Approved Document E - Resistance to the passage of sound - Knauf Insulation
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Welcome to the Knauf E-learning programme. This CPD module is about approved document part E, resistance to the passage of sound.
The Knauf group was established in Germany in 1932 and today remains one of the world's leading building materials producers, with over 100 manufacturing locations. Knauf Insulation have over 30 manufacturing sites worldwide producing rock and glass mineral wool and expanded and extruded polystyrene insulation. In the UK the four manufacturing plants can be found in Saint Helens and Cwmbran where they produce glass mineral wool Hartlepool where they produced polyfoam extruded polystyrene and Queensferry where rock-silk rock mineral wool is produced. These four plants ensure that Knauf insulation remains today the UK's principle insulation producer.
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Over the past 30 years pressure on the availability of building land has led to increasing numbers of people living in flats and townhouses often in very close proximity to adjacent properties. This coupled with changes in lifestyle means that more and more people are suffering from the direct effects of noisy neighbours. In 2003 part E of building regulations was amended to try and improve the standard of acoustic construction. This program addresses the issues faced in four sections.
Once you've completed the program you will:
- Have been introduced to the theory of how sound travels around buildings and something about how it can be suppressed
- Understand more about the requirements of part E of building regulations relating to sound insulation
- Understand the concept of robust details and how they make compliance with building regulations easier
- Be familiar with the robust details for a range of floor and wall types
- Be more aware of the Knauf range of sound insulating products.
In this four-part program:
- Section 1 introduces some basic sound theory and how sound insulation works.
- Section 2 then looks at part E of the building regulations and goes on to examine specifically parts E1 and E2 and explains what is meant by deemed to satisfy, on site testing, and robust details.
- Section 3 details wall constructions that could be used to meet the requirements of either part E1 or E2 including specific details of some robust detail walls.
- Section 4 concentrates on floor constructions that could be used to show compliance with either parts E1 or E2, and explains in some depth the issues surrounding the various components of separating floors.
Part 1: What is Sound?
The theory of sound and sound insulation.
Sound is a modulating pressure wave that transfers energy through any medium but we normally associate sound transmission with air water and solid objects. It varies from very low frequencies that are undetectable to the human ear, through the normal hearing range, which is 20HZ to 20,000 Hertz, to very high frequencies such as the tone used in a dog whistle going right through to sounds that bats use for navigation. Real noises are a combination of many frequencies.
The human ear is most sensitive to sounds at about 4000HZ interestingly this is the frequency at which babies crying the referee's whistle sounds and this helps to explain the problem with linking decibels or dB to volume. Volume is subjective and depends on the sensitivity of the person hearing the noise. dB measures the pressure of the wave which can be measured non subjectively.
The Effect of Sound Frequency on Sound Insulation
A sound at 4000HZ will appear to have a louder volume to normal human hearing that sound with the same dB thereby, causing the same air pressure but with a frequency at for example 100HZ. Structures are tested for sound transmission across the range of frequencies sensitive to human hearing because different types of structures will be more or less effective at different frequencies, and sounds that could become problem noises are generated right across the frequency range. So, the sound reduction or transmission figure that is quoted for a structure is some form of average across the frequency range. Generally, it's harder to stop low frequency sound than mid to high frequency sound.
Sound Transmission within Buildings
Sound transmission within buildings is made up of two elements; airborne which is sound Vibrations transmitted in the air, and impact which is the energy of a striking force in a surface that is converted into sound energy and transmitted through that structure. In designing construction our primary concern is the passage of sound from a noisy area within a building to quiet areas such as bedrooms or adjacent properties. This transmission can take place either directly through a separating wall or floor or indirectly through other structures or spaces. This indirect transmission is known as flanking sound. The purpose of sound insulation is to resist the passage of sound from the noise source to the quiet area. This could be from one dwelling to another or from a living room to a bedroom, the principles are the same even if the levels of performance required vary. The aim of sound insulation is to successfully restrict the methods of sound transmission that apply to the construction affected.
Airbourne Sound Transmission
Airborne sound as we have said is the transmission of sound vibrations in the air. Sound is energy in the form of a wave of air pressure and the air pressure is in effect the volume of the sound. Sound emanates from its source rather like the ripples caused by stone being thrown into a pond, in other words in concentric circles. As the sound wave moves away from the source the air pressure diminishes and the volume reduces. As the sound hits the walls floor and ceiling it can cause these surfaces to vibrate and this energy is transmitted through the layers of the construction and can then be emitted from the far side as sound. This is how the airborne sound passes through walls and floors; and the purpose of sound insulation is to stop this.
One of the biggest fears people have in acoustics is the terms is to describe sound energy and sound reduction. The term used to describe sound power is dB. This is a measure not a volume but of the power of the sound source and air pressure at the receiver. The higher the pressure the greater the power required to create it.
dB refers to a logarithmic scale where an increase of 3dB is a doubling of the air pressure. An increase in air pressure will result in an increase in volume heard but the relationship is not directly proportional.
Airborne sound insulation is expressed in terms of a sound reduction index in dB. In other words, how much sound does the construction stop.
Resisting the Passage of Sound
The ability of a construction to resist the pattern just sound is affected by a number of factors. The first factor is the mass of the construction. A wall or floor with high mass will better resist the passage of sound than one with low mass. The mass resists the vibration that is caused by the sound hitting its surface, roughly speaking a doubling of the mass of an element will improve the sound insulation offered by 5dB. So mass is good but it's not always possible or even desirable to use structures with high mass.
The second consideration is the sound absorption within cavities. Partition walls could always be built with dense concrete blocks but normally it's necessary to build a frame structure with two hard surfaces and a cavity. The lower mass of this structure can be compensated for by improving the sound absorption of the cavity. This can be achieved by installing a sound absorbing layer such as mineral wool in the cavity. The same principle applies to floors and ceilings as well.
Another factor is the structural isolation between the surface layers obviously if the sound is transmitted by vibrating the structure and the two faces of the structure are isolated from each other it will improve the resistance to the passage of sound. This can be achieved by building separate frames using acoustic frames or resilient bars or its most simple level, ensuring that the surface layers are fixed at maximum recommended centres.
Next the quality of detailing and workmanship, any construction can be fatally compromised by poor workmanship such as not sealing air paths, not ensuring that sound absorbent layers are continuous, or even using too many fixings. Equally, details that compromise the construction such as pipes electrical cables or joists and poor joining details can have similar impact.
Impact Sound Transmission
Impact sound is the effect of the energy transfer on an object striking a surface causing a vibration in the structure the structure and this energy is then manifesting itself as airborne sound in the receiving space. An example of this could be effective footsteps on the floor being heard in the room below.
The control of impact sound is only required in part E in floor or ceiling structures; however, impact sound can be transferred through walls for instance by pushing a plug into an electrical socket. The ability of the floor to resist impact sound is generally improved by isolating the floor surface receiving the impact from the structure especially the ceiling. This can be achieved either by building a separate ceiling or deadening the effect of the impact on the structure by installing a resilient layer to separate the floating floor surface from the structural floor deck. The insulation of a resilient floor surface such as carpet and underlay will also improve the isolation, but this is not a structural solution to the problem as the carpet may later be replaced with a hard surface.
To set performance levels we measure the ability of a floor to transmit impact sound and consequently set a maximum level for transmission. It's measured in terms of transmission because there's no actual sound source for impact sound. The source is a striking force that is converted into sound by the structure. A lower figure signifies a higher level of protection from impact sound. These values are measured and reported in dB.
Flanking transmission is the transmission of either airborne or impact sound around the structure that has been built to resist the passage of either type of sound. The sound energy is being transferred by unforeseen overlooked paths. If we consider a room with a partition separating it from the adjoining room, the airborne sound created in the first room will act on all the walls, ceiling and floor of the source room.
The same vibration will be set up in all of these elements. There are a number of alternative paths that the sound could travel along. One path is through the ceiling across the roof void and back through the ceiling into the adjoining room. If the sound resistance of this path is lower than the partition between the two rooms, the sound insulation is fatally compromised. Similarly, the adjoining walls and floor can provide similar sound paths.
Similar problems can occur with floors designed to resist impact sound; for instance, if a floating floor deck is not isolated from the structural walls of the building, the impact energy may be transferred through the walls to the room below.
The issues to consider when trying to eliminate flanking sound are ensuring that the flanking wall is sufficiently heavy, there are no unstopped external wall cavities or unstopped false ceiling voids above partitions, floating floor decks are isolated from walls, and there are no pipes and ducts passing between one space and another. Eliminating the possibility of flanking sound is just as important as building the sound resisting floor or wall correctly.
The Role of Mineral Wool in Sound Insulation
Mineral wool is a generic term for mineral wool of woolly consistency normally made from glass or rock. Generally, mineral wool is not dense enough to add significantly to the mass of structures, so it works by absorbing sound.
Sound enters the woolly matrix of the product and as it passes through it, is repeatedly deflected and broken up by the strands. This disruption converts sound energy into heat energy which is then absorbed by the wool. This mechanism is not significantly enhanced by the density of the wool itself, although the thickness of the insulating layer will increase the level of sound absorption. However, when formed into dense slabs mineral wool can act as a resilient layer under a floating floor to reduce the effect of impact sound transmission on the floor. The inherent nature of mineral wool will mean that even dense compression resistant slabs will still act as a spring to dampen sharp impact on a floating floor deck.
Sound Insulation Demonstration
This demonstration shows how much a layer of mineral water can suppress sound, the speaker in the box represents a sound source. To show the difference between plane plasterboard and plasterboard with a layer of mineral wool. The mineral wool reduces the sound energy by 40dB.
Terms and Symbols for Sound Insulation used in Part E
In order to understand the requirements of building regulations we need to understand a little about the terms and symbols associated with sound insulation.
RW is a measure of the ability of a construction to suppress sound, and is an average value taken from the laboratory tests across a range of frequencies. This is the figure that manufacturers will quote in their literature.
DnT,W is a similar measure but represents the construction tested on site. As a rule of thumb, a construction tested on site to DnT,W will be 5dB worse than the RW figure achieved in a lab test.
For part E separating constructions the regulations also require that a further correction to the DnT,W figures supplied to give extra weighting for low frequency sound, as this is the source of most complaints. This is identified by the symbol Ctr.
As low frequency sound is harder to stop the mid to high frequency sound this waiting has the effect of further worsening the measured performance of a structure by up to 8dB.
Note here that laboratory tested figures are difficult to relate directly to the part E requirements for separating elements because the practicalities of working onsite and the extra weighting for low frequency sounds could mean a 10dB to 15dB worse figure than you might expect from the laboratory ratings. Finally, the symbol used to identify the standard for impact testing in part E.
L'nT,W also requires onsite testing.
Section 2 Building Regulation Part E 2003 : Requirements and Compliance
Part E 1992 Buiding Regulation
The regulations that existed prior to the last amendment were introduced in 1992. These previous regulations covered separating walls, floors and stairs but did not require any level of sound insulation internal rules within a dwelling. The main way to comply was based around deemed to satisfy generic solutions. These solutions specified the component products of a wall or floor largely by their mass and gave guidance on how they should be assembled. If these deemed to satisfy solutions were used there is no requirement to prove the sound insulation provided by testing. Consequently, many of these elements failed to provide the expected level of protection as either the wrong product had been used, or they hadn't been assembled correctly.
Part E 2003 Building Regulations for England and Wales
After extensive consultation the amendments to part E became law on the 1st of July 2003. There are four sections but we primarily concerned with parts E1 and E2.
- Part E1 concerns sound insulation from other parts of buildings and adjoining buildings such as dwelling houses flats and rooms for residential purposes known as RRP
- Part E2 concerns sound insulation within dwelling houses flats and RRP
- Part E3 concerns reverberation in the internal common parts of buildings containing flats and RRP
- Part E4 concerns acoustic conditions in schools.
Requirement E1 - Protection from your Neighbours
This extract from the approved document dealing with requirement E1 seems fairly straight forward, but it can prove to be contentious, so we need to understand what is meant by reasonable resistance, let's see how the document defines it.
Requirement E1 - Performance Standards
Here we see the values that must be achieved to meet the requirements of part E. You'll notice that the values for renovation and conversion with a material change of use are less onerous than those for new build both in terms of airborne and impact. This is recognition of the fact that it's difficult to achieve the same levels of performance in renovation.
Note that the requirement for new build separating walls in rooms for residential purposes is 43dB indicated in brackets in this table. The sting in the tail of these amendments is that the measures for airborne and impact sound insulation or in terms of DnT,W plus Ctr or L'nT,W and so require onsite testing of constructions. This is a major departure for the house building industry in particular as there's been very little on site testing of acoustic performance in the past. The introduction of testing is intended to place an additional quality standard of workmanship and details.
The penalties for failure to comply are high as it will delay completion while remedial measures are taken to bring the failing structures up to standard. A further complication is the correction for low frequency sound or Ctr that must be applied to the test results obtained. This correction has the effect of reducing the sound insulation values recorded in a test.
Requirement E1 - Methods of Compliance
For new build RRP and both dwellings and RRP formed by material change of use, E1 came into force on the 1st of July 2003. However, it did not apply to projects that had already received complete planning approval or were already underway. At that stage the only way to comply was to complete a series of sound tests for each site, measuring the acoustic insulation provided by any separating walls, floors and stairs. Tests were to be carried out once the building was complete but before decoration and soft floor coverings were fitted. There was and still is no need to test walls, floors and stairs separating living spaces and common areas.
The approved document gives extensive guidance on how to complete a series of tests and how to group similar types of construction. It may be possible to group these constructions to an extent where tests are only required for one in 10 of each type. From July 2004 these regulations remain for material change of use, but an alternative was created for new build dwellings. The alternative for new build dwellings from 1st of July 2004 is to build systems that have been specially developed as robust details. So, with new build it's permissible to either test on site or build wall and floor systems that have been specially developed as robust details.
Requirement E1 - Background to Robust Details
The option to use robust details was developed in a project sponsored by the house builders Federation. Their aim was to create robust standard details that could be proven to be construction proof and meet the requirements of part E1 even when built on site. This would remove the need for pre completion testing. For a construction to be accepted as robust detail it would have been subjected to a rigorous site testing program that required 30 constructions to be tested, spread over a number of sites. The results obtained for every test must exceed the requirements of part E.
The rigour of this testing process gave the government confidence and accepting robust details as an alternative method of showing compliance to site testing every construction. Robust details or RD’s will be subject to random spot testing and rigorous investigation of complaints and any that consistently fail will be deleted. Similarly, RD’s may be added if they've satisfied the same requirements as the original program.
Requirement E1 - Using Robust Details
How to use a robust detail. Make sure that the robust detail is suitable for the required application, paying particular attention to the matching of walls and floors in flat developments, if the walls and floors are not compatible then it may still be necessary to test either the wall or the floor even though both are robust details. Register each plot where a robust detail is proposed with Robust Details Limited.
Requirement E1 - Benefits of Robust Details
Pay a fee of £30 per plot which is the same irrespective of number of details used per plot, and finally sign a compliance certificate like the one shown for each plot, stating that the robust details on that plot have been constructed as per the specification in the robust detail handbook. Many people consider that pre-completion testing is still a superior method of quality control over the use of RD's as most problems of sound transmission are associated with poor workmanship, including poor ceiling, structures bridged when they're meant to be separated, and specifications not followed.
Pre completion testing will expose poor workmanship and poor installation of details. In their defence robust details are tested widely and designed to overcome common problems. The details were designed to exceed the minimum requirements of part E and were also designed for their build ability which has been proven. The major benefit of using RD’s is that they remove the uncertainty that exists when testing to show compliance.
Requirement E1 - Protection from Your Family
Part E2 deals with walls and floors within a single unit whether it's a flat, a house, or a room for residential purpose RRP. It captures all internal floors and all walls between a bedroom or a room containing a WC from all of the rooms. There are exceptions however the first being any existing wall or floor in a building that is subject to a material change of use, and secondly any internal wall with the door in it or any internal will separating a bedroom from an associated ensuite bathroom. In practice it's likely this exception will not be adopted to ease site organisation and simplicity of design. The normal way of satisfying requirements E2 is to use constructions that meet the sound insulation values in the performance table, table two in the approved document.
Requirement E1 - Performance Table
E2 requires an airborne sound reduction of 40dB for internal walls and floors captured by the regulation for both new build and in units that are created by material change of use. There's no need for onsite testing to prove performance. Laboratory test figures obtained by manufacturers of systems or components will be acceptable.
Section 3 - Practical Solutions to Part E 2003
Wall constructions to meet parts E1 and E2. As we've discussed the requirements fall into two categories part E1 and part E2.
You'll remember from Section 2 that there are certain values that must be achieved to meet the requirement of part E. You'll notice that the values for renovation and conversion with a material change of use are less onerous than those for new build both in terms of airborne and impact. This is a recognition of the fact that it's difficult to achieve the same levels of performance in renovation. Note that the requirement for new build separating walls in rooms for residential purpose is 43dB, indicated in brackets on this table.
Solutions for Requirement E1: Separating Walls
There are a number of RD’s for separating walls, the icons on this slide link to full explanations of masonry, timber frame, and metal frame RD walls, as well as PPST solution for a masonry wall. This is a typical robust detail for a masonry separating wall. There are a number of masonry wall RD's all have either a wet plaster or render coat to seal all joints, except EW M8. The results of this detail average 52dB with a range of 48 to 55 decibels, the size of this range of test results emphasises the need to ensure good levels of workmanship once the RD has been accepted. It should also be noted that the RD includes precise instruction for detail injunctions with floors and flanking walls. These additional requirements also apply to all other RD’s.
This slide is an extract of the supporting information for RDEWM2 showing how to drink the flanking wall to ensure that the separating wall is not compromised by flanking sound. It's worth noting that if a fulfil cavity wall insulation, such as Crown Dritherm cavity slab, is used then there's no need for the cavity close to be used, because the cavity is already stopped.
Here the typical construction details for the conversion of an existing brick or block wall with plaster on both sides, to a separating wall that meets part E requirements. An independent ‘I’ stud partition framework is constructed on one side of the wall, 10mm clear of the existing separating wall. 50mm glass mineral wool roll is installed between the studs and finished with two layers of 12.5mm plasterboard. All gaps are sealed at the perimeter of the plasterboard lining and where services such as electrical sockets penetrate plasterboard finished with acoustic sealant.
Both 50mm flexible rock mineral wool slam and 50mm glass mineral wool slab are also suitable for use in this application, but all products should be installed with no gaps. This construction is for refurbishment only and complies with wall treatment 1 in Section 4 of approved document E but pre completion testing is required.
A room-in-roof separating wall provides additional challenges, since the acoustic performance of the separating wall could be compromised by sound passing out through the roof and back into the adjacent property the same way.
Normally the only consideration for the insulation between the rafters would be to meet the requirements of part L and rigid PIR and PUR boards are popular for this type of application. However, these offer virtually no acoustic insulation, but the use of mineral wool would deal with both acoustic and thermal insulation.
To comply with masonry wall RD’s in room-in-roof applications, it's necessary to install a minimum of 100mm of mineral wool insulation between the rafters. This is unlikely to provide sufficient insulation to allow compliance with part L. In this application however, rafters are normally 200mm or more deep and installing a high-performance glass mineral wool roll to this full raft of depth will provide the performance required.
Here we see an RD for timber frame walls without cavity sheathing board. This detail has achieved an average performance of 55dB within a range of 47dB to 65dB. The wall benefits from a high degree of structural isolation and the highly absorbent material on either side of the cavity. The mineral wool insulation is described in the robust standard detail as 10kg to 60kg per cubic metre, a minimum 60mm thick. It would be usual to use 90mm or even 140mm of glass mineral wool rolls or slab for convenience, if this was the material being used for the external walls. The mass of the plasterboard to either side must be achieved. Finally, there must be a minimum of 240mm separation between the plasterboard faces.
This is an RD for a steel frame separating wall. This construction achieved an average performance of 51dB with a range of 47dB to 57dB. Like the timber frame walls, it utilises a high mass of plasterboard lining the frame and a mineral wool insulation as an acoustic absorber in the cavity. The insulation slab is specified as 33kg to 60kg per cubic metre minimum 50mm thick. For example, 50mm flexible rock mineral wool slab, the separation between the plasterboard faces is 200mm.
Solutions for Requirement E1: 'Material Change of Use'
Solutions for E1 when attached dwellings or rooms for residential purpose RRP are created by the material change of use of the existing building cannot be covered by RD’s. By material change of use of an existing building we might mean a change from a large house into a series of flats for example or a hostel from a dwelling. However, the simple refurbishment and renovation of a pair of semi-detached properties where no change was made to the party wall, would not be captured under the regulation. The only way to show compliance is through pre completion testing. These can be grouped if the opportunity exists.
There's guidance in the approved document with potential solutions for walls floors and stairs, but this is no guarantee of compliance. One way of dealing with separating walls is to build an independent wall lining, the independent wall lining creates structural isolation and the absorbent layer of mineral wool, 50mm glass mineral wool roll, or 50mm flexible rock mineral wool slab, or 50mm glass mineral wool slab, absorb sound reverberated in the cavity. The total mass of plasterboard is specified, because this will add mass to the independent lining, helping it to achieve the airborne sound reduction required. It's crucial that the frame does not touch the existing wall.
Solutions for Requirement E2
The requirement of part E2 can be made in one of two ways either, build walls and floors exactly matching constructions that have been laboratory tested to achieve an airborne sound reduction of 40dB, or build walls and floors that match exactly the deemed-to-satisfy solutions in the approved document. There is no requirement for onsite testing to show compliance with part E2.
Requirement E2 - Internal Walls - Timber Stud Partitions
Most masonry walls that are built as partitions will meet the requirement E2 with no additional measures required. If we consider lightweight framed partitions there are two basic options; timber framed, or metal framed. Both of these can show compliance in two ways. Either, by building a deemed to satisfy solution or by building a laboratory tested solution.
Generally, these are owned by manufacturers such as ourselves. The deemed to satisfy timber solution is illustrated here. The main disadvantage of deemed to satisfy solutions is that they generally require higher specifications of materials than a manufacturers laboratories test, by their nature they're conservative. Also, the generic specifications are often out of date, for instance in this construction the specification requires plasterboard that has mass of 10kg per square metre, 12.5mm.
Plasterboard manufactured today generally has a mass of approximately 8.5kg per square metre. Also, 75mm timber studs are rarely used, it is more often 63mm CLS. For this reason most builders will use a laboratory tested system. With laboratory testing it's possible to achieve the required level of performance using more readily available products which should make the final construction more cost effective. This is demonstrated in the results obtained for 63mm timber framed partition using 12.5mm standard plasterboard and absorbent layer of mineral wool infill. The absorbent layer of mineral wool is 50mm glass and mineral wool roll. There are other tested solutions that involve denser plasterboard and less in mineral wool infill.
Requirement E2 - Internal Walls - Metal Stud Partitions
Similarly, for metal stud partitions laboratory tests show that the deemed-to-satisfy solutions can be over specified. Numerous tests for this type of partition have been carried out. This particular solution requires only Knauf wallboard standard stud and a 50mm glass mineral wool role as an absorbent layer. With metal stud partitions there are several laboratory tested solutions that do not require a mineral wool absorbent layer. This is achieved by using dense plasterboard and special metal studs. The simplicity of these systems may seem attractive and they obviously made the performance requirements for stopping airborne sound and from one room to another, but tend to have a hollow sound and lightweight. This is because sound is able to reverberate inside them as the surface is within the cavity have poor sound absorption coefficients.
Section 4 - Solutions for Requirement E1 - Separating Floors
Floor constructions to meet the requirements of parts E1 and E2. You'll remember from Section 2 that there are certain values that must be achieved to meet the requirement of part E. You'll notice that the values for renovation and conversion with a material change of use, unless Send those for new build both in terms of airborne and impact. This is a recognition of the fact that it is difficult to achieve the same levels of performance in renovation.
All separating floors have to provide protection from both airborne sound and impact transmissions. As with separating walls the designer of new build housing has an option to use either an appropriate robust detail, or alternatively a system that requires testing. For other types of development, of course, it is necessary to test the floor to prove compliance. Whether the floors are a robust detail or not it will consist of three basic elements; the structural floor, the floor surface, and the ceiling. The latter two are normally isolated from the structural floor to restrict impact transmissions.
The first thing that a designer is likely to decide upon is the type of structural floor. Robust details exist for the following types; institute cast concrete slabs, precast concrete planks, steel concrete composite, in situ cast concrete slabs, and timber I joists. It is of course possible to build separating floors with other types of structural floors, but it will be necessary to test these for compliance.
Solutions for Requirement E1 - Separating Floors - Ceiling Types
The ability of the floor to resist airborne sound and impact energy transmission is of course the sum of the three parts; floor surface, structural floor and ceiling. In concrete floors with high mass the ceiling treatments can be quite simple such as a single layer of standard plasterboard on metal systems or timber battens.
But on lightweight joisted structures, it's necessary to include multiple layers of plasterboard, mineral wool sound absorbing insulation, and resilient sealing bars. The ceilings required for use with the robust details follow this pattern and the Handbook gives precise details of the options available.
It's noted that whilst sound absorbing mineral wool insulation is not a requirement in ceilings under concrete floors, it will improve the sound insulation performance. Bearing in mind the influence that workmanship has on the performance of acoustic systems, it may be a sensible insurance policy to include this layer.
Solutions for Requirement E1 - Separating Floors - FFT
Creating a floating floor is the normal method of isolating the finished floor from the structural floor and a major factor in the reduction of impact transmissions. The choice of structural floor and the floor surface either timber or screed will determine the choice of floating floor treatment, of course there are a high number of options so it may be easiest to describe the solutions available as robust details. For all the concrete and steel concrete floor decks there are five options if the finished floor surface is timber, these include three variations where the chipboard deck is supported by a batton that is isolated from the structural floor by resilient pad, or cradle and avoid is created.
The other two options isolate the chipboard deck is laid upon a resilient layer which isolates it from the structural floor. FFT4 a resilient layer option is illustrated here. If however, the designer requires a screeded finished floor surface then he has two options. Both use resilient layers underneath the screed to isolate the floor surface from the screed. These options can only be used as a robust detail with precast concrete planks.
The construction solution illustrated here uses a 25mm insulation layer either mineral wool or polystyrene underneath the 5mm foam polyethylene layer with a screed on top. Previously this was robust detail E FC-3 and although this has now been withdrawn it can still be used to show compliance through pre completion testing. This solution has particular merit when used with underfloor heating systems as it places a thermal insulation layer underneath the heat source ensuring that heat is directed towards the intended space. For a timber structural floor there's only one type of floating floor that can be used as a robust detail. This requires a deep resilient batten laid on the structural floor deck and is loaded with 19mm Gypsum plank below an 18mm chipboard floor layer. A 25mm layer of mineral wool is laid between the resilient battens, the purpose of this layer is not to reduce impact sound but rather to absorb airborne sound reverberating in the cavity created by the resilient battens between the floating floor and the structural floor.
The ability of a floating floor to restrict the transmission of impact energy can be compromised if the floating floor is unintentionally linked to the supporting walls. To prevent this, it is necessary to ensure that all resilient impact absorbing layers are installed around the perimeter of the floating floor to isolate it from the supporting walls. All skirting boards should be installed so there is either a small gap or a resilient layer between the bottom of the board and the top of the floating floor, again to stop a flanking route for the impact energy.
The illustration shows the flanking detail with both the mineral wool slab and the floor foam installed vertically around the screed at the perimeter. The floor foam is also isolating the skirting from the floating floor. This will require pre completion testing to confirm compliance.
Solutions for Requirement E1 - Separating Floors
Pulling all these items together will give us a complete floor that should provide resistance to both impact and airborne noise which will not be compromised by flanking effects. The construction detail illustrated here requires pre completion testing for compliance with regulations. This consists of a precast concrete plank with a mass of at least 300kg per square meter and minimum depth of 150mm.
The ceiling is formed on a simple metal ceiling system with a minimum depth of 100mm and is simply a 15mm standard wallboard. The floor surface is either a 65mm sand cement screed or proprietary screed with a mass of at least 80kg per square metre supported or floating layer. The floating layer consists of two components a 25mm, 140kg for cubic metre density rock slab and a 5mm polyethylene foam.
EFC-1 utilises a precast concrete plank with a ceiling specification that includes a chipboard floor surface. The plank is topped with a screed 65mm for sand cement screeds or 40mm proprietary screed with a mass of 80kg per square meter, which has the floating floor placed above it. The floating floor illustrated here complies with robust detail floating floor treatment 4 and consists of 18mm chipboard placed above a 30mm thick mineral wool slab that has a density of 140kg per cubic metre, and has been lab tested to provide at least 17dB impact sound resistance.
The product illustrated 140kg per cubic metre dense rock mineral wool slab achieved 26dB. EFS-1 is a robust detail for a steel concrete composite in situ cast slab, again the ceiling and floating floor treatments are identical to EFC-1. The concrete slab needs to have a density of 2,200kg per cubic meter and minimum thickness of 80mm and be at least one 130mm thick at the deepest point of the metal deck. There's no need for screed below the floating floor treatment unless it's required to smooth the finished surface.
Here we see the separating timber floor detail in full with the floating floor treatment, basic floor unit, and ceiling treatment. The engineered timber I joists must be a minimum of 240mm deep. The sub deck board must be a minimum of 15mm. 100mm glass mineral wool roll minimum density 10kg per cubic meter is installed between the I joist to absorb reverberant sound. The ceiling treatment for robust standard detail FT1 is 19mm plasterboard plank and 12.5mm plasterboard. This is fixed to a resilient ceiling bar which is fixed perpendicularly to the underside of the joists at 400mm centres. Also included in the RD are details of the junction with separating an external wall and details of how to treat downlighters in the ceiling. This is only suitable for use with timber frame walls. There's no RD for a timber separating floor on masonry walls. This RD achieved a mean airborne sound reduction of 50 decibels and mean impact transmittance of 53dB over the RD testing programme. The robust detail handbook clearly illustrates the measures that have to be taken to ensure that neither airborne nor impact sound transmission can flank around the timber I-beam floor.
To comply with robust detail EFT-1 note the resilient flanking strip around the floating floor deck. In September 2005 a robust detail EFT-2 was added for a solid timber joisted floor. The floating layers and ceiling treatments are identical to those shown for the I-beam floor.
Timber Floor PPST
This solution for a timber separating floor is suggested in the approved document as a system that has the potential to meet the requirements of part E1. The fact that it is suggested in the approved document gives no guarantee that it will pass pre completion testing. Provided care is taken in the construction of the floor this should achieve good results, as there's a great deal of structural isolation between the floor and the ceiling.
The platform floor with a resilient mineral wool slab beneath the floating floor deck further reduces impact sound, and the infill of mineral wool on the independent ceiling cuts down on reverberated sound in the cavity. Full details of this system can be found in the approved document on pages 49-51, this includes generic descriptions of the components, and details of how to treat wall junction's and penetration. This solution should be compatible with masonry walls.
'Material change of use'
Solutions for E1 when attached dwellings or rooms for residential purpose RRP, are created by the material change of use of an existing building cannot be covered by RD’s. By material change of use of an existing building we might mean a change from a large house into a series of flats for example or a hostel from a dwelling. However, the simple refurbishment and renovation of a pair of semi-detached properties where no changes made to the party wall would not be captured under the regulation. The only way to show compliance is through pre completion testing, these can be grouped if the opportunity exists.
There is guidance in the approved document with potential solutions for walls, floors and stairs, but this is no guarantee of compliance. The biggest hurdle to overcome in material change of use is normally achieving the sound resistance in timber floors, particularly impact sound this is a very common occurrence when creating flats from an existing property. One of the best solutions is to build an independent ceiling under the existing ceiling, this isolates the new ceiling from any impact on the existing floor.
The system recommended requires the upgraded the existing ceiling by adding extra layers of plasterboard, so that a total of 20kg per square metre masses achieved laugh and plaster ceilings can have weight of up to 25kg per square metre, but they do vary considerably so it's probably sensible to install at least a single layer of 12.5mm plasterboard under the existing ceiling to be sure.
The new ceiling is supported on independent timber joists and minimum of 100mm deep supported at the surrounding walls alone, or if necessary, with additional support provided by resilient hangers attached directly to the existing floor base.
The independent ceiling must be at least two layers of plasterboard with a minimum total mass of 20kg per square metre, say two layers of 15mm plasterboard and absorbent layer of 100mm mineral wool is laid over the new ceiling. As with all separating elements care must be taken to ensure that the perimeter and joints are well sealed and that there is no direct connection between the independent ceiling and the floor base.
An alternative method suggested in the approved document of creating a separating floor in an existing building is to create a platform floor above the existing floor. This requires a floating floor to be laid with a resilient layer separating it from the existing deck. Sound absorbent material laid between the joists, and the mass of the existing ceiling to be increased to 20kg per square metre. The floating floor must be two layers achieving 25kg per square metre in total, 18mm chipboard and 19mm plasterboard meets this specification. The resilient layer should be a minimum 25mm thick mineral wool, density 60 to 100kg per cubic metre the absorbent layer is 100mm thick mineral wool with a minimum density of 10kg per cubic metre. There's no significant benefit in using a denser mineral wool as the absorbent layer, as with all separating elements care must be taken to ensure that the perimeter and joints are well sealed and that there's no direct connection between the floating floor and the existing deck. The performance requirement for both these floor systems is for airborne 43 DN TW + Ctr and for impact 64 L'nT,W. Which is slightly less onerous than required for new build. This system has to be pre completion tested on site.
E2 requires an airborne sound reduction of 40dB for internal floors captured by the regulations for both new build and in units that are created by material change of use. There's no need for onsite testing to prove performance. Using deemed to satisfy constructions or laboratory test figures obtained by manufacturers of systems or components will be acceptable.
The deemed to satisfy solutions for floors are more in line with up to date practice. Generally, for timber joisted floors all that's required is the addition of an absorbent layer of 100mm thick mineral wool, for instance 100mm glass mineral wool rolled, minimum density 10kg per cubic metre or 100mm flexible rock mineral wool slab, the ceiling is 15mm plasterboard. It's possible to do away with an absorbent layer with certain engineered I-beam systems where the floor deck is glued rather than fixed and the I-beam is above a certain depth. However, this system has to be pre completion tested on site.
This is a deemed-to-satisfy solution for beam and block internal floors where the ceiling is fixed to resilient channels. The insulation 25mm glass mineral wool roll absorbs any sound reverberating in the cavity, the plasterboard ceiling must be at least 10kg per square metre. It's possible to do away with an absorbent layer with certain engineered I-beam systems when the floor deck is glued rather than fixed and the I-beam is above a certain depth. However, again it's likely that the floor will sound hollow and the effect of impact noise will be greater.
In conclusion there are a number of observations to make about the implications of part E 2003. Firstly, there is a requirement for on-site testing for separate elements unless the robust standard details can be used. This will measure the quality of the building as well as design and detailing. The robust standard details are over engineered for safety and as such may prove to be more expensive in the cost of building and testing alternative details. Using robust details will however remove the doubt regarding whether the construction will pass testing.
Most internal walls and all internal floors within a single dwelling now have to provide a specified level of sound insulation. This can be complied with by using deemed to satisfy constructions or systems that have been laboratory tested to achieve the required level of performance. Mineral wool plays a significant role in most solutions either as a sound absorber or my acting as a resilient layer. It also brings the extra benefit of providing thermal insulation and being fire safe. However perhaps the single most important factor in successfully providing walls and floors that complying with this regulation, is to ensure that specifications and installations for the constructions are adhered to strictly.