Introduction & Terminology

Insulation is the most effective way to improve the energy efficiency of a home or a building. Insulation of the building envelope helps keep heat in during the winter and out in summer to improve comfort and save energy. Insulation could add additional benefits such as acoustics and waterproofing. Effective draught proofing, moisture control and ventilation are important at design stage.

The appropriate level of insulation intervention will depend on climate, building construction type, and whether auxiliary heating and/or cooling is used.

Insulation – Overview

Insulation reduces heat flow and is essential to keep a building warm in winter and cool in summer. A well-insulated and well-designed building will provide year-round comfort, decreasing energy costs. This, in turn, will reduce greenhouse gas emissions.

Climatic conditions will influence the appropriate level and type of insulation. Establish the climatic zone from the Map of Climatic Zones of South Africa.

Passive design techniques must be used in conjunction with insulation. For example, if insulation is installed but the building is not correctly shaded, built up heat can be trapped in by the insulation creating an ‘oven’ effect. Air tightness of a building is important, as draughts can account for up to 25 percent of heat loss in winter.

Ensure proper ventilation in buildings where fossil fuels are burned as an energy source.

Certain types of insulation can assist with weatherproofing and control moisture problems such as condensation. Some types of insulation also have soundproofing qualities. Some products are environmentally friendly and contain recycled material.

The most economical time to install insulation is during construction.

How does insulation work?

An un-insulated home is subject to considerable winter heat losses and summer heat gains.


The term ‘insulation’ refers to materials or a combination thereof which provide resistance to heat flow.

When these materials are installed in the roofs, ceilings, walls, and floors of a building, heat flow into and out of the building is reduced, and the need for heating and cooling is minimized. Although ceilings and walls may be insulated, heat loss will still occur in winter if there are large areas of unprotected glass or through fixed wall vents, gaps electric light entry points and cracks around external doors and windows.

Appropriate internal window coverings (e.g. lined drapes with pelmets) and draught proofing are vital to complement insulation. Insulation should always be coupled with appropriate shading of windows and adequate ventilation in summer. Without shading, radiant heat entering the home through the windows will be trapped inside by the insulation and cause discomfort.

Principles of Insulation

Resistance to heat flow is achieved by the use of either bulk insulation, reflective insulation or a combination of both, which work in different ways. 

What you need to know

There are various factors to consider before making an insulation decision: 

Thermal Performance – Installed R-value

When insulating a home or building, it is important to ascertain the R-value specified by the National Building Regulations.

It’s also important that the product provide long-lasting thermal performance. It is the overall R-value installed that is important. 

Life Time Performance

In order to ensure the expected energy savings, it is important that the insulation does not deteriorate, or settle, over time.

Fire Safety

In accordance with the application of the National Building Regulations SANS 10400-T Fire Protection, all insulation products should be independently tested in accordance with SANS 428 Fire performance classification of thermal insulated building envelope systems, prior to being sold.

SANS 428 incorporates all factors required for fire-hazard or fire-risk assessment of the materials, products, or assemblies under actual fire conditions.

SANS 428 provides a standard testing procedure to measure:

  • combustibility;SANS 10177-5:2007, Fire testing of materials components and elements used in buildings Part 5: Non-combustibility at 750 ºC of building materials.
  • surface fire properties;SANS 10177-10:2007, Fire testing of materials, components and elements used in buildings Part 10: Surface burning characteristics of building materials using the inverted channel tunnel test
  • designated use and application.SANS 10177-11:2007, Fire testing of materials, components and elements used in buildings Part 11: Large-scale fire performance evaluation of building envelope thermal insulation systems (with or without sprinklers)


Insulation will lose its insulating efficiency or R-value when exposed to moisture. Some insulation products are not absorbent and, if exposed to moisture, will not wick up or hold water. If allowed to dry out insulation may retain its original R-value. In wall applications certain insulation material may be applied as vapour retarders, or moisture barriers.

Air Infiltration

Air infiltration generally occurs in the areas of a home that are not correctly sealed or insulated, such as around windows, doors, fireplaces, HVAC ductwork and perimeter joints. It can, and should, be controlled with proper caulking, and sealing of band joists, sill plates, header plates, and around doors, windows, electrical outlets and other openings.

Environmental Benefits

In assessing the environmental characteristics of insulation materials, consideration must be given to a broad range of issues relating to the resources going into their production, manufacturing processes, pollutants given off during their lifecycle, durability, recyclability, and impact on indoor air quality. Recycled content is the most recognized environmental feature of building products.

Materials with recycled content have four advantages:

  1. they require less natural resource;
  2. they divert materials from the solid waste stream;
  3. creating additional job opportunities for the unemployed by collecting waste;
  4. they use less energy during manufacturing.

The insulation industry is full of good examples of recycled material use:

  • Cellulose Fiber uses recycled newspaper by weight; the rest is comprised of fire retardant chemicals and—in some products—acrylic binders.
  • Fiberglass uses recycled glass
  • Mineral wool actually refers to two different materials: slag wool and rock wool. Slag wool is produced primarily from iron ore blast furnace slag, an industrial waste product and Rock wool is produced from natural rocks.
  • Polyester Fiber uses recycled PET bottles and some use Kenaf (similar to hemp)
  • Polystyrene uses recycled plastic resin in some extruded and expanded polystyrene.

Life-cycle analysis

A life-cycle analysis is an appraisal of the environmental impacts connected with a product through an examination of the product’s environmental traits during many stages including pre-manufacturing; manufacturing; distribution/ packaging; use, reuse, maintenance; and waste management. In reviewing each of these stages, a life-cycle evaluation clearly shows its environmentally beneficial attributes.

This is just the first step…”


How insulation performance is measured.

The thermal performance of all components and systems except windows and doors is expressed in terms of R-value; for windows and doors, performance is expressed in terms of U-value.

What is an R-value?

Insulation materials are rated for their performance in restricting heat transfer. This is expressed as the R-value, also known as thermal resistance. The R-value is a guide to its performance as an insulator—the higher the R-value, the better the insulation (i.e., resistance to heat flow) it provides.

R-values are expressed using the metric unit’s m².K/W, where:

m² refers to one metre squared of the material of a specified thickness;

• K refers to a one degree temperature difference (Kelvin or Celsius) across the material;

• W refers to the amount of heat flow across the material in watts.

Use the nominal R-values as listed by the manufacturer on the packaging of the insulation to determine the performance.

Products which have the same R-value will provide exactly the same insulating effect as each other, provided they are correctly installed. The higher the R-value the more effective the insulation. Products must be installed in accordance with the manufacturer’s specifications.

The information available on the product data sheet and/or label must include the R-value and whether it must be installed professionally or DIY. Ensure that it suits your particular application. Ask if performance guarantees and/or test certificates are available.

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Material R-values – the thermal resistance values of bulk/mass type insulation are measured on the product alone according to international standards.

System R-values – the thermal resistance value of reflective insulation is calculated based on international standards and depend on the product being installed as specified in accordance to manufacturer’s specifications. This is known as a system R-value which incorporates air spaces.

Composite R-values – the thermal resistance values of composite insulation products are measured by testing the composite product as a unit according to international standards.

Direction of heat flow effect

R-values can differ depending on the direction of heat flow through the product. The difference is generally marginal for bulk insulation but can be pronounced for reflective insulation.

  • Up R-values describe resistance to heat flow upwards (sometimes known as ‘winter’ R-values).
  • Down R-values describe resistance to heat flow downwards (sometimes known as ‘summer’ R- values).

What is a U-Value?

Sometimes insulation or systems are rated in terms of its thermal transmittance (U-value), rather than its R-value. The U-value measures the transfer of heat through a material or a building element (thermal transmittance), whereas the R-value measures the resistance to heat transfer. U-values are often used in technical literature, especially to indicate the thermal properties of glass and to calculate heat losses and gains.

The U-value is the reciprocal of the R-value, R=1/U or U=1/R. For example, with an R-value of 2.0, the U-value is 1/2 or 0.5.

The U-value is expressed using the metric units (W/m².K) where:

  • W refers to the amount of heat transmitted across the face or through the material in watts;
  • m² refers to one metre squared of the material of a specified thickness; and
  • K or ‘degree Kelvin’ refers to each °C temperature difference across the face of the materials or through the material.

A smaller U-value results in lower heat flow, and therefore less heat loss. Higher U-values mean greater heat loss.

What is an Overall R-value?

The overall R-value is the total resistance of a building element or system combination. It takes into account resistance provided by construction materials used in a wall or ceiling, internal air spaces, thermal bridging, insulation materials and air films adjacent to solid materials. Each of these components has its own inherent R-value, the sum of which provides the overall R-value.

What is Intervention or Added R-value?

The intervention added R-value or added thermal resistance is the value of the insulating material alone. This is the term most used when buying thermal insulation.

The manufacturer should provide the R-value of the insulation on the packaging. Some products will have a higher R-value for a specified thickness. For example, a 70 mm thick extruded polystyrene board and 100 mm thick glass wool blanket may have the same apparent R-value.

Reflective insulation requires that air spaces are positioned correctly within the building system to be effective, reflective membranes cannot have an R-value without the air space or air spaces.

To compare the relative performance of bulk and reflective insulation membranes, the resistance of such membrane in combination with air space(s) must be calculated. Reputable manufacturers can supply this information. Note: The effectiveness of reflective insulation installed on horizontal or sloping surfaces may eventually be reduced due to dust build-up, which reduces reflectivity, thereby increasing absorption. 

What is the difference between R-Value and Total R-Value?

The R-value is the material thermal resistance, i.e. product only whereas the Total R-value describes the total thermal resistance of the system to heat flow provided by a roof and ceiling assembly (inclusive of all materials and air films), a wall or a floor. These values are calculated from the resistance of each component, including the insulation. Total R-values are the best indicator of performance, as they show how insulation performs within the building envelope. See example in section 7.5. 

What is Thermal Bridging?

Thermal bridging is the transfer of heat across building elements, which have less thermal resistance than the added insulation. This decreases the overall R-value. Wall frames and ceiling beams are examples of thermal bridges, having a lower R-value than the insulating material placed between them. Because of this, the overall R-value of a typical ceiling and/or wall is reduced.


SANS 10400-XA Energy usage in buildings and SANS 204 Energy efficiency in buildings are currently under review, all publications will be republished.