these headline solutions to satisfy Part E.

Concrete floors
There are four robust detail concrete separating floor solutions, which are based on precast concrete floor planks with a directly applied screed, floating screed or insitu concrete slab A steel deck and in-situ concrete composite floor option is also described.

Timber floors
The robust detail solution is based on I-joist floor structures.

Whole-life costs

Acoustic flooring falls in the category of long-life components, which means it should not incur a cost through its service life. However, costs may arise when the design or installation does not comply with good practice. The costs of remedial work can involve testing, investigation, intrusive repairs and retesting; they are typically are in the region of £1,000 - £10,000.

One unknown factor is the long-term performance of the resilient layers used to create a sound-deadening floor structure. Some products have a track record of 20 -30 years. Resilient layers with high compressive strength should not deform or compress with use.

Experience suggests that the most important performance issue, and therefore whole-life cost issue for acoustic insulation is workmanship. Critical areas include:
• All junctions especially where air-tightness may be compromised, for example, around services and though discontinuous components
• Compressible resilient layers under areas of localised higher loads such as partitions, or where the compressibility of the floor may conflict with rigid plumbing.

Although designing to the minimum standard may seem a cost-effective solution, the big “but” is that there is a high price to pay for failing to attain it. Over-specification may at worst reduce the risk of poor sound performance and at best provide sound insulation that is better than the minimum for the benefit of the building user.

In–use issues

BS 6093 recommends inspection of movement joints after the first year and all joints at intervals of one–fifth of their expected service life. Maintenance may be necessary where sealants attract dust, mould or mildew. Cleaning can be minimised by appropriate selection of sealants.

Specification options

	Capital cost (£/m²)
150mm precast concrete floor planks with a mass of 300kg/m³, 40mm sand-cement screed 80kg/m²; metal ceiling system with 100mm void and one layer of 8kg/m² gypsum board; floating floor: 70mm deep resilient battens with 18mm tongued and grooved particleboard.	87 - 107
250mm insitu concrete floor slab with a mass of 2400kg/m³; metal ceiling system with 75mm void and one layer of 10kg/m² gypsum board; floating floor: resilient cradle and batten system min 45mm deep, with 18mm tongued and grooved particleboard.	105 - 128
250mm timber I-joists, 100mm quilt insulation 10 – 33kg/m³ between joists; ceiling: resilient metal bars, two layers of gypsum based board 23kg/m²; floating floor: 70mm deep resilient battens, with 18mm tongued and grooved particleboard, gypsum based board 13.5kg/mœ and 13mm quilt insulation 10 – 33kg/m² between battens.	85 - 104
Composite in-situ concrete and profiled metal decking floor 2200kg/m³, concrete at least 80mm deep at thinnest point and at least 130mm thick at deepest point; Metal ceiling system at least 300mm from concrete surface and one layer of 8kg/m² gypsum board; Floating floor: resilient overlay platform floor system at least 16kg/m².	101 - 123

Table notes

• Costs based on 100² separating floor construction with allowance for service penetrations.

• Floor build-ups detailed above based on the Robust Details description. Robust Details Limited manages a registration scheme.

First published in Building 2005

Further information

Building LifePlans provides latent defects warranty for all buildings.

BLP Construction Durability Database at www.componentlife.com provides durability information for building components.

Further information contact peter.mayer@buildinglifeplans.com or telephone: 020 7204 2441.