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E – Resistance to the passage of sound

The following applies to England but Scotland, Northern Ireland and Wales use very similar principles.

Acoustic insulation is a complex subject. Most of our forebears have lived with very little of it for millions of years. Extended families living in long houses, yurts, tents, caves etc. could hear most of what was going on around them. Indeed it was possibly quite important for that to happen. Often children sleep better if they can hear a certain amount of domestic noise around them. It is somehow reassuring. People find it difficult to stay in the world’s quietest room for more than 45 minutes.

On the other hand there is nothing more annoying than someone repeatedly playing some track you cannot stand in the bedroom next to you.

Although the amount of acoustic insulation you might want in a house is quite a personal matter, the building regulations have been tightening up on this issue and now cover several aspects of it in part E – Resistance to Sound. (spelled out in the Approved document). Before reading this take a deep breath. It gets very technical!

It’s quite complicated stuff because sound insulation involves airborne sound and impact sound. It’s also quite difficult to understand the units of measurement, decibels, because they work on a logarithmic scale rather than a linear one because our ears tend to work that way.

The regulations cover two types of situation:

Between dwellings

needs considering if you are building a separating wall or separating floor or stairs which have a separating function. (so this covers the boundaries between separate dwellings, such as semis, terrace houses and flats or converting part of a house into a self contained flat)

Within a dwelling

the regulations are mainly about the sound resistance between

  • bedrooms and other rooms (so you can sleep well)
  • rooms containing a water closet and other rooms (yes – you guessed it)
and also internal floors (high heels above and broom handles below)
The regulations give you two ways of ensuring you have met the correct standard:
  • pre completion testing (this entails getting a registered tester person to make loud noises and test whether there is enough sound insulation)
  • robust details (this is about using approved design and building methods which are known to achieve the appropriate standard)
and this is all described in vast detail in the approved documents part E, including no end of construction details which fulfill the requirements.

Airborne sound and Impact sound

Airborne sound is a fairly easy concept to understand but what is not so obvious is how much sound can squeeze through a tiny gap. Party walls between semis or terrace houses are notorious for leaking large amounts of sound where bricklayers have not properly filled the perpends with mortar and there is only a thin covering of plaster.

There are two main ways of stopping airborne sound and because sound is energy they are both about absorbing that energy (and turning it into tiny amounts of heat).

  • shear mass (this is the easy one to understand – think solid concrete)
  • specially designed (often quite lightweight) absorbent material. (this is more difficult to understand or design. Think NOT egg boxes)

The ‘NOT egg boxes’ refers to the enormous number of budding rock stars who would like to establish a recording studio in their basement without annoying their neighbours and have heard somewhere that if you line all the walls with egg boxes it will miraculously dampen all the sound. Well it’s partly true but there are more sophisticated materials than egg boxes specially designed for the purpose.

How does this work? Well they defray the sound energy. As the sound waves hit the material (such as a special acoustic grade of rock wool on a wire netting backing) the fibres vibrate and warm up (ever so slightly) and the sound turns to heat and doesn’t get through.

Impact sound  is the sort of sound that will carry through a structure. So if you scream at a concrete wall the person on the other side hears nothing but if you tap it gently they hear it well and this is the problem with impact sound. Since people don’t generally go around tapping walls very much the problem is more with floors where the impact of footwear or tables and chairs being dragged around is a problem for those below. Solid objects propagate sound very well due to impact.

The way you need to deal with this (with floors/ceilings) is by isolating the top surface from the structure with a material which dampens the sound.

The most obvious one is a carpet but a carpet can’t be relied upon to exist.

Floating floors

Enter the ‘floating floor’. A floating floor is similar to having a carpet inserted just below the level of the floor finish. Instead of a carpet there are various proprietary materials which do the same job of isolating the layer above from the one beneath. Floating floors are often used in conjunction with timber floors where acoustic insulation is required. It is very common where houses are divided up/down into flats.

It is also important that the upper layer of floor is completely isolated from the walls around its edges (by thin strips of foam proprietary material) so that impact sounds don’t go sideways into the walls and transfer down through that route. There must be no direct contact anywhere between the top surface and the one below

External noise

Where external sound such as traffic or aeroplane noise may be a problem then it is likely that the windows need special design attention.

In this case the most important factor is the sheer mass of the glass: the heavier the better. 6mm glass (such as is used in shop windows) is useful and the more sheets of glass with differing spaces between them the better.

Another important factor is to have different weights in different panes. This is so that the panes don’t resonate with each other and propagate the sound (like, say, the two skins of a base drum do). For serious sound attenuation (say on a very noisy main road) it can work well to have an outer double glazed sealed unit of 2 x 4mm glass with an 18mm gap, a large space of 75 or 100mm (which makes it harder for sound to get through), and then a single pane of 6mm glass on the inside. This will also provide excellent heat insulation.

The Approved Documents are ‘standard’ ways of getting Building Regulations approval. There are other ways. see more

If you follow the principles and rules given in the documents you can be sure that they will be approved. Of course you don’t have to use the Approved Documents, as the Regulations make clear:

Approved Documents are intended to provide guidance for some of the more common building situations. However, there may well be alternative ways of achieving compliance with the requirements. Thus there is no obligation to adopt any particular solution contained in an Approved Document if you prefer to meet the relevant requirement in some other way.

In fact the Approved Documents are a bit of a mishmash of traditional ‘rules of thumb’ and technical standards and they have gaping holes in them. Whereas, for instance, there are many pages on how to construct traditional masonry walls, there is nothing about timber frame construction except the odd reference to British standards.

They are also struggling to keep up with the times. If the Passivhaus Standard or zero energy new house building is introduced at some point then whole swathes of the Approved Documents will need rewriting because many of the constructional principles are based on quite low levels of insulation.

There are other ways of satisfying the regulations. For instance they make copious references to BS, BS EN and BS EN ISO standards which may be another way of fulfilling the criteria. It is even possible in some very rare cases to prove that something works by building it first and then testing it afterwards (though this is not for the faint hearted).

Although a self builder cannot be expected to understand all the building regulations, it often pays to have a grasp of what is involved, especially if last minutes changes need to be made to construction details.

The full official set of Aproved Documents is available HERE.

See also: Wall Construction

Below is a direct link to the Gov.UK Approved Document,  E – Resistance to the passage of sound (England)

It is a large PDF file and may take a moment to load

Download (PDF, 3.74MB)

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