sound insulation testing guide

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Floor insulation guide

When looking at floor constructions, two major aspects need to be considered. These are both the airborne and impact sound insulation performance. Indeed, Building Regulations Approved Document E requires floors to be tested for these two types of noise transmission.

The overall sound insulation performance rating of a floor is the end result of the floor’s individual airborne and impact sound insulation indices.
A properly constructed floor system should therefore satisfy both types of sound insulation with the right choice of materials and proper installation and fitting.

Impact noise isolation

The most effective method of reducing impact noise (i.e. noise generated from footfall) is to install an element offering a good degree of resilience, so that the impact energy is absorbed. There are many types of treatments for impact sound, including:

  • Soft floor coverings
  • Resilient battens
  • Resilient cradle systems
  • Platform floors

Most of the above systems would also contribute to the improvement of airborne sound insulation. Generally, when installing a resilient floor treatment care should be taken not to puncture or bridge the layer by laying it on sharp floor surfaces or mechanically fixing (nails, screws) to a subfloor decking.

Soft floor treatment

Soft floor coverings are the most practical way to improve the impact sound insulation performance of a floor. Carpet underlays are usually confused with bonded soft floor layers, however the latter are more sturdy  and present a significantly better acoustic performance. Thicknesses vary from approximately 4mm to 22mm in thickness and they are usually fixed by adhesive bonding.

In the case of a proprietary floor system (e.g. laminate) being applied on top of a soft floor, care should be taken to isolate the boards from the perimeter walls and skirtings either by a flanking strip or by stopping the boards short of the surrounding walls by approximately 5mm in order to isolate any bridging that would allow footsteps to flank into the space below.

Platform floors

They are mainly comprised of a resilient layer as a backing to a deck system with tongue and groove edges, such as compressed chipboard. Thicknesses vary from 15mm to 55mm.

The pre-bonded resilient layer ensures that the whole floor surface is treated uniformly while the hard surface reduces the potential for the resilient layer to be damaged. For most platform floor systems, services and underfloor heating should not penetrate the resilient layer as this would significantly reduce the impact sound insulation performance.

Resilient battens

This system involves timber channels which have a pre-bonded resilient strip along their length. The resilient layer is composed of foam or a fibrous polyester product. Systems vary according to the degree of resilience, isolation and performance. Resilient battens must always be installed onto a flat surface (e.g. decking boards, floorboards, concrete floors) and must never be directly laid on joists. For timber joist floors, resilient battens must be installed on a sub-deck system.

Resilient cradle floor systems

These are primarily composed of a deck system resting on timber battens which in turn are supported at set centres by resilient supports. These supports are the cradles and can be useful in cases when multiple services run in several directions within the floor.

Ceiling systems

Ceiling treatments constitute the most functional way of improving the airborne sound insulation of a floor system. The treatments which usually employ secondary ceiling systems include direct fix ceilings, special hanger ceilings or independent systems.

Direct fix ceilings

Direct fix secondary ceilings should present a minimum spacing of 100mm from the existing floor system. However, optimum acoustic performance is achieved with voids of 200-250mm.

Generally, the greater the ceiling void and the less direct connection with elements of the original floor, the better the performance. The installation of an absorptive layer within the void of a ceiling can significantly increase the overall performance of the floor both for airborne and impact.

Metal resilient bars are the most common way of attaching the new ceiling boards to the existing structure. These provide the necessary degree of isolation by introducing resilience at the point where the bar is fixed to the ceiling board. They are typically 11-16mm thick and vary in design. They should never be mounted directly to the underside of an existing ceiling as this creates full contact between the ceiling and the bar for its entire length. It is always preferable to install a metal or timber rafter and then mount the resilient bars at right angles to the direction of the frame’s elements. In the case of timber joist floors, the resilient bars may be directly connected to the joists provided they are perpendicular to the direction of the joists.

When fitting ceiling boards on resilient bars, care should be taken for the fixing to penetrate only the resilient bar and not come into contact with any other component.

Hanger systems

Proprietary hanger systems (spring, acoustic or resilient hangers) allow a significantly greater improvement in airborne sound insulation than other systems. However, they are more costly and more challenging to install.

Independent ceilings

These mainly consist of timber frames supported off a perimeter wall hanger system. A typical frame section would be 100 x 50 mm but the size would increase with span.

Minimum ceiling depth should not be less than 125mm but preferably 250mm for optimum performance.

For an effective improvement in sound insulation, the ceiling joists should be offset at least 25mm below the existing ceiling or floor structure. The frame should employ a minimum of 100mm mineral wool quilt between the joists. The ceiling is usually finished with two layers of normal density plasterboard (min. 8kg/m3 per layer), although higher density acoustic plasterboards could be used for higher airborne performance.

 

 

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