What is insulation?
Insulation is a general term used to describe products that reduce heat loss or heat gain by providing a barrier between areas that are significantly different in temperature. Insulation also acts as a sound barrier by reducing the level of sound transmitted from one room to another via partition walls or ceiling voids. Insulation therefore reduces the amount of heat that escapes from a building in the winter and protects it from getting too warm in the summer. It also helps create quieter living environments thereby increasing the overall comfort level of building occupants.

Why is insulation required?
Insulation is the easiest and most inexpensive way to increase the energy efficiency of a residential home or commercial building. An energy efficient building is a cost-efficient building as well.

Take for example a residential home. Studies have shown that a home that does not have proper insulation will leak heat during the winter time. 30% of heat – heat that a homeowner is paying for – will be lost through the roof, 10-15% through windows, 20-30% through walls, and even 10-15% through the floor.

With a home that is properly insulated, that heat loss is stopped and the heating unit will not have to work as hard as it does.

Studies show that a properly insulated residential home will be cooler in summer and warmer in winter by an average of 7º C., and thus, simply more comfortable overall, with less energy cost.
Indeed, properly insulated homes will not need as powerful a heating/cooling unit as those that are not insulated, and so there is a saving there as well, as smaller and therefore less expensive units can be installed.

What is ‘glasswool’ insulation?
Glasswool is made from fibres of glass which are arranged using a binder which gives them a texture similar to wool – hence the name.

Glasswool can be manufactured as a loose fill material, or as batts. Regardless of the form it takes, the process of making this insulation material traps millions of tiny pockets of air between the strands of glass. Because the pockets of air are trapped in this way, there is little to no movement, and thus no heat transfer by way of convection.

Ceiling and wall glasswool batts are lightweight, flexible and resilient. They are specially designed to provide thermal insulation of ceilings and wall cavities in both domestic and commercial buildings.

What is ‘reflective’ insulation?
Reflective insulation prevents radiant heat gain. It does not particularly protect well against heat transfer via conduction or convection. All reflective insulation has an “R” or thermal resistance value. Heat radiated from the sun warms up the roof of a home or commercial building. The heat is transferred into the attic or other area of the building by conduction.

Reflective insulation in the attic or crawl spaces reflects 95% of that heat back up toward the roof, and the insulation material below the reflective barrier (foil) lets very little heat continue downwards (or to put it technically, emits very little heat).

Are there any other types of insulation?
Yes. There are numerous types of insulation materials each with their own set of unique features and benefits. Some additional types of insulation are described below.

– Polyisocyanurate Insulation
Polyisocyanurate insulation (commonly referred to as PIR) is a thermoset, rigid foam insulation typically faced on one or both sides with a reflective foil laminate. PIR provides exceptional Material R-values at lower thicknesses compared to traditional bulk insulation products. It also delivers excellent fire and moisture absorption properties.

– Extruded Polystyrene Insulation
Extruded Polystyrene insulation (commonly referred to as XPS) is a closed cell foam insulation that is produced by expanding a polystyrene polymer via an extrusion process. XPS provides exceptional compressive strength properties typically reaching values of ≥300kPa.

– Expanded Polystyrene Insulation
Expanded Polystyrene insulation (commonly referred to as EPS) is a closed cell foam insulation that is produced by ‘expanding’ a polystyrene polymer . It is typically supplied in a rigid board form and is used in applications where thermal performance is required.

– Rockwool insulation
Rockwool is a fibre that is made by spinning or drawing molten minerals, such as ceramics. Rockwool insulation is designed to provide thermal insulation of ceilings and wall cavities. More importantly, it provides high service temperature a property thus is commonly used in buildings to provide adequate fire resistance. Additionally, rockwool is commonly used in industrial applications to wrap pipes, vessels, burners etc.

– Polyester insulation
Polyester insulation, as the name implies, is made from polyester fibres. Polyester fibres are made from synthetic polymers known as polyethylene terephthalate (PET) – chemical substances found mainly in petroleum. Polyester fibres are soft and easy to handle, and thus are easily installed.


How is heat transferred?
Although heat can be transferred in a variety of ways, the three most common ways are:

  • Conduction
  • Convection
  • Radiation

In Conduction, heat travels through a solid material such as ceiling tiles, floor tiles, and walls.

In Convection, heat travels through a fluidic medium, such as air or water. When air is heated it expands, becoming less dense, and therefore rises as far as it can go (in an oven, in a room, or in the open air). As the air rises away from the heating source, it gradually cools, condenses, and sinks closer to the heating unit again, and the process is repeated. The hotter air (or water) transfers energy to the cooler air (or water) as it circulates.

With Radiation, heat is transferred from a hot body to a colder body through the use of electromagnetic waves. There is no need for the hot body to contact the cooler body for the heat to be transferred.
Terms can sometimes be misused. For example, despite its name, a radiator transfers most of its heat into a room by convection, not radiation.

Reflective insulation in the attic or crawl spaces reflects 95% of that heat back up toward the roof, and the insulation material below the reflective barrier (foil) lets very little heat continue downwards (or to put it technically, emits very little heat).

What is an R-value?
The R value, or thermal resistance of a material, expresses the ability of a particular thickness of that material to resist heat flow. A higher the R-value represents a greater ability to resist heat transfer.

What is the difference between a Material R-value and a Total R-value?
A Material R-value or ‘insulation value’ is simply the R-value of the insulation material itself. A Material R-value does not consider any other elements of construction.

A Total R-value or System Value takes into account all elements of a wall, roof, or floor system including insulation, air gaps, air films, cladding types etc.

What does Section J refer to?
Section J refers to a part of the BCA (Building Code of Australia) relating to energyefficiency. The aim of Section J is to ensure all new buildings are built in an energy efficienct manner to reduce levels of greenhouse gas emissions. All new commercial building projects are required to demonstrate compliance to Section J (generally at construction certificate stage) to verify the building works complies with the provisions outlined in the BCA.

Fletcher Insulation uses Section J to complete thermal calculations, which we then provide to architects and energy consultants, so that we can provide the best value insulation to meet the requirements for their building. As a matter of fact, Fletcher Insulation serves as a consultant for the BCA’s Section J and Australian standards regarding insulation.

What is a thermal calculation?
Thermal calculations are used to obtain the thermal resistance for wall, floor and roof systems. These calculations take into account such elements as:

  • Class of building
  • Climate zone
  • Construction elements

Of course, all buildings – residential, commercial and industrial – have different energy efficiency requirements. Fletcher Insulation uses Section J to complete thermal calculations, which we then provide to architects and energy consultants, so that we can provide the best value insulation to meet the requirements for their building. As a matter of fact, Fletcher Insulation serves as a consultant for the BCA’s Section J and Australian standards regarding insulation.


How can insulation provide acoustic benefits?
The heavier the mass of a layer of plasterboard, and the greater the cavity depth between two partitions, the better the sound isolation provided. Insulation within the cavity will also provide excellent sound isolation.
The “mechanical connection,” in other words the studs used between the two partitions is also important. “Bridging” actually reduces sound insulation.
Twin studs are typically best, followed by staggered studs, then timber or steel studs.

  • 2 to 4 dB increase in Rw for timber stud partitions
  • 5 to 7 dB increase in Rw for steel stud partitions.
  • 8 dB (insulation on one side) to 14 dB (insulation on both sides) increases in Rw for twin steel and timber stud construction.
  • 25 dB increase (insulation both sides) for Partiwall.

Depending on the system, it is best to fill the partition cavity at least 75%, and oftentimes as high a 100%, depending on the system.
Increasing the density of insulation has only a marginal effect on the decibel level – just 1 dB.

Does acoustic insulation block out 100% of external noise?
Not quite. Whilst insulation significantly reduces sound transfer, typical sources of sound leakage will impact the overall acoustic atmosphere of a building.
Typical sources of sound leakage include the following:

  • Lightweight panels above doors
  • Doors
  • Air leaks through gaps, cracks or holes
  • Sound transmission via suspended ceiling partitions
  • Common ventilation systems without sound absorbent treatment
  • Common floor ducts
  • Electrical outputs and service pipes
  • Lightweight mullions or mullion/partition closers
  • Continuous runs of ducting
  • Partition performance

It is important to seal all possible paths for sound leakage, or “flanking noise.” Noise not only passes through a shared wall, but finds “flanking paths” through poor joints between the wall and floor, poorly sealed penetrations, ceiling spaces, floor spaces, ductwork, and even other walls.

How can I Reduce Leakage/Flanking?
There are a variety of ways to prevent sound flanking.
All floor/wall junctions must be sealed along the perimeter with a flexible fire/acoustic sealant. Skirting alone is not sufficient to seal gabs.
A correctly installed cornice can also provide an acoustic barrier to minimize flanking, as long as an airtight seal is achieved and maintained.
If the gaps around the wall perimeter are not sealed correctly, the wall system would be degraded. For example, a Rw=62 dB wall system would be reduced to:

  • Rw = 50 dB if there is a 0.01 mm gap left around the perimeter*
  • Rw = 25 dB if there is a 2 mm gap left around the perimeter*

* Based on a 6mx6m wall area.

The purpose of an acoustic system for walls or ceilings is to reduce the transmission of sound, both airborne and structure-borne. This can be accomplished by sealing all leaks that would otherwise permit the transmission of airborne sound, and through the use of proper construction at wall and floor intersections, prevent the transmission of structure-borne sound.

What is a ‘Weighted Sound Reduction Index’?
A Weighted Sound Reduction Index or Rw, is the rating used to measure the level of sound insulating abilities of walls, floors, windows and doors. It is expressed in decibels (dB), and is used for a partition or single component only.
The higher the Rw figure, the better the sound isolation that is provided.
It must be noted, however, that the Rw figure is not reliable for sounds which contain a significant amount of low frequencies – for example music or sounds emanating from home theatre systems.

What does Rw+Ctr refer to?
The end results for the Weighted Sound Reduction laboratory tests are subject to a “spectrum adaption term” (CTR). This accounts for distinct types of noise sources, such as traffic, or music which has a large low-frequency component.
This is always a negative number, typically between -1 to -15. A large negative number means a large dip in sound insulation performance in relation to the performance in other frequency bands. A large negative number does not necessarily mean poor low-frequency performance, however.
Rw + Ctr is Rw with the addition of a low frequency sound correction factor Ctr (always a negative number remember). Rw + Ctr is used because of the increase in low frequency sound sources such as surround sound systems, drums or bass guitars, and of course traffic or aircraft noise. Two walls can have the same Rw rating, but have different resistance to low frequency sound, thus a different Rw + Ctr.

What does a Noise Reduction Coefficient (NRC) represent?
The Noise Reduction Coefficient is a scalar representation of the amount of sound energy absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection; an NRC of 1 indicates perfect absorption. Because of the formula used for the NRC, the coefficient is not a percentage, and therefore values larger than 1 are quite common.

What does αw signify?
αw is calculated in accordance with ISO 11654 using the sound absorption coefficient αp values at standard frequencies, and comparing them with a reference curve.
The practical sound absorption coefficient αp is the average of the three 1/3 octave αs values centred on the octave band frequency and rounded in steps of 0.05. The reference curve is shifted downwards in increments of 0.05. This shifts the reference curve to the point where the sum of the negative deviations from the measured values ≤ 0.10 in relation to the values of the reference curve. If this is the case, then the value of 500 Hz on the reference curve is theαw value.
αw is used by all suspended ceiling suppliers in Europe because it is the method which has been adopted as the norm for CE marking of suspended ceilings.

Sound Absorption ClassαwAbsorption class(as per VDI 3755/2000)Approximate NRC


Sound Absorption
αwAbsorption class
(as per VDI
Approximate NRC
A0,90; 0,95; 1,00Extremely AbsorbingNRC >=0,75
B0,80; 0.85Extremely AbsorbingNRC>=0,75
C0,60; 0,65; 0,70;
Highly Absorbing0,5 <=NRC <0,75
D0,30; 0,35; 0,40;
0,45; 0,50; 0,55
Absorbing0,5 <=NRC <0,75
E0,15; 0,20; 0,25Hardly Absorbing0,25 <=NRC <0,5
Not Classified0,05; 0,10Reflecting
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