How to Pass a Sound Insulation Test First Time

How to Pass a Sound Insulation Test First Time

Most sound test fails are built in long before we arrive. A half-filled mortar joint, two sockets back to back, a floor that touches the wall. Here is what Approved Document E asks for, how the testing works, and what we see on sites that pass first time.

Who needs a sound test

Regulation 41 of the Building Regulations requires sound insulation testing before completion where homes share a separating wall or floor. That covers new-build houses and flats, and homes formed by a change of use, such as an office or a house converted into flats. Detached houses don't need one.

New-build homes can use Robust Details for the separating walls and floors instead of testing. The builder must tell building control which detail is used, with its Robust Details unique number, no later than the notice to start work, and then build it exactly as the detail says. Conversions can't use Robust Details, so they are always tested.

The figures to meet

Table 0.1a of Approved Document E sets the standards:

• New-build homes: airborne sound at least 45 dB DnT,w+Ctr for walls, floors and stairs, and impact sound no more than 62 dB L'nT,w for floors and stairs.
• Homes formed by a change of use: at least 43 dB airborne and no more than 64 dB impact.

There is no margin. The figures already allow for measurement uncertainty, so a result that misses by any amount is a fail.

How many tests, and when

Houses and flats are treated as separate groups, split again into sub-groups where the separating wall or floor construction differs. Each group or sub-group needs a set of tests between the first homes completed, then at least one set for every ten homes. Approved Document E also says to test more often at the start of a run of completions. So book the first test early.

For houses, a set is two airborne tests across the separating wall. For flats with separating walls and floors it is six tests: four airborne and two impact. Flats with separating floors only need four: two airborne and two impact. We test between pairs of rooms, ideally living rooms and bedrooms, not corridors, stairwells or hallways.

Walls: the usual causes of a fail

The "points to watch" for separating walls in Approved Document E are the same faults we find on failed jobs:

• Fill and seal every masonry joint with mortar. An empty joint lets sound straight through.
• Stagger sockets on opposite sides of the wall. No back-to-back sockets and no deep chases.
• Carry the wall up to the underside of the roof and fill the junction with a flexible closer.
• On timber-frame and dry-lined walls, seal all joints with tape or sealant.
• Control flanking. Sound also travels round the wall, through the floors, ceilings and outer walls joined to it, so build every junction to the detail.

Floors: the usual causes of a fail

In our experience, floor fails come from the edges and the services. A floating floor or screed that touches the wall, a skirting fixed hard down across the gap, or downlighters and pipes cut through the ceiling below all give sound a way round. Build to the separating floor details in Section 3 of Approved Document E or the system you have specified, and make sure later trades don't cut into them.

Impact tests are normally done without a soft floor covering, so carpet won't rescue a poor floor. Plan for it to pass bare.

Getting the site ready for test day

Tests are carried out once the homes are essentially complete, except for decoration. That means rooms finished on both sides, with windows and doors fitted and closed, doors to corridors fitted with their perimeter seals, floors bare, a quiet site, mains power and access to both sides of every wall and floor being tested.

If a test fails

The rooms that failed need remedial work. Building control will also want to know that other rooms sharing the same wall or floor are fine, through more tests, remedial work, or evidence that the cause isn't there. The testing rate goes up until building control is satisfied, and the remedial work is normally checked with another test.

We tell you where the sound is getting through and the usual fix, then test again.

Sending the results to building control

The person carrying out the work must give the results to building control. On most jobs that is no later than the completion notice, which is due within five days of completion. Our report comes within 5 working days of the visit, so book the test with time to spare.

Our sound testers are registered with SITMA. We can do the sound tests on the same visit as the air and ventilation tests, which costs less because we save on travel.

Questions we get asked

Can Robust Details be used on a conversion? No. Robust Details is only for new-build houses and buildings containing flats. Converted flats and houses are always tested, against at least 43 dB airborne and no more than 64 dB impact.

Will a carpet help us pass the impact test? No. Impact tests are normally done without a soft floor covering, so the floor has to pass bare.

What if we miss by 1 dB? It is a fail. The Part E figures already allow for measurement uncertainty, so there is no rounding up. The rooms need remedial work and a retest.

When should we book the first test? As soon as the first homes are complete apart from decoration. Testing early catches a construction fault before it is repeated in every home.

More

More: Sound Insulation Testing, Air Tightness Testing, Ventilation Testing, and our guides to passing an air tightness test first time and ventilation testing for new homes.

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