Find out more about the different types of insulation, their pros and cons

Good insulation keeps your home warm, could save you hundreds of pounds a year on energy bills and lowers CO2 emissions. The cost of energy is not exactly cheap, with forecasts that average bills could reach £2,000 for many homes. Making sure your home is properly insulated is enormously important. A third of all heat in the home escapes through walls while a quarter is lost via uninsulated roofs, according to the Energy Savings Trust.

When insulating your home, you can choose from many different types of insulation – each with its own pros and cons. The type you pick will depend on where you plan to use it and your budget. Other factors to consider include should it be man-made or natural? Is one a better insulator or easier to install than another?  

Blanket batts and rolls

Soft rolls and semi-rigid batts of insulation can be used for all areas, including floors, ceilings and unfinished walls. It consists of flexible fibres, most commonly fibreglass but also mineral (rock and slag) wool and natural fibres, such as cotton or sheep’s wool. Typically fitted between studs, joists and beams that are relatively free from obstruction.

Pros

• Suitable for DIY installation as it’s quick and easy to install, especially when applied in pre-cut batts
• Affordable – relatively inexpensive compared to other types of insulation
• Should keep its shape as it doesn’t shrink over time
• Natural products are available made of non-irritant cotton and sheep’s wool.

Cons

• Rolls of blanket can sag on vertical surfaces, making the insulation less effective so it needs to be fixed firmly to the blockwork skin of a wall
• Can be too bulky to fit around obstructions or into small spaces
• Essential to wear protective gear when installing rockwool and fibreglass insulation to prevent itching, skin rashes and lung disease if inhaled.

Rigid foam or foam board insulation

Rigid panels of insulation or foam boards can be used to insulate almost every part of the house from the foundations to the roof. The most common materials used in making the foam boards include: polyurethane, polystyrene and polyisocyanurate; all made by mixing chemicals. When extending a property, foam board insulation would normally be installed in the cavities or stud work during construction. Alternatively, if you are refurbishing an older property with solid walls, it can be applied inside a timber frame internally or by insulated plasterboard attached directly to the wall.

Pros

• Good insulating value for relatively little thickness (R-value), up to twice that of other insulating materials.
• Strong and less likely to sag than soft batt and blanket insulation
• Resists water and air leaks better too

Cons

• It is more expensive due to its density
• Joints between sheets boards must be taped to prevent air leakage
• Flammable toxic gases after combustion
   

Spray foam insulation

Spray foam insulation is used to reduce air leakage in unfinished attic floors, new wall cavities and enclosed existing walls.  Spray foam is extremely versatile and can be injected into even the smallest of cavities, such as cracks in window and door frames as well as large and unusually shaped spaces.  It expands after being applied to fill every nook and cranny, creating a virtually airtight seal.

There are two types of foam insulation: breathable (open-cell) and non-breathable (closed-cell). Both are typically made with polyurethane. The high density closed cells are filled with a gas that helps the foam to expand to fill the spaces around it whereas open-cell foam is filled with air, giving the insulation a spongy texture. Closed cell provides a stronger resistance to air leakage and moisture but is more expensive. Open cell costs less but shouldn’t be used below ground level, for example in a basement, where it might absorb water. Consult a building professional to decide which type of insulation is best for you.

Pros

• Good for adding insulation to existing finished areas
• Ideal for insulating irregularly shaped areas and around obstructions, such as pipes.
• Doesn’t settle or sag and fills all the nooks and crannies where it is installed
• High insulation value per unit thickness
• Eco-friendly – most foam materials today use foaming agents that don’t include CFCs that are harmful to the earth’s ozone layer.

Cons

• Can be more expensive than other types of insulation, such as traditional batt insulation
• Not a DIY job. Needs professional installation by a licensed contractor, adding to the cost
• Eco-friendly credentials open to question. Most are made from polyurethane that contain toxic compounds, potentially harmful to health.

Loose-fill and blown-in insulation

Made from a variety of lightweight materials such as cellulose, fibreglass or mineral (rock or slag) wool, either supplied loose or blown into place using specialist equipment. Suitable for both enclosed existing walls or new wall cavities as well as unfinished attic floors and other hard-to-reach places. Eco-friendly versions include recycled newspapers (cellulose) and wool, usually treated with borax to prevent insect, fungus and rodent attack.

Pros

• Cost-effective
• Good for adding insultation to existing finished areas, irregularly shaped areas and around obstructions such as pipes.
• Sustainable, natural versions include cellulose (old newspapers) and wool. Be aware borax used to treat wool insulation is a poison, pesticide and fungicide.

Cons

• Can be more pricey than other types of loft insulation
• Not suitable for DIY installation
• Sagging over time, cellulose and wool can sag, thereby decreasing its U-value
• Dust – essential to wear a protective mask when installing.

Insulating concrete forms (ICFs)

Usually foam board or foam blocks that are installed as part of the building structure. The cores in the blocks are typically filled with concrete. Ideal for foundation walls of new extensions and unfinished walls

Pros

• Insulation is literally built into the home’s walls, creating high thermal resistance
• Little need for any other insulation

Cons

• The walls can be very thick which may be a problem in a small space
• A bracing system is needed to keep the walls straight
• The cost is a factor to consider

Structural insulated panels (SIPs)

Another eco-conscious building system that is pre-insulated through an insulating foam core sandwiched between two structural panels, either wood or cement particle board. SIPs come as individual panels for walls, floor and roofs or in a kit form that can be fitted together to make an entire home extension. They can even be supplied with the doors and windows ready-installed and plasterboard lining.  

Pros

• Extremely efficient insulation compared to their thickness
• Quicker build speeds as panels are pre-cut and ready to go.
• Thermal and sound-insulation factors of SIPS comply, or, in many cases, beat current Building Regulations
• A home extension made entirely from SIPs will require very little extra insulation

Cons

• As SIPS are factory-made, on-site changes are not possible, so all decisions made be made before the build begins.
• The panels aren’t cheap

Thermal conductivity

Ultimately, the aim of insulation is to stop or at least slow the transfer of heat. Any insulating material needs to be a poor conductor of heat. The K-value (sometimes called the lambda value) is a measure of the material’s thermal conductivity, expressed as W/mK. The lower the K value, the better. Most insulating materials have K values around 0.03/W/mK.

An insulating material is also measured or rated according to its thermal resistance or R-value. The R value is calculated by dividing the thickness of the material in mm by its K value. The R-value will vary with the type of insulation, its thickness and density.

Natural insulators

Most insulation is made from petroleum-based plastic or mineral fibres which use a lot of energy in the production process. Natural alternatives, such as wood fibre, cotton and wool, are no longer niche products.  Natural materials don’t tend to be better insulators and can be more expensive. That said, they are more sustainable and environmentally friendly materials.

Ultimately, the performance of the insulation will be determined by how well it is installed. It’s possible to do simple insulating jobs yourself relatively cheaply, such as insulating a loft with blanket rolls or batts. But more complex jobs are best left to the professionals, for example cavity wall insulation and internal solid wall insulation. Find a professional registered with a trade association recommended by Which? such as the National Insulation Association (Nia) or the Cavity Insulation Guarantee Agency. Check that any insulation complies with the current Building Regulations. Do your homework and find out about the products before you buy.

Insulation can be pricy, so it’s worth checking if you’re eligible for free insulation or a Green Homes Grant voucher to help pay for it https://www.gov.uk/guidance/apply-for-the-green-homes-grant-scheme. Over time, insulation should pay for itself with the savings you make on your energy bills. And you will be doing your bit to save our planet.