Resistance To The Passage Of Sound Construction Essay

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Noise is an unwanted sound. Music is a noise if played at a certain level however noise does not have to be loud to be unwanted. Over a million workers in UK are exposed to levels of noise that puts their hearing at risk. HSE

One way we can tackle some noises is by distancing ourselves from source. Noise levels drop between 3 and 6 dBA when our distance is doubled but this is may not be possible inside a building.

Controlling noise has a better effect at design stage, using materials and insulations that counter this problem, in the construction stage of a building we can eliminate the annoyance of noisy equipment, people or their actions in advance. Environmental Science in Building

Noise is generated at source and carried by different forms around a structure, two main types identified being, airborne sound and impact sound.

Airborne sound travels through the air reaching objects passing through small holes or openings in the construction, cracks in masonry or plasterwork insufficient sealant around pipes etc passing through the wall along ducts, transmission through partitions doors, windows, they can be direct or reflected sound.

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Impact sound is a sound which is generated on a hard surface of the structure sometimes called structure borne sound, generated by footsteps, slamming doors, noisy pipes, vibration from machines eventually this travels through the air to the ear but not the same as airborne.

Noise Control Manual for Residential Buildings

Insulation is the process of controlling airborne and impact sound in a structure, and by how well its carried out and fitted determines the effect it has on reducing noise travelling throughout the building.

Detailing to the work and competence is essential to achieving the requirements of approved document E, good thought to the construction and craftsmanship to avoid failure when testing.

Excellent sound insulation relies mainly on four rules:

Mass

Air tightness

Vibrations

Separation

Mass

The density of heavy structures conduct less sound energy\vibration therefore materials used for sound reduction should be where possible carry the least vibration.

Mass law states that a unit of an area in material that doubles in mass increases sound insulation of 6dB (realistically its 5dB) also increases by 5dB when frequency is twofold. For example an average single brick wall (half brick) has an SRI about 45dB a brick wall say English bond only has a SRI of 50dB but the doubling of its thickness is not important its increasing its Kg\m² which is its mass. This also relates to the frequency, sound insulation increases by 5dB whenever frequency doubles, for instance a brick wall gives about 10dB more insulation against 400Hz sounds than 100Hz sounds.

Air Tightness (flanking)

When insulating for sound considering the mass theory is one thing but if the goods or materials supplied achieve above standard regulations, they can't perform correctly if the passage of sound can penetrate through or around the materials that are not fitted properly, i.e. gaps in the brickwork and the air tightness of these materials are of low standard. For example a brick wall has a gap or crack to 0.1 percent of the total area the average SRI would reduce from 50dB to 30dB. This could be badly fitted seals around partitions, floors ceilings, windows, pipes and ductwork, even ceiling or floor joists. Different materials have different properties some porous enough to allow sound to pass through its structure, therefore brickwork should be sealed or plastered. Doors and windows be airtight when closed, special seal for thresholds and can be adjusted, sound escape should be considered with the same importance as water leakage. Environmental Science in Building

Doors are the weakest part of a sound proof barrier, most important part of keeping the door and frame soundproof is the air tightness, an air leak is also a sound leak or what is known as airborne flanking, to be efficient the door needs to have airtight seal when closed, for example a badly fitted door of a half brick wall reduces SRI by nearly 50%.

To improve the insulation properties of a structure, the parts with the lowest performance should be improved first, ie doors and windows.

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Vibration.

Flexibility of materials depends on the properties, this can help reduce the transmission of noise through absorption, inflexibility creates more resonance, if a material can't absorb it will resonate and increase vibrations, transferring to other compartments. This in turn is conveyed into the air and other compartments bypassing the insulation, usually travelling through cavities, ducts, pipes. Sound can't pass through a wall, only if there are leaks (gaps cracks) but a wall can act like a giant audio speaker, the sound energy hits the wall this then generates a vibration and the wall, ceiling or floor itself becomes the transmitter.

Isolation

Noise travels through many different forms as it converts to different waves at the junctions of materials, a little of its energy is lost at transference and a valuable amount of insulation recovered. This is where the effectiveness of cavity windows takes place, floating floors and resilient mountings for a machines vibration. Insulation fails when strong flanking transmits through fixed links. Cavities must be at least 150mm wide and lined to allow for air flexibility, resonance and coincidence can reduce insulation at certain frequencies.

Environmental Science in Building

Reducing Noise levels in the Workshop and Offices.

"The Control of Noise at Work Regulations 2005 (Noise Regulations 2005) require employers to prevent or reduce risks to health and safety from exposure to noise at work." http://www.hse.gov.uk/noise/employers.htm

Building regulations are designed to set minimum standards for the construction of new developments, and amongst all the regulations there are certain requirements to be met for the passage of sound in approved document E.

Specifications for woodwork machine shop.

Siting for the machine would have to be the furthest part of the building from main offices and away from any exterior doors of the main building 200mm away from boundary (party) walls.

Floating floor

Sound insulation for a floor slab which is totally independent and mechanically isolated from the existing structural floor. Cut out required size of floating floor, the sub floor must be clean, and free from loose dirt, it must also be dry, and it should be flat, a 50mm blinding coat of coarse sand should of already been laid by the existing concrete slab. Preparation work complete, after rolling out rubber matting and a few hours to settle, fit into void specially prepared for the isolated floating floor, when installing anhydrite screeds, lay a damp proof membrane, at a minimum thickness of 0.2mm over the entire area, overlapping by at least 100mm and should also cover the upturned edges of the Rubber. Joints of the rubber can be overlapped by 50mm or cut with a sharp utility knife, making a tight joint and taping all joints to prevent movement during the casting process. Taking the usual precautions to avoid damaging or moving the membrane and Rubber. A 20 to 50mm wire mesh may be used to reinforce with 100mm concrete, a suitable proprietary mix with a mass per unit area of at least 80kg/m² can be poured, trimming off overlap when cured. leaving a small gap between the floating layer and existing concrete slab and filled with a flexible sealant. (ADE)

Resilient mountings are imperative on all motors, the designs take into account frequencies, rpms, mass of the vibrating equipment, even temperatures of a machine.

Pictures from http://www.acoustic-supplies.com/

Installation of the rubber absorption membrane Concrete laid with visqueen dpm and rubber absorption.

Wall Construction for sound insulation to house a machine.

Footings (assuming )on the existing concrete slab (floating floor completely independent) so no foundations required, Blockwork walls 190mm self supporting from existing workshop building, attention to detail for mortar joints with no gaps, next 2 x12.5mm acoustic plasterboard to the inside of booth staggered fixed with resilient bar, a vibration absorbing thin steel channel used on timber studs 600mm centres and same specification applied to the joists of the ceiling. At junctions of wall to ceiling and wall to floor leaving small gaps (5mm) enough for application of acoustic sealant. 12.5mm plasterboard on exterior of booth with wall board adhesive installation, skimmed or rendered. Allowing the walls and ceiling to be de-coupled from the vibrating surface which will reduce both vibration and impact noise penetration. Sockets on either sides must be staggered service ducts to and from machine must be flexible to absorb and not resonate sound, acoustic sealant to be used on openings.

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Doors

Installation of doors for access ensuring that the door has good fitting sealing including the threshold a minimum mass per unit area of 25kg/m² or a minimum sound reduction index of 29 dB Rw The door should also comply with the Requirements of Building Regulation Part B Fire safety.

Office Noise reduction.

The office wall dividing workshop to be treated should not have any holes that may allow sound and noise through. As usual the most likely places these occur is windows, doors and where the flooring and ceiling joists are connected to the wall.

For maximum soundproofing performance, a wall with at least 150mm cavity would have to be built, up to the underside of the roof not connected to existing party wall. To reduce leakage of airborne noise, care should be taken to ensure an airtight seal exists, depending on type of roof fitted there are many types of profile roofing acoustic barriers, failing this spray-applied foam can be applied as a liquid to roofs and walls. It expands to create an insulation and acoustic barrier. It adheres to everything, sealing gaps and preventing surface interstitial condensation. http://www.insulationsprayfoam.co.uk/test_results.pdf (see appendices)

Where the wall meets the roof and this can be helped by using acoustic sealant and a fluid caulk to fix it in place aiding air tightness. Further improvements can be gained by infilling between the joists with acoustic mineral wool and boarding out the area above the offices with 22mm tongued and grooved high density acoustic flooring board.

A less expensive reduction of noise can be with acoustic panels glued to the workshop side of office dividing wall using Acousticel M20AD, this is a three layer procedure, making sure there are no gaps or possible sound leaks, with doors and windows having where possible air tightness, depending on how much the company has to spend on the noise reduction, where doors directly opening into workshop area, there could be an vestibule system type of mechanism, creating an air lock between areas where only one door opens at a time, both being close fitting and air tight seals installed.

On 1st floor ceiling and floorboards of office nearest dividing party wall taken up and if joists are entered into wall any gaps around joists should be sealed, if timber frame wall it should be packed with acoustic mineral wool, with high density or rubber packings if possible under all joists, ensuring the wall is airtight, and transference of sound is minimised.

Workshop Party wall.

Clean dry and fairly flat, all fittings power switches, sockets etc to be removed checking there are no gaps, fill where necessary acoustic caulking. To ensure full contact with walls and sound proofing the two surfaces to be glued should be right angle glued application.

Panels are applied first at ground level across the floor then working up, keeping the joints as tight as possible, cutting out for any sockets, switches along the way, allow overnight drying before applying two layers of acoustic plasterboard with all joints staggered. A small gap should be left around all junctions of ceiling, walls, and floor using packings if required. The use of recommended adhesive for the resilient layer flowed by good quality wallboard adhesive for plaster board.

Taken from http://www.soundservice.co.uk/Installation_M20.html

When adhesives have been left a few days to dry, a plaster skim coat can be applied and a decoration finish thereafter. It is necessary to leave a small gap around edges and fill with acoustic sealant, skirting should be fitted with glue leaving a small gap, so as not to allow transference of noise and to keep the wall an isolated floating wall.

Part B. 1 With reference to ADE to provide an acceptable means of resistance to sound adjoining new dwellings. Choosing a wall type cavity masonry.

A party wall of two dwellings has to comply with part E resistance to passage of sound regulations. Starting from the foundations, 100mm block leaves with 50mm cavity construction together with stainless steel butterfly ties "cleaned" filled with mineral wool, and fire stopped is essential for maximising sound resistance. Applying direct to wall with adhesive 2 x 12.5mm plasterboard bonded together with staggered joints, a mass per unit area of 20kg/m² on both sides of party wall, gaps at junctions ceilings, floors to allow for flexible acoustic sealant. This exceeds ADE, minimum mass per unit area including plaster 415kg/m². Services, sockets etc should be staggered if on party walls.

At ground level a 100mm concrete floating floor, consisting of a a layer of mineral wool of minimum thickness 25mm with density 36kg/m³, paper faced on the upper side to stop

the screed entering the resilient layer and to isolate floor from structure, with a DPM for any sulphates.

1st Floor and ceilings construction, timber joists suspended on hangers, running parallel to party walls. Ceilings two layers 12.5mm plasterboard bonded together with wall board adhesive, all joints staggered, taped and a skim coat leaving a gap around perimeter of ceilings to be filled with flexible sealant. Exceeding ADE 2004.

Timber floors and loft space100mm layer Rockwool flexi (mineral) supported by polypropylene netting, in between joists as close as practical to the underside of floor deck to avoid any air gaps, covered with T&G flooring grade chipboard. Leaving a 5mm gap at junctions for a flexible acoustic sealant.

The following pages are mostly according to ADE 2004.

By ensuring all joints of masonry are pointed with no gaps, and keeping the cavities clean of debris to below ground level, filled with mineral wool or polystyrene beads.

Eliminate all flanking transmission possibilities by installing a flexible closer if cavity is not filled with insulation.

stagger the position of sockets on opposite sides of the party/separating wall.

ensure that flue blocks will not adversely affect the sound insulation and that a suitable finish is used over the flue blocks.

The wall ties used to connect the leaves of a cavity masonry wall should be butterfly ties as described in BS 1243:1978 stainless steel ties for cavity wall construction, and spaced 450 mm vertically and 900 mm horizontally with successive rows staggered for structural purposes.

The HRT4 tie, when tested in a 50 mm wide cavity at a standard density of 2.5 ties per m2, achieved a dynamic stiffness value of less than 4.8 MNm-3. This satisfies the requirements of Approved Document E. Therefore, the HRT4 tie can be used, at the same standard density, in separating walls with cavity widths up to 100 mm.

No deep sockets and chases in the separating wall and do not place them back to back.

Two leaves of dense aggregate concrete 100mm block density of 1990kg/m³ with 50mm cavity, 225mm coursing, 13mm lightweight plaster (minimum mass per unit area 10kg/m²) on both room faces.

Plasterboard to be of minimum mass per unit area 10kg/m²; all joints should be sealed with tape or caulked with sealant.

Diagram from ADE Flexible closer if cavity is not filled with insulation, to stop transmission of sound through floors.

The external wall should abut the separating wall and be tied to it. Where there is also a separating floor then the requirement for a minimum mass per unit area of 120kg/m² excluding finish should always apply.

The masonry inner leaf should have a mass per unit area of at least 120kg/m² excluding finish.

Floors.

Internal concrete floors should generally be built into a separating wall and only carried through to the cavity face of the leaf. The cavity should not be bridged.

If the floor joists are to be supported on the separating wall then they should be supported on

hangers and should not be built in. Where the joists are supported on hangers, spaces between the floor joists should be sealed with full depth timber blocking.

Concrete ground floors.

The ground floor may be a solid slab, laid on the ground, or a suspended floor.

A concrete slab floor should not be continuous under a cavity separating wall. The cavity should not be bridged.

Ceiling and roof space Junctions

Where a cavity wall is used it should continue to the underside of the roof.

The junction between the separating wall and the roof should be filled with a flexible closer which is also suitable as a fire stop.

Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area of 10kg/m² with sealed joints, then the mass per unit area of the separating wall above the ceiling may be reduced to 150kg/m² , but it should still be a cavity wall.

If lightweight aggregate blocks of density less than 1200kg/m³ are used above ceiling level,

then one side should be sealed with cement paint or plaster skim.

Where there is an external cavity wall, the cavity should be closed at eaves level with a suitable flexible material e.g. mineral wool.

A rigid connection between the inner and external wall leaves should be avoided. If a rigid material is used, then it should only be rigidly bonded to one leaf, with flexible filler on other side.

Independent panels.

These panels should meet the following specification minimum mass per unit area of panel

(excluding any supporting framework) 20kg/m² panels should consist of either

a. at least 2 layers of plasterboard with staggered joints, or

b. a composite panel consisting of 2 sheets of plasterboard separated by a cellular core;

if the panels are not supported on a frame they should be at least 35mm from the masonry core; if the panels are supported on a frame there should be a gap of at least 10mm between

the frame and the masonry core.

Junctions with an external cavity wall with masonry inner leaf

Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any construction; and

b. the cavity should be stopped with a flexible closer unless the cavity is fully filled with mineral wool or expanded polystyrene beads.

Where the inner leaf of an external cavity wall is masonry:

a. the inner leaf of the external wall should be bonded or tied to the masonry core;

b. the inner leaf of the external wall should be lined with independent panels in the same manner as the separating walls, as below.

Diagram from ADE

Diagram showing cavity stop for walls without insulation. Internal walls construction for isolating connecting walls to separating walls without insulation.

Where there is a separating floor the masonry inner leaf of the external wall should

have a minimum mass per unit area of at least 120kg/m² excluding finish.

Where there is no separating floor and the masonry inner leaf of the external wall is lined with independent panels in the same manner as the separating walls, there is no minimum mass requirement on the masonry inner leaf.

Where there is no separating floor with separating wall type 3.1 or 3.3, and the masonry inner leaf of the external wall has a mass of at least 120kg/m² excluding finish, then the inner leaf of the external wall may be finished with plaster or plasterboard of minimum mass per unit area 10kg/m².

Part B. 2.

Acceptable means of providing resistance to the passage of sound between adjoining flats to an existing building. In Accordance with ADE.

Part B 1 discusses the reduction of unwanted sound for party walls and floor isolation, the majority of points have been covered in the previous tasks, trying not to be repetitious.

When considering sound improvements the most obvious would be tackled first, such as gaps, spaces where sound can travel and pass through, doors and windows are the most likeliest and probably the easiest to correct. Having close fitting doors, windows that seal when closed are the first steps that should be taken when reducing unwanted sound.

Looking at the flooring and if there are any gaps such as between floor boards a sealant could be used or overlaying hardboard sealing at junctions and edges.

Replacing floorboards should be at a minimum thickness of 12mm and mineral wool minimum thickness 100mm, minimum density 10kg/m³ should be laid between the joists.

Concrete floors if the MPUA is unknown then the mass of the floor should be increased to at least 300kg/m². Any air gaps through a concrete floor should be sealed. Laying a screed may also be necessary.

Existing lath and plaster ceiling and walls should be retained as long as they satisfy

Building Regulation Part B Fire safety.

Where the existing ceiling is not lath and plaster it should be upgraded as necessary to provide at least two layers of plasterboard with joints staggered, total mass per unit area 20kg/m². Diagram from ADE

This includes any walls to be upgraded, only if the panels are free-standing they should be at least 35mm from masonry core if the panels are supported on a frame there should be a gap of at least 10mm between the frame and the face of the existing wall.

Mineral wool, minimum density 10kg/m³ and minimum thickness 35mm, in the cavity between the panel and the existing wall, all junctions of the perimeters to be flexible sealant.

Ceilings, reducing flanking and impact sound depends on how well the material is fitted, air tightness, absorbance and isolation. Construction consisting of at least 2 layers of drywall with staggered joints, minimum total mass per unit area 20kg/m²; an absorbent layer of mineral wool laid on the ceiling, minimum thickness 100mm, minimum density 10kg/m³.

The ceiling supported by installing joists fixed to the surrounding walls with additional support provided by resilient hangers attached directly to the existing floor base. This construction involves a separation of at least 125mm between the upper surface of the independent ceiling and the underside of the existing floor construction.

Diagram from ADE

Where a window head is near to the existing

Ceiling, the new independent ceiling may be raised to form a pelmet recess.

Consideration taken at the design stage to ensure

that enough ceiling height is available.

Gap at perimeter of ceiling left for flexible sealant to be applied.

Stairs Require the same sound insulation as floors, where they provide a dividing purpose, this all depends on the mass and whether the stair is enclosed in an airtight cupboard underneath, the covering of stair reduces the impact at source, 6mm covering glued can be adequate, with plasterboard to the underside, with minimum mass per unit area 10kg/m² and a layer of mineral wool (minimum density 10kg/m³), within the space above the lining. Cupboard walls lined with two layers of plasterboard each sheet of minimum mass per unit area 10kg/m²;fitting a small heavy close fit door for the cupboard.

If there is no cupboard under the stair an independent ceiling must be installed.

Diagram from ADE

Insulation to underside of staircase to reduce airborne sound. Carpeting stair treads will improve impact sound enormously.

Floor penetrations.

Services, excluding gas pipes, and ducts which pass through separating floors in conversions should be surrounded with sound absorbent material and a fire stop for their full height and boxed in with a duct above and below the floor, leaving a small gap for sound isolation of floating layers, filled with flexible sealant. Either line the enclosure, or wrap the duct or pipe within the enclosure, with 25mm mineral wool. Fire stopping should be flexible and also prevent rigid contact between the pipe and floors. Gas pipes should be contained in a separate

ventilated duct.

Design and layout of a structure is important when deciding what rooms are less resistant to noise or sensitive areas, it is good practice to consider these at design stage.

Corridor walls and doors

Dividing walls described in previous paragraphs should be used between rooms for residential reasons and corridors in order to manage flanking transmission, providing the required sound insulation between the dwelling and the corridor. But the sound insulation will be reduced by the presence of a door, and whether its air tight if it leaks air it will leak noise. Ensure any door has good perimeter sealing (including the threshold where practical) and a minimum mass per unit area of 25kg/m² Approved Document E 2003

Adding materials to a building will impose extra loads on the existing structure. The structure should be assessed to ensure that the additional loading can be carried safely, with appropriate strengthening applied where necessary.

Sound Myths A room in a church was found to be noisy, with plaster board ceiling, walls and hardwood floor, the echoes from just a few people, were extremely annoying, advice from a sound manufactures representative, suggested a sound absorbing device that could be hung in the centre of the hall, to solve the problem. The claim was the device about the size of a wheelie bin was tuned, and had the same absorptive characteristics as a whole ceiling of tiles. It was true the contraption had reduced the echoes but not enough, someone concluded that purchasing another might do the trick, it seemed logical if one unit worked two would work twice as well. Funny thing nothing noticeable occurred with the second absorber.

Few reasons why. Sound absorbing material has to be spread around the area to be effective, single point of absorption no matter how good can only absorb as much as what reaches the absorber the rest carries on bouncing off the other surfaces. To be efficient the whole area has to be treated with the same to be efficient. Noise Control Manual for Residential Buildings