Floors - Intermediate

Acoustic insulation is an important design consideration to prevent noise transfer between rooms and apartments on different levels. Floors must be correctly specified and constructed if they are to provide the required level of sound insulation.

Several research studies have highlighted that millions of people have their lives and privacy disturbed by noise from neighbours.

Glasswool products offer an ideal solution when used as a sound absorbent.

Glasswool provides an alternative method of controlling airborne sound transmission through a floor as opposed to simply increasing the mass. Installing glasswool in the floor / ceiling space voids will absorb energy from airborne sound waves. A secondary benefit of glasswool is to provide thermal separation between floors so that rooms can be zoned independently for heating.

Knauf Insulation Products

• Classic 040 Roll is a roll of unfaced glasswool, available in a range thicknesses to suit various building applications It is lightweight, flexible, resilient and non-combustible.
• KiDoo is a resilient, medium density glasswool roll encapsulated with a polythene laminate. The facing has a overlap along one edge to lap the edge of the adjoining roll.
• Rocksilk Acoustic Floor Slab is a rigid, non-combustible, compression resistant slab of rock mineral wool.
• Rocksilk Acoustic Floor Slab Plus is a dense, rigid, non-combustible slab of rock mineral wool which is highly compression resistant.

Summary

Knauf Insulation provide products that can be used as resilient layers for the control of impact sound transmission in separating floors and absorbent layers for the control of airborne sound transmission in both internal and separating floors.

Detailed below are separating floors for both new build and refurbishment as well as internal floors in both timber and masonry.

Detailed Design Considerations

Sound Insulation

Sound Insulation, otherwise known as sound reduction, is the prevention of noise being transmitted from one part of a building to another, for example by erecting a partition or wall.

Improving the sound insulation of walls and floors between dwellings is the main way in which the noise transmission between dwellings can be reduced. When considering sound insulation, three methods of sound transmission need to be considered:

• Airborne sound
• Impact sound
• Flanking sound

The air tightness of the construction is also important.

Performance Standards for Separating Floors and Stairs with Separating Function

* The weighted average sound reduction index modified by the addition of a factor to take into account problematic low frequency sound.
** This is allowed to be qualified by laboratory rather than field testing.

Airborne Sound

Airborne sound sources produce noise by vibrating the air immediately around the sound source. Typical sources include the human voice, musical instruments, home entertainment systems and noisy dogs.

The ability of an element of construction to resist the passage of airborne sound is largely determined by three factors:

1. The sound absorbency of any cavities in the construction
2. The structural isolation between the two outer surfaces
3. Its mass

Increasing the mass of a floor will improve its sound insulation but the amount of extra weight that can be safely supported is often limited. As a result, other design approaches are usually employed ie, isolation, absorbent materials and resilient layers.

Impact Sound

• Providing a resilient layer at the point of impact - such as a carpet
• Structural isolation - such as adding a resilient layer between the floor deck and the floor structure.

Flanking Sound

Flanking sound transmission usually refers to sound that travels through ‘flanking’ structural elements, such as the external wall that flanks a separating wall between two dwellings.

Flanking sound can also include sound that travels along unintended airpaths, such as unsealed gaps in the structure and around service penetrations.

The rationale for using glasswool for noise control

The sound absorption characteristics of glasswool make it ideal for use in modern buildings to reduce sound transmission. In addition, the thermal properties of glasswool provide a secondary benefit of minimising heat loss either between attached dwellings or between storeys within a dwelling. A further benefit is to minimise the overall mass of the floor, easing construction processes.

Typical Specification Clauses

1. Timber floor with I beams

Classic 040, 100mm thick, to be placed between the timber I beams. 

2. Timber separating floor

Classic 040, 100mm thick, to be placed between the independent ceiling joists.

3. Concrete separating floor

Rocksilk Acoustic Floor Slab Plus, 30mm thick, to be placed over the structural floor. All joints to be close butted.

The floating chipboard floor to be as specified by the designer. 

4. Floating timber deck on concrete separating floor

TI 120 (available in thicknesses 20mm and 30mm) on the concrete floor between battens.

Minimum 18mm thick t&g timber boards or flooring grade chipboard fixed to battens, minimum 45mm deep over and isolated from wall and structural elements in the floor. Nails used to fix the boards to the battens must not project below the battens. 

5. Internal floor

Classic 040, 100mm thick, to be placed between the floor joists. The ceiling and floor deck to be as specified by the designer.