Why do I need sound tests?
The requirements of Part E of the Building Regulations are presented in Approved Document E.
In summary, there are three requirements (E1, E2 and E3), and Requirement E1 stipulates a minimum level of sound insulation between dwellings. This needs to be demonstrated with accredited testing prior to completion, and Building Control will have the final say over whether the results are acceptable.
For new-build dwellings, you need to provide 45 dB of protection from airborne noise across party walls and floors, and impact noise (footfall and objects falling on the floor) is limited to 62 dB.
Converted dwellings require a slightly lower standard (43 dB airborne, with impact limited to 64 dB).
We will follow up this blog post with one describing the requirements in more detail, but for now, here is our straight-forward guide to improving your chances of getting a pass during testing.
1. It's all about the mass
It's telling that when we can hear our neighbours, we say, "The walls are paper thin." This is a demonstration of what we all intuitively know, that, without mass, we can't have good sound insulation. It's a fundamental rule of physics that the heavier a construction is, the better it is at containing sound. This is why acousticians often specify concrete boxes for gyms, night clubs or other high noise spaces. Broadly speaking, each time you double the mass of a construction, its performance will improve by 5 or 6 dB. That's not to say that mass is the only thing acousticians look for, but it is certainly a fundamental requirement, along with the other items discussed below.
2. Two frames are better than one
If you're using a lightweight construction (e.g. timber floor, stud walls), it's also beneficial to provide two separat frames to each leaf. If we use independent frames for a party wall, we get a much better acoustic separation than we do if using a single frame, as the sound can't travel directly through the frame. Where possible, avoid wall ties or any other rigid fixings which connect the two leaves across the cavity. Acoustic wall ties might be acceptable.
Similarly, if you're converting an existing timber floor into a separating floor between dwellings, an independent ceiling is one of the best ways to improve your chances of passing your sound tests.
The other thing to consider here is that the benefit of the cavity is related to how deep it is. As the cavity is made wider, it becomes better at insulating lower frequency sounds. This is why high noise rooms (like night clubs or music venues) need deep cavities - to tackle the lowest frequency sounds.
3. Close external cavities
Have you ever heard the term 'flanking transmission'? This is the effect of sound travelling around a wall or floor. This could be sound travelling vertically through a wall into the room above, or through the ceiling and into the room next door. By ensuring you provide cavity closers to any continuous cavities in wall, floor or ceiling junctions, you will already be ahead of the game. In addition to residential developments, this is also important for providing sound insulation to cellular offices in the form of floor or ceiling void barriers.
4. Discontinuous linings
It sounds simple, but it's often overlooked. If you are providing a lining to an external wall, or along a corridor, don't let the plasterboard lining pass across a party wall from one dwelling to another. Doing this would provide an efficient route for sound to travel through the lining and out into the adjacent space.
5. Keep it simple, stupid
If you're stuck for ideas, or feeling out of your depth, it's always a good idea to go back to basics. There is plenty of good advice contained in Approved Document E (ADE) on constructions which are capable of meeting the requirements. ADE also contains some good ideas for improving the sound insulation of existing walls and floors if you are working on a project which is undergoing a change of use. For more unusual constructions, the Robust Details Handbook also provides a useful reference for timber, steel and masonry build-ups and junction details which can meet the requirements.
6. Don't believe the hype
When looking at a product manufacturer's acoustic data, it's essential to understand where the data comes from. Typically, most product data comes from one of two places; an acoustics laboratory, or in-situ testing. Laboratory testing is undertaken to British and International standards, and gives us an idea of how the product performs irrespective of the environment in which its being used. In-situ testing gives us an idea of how an overall floor build-up performs (including junction details and all the flanking routes). Both tests methods are valid, but we still need to make adjustments to apply the test results to a separate real-life scenario. Laboratory test values will typically be 5 to 15 dB higher than in-situ test results, and it's important to factor this in when specifying a product using laboratory test data. In-situ data comes with lots of caveats and uncertainty that often make it unsuitable for the project in hand.
7. Seal, seal, seal
Services penetrations are easy to forget about because they are usually hidden away in a cupboard, or a ceiling or floor void. However, if the holes around pipes, ducts and cables aren't sealed properly, they will let sound pass straight through, just like a hole in the main wall or floor construction. Ideally, services should be routed into apartments over front doors, and avoid penetrating through party walls or floors. The logic behind passing services over doors is that the doors are already acoustically weak, andthe additional penetration from the services will have little effect. Small penetrations should be sealed with mastic, while larger holes might require plasterboard pattresses. Similarly, sockets and downlights in party walls and floors will usually require suitable plasterboard backboxes.
8. Early testing
While acoustics calculations and previous test data are helpful in deciding an approach, design and specification in acoustics is more of a risk management exercise than precision engineering. That's why early testing can be a great way of reducing the risk of non-compliance. Where possible, get an acoustic test done at the earliest stage possible, so that you have an idea of which direction your project is heading in. This is particularly useful on conversions and new-build premises using unusual or novel construction methods.