PART 8: ACOUSTICS TECHNICAL REPORT

Acoustic Review 

Dial Corner is a proposition for an earth-sheltered dwelling to be constructed on a paddock that is located between London Road (B1172) and the A11 exit slip road. Achieving the peaceful ambience desired by its future occupiers, effective sound attenuation measures are proposed. 

Dial Corner is to be located 52 metres from the A11 slip road and 92 metres from the A11 dual carriageway. 

A useful recent planning precedent is a new dwelling on Silver Street in Besthorpe, granted planning consent in May 2019 application 3PL/2019/0157/F This dwelling that is approximately ten metres from the A11 and at the same level as the dual carriageway. Acoustic fencing was installed in compliance with the planning consent, satisfying Policy DC1 of the Adopted Core Strategy and Development Control Policies Development Plan Document 2009. Another useful example is on Wymondham’s Swallow Drive (Off Silfield Road) A group of houses that are less than 50 metres from the A11 only screened from the road by a belt of trees. 

The applicant has undertaken sound measurements using an NIOSS approved iPhone app. 

Minimum Acceptable Noise Levels 

The Institute of Acoustics recommends that sound levels within a home should not exceed 35dBviii. This is supported by the UK Government which states that 34dB is the permitted noise level, above which noise can be considered a nuisanceix . (According to the Health & Safety Executive, a quiet office environment typically measures 40dB, playing the piano measures 80dB and a full symphony orchestra 110dBx.) 

Proposed Sound Attenuation Measures for Dial Corner 

1. To the London Road elevation, earth-bunding combined with a 300mm thick dense concrete rear wall form the north wall. Sound attenuation from the north will be significantly more than the minimum standards recommended. 

2. Triple glazing with acoustic glass (slightly thicker) to the south elevation will (according to manufacturers) reduce sound transmission by 54dBxi . The Glass and Glazing Federation make a more cautious claim of 38db noise reduction with triple glazed windowsxii . 

3. Mitigating sound travelling from the A11 is a 3metre high timber acoustic fence located along the southern, eastern and western boundaries. According to acoustic fencing manufacturer Jacksons, this will reduce noise transmission by 28dBxiii . 

4. Planting trees and a hedge beside the fence will provide additional sound attenuation while reducing the visual impact of the fence. Species will be selected for their sound attenuating qualities. The UK Arboricultural association suggest that planting like this can reduce noise transmission by a further 6 – 10dBxiv. The embankment and the land between the slip road and the main carriageway was planted with trees in 1996, which are now mature and provide additional sound screening. 

5. Scheduled asphalt resurfacing of the A11 this summer 2021xv will reduce traffic noise amplification currently caused by the A11 concrete surface. 

Useful Observations 

Sound measurements undertaken beside the B1172;

 passing car 50db 

 lorry or bus 60db.

Conclusion A reduction in traffic noise levels within and around Dial Corner is to be achieved with a combination of earth-bunding, triple glazing, acoustic fencing, tree and hedge planting. It is anticipated noise levels outside the south elevation will be reduced to below 30dB. A further 15dB reduction is expected on the completion of the A11 resurfacing works.