Insulation explained
What Is Insulation?
A clear introduction to insulation: what it means, what it does in a home and how to take the next step with confidence.
Start with the definition
Insulation meaning, in simple terms
Insulation is a material or system that reduces the transfer of heat between spaces. In a building, it helps separate the temperature inside a home from the conditions outside.
Think of a house on a hot afternoon. The roof and outside surfaces warm up, and heat moves towards the cooler interior. Thermal insulation adds resistance along that path. When the inside is warmer than the outside, it also slows heat travelling in the opposite direction.
The word insulated describes something fitted with, or protected by, insulation. An insulated ceiling, for example, has an insulating layer as part of its construction. Here, we are discussing building insulation; the same word also has other uses, such as electrical insulation around a wire.
Its role in a home
What is insulation used for?
The main purpose of thermal insulation is to make heat move less easily through parts of a building. This can help the indoor temperature change more slowly and reduce the demand for heating or cooling.
Warmer weather
Limit unwanted heat gain
Insulation helps resist heat moving into a cooler home through the insulated parts of its roof, walls or floor.
Colder weather
Slow heat loss
It helps retain warmth by reducing heat transfer from a warmer interior towards colder surroundings.
Results depend on the building, the product and the quality of the installation. For a broader look at comfort and energy use, read our guide to the benefits of insulation. The separate how insulation works guide explains the science in more detail.
Two related terms
Thermal and acoustic insulation
Thermal insulation deals with heat transfer. Acoustic insulation is concerned with sound. Some materials contribute to both, but a product’s thermal rating does not describe the sound performance of a complete wall, floor or ceiling.
Sound-absorbing material can help improve the acoustic performance of a building assembly. The complete construction, including its layers, connections and gaps, affects how much sound travels between spaces. Explore our soundproofing information if noise is your main concern.
A place in the building
Where is insulation used in a house?
Insulation can form part of the boundary around the spaces you want to keep comfortable. The right position depends on the building’s construction and the purpose of the insulation.
Ceilings
In many homes, an insulating layer above the ceiling helps separate the occupied rooms from the roof space.
Explore ceiling applications →Roofs
A roof may include insulation or a reflective layer within its build-up, depending on how the roof is designed.
Explore roof applications →Walls
Insulating materials can form part of a wall system, with the specification depending on its thermal or acoustic role.
Explore wall applications →Floors
Floor insulation may be included within a suitable floor construction to help reduce heat transfer through that part of the home.
Explore floor applications →Look at the complete home
Insulation, air sealing and ventilation
These are connected parts of a building’s performance, with different jobs to do.
Reduces heat transfer through the parts of a building where it is fitted.
Addresses unwanted air movement through gaps and openings. An insulating layer does not automatically make a home airtight.
Provides planned air exchange. It still needs to be considered when improving insulation or reducing unwanted air leakage.
A roof leak, a draught or a ventilation problem may need separate attention. Our air-sealing guide explains that part of the picture.
From understanding to choosing
What should you read next?
Once the meaning is clear, the next question is usually about the material, the performance required or the work involved. Use the guide that matches your project:
For an existing home, start by identifying what is already installed and what you want to improve. Our existing-home insulation guide can help you plan your next questions.
A few common questions
Insulation questions, answered
What does “insulated” mean?
It means that something has been fitted with, or includes, insulation. In a home, an insulated part of the building is designed to resist heat transfer, sound transmission or both, depending on its construction.
Does insulation create heat?
Insulation does not generate heat. Its thermal role is to slow heat transfer. The indoor temperature also depends on the weather, sunlight, air movement and any heating or cooling in use.
Is insulation useful in a warm climate?
Yes. Heat transfer matters in hot weather too. The appropriate insulation system can help limit heat entering a cooler building. Its performance depends on the roof or wall design, the product and how it is installed.
What is an example of building insulation?
A glasswool or polyester roll fitted above a ceiling is one example. Insulation also comes in other forms, including rigid boards and reflective systems. Visit our material-types guide to compare their different uses.
Further reading: U.S. Department of Energy: heat flow; DOE consumer guide to air sealing (PDF); Knauf Insulation: acoustics. These references explain general building principles; product suitability and project requirements should be checked locally.
Take the next step
Understand your options.
Plan a more comfortable home.
Speak to Home Insulations about product supply or professional installation in Johannesburg, Centurion and Pretoria.