# Section 7 Reverberation in the common internal parts of buildings containing flats or rooms for residential purposes

Reverberation in the common internal parts of buildings containing flats or rooms for residential purposes

# Introduction

**7.1** This Section describes how to determine the amount of additional absorption to be used in corridors, hallways, stairwells and entrance halls that give access to flats and rooms for residential purposes.

**7.2** For the purposes of this Section, a corridor or hallway is a space for which the ratio of the longest to the shortest floor dimension is greater than three.

**7.3** For the purposes of this Section, an entrance hall is a space for which the ratio of the longest to the shortest floor dimension is three or less.

**7.4 **When an entrance hall, corridor, hallway or stairwell opens directly into another of these spaces, the guidance should be followed for each space individually.

**7.5** The choice of absorptive material should meet the Requirements of Building Regulation Part B – Fire safety.

**7.6** Two methods are described to satisfy Requirement E3, Method A and Method B.

**7.7** **Method A:** Cover a specified area with an absorber of an appropriate class that has been rated according to BS EN ISO 11654:1997 Acoustics. Sound absorbers for use in buildings. Rating of sound absorption.

**7.8 Method B:** Determine the minimum amount of absorptive material using a calculation procedure in octave bands. Method B is intended only for corridors, hallways and entrance halls as it is not well suited to stairwells.

**7.9 **Where additional guidance is required, specialist advice should be sought at an early stage.

# Method A

**7.10 **For entrance halls, corridors or hallways, cover an area equal to or greater than the floor area, with a Class C absorber or better. It will normally be convenient to cover the ceiling area with the additional absorption.

**7.11** For stairwells or a stair enclosure, calculate the combined area of the stair treads, the upper surface of the intermediate landings, the upper surface of the landings (excluding ground floor) and the ceiling area on the top floor. Either cover at least an area equal to this calculated area with a Class D absorber, or cover an area equal to at least 50% of this calculated area with a Class C absorber or better. The absorptive material should be equally distributed between all floor levels. It will normally be convenient to cover the underside of intermediate landings, the underside of the other landings, and the ceiling area on the top floor.

**7.12 **Method A can generally be satisfied by the use of proprietary acoustic ceilings. However, the absorptive material can be applied to any surface that faces into the space.

# Method B

**7.13** In comparison with Method A, Method B takes account of the existing absorption provided by all surfaces. In some cases, Method B should allow greater flexibility in meeting Requirement E3 and require less additional absorption than Method A.

**7.14** For an absorptive material of surface area, S in m², and sound absorption coefficient, α the absorption area *A *is equal to the product of *S *and α.

**7.15** The total absorption area, AT, in square metres is defined as the hypothetical area of a totally absorbing surface, which if it were the only absorbing element in the space would give the same reverberation time as the space under consideration.

**7.16** For n surfaces in a space, the total absorption area, AT, can be found using the following equation.

**7.17 **For entrance halls, provide a minimum of 0.20m² total absorption area per cubic metre of the volume. The additional absorptive material should be distributed over the available surfaces.

**7.18** For corridors or hallways, provide a minimum of 0.25m² total absorption area per cubic metre of the volume. The additional absorptive material should be distributed over one or more of the surfaces.

**7.19** Absorption areas should be calculated for each octave band. Requirement E3 will be satisfied when the appropriate amount of absorption area is provided for each octave band between 250Hz and 4000Hz inclusively.

**7.20** Absorption coefficient data (to two decimal places) should be taken from the following:

- For specific products, use laboratory measurements of absorption coefficient data determined using BS EN 20354:1993 Acoustics. Measurement of sound absorption in a reverberation room. The measured third octave band data should be converted to practical sound absorption coefficient data, ap in octave bands, according to BS EN ISO 11654:1997 Acoustics. Sound absorbers for use in buildings. Rating of sound absorption.
- For generic materials, use Table 7.1. This contains typical absorption coefficient data for common materials used in buildings. These data may be supplemented by published octave band data for other generic materials.

**7.21 **In Method B, each calculation step is to be rounded to two decimal places.

*Table 7.1 Absorption coefficient data for common materials in buildings*

# Report format

**7.22** Evidence that Requirement E3 has been satisfied should be presented, for example on a drawing or in a report, which should include:

1. A description of the enclosed space (entrance hall, corridor, stairwell etc.)

2. The approach used to satisfy Requirement E3, Method A or B.

- With Method A, state the absorber class and the area to be covered.
- With Method B, state the total absorption area of additional absorptive material used to satisfy the requirement.

3. Plans indicating the assignment of the absorptive material in the enclosed space.

# Worked example

**7.23** Example: Entrance hall

The entrance hall has dimensions 3.0m (width) x 4.0m (length) x 2.5m (height). The concrete floor is covered with carpet, the walls are painted concrete blocks and there are four timber doors (1.0m x 2.4m).

To satisfy Requirement E3, either use:

- Method A: Cover at least 3.0 x 4.0 = 12m² with a Class C absorber or better, or

- Method B: Provide a minimum of 0.2m² absorption area per cubic metre of the volume.

**7.24 **Method B is described in steps 1 to 8 in Table 2. In this example, the designer considers that covering the entire ceiling is a convenient way to provide the additional absorption. The aim of the calculation is to determine the absorption coefficient, α*ceiling*, needed for the entire ceiling.

**7.25 **In this example, the absorption coefficients from Method B indicate that a Class D absorber could be used to cover the ceiling. This can be compared against the slightly higher absorption requirement of Method A, which would have used a Class C absorber or better to cover the ceiling.

*Table 7.2 Example calculation for an entrance hall (Method B)*

## Example: Entrance hall

7.23The entrance hall has dimensions 3.0m (width) x 4.0m (length) x 2.5m (height). The concrete floor is covered with carpet, the walls are painted concrete blocks and there are four timber doors (1.0m x 2.4m). To satisfy Requirement E3, either use:

- Method A: Cover at least 3.0 x 4.0 = 12m
- Method B: Provide a minimum of 0.2m

7.24Method B is described in steps 1 to 8 in Table 7.2. In this example, the designer considers that covering the entire ceiling is a convenient way to provide the additional absorption. The aim of the calculation is to determine the absorption coefficient, aceiling, needed for the entire ceiling.

7.25In this example, the absorption coefficients from Method B indicate that a Class D absorber could be used to cover the ceiling. This can be compared against the slightly higher absorption requirement of Method A, which would have used a Class C absorber or better to cover the ceiling.