Quick answer: building control normally asks for at least one set of tests for every ten dwellings in a group or sub-group, plus a set among the first completions in each group — Approved Document E, paragraphs 1.29 and 1.30. A set is 2 tests for houses, 4 for flats with a separating floor, and 6 for flats with both a separating floor and a separating wall.
Work out the programme
Enter the dwellings of each kind, and how many different constructions (sub-groups) there are among them.
Houses and bungalows (separating wall)
A set here is 2 tests. 2 airborne tests through the separating wall — one pair of rooms suitable as living rooms, one pair suitable as bedrooms.
Flats with separating floors but no separating walls
A set here is 4 tests. 4 tests through the separating floor: 2 airborne and 2 impact.
Flats with both a separating floor and a separating wall
A set here is 6 tests. 6 tests: 4 airborne (2 through the wall, 2 through the floor) and 2 impact through the floor.
How the count works
Approved Document E asks building control to consider a development as a number of notional groups, each with the same construction type, because a test result only strictly applies to the construction tested. Houses, flats and rooms for residential purposes start as three separate groups. Within each, you sub-group by the separating construction — wall type for houses, floor and wall type for flats — and again where flanking construction differs significantly or a plot has an unfavourable feature such as a long gable flank without a window.
Then the rate: a set of tests among the first dwellings completed in each group or sub-group, and at least one set for every ten dwellings in that group or sub-group. Testing should be weighted towards the start of the completions, so that a problem shows up while it can still be fixed cheaply rather than in the last plot on the site.
Approved Document E (2003 edition incorporating 2004, 2010, 2013 and 2015 amendments), paragraphs 1.11 to 1.31. The one-set-per-ten rule is addressed to the building control body, so treat the figure above as what will normally be stipulated rather than a self-certified minimum — and confirm the grouping with your building control body before booking.
The pass marks
| Element | Airborne DnT,w + Ctr | Impact L'nT,w |
|---|---|---|
| Purpose-built dwelling — separating walls | 45 dB minimum | — |
| Purpose-built dwelling — separating floors and stairs | 45 dB minimum | 62 dB maximum |
| Conversion (material change of use) — walls | 43 dB minimum | — |
| Conversion (material change of use) — floors and stairs | 43 dB minimum | 64 dB maximum |
Approved Document E, Section 0: Performance, Table 0.1a (the body text calls it Table 1a). The values already include an allowance for measurement uncertainty, so a shortfall by any margin is a failure — paragraph 1.6 — and a set is failed if any individual test in it fails — paragraph 1.32.
Robust Details instead of testing
For new-build houses and flats there is an alternative: build to a detail approved by Robust Details Ltd, register the plots, and notify building control of the detail and its unique number before work starts. Do that and pre-completion testing does not apply to those plots. It is not available for conversions or material changes of use — those always test — and the notification has to be in before commencement, not after.
Frequently asked questions
How many sound tests do I need?
Approved Document E tells building control to ask for at least one set of tests for every ten dwellings in a group or sub-group, plus a set among the first dwellings completed in each group or sub-group. So a development of 24 houses in one sub-group is normally three sets; the same 24 houses built with two different separating wall constructions are two sub-groups and normally four sets. The calculator above does the arithmetic for a mixed site.
What counts as a set of tests?
It depends on the dwelling. For houses a set is two airborne tests through the separating wall — one pair of rooms suitable as living rooms, another suitable as bedrooms. For flats with a separating floor and no separating wall it is four tests: two airborne and two impact through the floor. For flats with both a floor and a wall it is six: four airborne and two impact. A full set in flats needs access to at least three of them.
What is a group or a sub-group?
Houses, flats and rooms for residential purposes are three separate groups to begin with. Within each, sub-group by construction: for houses by the type of separating wall, for flats by the type of separating floor and separating wall. Significantly different flanking construction means another sub-group, and a plot with an unfavourable feature — a large gable flank wall with no window, for instance — should be its own sub-group. More sub-groups means more sets of tests, which is why a site with three wall types costs more to test than one with a single detail.
What are the pass marks?
For purpose-built dwellings, airborne sound insulation of at least 45 dB (DnT,w + Ctr) through separating walls and floors, and impact sound of no more than 62 dB (L'nT,w) through separating floors. For conversions the figures are 43 dB and 64 dB. There is no tolerance: the values already include an allowance for measurement uncertainty, so missing one by any margin is a failure, and a set fails if any single test in it fails.
Can I use Robust Details instead of testing?
For new-build houses and flats, yes — if you register the plots with Robust Details Ltd and notify building control of the detail and its unique number before work starts. It is not available for conversions or material changes of use, which always need pre-completion testing. Miss the notification deadline and you are back to testing.
What happens if a test fails?
The construction has to be investigated and remedied, and the rate of testing goes up until building control is satisfied the problem is solved — so one failure can turn a three-set programme into a much longer one. That is the argument for testing early: Approved Document E specifically says testing should be more frequent at the beginning of a series of completions, so problems surface while they are still cheap to fix.
Who is allowed to do the testing?
Approved Document E asks for a test body with appropriate third-party accreditation — preferably UKAS accreditation for field measurements, and it also recognises members of the ANC Registration Scheme.
Related: sound insulation testing · air test result checker · commercial services.