Wardle Storeys Reducing Rain Noise on Profiled Metal Roofing Systems Using DEDPAN DS2020 RDV
Wardle Storeys (Blackburn) Ltd has developed a simple but effective new solution to significantly reduce rain noise on metal roofing systems. Significant performance improvements have been quantified at BRE using the ISO 140-18 draft standard a new standardised methodology to measure noise generated by rainfall on roofing elements. Summary Noise caused by rain falling onto metal cladding is a commonly occurring problem, and is specifically referenced in the latest DfES produced BB93 (1) Acoustic design guide for schools. One recommendation is the use of damping on any profiled metal cladding. The DEDPAN family of lightweight highly efficient vibration damping products have been used extensively in automotive and other industries for many years. When applied to thin gauge metal panels these specialised products have a molecular morphology that effectively reduces the amplification of resonant vibration and hence the unacceptable NOISE that can be generated. A new product, DEDPAN DS RDV, is a welcome addition that retains the superior damping performance of the self-adhesive variants. The formulation has been enhanced so that the product can be supplied in rolls which makes it even easier to apply to the profiled roof sections for OEM s or alternatively as a post-treatment.
Representative Testing Historically, evaluating the performance of treated and untreated roofing systems in a laboratory has been difficult due to the absence of a common rain noise standard. However using the methodology detailed in ISO/CD140-18 (2) (committee draft) quantification to a provisional standard is now possible. A number of parameters define standard rain types including fall height, intensity (litres per minute per square metre) and median drop diameter based on definitions given in BS 7527-2.2 (3). BRE (4) advised on the various rain conditions options based on return rates. In the UK intense rain would typically occur with a return rate of 2 years whilst heavy rain would have a return rate of 50 years. A third rainfall type moderate rain was also suggested because it is more representative of UK rainfall. DEDPAN DS 2020 RDV 246mm strips on standing seam section. For maximum relevance the extreme rainfall conditions were chosen for our evaluations these being the least demanding moderate rainfall and the most demanding heavy rainfall'. Sound intensity, LI, measurements to ISO 15186-1:1997 (5) and ISO/CD 140-18 (specifically ISO TC43/SC2 N 0751 Dated 13-1-2004) were made on the roof section under these two rainfall conditions with and without DEDPAN treatments. Roof Specimen A very common standing seam roofing membrane was tested so that any results would have a broader relevance to the many constructions currently in use. Specifically the profiled metal roof was 400 mm wide, 0.9mm gauge, 3.5Kg/m 2, ribbed aluminium standing seam roof with Stucco emboss. To have the simplest possible test condition five 2.1m long sections of the profiled strips were seamed together without the usual supporting structures. This roofing element was then resiliently mounted on a wooden frame resulting in an open test area of 3.7m 2 and a pitch angle of 7º. Positioning the rain box for Heavy Rainfall test at the BRE test facility.
6dB(A), L IA, Improvement over Untreated Roof Section The results show that an improvement of 6dB(A) in sound intensity level (L IA ) is made to the roof section when a 246mm wide DEDPAN strip is applied to each of the five 2.1m long sections (equivalent to a 60% area coverage). Additionally the linear 3rd octave band centre frequency spectra also shows an even improvement across the frequency range. This result was achieved in both the moderate and heavy rainfall conditions. Smaller DEDPAN strip widths were also evaluated and some degree of proportionality between coverage and noise reduction was evident, especially under heavy rain conditions. For example, a 164mm strip (equivalent to 40% coverage) gave improvements in A-weighted sound intensity of about 4-5dB (L IA ). Plots of Sound Intensity Reduction Heavy Rainfall Improvement in Sound Intensity to ISO 15186-1 and ISO/CD 140-18.
Plots of Sound Intensity Reduction Moderate Rainfall Improvement in Sound Intensity to ISO 15186-1 and ISO/CD 140-18.
Plots of Sound Intensity and Total Loss Factor Improvement Heavy Rainfall Improvement in Total Loss Factor and Sound Intensity Reduction for Dedpan 246mm Strip Condition. As a separate exercise the total loss factor, h TOTAL, of the roofing element with and without DEDPAN was also measured. This showed the DEDPAN treatment gave an overall higher h TOTAL than the untreated structure which confirmed that the rain noise improvements were due to the increased internal losses of the DEDPAN treated aluminium standing seam roof.
Benefits of DEDPAN DS 2020 RDV in Metal Roofing Noise Control DEDPAN offers system designers and manufacturers a simple but effective alternative to improve rain noise on their imaginatively designed systems. By reducing at source the rain induced vibrational energy by damping, the structure borne vibration flanking to supporting elements of the roof structure is also reduced. i.e. The amount of acoustic absorption material and/or dense boarding in the overall standing seam roof structure may also be reduced when using DEDPAN. DEDPAN can be factory fitted and because DS2020 RDV is only 1mm thick it has only a minor effect on the gauge and appearance of roofing panels. The product is lightweight applying a 246mm wide DEDPAN strip to a typical 400mm wide aluminium panel increases the weight by only 30%. Testing to this new standard methodology has enabled a more reliable quantification of the beneficial affects of DEDPAN treatment on standing seam roof structures.
References: (1) Building Bulletin 93 Acoustic Design of Schools (2) ISO/CD 140-18 (ISO TC43/SC2 N 0751 Dated 13-1-2004) Committee Draft Measurement of Sound Insulation in Buildings and of Building Elements, Part 18:Laboratory Measurement of Sound Generated by Rainfall on Building Elements. (3) BS 7527-2.2: 1991- Classification of Environmental Conditions-Environmental Conditions Appearing in Nature-Precipitation and Wind (4) Building Research Establishment, Garston, Watford, WD2 9XX (5) ISO 15186-1: 1997- Acoustics-Measurement of Sound Insulation in Buildings and of Building Elements Using Sound Intensity-Part 1:Laboratory Measurements Sales Office Wardle Storeys (Blackburn) Ltd Durbar Mill, Hereford Road, Blackburn Lancashire BB1 3JU England Tel: +44 (0) 1254 583825 Fax: +44 (0) 1254 681708 E-mail: sales.blackburn@wardlestoreys.co.uk Web: www.wsbl.co.uk