Rain Noise Reduction
Why do metal roof panels generate so much noise when it rains?
Typical metal roofs are constructed from steel or aluminium sheets with a panel thickness between 0.46mm and 2.0mm.
When it rains, the raindrops excite the thin metal panels upon impact. The thin metal panels resonate, generating a high noise, especially during heavy rain.
‘Rain Noise’ requirements of the BQSH (Building Quality Standards Handbook) as stated below:
The roof design should control excessive noise from the rain in learning and speech-use areas. The noise effect from rain on a roof should not exceed the ambient noise levels within AS/NZS 2107 by more than 5dB(A) during a moderately heavy rain event (up to 10mm/hr rate).
Megasorber D14 and Megasorber LD5 are products specially designed for rain noise reduction on metal panels. These materials absorb the vibration energy and therefore reduce the rain impact noise of the thin metal roof panels. Both options can be installed on either side of the roofing panel – installing on the underside will extend the product service life.
Megasorber D14 is a self-adhesive vibration-damping sheet with an easy peel-and-stick application. Sheets are pre-cut to 260mm, 180mm or 150mm wide strips to work with most metal roof profiles. Megasorber D14 offers consistent vibration damping at elevated temperatures. Megasorber D14 does not need to be applied to 100% of the surface area – the recommended treatment area is 50 to 80% of the total area.
D14 damping demonstration video
The effect of D14 on metal purlin cladding panels before and after the installation
The estimated coverage for metal roof sheet
Megasorber D14 can be cut and supplied in strips designed to be fitted into the flat part of the metal roof sheeting. The standard strip size is 180mm x 1000mm; Take the Klip-Lok Classic 700 Metal Roof Sheeting, for example.
- Klip-Lok Classic 700 Metal Roof Sheeting profile:
- Flat surface: three sections of 180mm;
- Acoustic treatment product: Megasorber D14.
- Best option: 180mm wide D14 ( 77.14% coverage)
- Economic option: 150mm wide D14 (64.28% coverage); Note: 150mm wide D14 is a non-standard size and made to order only.
- Installation: Megasorber D14 can be installed on top or underneath the metal roof sheeting.
Megasorber LD5 is a water-based liquid deadener that can be painted, trowelled, rolled, or sprayed on. It has excellent bonding on metal roof panels and a high damping effect. Megasorber LD5 is ideal for panels with more complicated shapes and can be applied in various thicknesses, depending on the substrate thickness. Megasorber LD5 should be applied with full coverage on the panel (100% coverage) for the best effect. Typically recommended coating thickness is 2mm (wet) for metal roofing panels.
Using composite absorption & barrier products to reduce rain noise intrusion
Absorber-barrier composite ceiling material is also extremely useful for increasing speech intelligibility against external sound intrusion. Take the rain-drop impact noise, for example, as shown in the below schematics, Assuming the rain impact noise is 75 dB(A).
The left diagram: noise reduction through a composite product only, such as Megasorber CM28. The estimated total noise reduction is about 29dB(A). The estimated noise level is 46 dB(A) in the office.
The right diagram: noise reduction when combining the composite product with a vibration damping material such as Megasorber D14 on the roof (see damping page for more information). The damping treatment on the metal roof panels contributed an extra 13 dB(A) noise reduction. The combination of the CM28 and D14 provides an estimated noise reduction of 42 dB(A). The estimated noise level is 33 dB(A) in the office.
CM28 and D14
Further Technical Information
The estimated noise reduction (NR) after damping treatment
The damping treatment by D14 or LD5 is designed to provide 20dB(A) noise reduction for metal roof sheeting. The technical details are as follows:
The noise generated from rainfall in a lightweight roof structure can be estimated by*:
The estimated noise reduction (NR) after damping treatment:
*Reference: Ballagh, K.O., Marshall Day Associates, Auckland, New Zealand.
- NR (Noise Reduction) = 20 dB(A), for a large freely suspended metal roof sheeting.
Depending on the actual metal roof profile and roof construction, the metal roof sheeting tends to have some constraints on fixing points and edges, and as a result, the noise reduction after the damping treatment is less than 20dB(A). Based on the previously completed projects, the typical noise reduction is between 10 dB(A) to 18 dB(A) after applying damping material.
Demonstration videos on impact noise reduction of thick metal panels before and after the damping treatment
The measured noise reduction before and after the damping treatment is shown in two demonstration videos below. A tapping machine was used to simulate the continuous impact excitation. 5mm thick steel plate and 12mm thick aluminium plate were used. The design criteria are a system loss factor
Impact noise reduction demonstration
5mm steel plate and Megasorber DT2 damping tile before and after damping treatment. Measure noise reduction: NR = 15.5 dB(A).
Impact noise reduction demonstration
12mm aluminium plate and Megasorber DT2 damping tile before and after damping treatment. Measure noise reduction: NR = 13.1 dB(A).
For more details on how the damping materials work and typical noise reduction after applying the damping materials, please follow this link: Damping.