Choosing between different home insulation types can be a minefield, but get it right and your reward will be a warmer home and lower energy bills. Discover which insulation material is best for your project with our essential guide
With so many different home insulation types on offer – from natural hemp and sheep's wool to spray-on foams and rigid insulation boards – choosing the right material for your home needs careful consideration. The type you use will depend on the part of the home you plan to insulate, any depth restrictions and also what is appropriate for your home's construction.
Read on to find out everything you need to know about choosing the right insulation type, as we explain the different materials available and their various applications. You might also want to check out our complete guide to insulating a house.
Insulating a house is one of the most important things you can do to reduce heating bills and make it feel cosy and comfortable, but before starting out, it’s important to understand the potential complexities of insulating an old building. The pitfalls of using inappropriate insulation materials or of them being installed incorrectly include damp and mould – these may be damaging to both your health and that of the building.
When adding insulation the aim is to improve the thermal performance of the building’s external envelope – in other words the roof, walls and floors. With this in mind, you must weigh up the pros and cons of insulating each element and to understand whether doing so is cost efficient, practical and right for the house.
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Rarely will one type of insulation material will provide the answer to insulating all parts of a house. Instead, a palette of different products is often required to suit the specific requirements of each situation.
When choosing wall or roof insulation think about each material’s compatibility with the building, its thermal performance, acoustic properties, ease of use, cost and what it’s made of.
Some materials are thin and highly insulating so are ideal where space is limited; others are cheaper but a greater thickness is required to achieve the equivalent level of thermal performance.
Insulation comes in all shapes and sizes ranging from rolls, batts and boards to loose-fill, aggregate and spray foam products, with each suited to different applications.
Thoroughly research products and systems and be sure you understand the consequences of installing insulation in an old building. Most suppliers of natural, breathable materials will offer advice; some will prepare a specification for an appropriate system.
Most insulation is available from your local builders' merchant. Some types for very old homes might only be sold by specialist suppliers. A good builder will be able to help your find the right materials for you. Otherwise, look at the wide range available online from these stores:
Natural insulation products are breathable so tend to be particularly well suited to use in older buildings, are pleasant to use and have the least environmental impact.
Spray foam insulation is often used under roofs. Here, Icynene spray foam has been used in a listed barn conversion
Widely used in modern buildings, most petrochemical insulation materials are not breathable but have the advantage of providing high levels of thermal insulation relative to their thickness, so may be useful where breathability is not critical.
Old houses are different from those built after around 1919 because they generally have a breathable structure with solid walls that use mortars, renders and plasters of lime or earth. As long as the breathable nature of the building is maintained it will remain in equilibrium, so moisture-related problems are usually avoided.
At its simplest breathability is about the ease with which water vapour can pass through the building’s fabric. It is also to do with liquid water diffusion and capillarity – the process by which liquid water is drawn into a permeable material through open cells. Open-cell materials have interlinking cells or pores so are able to diffuse liquid water and water vapour.
Another aspect of breathability is a material’s ability to buffer moisture, a process sometimes referred to as hygroscopicity. An insulation product that easily absorbs excess water vapour as the relative humidity in a room rises, and then releases it as it falls, will help create a more stable internal environment.
Some insulation materials, such as wood fibreboard, help cut overheating in attic rooms and other areas as they delay the time taken by the heat from the sun to pass through the building envelope, a process known as decrement delay.
Any part of the building that acts as a thermal conductor is known as a thermal bridge. With the installation of insulation, any thermal bridges become more pronounced and tend to be a focus for the formation of condensation, so areas such as window reveals must not be forgotten.
Screws penetrating insulation materials will also allow heat to bypass the insulation so special ‘thermally broken’ fixings are generally used.
Some insulation products can cause severe irritation to the skin, eyes and respiratory tract and, depending on the material, face masks, gloves and protective clothing may be necessary.
Although natural insulation options are generally pleasant to handle, always wear a face mask in enclosed spaces such as lofts, especially where dust and previously installed insulation and other potentially hazardous materials may be present.
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