Insulation

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Insulation

Insulation for the building industry generally falls into two categories for the thermal and acoustic applications, both of which are controlled by the Building Regulations.

Thermal insulation

Thermal insulation is generally applied to the external building envelope to reduce the amount of heat loss. It is measured as the rate of thermal transmittance more commonly referred to as the ‘U’ value. The Building Regulations are now divided into the four following categories:
L1A - work to new dwellings
L1B - work to existing dwellings
L2A - Work to new buildings other than dwellings
L2B - work to existing buildings other than dwellings

Each stipulates the maximum 'U' value of the various construction elements for each building type. For dwellings these include ground floor, external walls, internal walls between a heated and unheated rooms (attached garage) intermediate floor between a heated and unheated rooms (integral garage) flat roof, inclined roof and ceiling to roof void. The area of external windows and doors is limited to a % of the total floor area and also given a 'U' value.

Buildings other than dwellings are classified in a similar way. The current issue the regulations should always be checked for the latest 'U' values as these are occasionally upgraded.

Type of insulation

Insulation products are produced from a variety of materials in different formats to suit particular applications. Some materials are better insulators than others and therefore a lesser thickness is required to provide the same 'U' value.

Insulation Quilts and Insulation Batts are alternative formats of the same materials produced for use in different applications. The two most common materials are glass fibre and mineral fibre (rockwool) and more recently natural wool fibre (sheeps wool insulation) has been introduced in response to the quest for sustainability.
Insulation Quilt, which is produced in rolls are generally used to insulate roof and ceiling voids being laid between and over the joists. Glass fibre is the most common material used for the housing market whereas mineral fibre offers a better fire resistance. The minimum thickness of quilt to meet the current Building Regulations 'U' value requirement of 0.16 w/m2 K is approximately 270mm laid between and over the joists. The main problems with quilts used in this way is the difficulty to access the area if maintenance is needed and the reduction in performance of the material is compressed or contaminated with a built up of dust. Quilts are generally unsuitable for fixing vertically without regular support as they will slump and tear.
Insulation Batts are a more rigid format of a quilt although still capable of being bent or folded and are more suited to vertical applications as infill to stud forming or cavity fill insulation to external masonry walls. They are produced in a variety of thicknesses and sizes to suit the application.

Loose fill insulation

Used as alternatives to external cavity wall insulation and infills between ceiling joists, this type of insulation is most suited to upgrading existing cavity walls and roof voids where access is restricted. Materials for these applications include loose mineral fibres, polystyrene beads and vermiculite and are applied by hose injection to the cavity or raking to a thickness.

Insulation boards

These are a more rigid form of insulation for use in flat roofs, infill to rafters, below ground floors or screeds and partial fill to cavity walls.They are made of both natural and synthetic materials including cork, foamed glass, wood wool, polyisocynurate foam, polyurethane foam, phenolic foam, extruded polystyrene, expanded polystyrene, urea formaldehyde foam. They vary in cost and performance but in some situations it may be necessary to pay the extra cost for the thinnest board to achieve the standard. Generally the phenolic foam boards have a better performance than the urethane foam boards. Foamed glass is a good insulant with a high compressive strength and is therefore ideal for roof deck parking. Boards for flat roofs are often produced with a tapered thickness to provide the falls. Some foam boards have a closed cell structure and are preferable in situations where there is the prospect of damp conditions.

Partial fill insulation batts for external cavity walls are often produced with a rebated edge to improve construction. They are generally fixed using purpose made tied fitted with clips to hold the insulation batt against the inner leaf.

Boards made for installation between timber floor joists and rafters can be supported on timber battens fixed to the edge or installed in conjunction with a reflective film draped and fixed over the timbers to cradle the insulation or supported by purpose made clips. Some manufacturers produce boards with a rebated edge so the insulation fits between and over the timbers for continuity. Boards are often produced in a plain format or with optional plastic and reflective foil facings to enhance the performance.

Foils & films

These are available as a single layer to be used in conjunction with other insulations to provide support and give enhanced performance or in a multilayer format to offer a thin and efficient way of insulating new or existing pitched roof timbers fixed over or under the rafter. The latter being a suitable way of upgrading existing roof structures.

Spray applications

There are two basic types of sprayed insulation, the first being a fibre reinforced slurry for application to the underside of new and existing floor structure which present a complication for the mechanical fixing for other types of insulation.
The second makes use of polyurethane foams which are more versatile for use as thermal insulation and condensation control to existing construction. It can be used to insulate the underside of pitched roofs to existing houses or upgrade the insulation to intermediate floors between heated and unheated areas. It may also be used to control condensation to the underside of single skin roofs of agricultural buildings and the like where there is high humidity. It is also useful to provide combined insulation and stabilisation to old cavity walls with problems of wall tie failure and will bond the leaves together.
Screeds
Insulated screeds are a useful alternative to insulation boards for new or existing solid ground floors, when the depth of construction is restricted.
There are two basis types the first using lightweight aggregates such as PFA, pumice or vermiculite and the second using air entraining agents.

Special & composite materials

In addition to the basic insulation products there are several others which make advantage of the ability to mould the materials or use them in a composite format. Moulded polystyrene is used for infill blocks to use in conjunction with precast floor beams. Foam insulations are used to make preformed pipe lagging and the backing for insulated plasterboards. They are also used to form the core for insulated cladding panels and industrial door panels.

Sound insulation

What is Sound?
Sound is defined as either airborne or impact sound subject to the source which produces it. Impact sounds are created when physical contact with the surface or a structure sets up sound waves within its fabric to transmit the sound through it. Airborne sound is produced from a source which vibrates the air molecules and sets up sound waves that travel through the air. Sound waves are produced over a wide range of frequencies with only a limited band between 15 to 20,000 Hertz being audible to the normal human ear. When airborne sound waves hit an element of structure they will transfer some of their energy into the fabric of the structure which passes through, setting up airborne sound waves on the opposite side. Some of the sound is reflected on the source sound of the element of structure and some will be absorbed as it passes through so reducing the level of sound.
Noise is unwanted sound which may interfere with the listening of another sound source or is simply an annoying nuisance. The relative pressure or intensity of sound is measured in decibels (dB) on a uniform scale of 0, which is the least perceptible to about 130 dB for the average threshold of pain. Whispering is approximately 25 dB whereas talking face to face is approximately 55 dB and shouting at close range is approximately 80 dB. The sound of a jet taking off will equate to the threshold of pain of 130 dB.

Accoustic standards

The Building Regulations Approved Document E - "Resistance to the passage of sound" sets out the standards for sound insulation as follows:
E1 - Sound Protection between dwellings and adjoining building. This includes other forms of residential accommodation such as hotels, hostels, student accommodation, nurses hostels and homes for the elderly.
E2 - Protection against sound within a dwelling, this applies particularly between bathrooms and habitable rooms or bedrooms and other rooms.
E3 - Control of reverberation noise between common parts i.e. stairs and corridors in buildings containing dwellings i.e. flats.
E4 - Specific applications to acoustic conditions in schools.

Although not covered by the mandatory standards of the Building Regulations there are many building design situations where sound insulation will need to be considered subject to the choice of construction. For example whereas a 100 mm thick dense blockwork wall plastered both sides will satisfactorily provide 40 – 45 dB sound reduction and be suitable for sub dividing walls to cellular offices to insulate against normal speech levels, a stud partition faced both sides with 12.5 Soundbloc plasterboard and skim will need to include a sound insulating quilt.

Recording studios, concert halls and the like will require specialist consideration to ensure adequate insulation between spaces and the appropriate acoustic conditions.

Types of insulation

Unwanted noise levels from impact and structure borne sound through separating walls and floors are reduced by the use of isolating construction and resilient pads or mats. A masonry cavity wall is the simplest form of isolated construction but generally the leaves will need to be tied together for structural reasons which unfortunately create a route for the transfer of sound. The Building Regulations specify types of tie to be used for internal and external cavity walls. The leaves of the wall which form the core should be constructed of dense brick or blockwork to provide mass to counter the transfer of airborne sound and be faced on the room side(s) with lightweight plaster or plasterboard which will act to absorb some of the sound.
A single leaf internal wall should be built of dense brick or blockwork to provide mass and be faced each side with dense panelling spaced 25mm minimum off the core wall for isolation.

A lightweight stud wall should preferably be constructed with two stud frames spaced apart and not tied together to create the isolation from each other. Isolation can be improved with the use of resilient pads fixed between the perimeter framing and the flanking floor and walls. The stud should be faced with one and preferably two layers of soundbloc quality plasterboard with joints staggered and be backed with a sound absorbent insulation. Alternatively a sound insulating quilt can be fixed in the cavity between the frames.
An alternative to the above to reduce the overall thickness is to overlap and stagger alternate studs so the facings on each side are fixed to separate sets of studs. Ideally the sole plate and head plates should be split with an isolation joint between so both sets of studs have an independent support. A sound insulating quilt (acoustic quilt) should be woven between the two sets of studs.
Separating floors fall into three types of concrete with a soft covering or floating layer and timber with floating layer (sometimes called a floating floor). The first type relies on the dense mass of the concrete to insulate against airborne sound and the soft covering to cushion the impact sound. The variation to this and to present a wider selection of hard floor covering is to lay the floor finish of either timber on battens or sheet/tile covering on screed over a resilient cushion layer to isolate the finish from the structure and insulate against impact sound. The cushion layer could comprise of synthetic close celled foams such as polyethylene or natural materials such as cork, rubber or fibre matting. In either of the above improved sound insulation can be added with a floating ceiling of plasterboard on battens with isolation pads to the fixings to the underside of the slab, or a suspended ceiling with insulation quilt laid above the tiles.

A timber floor can also be constructed in two ways. Firstly, as a platform floor in which the joists are overlaid with a base board of chipboard (Wemroc), or tongued and grooved boarding with glued joints overlaid with a resilient cushion layer as previously noted for the solid floor and a floating layer of floor finish. An absorbent layer of approximately 100mm thick rock fibre batts may be used between the joists to insulate from airborne sound. A ceiling of two layers of plasterboard with joists staggered will complete the construction. An alternative ribbed form of construction is to fix the floor board to 50mm thick timber battens laid on top of the floor joists with a resilient strip between to cushion against impact sound. A further alternative to the sound absorbent fibre batts is to fix polythene sheet and 6mm thick plywood to the underside of the joists prior to plaster boarding and overlay the polythene sheet with 50mm dry sand pugging to insulate airborne sound. Timber stairs are a common source of noise from impact sound and the quality can be improved by overlaying the tread with a floating layer of tread on resilient pad.

Sound levels may also be reduced with the addition of soft furnishing and surface coverings of drapes and carpets which act to absorb and nullify reflected sound.
An important consideration in the reduction of structure borne sound is the detailing of isolation joints and to avoid flanking conditions.