By Phil Rigby; Rock Mineral Wool Product Manager (Knauf Insulation Northern Europe)
The noise of rain falling on lightweight flat roofs can be very distracting and seriously affect the use of spaces below. In schools, it can affect the comprehension of speech between teacher and students, as well as between students. In hospitals it can affect the effective communication between staff as well as the wellbeing of patients.
Acoustic conditions in schools are subject to Approved Document E (ADE) of the Building Regulations (England and Wales) as well as the Schools Premises Regulations 2012.
In ADE, Requirement E4 says that the rooms in a school shall be designed so that they have the acoustic conditions appropriate for their intended use.
Section 1 of Building Bulletin 93 (BB93) The Acoustic Design of Schools and the Acoustic Performance Standards for the Priority Schools Building Programme (PSBP) also sets out requirements to meet the values for sound insulation, reverberation time and indoor ambient noise which should be followed for Building Regulation approval.
For hospitals, similar standards are set out in the Hospital Technical Manual HTM 09-01, Acoustics.
The main issue for buildings with lightweight flat roofs is to limit the noise from rainfall being radiated through the construction into the spaces below. The problem is most serious for roofs where the profiled metal sheets are used as the structural deck.
Given that the impact noise from rainfall on a lightweight roof can create an indoor ambient noise level of 70dB, it is often necessary to provide some attenuation of the impact noises from rainfall within the flat roof element. This can be done by adding additional mass and by incorporating acoustically absorbent insulation.
To check that a roof construction is suitable for a particular type of space, the first step is to carry out laboratory measurements to determine the sound radiated from the roof construction (Sound Intensity Level) using the calculation method set out in BS EN ISO 140-18.
To give confidence to specifiers, Knauf Insulation has carried out extensive acoustic testing on our flat roofing rock mineral wool product. This has been done by using Rocksilk Krimpact Flat Roof Slabs incorporating different numbers of layers of Knauf Acoustic Membrane , and the extensive results can be found below;
The table highlights a range of acoustic and thermal performances for various thicknesses of Rocksilk Krimpact Flat Roof Slab that meets and exceeds compliance with the necessary Approved Documents Parts E and L.
Krimpact Flat Roof Slab is a high strength, consistent density, non-combustible rigid rock mineral wool slab manufactured using Krimpact Technology and specifically designed for use in flat roofing.
It is available in two grades (Standard and Extra), with Extra having the greater compressive strength for roof areas with more regular foot traffic.
Knauf Acoustic Membrane – KAM 5 is a 3mm thick high density, flexible, acoustic membrane, which is designed to reduce sound transmission, and typically improves the impact sound insulation performance of a flat roof by up to 3dB.
Why would you risk not having a profiled metal deck flat roof ? The combination of the appropriate rock mineral wool insulation slab, with the addition of a specialist acoustic membrane, allows you to meet and exceed the regulatory requirements in schools and hospitals.