How to meet acoustic building regulations when converting a space above commercial premises to residential

In 2021, the UK government changed the planning regulations, which eased the process for converting underused commercial spaces into much-needed residential units. The new permitted development rights (PDR) meant, for example, that the first floor space above a shop could be converted into a flat without the need for planning permission, provided that a number of conditions could be met.

The policy change appeared to have the intended effect, with the number of property owners and developers undertaking conversion projects in England surging under PDR in the first year (2021-22). And today, it is an important dimension to the strategy to increase the housing supply chain.

However, it is important to remember that whilst PDR conversion projects avoid the need to go through the lengthy and sometimes complex planning process, they must be converted in accordance with the Building Regulations. This is also required for conversion projects that are subject to planning approval, of course.

In England and Wales, this means new residential units created through conversion projects must comply with Approved Document E relating to the passage of sound or insulation against noise in layman’s terms. This sets minimum performance standards for sound insulation in separating floors, ceilings and walls to ensure that the occupiers of flats or apartments can expect quietness to a satisfactory level, a factor that contributes to a decent quality of life.

What does Approved Document E demand for flat conversions?

The Building Regulations in England and Wales define commercial-to-residential conversion projects as ‘Material Change of Use’. The acoustic performance standards which apply to Material Change of Use projects are slightly more lenient than new build developments, but that does not mean corners can be cut when it comes to sound reduction.

Approved Document E contains two sections that apply to domestic houses, flats and apartments. Section E1 relates to protection against sound from other parts of the building and adjoining buildings, and E2 is concerned with sound within a dwelling, i.e. the acoustic performance of internal walls within the home.

In Material Change of Use projects, section E1 requires the following:

It is worth noting that these performance levels are 2 dB lower than in new build projects. In addition, section E2 does not necessarily apply to Material Change of Use projects, which may be welcome where space is limited or there is an aim of preserving original internal features.

Keeping the commercial premises fully functioning

One of the most important acoustic considerations in projects where a residential property is being created above a commercial unit, such as a shop or café, is how to maintain routine business operations whilst the work is undertaken. The sound-insulating properties of the floor and ceiling separating the two properties must be sufficient to accommodate the noise generated within the commercial premises, which varies according to its usage, and in the majority of cases, this will need an upgrade.

Any work to alter the separating floor/ceiling has the potential to disrupt business operations, which may need to be minimised or even avoided completely. This is particularly important in projects where the interior of the commercial premises could be very costly to alter, or if it is architecturally sensitive.

In addition, when an acoustic ceiling lining is added, the floor-to-ceiling height in the room is reduced.

This may be undesirable aesthetically, or it may make the ceiling too low for the commercial space to function properly.

Where the building has a timber joisted floor construction, the solution could be to choose an acoustic floor/ceiling system that can be upgraded from the upper floor side only. Hush Acoustics offers this in the form of the HD1006 Hush System 1, enabling impact sound performance of 48 dB L’nT,w to be achieved and 53 dB DnT,w + Ctr for airborne.

This exceeds the performance requirements in Material Change of Use projects without the need to alter the ceiling, because sound reductions can be achieved by removing the existing timber floor and creating a floating floor. The floor panels are separated using Hush Felt 25 resilient strips applied to the joists, and the voids are filled with both Hush Slab mineral wool sound absorbers and Hush Fill 60 heavy pugging.

Bespoke acoustic floor/ceiling systems can also be developed to accommodate specific requirements and masonry floor construction.

Remember too that the type of floor finish selected for the newly created residential unit could have implications for impact sound affecting the commercial unit below. A solid wood or laminate floor installed in the apartment may need additional acoustic underlay to prevent sounds such as footsteps from being heard in the property below. This could take the form of Hushlay 15, 12 or 8 sound matting or Hush FFR Resilient Underlay.

Acoustic upgrades to walls

Walls which separate two residential units need to achieve a minimum performance of 43 dB DnT,w + Ctr. If the space being subdivided was previously used for purposes including offices or store rooms, it is likely that the existing walls were never originally built with high levels of sound insulation in mind. They may well be single timber stud construction, for example.

A number of options are available to bring the separating walls up to the required level, such as creating a twin stud wall or adding a wall lining.

The approach you choose will usually depend on how much floor space you are prepared to lose and the desired level of acoustic performance, i.e. compliance level, better or superior.

Generally speaking, the thicker the wall construction, the more scope there is to add mass and separation, and a higher acoustic performance will be possible.

The good news is that Approved Document E compliance is still possible in projects where the ideal world scenario is not possible.

Special consideration must also be given to walls which separate the residential unit from communal areas, such as a staircase to other properties within the same building.

The acoustic performance here does not need to be to the same standard as walls which separate two properties, but it still needs to achieve an acceptable level.

In one recent project, a customer approached Hush with this exact issue. The conversion involved creating an apartment above a shop, which already had another apartment above on the second floor. The existing separating wall between the newly created apartment and a communal landing was a 4×2 timber stud with a single layer of plasterboard, which offered a fairly poor level of acoustic insulation. Any acoustic upgrade, however, had to take into account that there was limited space available to add to the wall thickness.

The go-to solution for a project of this kind would be to add a twin-stud wall, which is typically recommended to provide superior sound insulation, but the space limitations meant this was not an option. Instead, a slim acoustic wall lining system was recommended in the form of the Hush HD1041 System, which adds less than 60mm to a wall’s thickness.

A wall featuring this system achieves airborne sound performance of 48 dB DnT,w + Ctr, thanks to the way the lining adds mass and provides separation. It features Hush Bar Deep resilient bars which create a void when fitted to the studwork that can be filled with Hush Slab 25 sound absorbers. High mass Hush Multi-Panel boards are then attached to the resilient bars prior to installing a further 15mm plasterboard layer.

Conclusion

There is no doubt that the changes introduced in 2021 have enabled more residential dwellings to be created in what would otherwise be empty or under-utilised floors within commercial buildings. And embarking on a conversion project can be an attractive prospect for property owners seeking to leverage more income from their buildings.

However, conversion projects can present all kinds of issues given the variability of construction quality and material choices according to the era of the building. This can impact efforts to meet all areas of the Building Regulations, whether that is in respect of the thermal standards, security, accessibility, acoustics or anything else.

Costly mistakes relating to soundproofing can be avoided through early consultation with an acoustic consultant or Hush Acoustics. We are experienced in advising on conversion projects of all kinds, backed by extensive knowledge of how different types of acoustic products can be combined with the substrates present in the building to achieve the desired sound reduction through walls, floors and ceilings.