The acoustic insulation question

Rain noise is transferred to us in the form of sound waves. During rain fall a variety of frequencies relating to the impact of rain drops on to the roof surface are produced. The existing roof structure will be acting as a soundproofing material in some capacity but perhaps rain noise control was not a primary consideration when the roof in question was constructed. When confronted with attempting  to soundproof a roof against rain noise, the first consideration will most likely be to add acoustic materials to combat  the range of frequencies of sound (rain noise), that is emanating from the roof structure. Any structure will vibrate at certain frequencies, the roofing panels be they metal or composite will behave like a drum skin and when impacted will produce sound. Is it not logical therefore to introduce acoustic treatment materials that are designed to  tackle this noise problem head on.

The conventional approach would be to add mass to the roof. We all know intuitively that a thicker roof or wall will inhibit the propagation of noise (sound waves). So make the roof thicker to attenuate the noise level produced by rain fall, is this not the obvious answer?  The most well-known law of soundproofing is the Mass Law. This states that by doubling the weight of the acoustic barrier you will gain roughly a 6dB improvement in sound reduction.  In other words, if you doubled the size of a brick wall for instance, you would get around a 30-40% improvement in soundproofing.  Likewise with a roof, but now we have to consider the additional loading we are about to introduce, can the roof support this additional loading and at what cost?

OR SHOULD WE BE LOOKING AT THIS PROBLEM FROM A DIFFERENT PERSPECTIVE?

Adding mass to the roof is all to address the problem of rain noise AFTER it has occurred. An alternative solution would be to prevent the rain noise BEFORE it occurs? Silent Roof Matting Material (SRM) does exactly that as it is installed on the OUTSIDE of the roof on top of the existing roof surface. Furthermore, SRM only weighs 800gms per square metre, any roof structure should be able to support this minimal addition. So instead of adding mass, how is the Silent Roof approach going to work?

Silent Roof Matting Material (SRM) is a unique product that in simple terms quietly shatters falling rain drops on it’s upper smooth surface without transferring the impact noise produced to the roof surface beneath. The rain water then trickles through the lattice of the SRM then drips quietly on to the original roof surface and away in to the rain water drainage system. Silent Roof will stop the great majority of rain noise on any composite roofing structure to a mere whisper. The material is black in colour and is UV stabilised. Due to the flexible properties of the material it can be utilised on any surface be it flat or curved. We have developed various means of securing the material to a variety of surfaces.

Reuse
As SRM is not bonded to the roof structure in any way, it can be utilised to protect temporary structures against rain noise pollution. This is a unique property of the product with obvious benefits to the purchaser.

In Technical Terms
Silent Roof Matting Material (SRM) is a flexible, three dimensional matting, produced from polyamide mono filaments welded together where they cross to form a tough, open structure. It has a flat back on one side produced from mono filaments in an irregular, two dimensional structure which is thermally bonded to the three dimensional structure. Follow this link to see a full specification.