Sound Insulation Regulations UK: What Part E Actually Requires

Four numbers cover almost every home, and the one most refurbishments miss is not a number at all, it is whether Part E applies to you in the first place.

The sound insulation regulations that apply to homes in England sit in Part E of the Building Regulations, and the practical detail is in Approved Document E, whose current edition was published on 4 March 2015 and carries amendments made in 2004, 2010, 2013 and 2015. It is short, and the part that governs a home comes down to four performance figures and one question about scope.

That scope question decides most projects. Part E bites on new dwellings and on a material change of use, for example splitting a house into flats or forming a new flat in a basement or loft. Reordering the inside of an existing single home does not trigger it. What often does bite instead, in a London flat, is the lease.

The four requirements, in order

Approved Document E is organised into four requirements, and knowing which one you are under stops a lot of wasted specification.

• E1 covers separating walls and floors between one dwelling and another, or between a dwelling and any other part of the building. This is where the 45 dB and 62 dB figures live, and where testing applies.
• E2 covers internal walls and floors within a single dwelling: walls between a bedroom or a room containing a water closet and other rooms, plus internal floors. The standard is a laboratory value of at least 40 dB R_w, and there is no site test.
• E3 covers reverberation in the common internal parts of buildings containing flats: stairwells, corridors, entrance halls. It is a building-wide matter rather than a flat one.
• E4 covers acoustic conditions in schools, through Building Bulletin 93.

Reading the numbers properly

Airborne and impact figures run in opposite directions, which is the most common misreading.

Airborne is measured as D_nT,w + C_tr, an on-site weighted level difference between two rooms. Higher is better, and 45 dB is a minimum to beat. The C_tr correction is what makes the standard honest: it weights the result towards low frequencies, so a partition that stops conversation but not a subwoofer or a passing bus does not pass on a technicality.

Impact is measured as L'_nT,w, the sound level heard below when a standard tapping machine runs on the floor above. It is a level, so lower is better, and 62 dB is a ceiling not to exceed. Footfall on a hard floor is the everyday version of that test, which is why hard flooring is the single most common cause of a dispute between flats.

Conversions get a modest relaxation, 43 dB airborne and 64 dB impact, in recognition of what can realistically be achieved inside an existing structure. It is a relaxation of two decibels, not of the principle.

How compliance is proved

There are two routes, and you pick one before work starts rather than after.

1. Pre-completion sound testing. An acoustic consultant tests a sample of completed units before occupation and submits the results to building control. Fail, and you are opening up finished work.
2. Robust Details. For new-build attached dwellings you can instead build a separating construction from the Robust Details handbook, registering the plots with Robust Details Ltd before work starts. The details are specified to perform above the regulatory minimum precisely so that the site test can be dispensed with. Register late and the route is closed to you.

Conversions cannot use Robust Details. If you are forming flats out of a house, testing is the route, and it should be priced in from the first cost plan rather than discovered at practical completion.

What actually delivers the numbers

Sound insulation is not a product you buy, it is four things working together, and weakening any one of them undoes the other three.

Mass

Heavy stops sound. Dense blockwork, concrete, multiple layers of dense plasterboard. Doubling the mass of a partition buys you a useful few decibels, and it is the cheapest thing on the list to get right at design stage and the most expensive to add later.

Isolation

Above about 45 dB, mass alone runs out. You need to break the structural path: independent stud walls with no fixings bridging the cavity, resilient bars on a ceiling, a floating floor on a resilient layer. A single screw through a resilient bar into the joist behind it will cost you more decibels than the bar was ever going to give you.

Absorption

Mineral wool in the cavity damps the resonance between leaves. It is cheap, it is easy, and it is often the difference between a marginal fail and a comfortable pass.

Sealing

Sound behaves like water. A gap at a perimeter, an uncapped socket back box, a badly sealed service penetration or a poorly detailed junction between a new partition and an existing floor will leak straight past a specification that was fine on paper. Flanking transmission around the edge of a good separating element is the usual reason a test fails.

The corollary for interiors work is worth stating plainly: a 40 dB internal wall fitted with a hollow-core door and an undercut is not a 40 dB barrier. If acoustic privacy matters in a bedroom or a home office, the door and its seals have to be specified alongside the wall.

The London flat problem: leases beat regulations

The most common acoustic conversation we have in London has nothing to do with Part E. It is a leaseholder who wants to take up carpet and lay engineered timber, in a flat where the lease requires floors to remain carpeted, or where the freeholder's licence to alter demands a specified acoustic underlay and, sometimes, a test.

Part E does not apply to that work, because there is no new dwelling and no material change of use. The lease does apply, and it is enforceable against you personally. Deal with it before the floor is ordered, not after a neighbour complains. Our guides to a licence to alter in a leasehold flat and to building regulations for a London renovation cover the consent process around this, and the Party Wall Act covers the separate notice regime that applies when you cut into a shared wall.

Sensible targets when the regulations do not apply

In a single house where Part E is silent, the figures are still the best available yardstick. A 40 dB R_w partition is the right starting point for a bedroom wall, a home office or a media room, and a floating floor build-up over a resilient layer is worth doing over any room where footfall will be heard below. Plant noise deserves the same attention: an MVHR unit, a heat pump or a boosted shower pump in a cupboard next to a bedroom will undo a well-detailed wall.

If you are planning a room where sound genuinely matters, our home cinema design guide and home office design guide deal with the layout side of the same problem, and the Vertigo Interiors homepage sets out how we work. The regulations themselves are free to read: Approved Document E is published on GOV.UK, and the alternative compliance route is set out by Robust Details Ltd.