Home insulation: Types of insulation, eco options plus where each works best

Getting your home insulation right should be a top priority, no matter whether you are self building, renovating or extending a house — both for environmental reasons and the savings you could make on heating bills. 

All new homes have to meet certain levels when it comes to thermal performance, but understanding exactly how you do this can be daunting to those new to the world of building.

The professionals you may be working with on your project will already have methods they are familiar with, but as a client it is helpful to know how to insulate your house and what types of insulation are available — as well as the pros and cons of each.

What is home insulation and what do I need to know?

Taking a ‘fabric first’ approach is all about building a highly insulated and airtight home. Put simply, it’s about wrapping your home in a thermal blanket to create a sustainable home that demands less heating, increases comfort levels and reduces energy bills — internal wall insulation is just one way of doing this, but the roof, floors, windows and doors all also need consideration.

“Insulation is an essential component of comfortable and efficient buildings. It not only reduces heat loss or heat gain by providing a barrier between inside and outside temperatures but its use can also support some of today’s biggest sustainability and development challenges, from energy consumption to noise pollution and fire resilience,” says  James Francis, product manager GBI at ROCKWOOL® UK. “And the latest edition of the Building Regulations (changes to Part L and new Part O) reflect these points,” says energy efficiency expert Tim Pullen.

But what does this all mean if you’re building your own home, renovating or extending? “It certainly means you have the option to choose what will work best for your build project – from the walls, to the floors and roof – and the set minimum standards in the Building Regulations do make decision making that little easier,” continues Tim. But, what should you know about insulation to ensure you choose the right type for your project and can have constructive conversations with your build team before the project gets underway?

What types of insulation are there?

Insulation isn’t available in just one material type, there are a range of different versions on the market that can make deciding which one to use a little overwhelming. We take a look at the options and describe their characteristics, pros and cons. 

There are a multitude of insulation types on the market. “The most familiar types of insulation are probably the big rolls of loft quilt you see in DIY stores,” says chartered surveyor and renovator Ian Rock. “But, there are many types of insulation, including stone wool, glass wool, sheep’s wool and wood wool,” explains James. “There are also plastic foam insulations such as polyisocyanurate (PIR) and spray foam. In addition, you may come across cellulose (recycled newspaper), hemp, polyethylene, cellular glass and ceramic fibre.”

Is foam plastic insulation a good choice?

“Foam plastic (or plastic foam) is a term used to describe insulation materials derived from petrochemicals,” says James Francis. “These oil-based chemicals are used to create various insulation products, which are commonly formed into rigid slabs or pipe sections.

“Rigid foam board insulation can be used almost anywhere insulation is needed in your home, for example in the roof, floor and cavity walls. It’s a popular choice in basements or near external foundations or walls, and can be used in external applications as well as internally. You will find you have several options.”

• Polyurethane (PUR) insulation PUR and PIR are both derived from polyurethane, a thermoset plastic, produced by reacting a polyol component and an isocyanate (MDI) component, formed into a closed-cell foam. A chemical blowing agent is used in the production of PUR and PIR, which is retained in the final products to improve thermal performance.
• Polyisocyanurate (PIR) insulation Although similar to PUR, PIR is produced using a different type of polyol and a higher proportion of isocyanate (MDI), resulting in a significantly different chemical structure.
• Phenolic foam (PF) insulation PF is a closed-cell, rigid insulation produced using phenol and formaldehyde resin, which is expanded between two facing layers. The chemical mix bonds to both facings and is cured to form the final product.  A chemical blowing agent is used in the production of PF, which is retained in the final product to improve thermal performance. PF claims to have better thermal properties than other types of foam plastic insulation.
• Expanded Polystyrene (EPS) insulation EPS is a semi-open-cell, rigid foam plastic material made from solid beads of polystyrene fused together. The beads are manufactured from styrene expanded using a pentane blowing agent that is not retained in the finished product. EPS insulation products are also available with particles of graphite integrated into the polystyrene beads to improve thermal performance.
• Extruded polystyrene (XPS) insulation Although similar to EPS, XPS is a closed-cell rigid foam plastic produced by melting polystyrene granules. The molten liquid is extruded through a die and expands during the cooling process. A chemical blowing agent is injected into the extruder and is retained in the final product to improve thermal properties.
• Spray foam insulation Spray foam insulation is typically an open or closed-cell polyurethane liquid that is sprayed into position to form an insulating layer when set. 

What eco-insulation types are there?

Eco-insulation consists of two categories, natural insulation and recycled insulation. Natural insulation doesn’t require manmade chemicals in their formation, therefore are less likely to release toxins into your home. They also are more likely to be biodegradable at the end of their life and have a smaller carbon footprint. Recycled insulation makes use of existing manmade materials, both removing the need for new manmade materials to be made and virgin resources being consumed, but also stopping these recyclable materials from ending up in landfill.

• Sheep’s wool is not only a sustainable natural resource, but it has some characteristics that make it a brilliant material for producing internal wall insulation. “Sheep’s wool is one of the most breathable insulation types,” says Mark Lynn, MD of Eden Renewable Innovations Ltd — makers of products such as Thermafleece. “This means that the insulation is extremely efficient at absorbing and releasing moisture whilst still remaining dry to the touch.” Sheep’s wool insulation in a sheet form, which has largely the same application and uses as mineral wool insulation in the home. The thermal conductivity is also comparable.
• Mineral wool “The term mineral wool is used to describe insulation made from minerals, including stone and silica. There are two common types of mineral wool; stone wool, is created by spinning molten rock and minerals with steel slag to create a cotton-candy-like wool product, and glass wool or glass fibre, which is made from silica or glass cullet,” explains James.  “Mineral wool is an excellent insulator and has proven thermal insulation properties. By reducing airflow and heat flow, mineral wool can help keep buildings warm in winter and cool in summer. The same properties give it good acoustic capabilities and make it fire resilient. And it maintains its shape and density, making it resilient and durable.”
• Straw bale has a long history as a construction material, but it’s a material that’s still developing in its uses to this day. Straw bales work to insulate much in the same way as sheep’s wool, with air pockets in the material creating a thermal break. 
• There are several ways that straw bales can be used to build a house or extension, providing the insulation. “First, there’s the load bearing method, where the straw acts as structure, insulation and surface for plaster,” explains Barbara Jones of Straw Works, an expert in building with straw bales. This type of construction is specialist and doesn’t require a frame.  “Next, is the infill or timber frame method, where the straw is only used as insulation and a surface for plaster.” There are also hybrid constructions that make use of both ways of building, and you can also now find pre-fabricated panels that use straw as an insulating material. 
• Hemp insulation may be slightly more expensive than the alternatives for insulating your home, but with thermal conductivity that goes toe-to-toe and impeccable sustainable credentials, you might find it worth the expense. Plus, there are some prefabricated boards that include hemp insulation. “Hemp can be grown on low-quality land and requires minimum use of pesticides to produce economic crop yields,” says Mark Flynn.   “Technical fibres can be obtained from the main hemp plant stalks and can be used in quilted insulation but are particularly suited to a fibre component in materials such as hempcrete or hemp lime plaster providing enhanced insulation performance in the elements within which it is used.”
• Cork is an interesting option for insulating the walls and floors of your home. It has excellent thermal properties and is resistant to issues such as dampness, while being a fast-growing, naturally occurring material that adds to its sustainability factor. It also has an incredibly low whole life carbon impact. However, when it comes to cork, you can’t always take its sustainability at face value, says sustainable building expert Tim Pullen. “There are question marks over the use of cork as the over-harvesting of bark has significantly reduced the number of cork trees in the world.” He suggests that cork doesn’t perform any better than wood fibre, which may have more indisputable sustainability credentials.   There are also expanded cork insulation systems that can be used for external wall insulation, while it’s a material that continues to be developed in use for house building. 
• Wood fibre insulation “There is possibly more development invested in wood fibre insulation than any other insulator,” says Tim Pullen. “There are products available for any and every application, including waterproof boards for roof sarking.” Wood fibre insulation is available in several forms, including wool-like rolls, semi-rigid boards or rigid boards — the latter of which offers some interesting applications for housebuilding when it comes to natural insulation. "Rigid wood fibre insulation can be installed against solid walls without the need for a timber frame to support the insulation,” says Mark Flynn from Eden Renewable Innovations Ltd. “It can also be installed over rafters without the need for supporting timbers. In both of these applications, thermal bridging is reduced because a continuous layer of insulation can be installed.”

What is recycled insulation?

When we talk about recycled insulation, we’re largely referring to insulation made from recycled PET made from plastic bottles. But, with natural insulation options available, often with better thermal efficiency, is there a reason we should specify recycled insulation? “While natural fibres are renewable, their supply is not infinite,” explains Mark Lynn, “so we also need lower impact alternatives to use where the benefits of using natural fibres are less significant.”  Cellulose is recycled newspaper treated with (usually) boric acid to prevent insect, fungus and rodent attack. It is supplied either loose or damp blown into timber-frame wall panels.

This type of insulation tends to be used in timber frame constructions where the insulation can be blown into cavities under air pressure.  

“Because the installation cost is high in relation to the insulation material, cellulose tends to be most economic when used in larger properties or developments in timber frames with above average depths,” explains Mark. Cotton insulation is recycled clothing, often denim. As with cellulose, it is treated to prevent insect, rodent and fungus attack and is available loose or in rolls. It tends to be relatively affordable and it has a low carbon impact as recycling the denim isn’t energy intensive. 

While its K-value isn’t quite as low as mineral wool when it comes to thermal conductivity, it’s still an effective choice with great thermal properties.

What forms of insulation are there?

Rigid, semi-rigid boards, spray foam — these are just some of the insulation types available but why pick one over the other? Here, we look at the options and where best to use them in your home.

• Rigid boards known as PIR (polyisocyanurate) are usually made from foam with aluminium foil facings either side of the board. But, you can also get it bonded with OSB (oriented strand boards) or with plasterboard, for example. The boards can be used for walls, floors, pitched roofs and ceilings. They can usually be cut to size and are relatively easy to install.
• Semi-rigid boards comprise mineral fibres such as stone wool and glass. Being semi-rigid means that it can be used in vertical applications (filling the void between stud work for instance), as well as horizontal. ROCKWOOL’s semi-rigid boards in their RW3 range come in a variety of thicknesses and can be used in between framework construction. Thermafleece offers hemp-based, and sheep’s wool products.
• Flexible or blanket insulation comes in rolls. This type of insulation is usually used to insulate lofts as they are soft and pliable and therefore easier to lay in often cramped attic spaces. ROCKWOOL’s stone wool insulation is also available in flexible rolls. Rolls of insulation can be used on internal facing stud walls but flexible rolls do tend to sag in vertical applications. While they can be used vertically they need special attention to prevent sagging when in situ.
• Spray foam insulation “Spray foam insulation (SFI) is a mix of liquid chemicals that expand into a foam when sprayed into position, where it sets into an insulating layer,” explains energy efficiency expert Tim Pullen. “There are two types of spray foam insulation: Closed cell is more like conventional rigid foam insulation boards, in that it is rigid once it sets and can offer some structural stability, but it does not allow air or moisture to pass through it. Open cell is more flexible and, because it adheres to the material it is sprayed onto, will tend to move with that material as it expands and contracts. It also allows air and moisture to move through it, giving it an almost ‘breathable’ quality.”

Which type of insulation works best where?

The best solution for you will depend on what you want to achieve and the area of your home you are insulating — someone looking at the best ways of insulating lofts, roofs and floors, for example will have very different needs to those looking for external wall insulation.

“Whether undertaking a whole-house renovation or building from new, the insulation used should be suitable for the intended application,” explains James:. “Insulation materials differ in how stiff they are,” says Ian Rock. “The three main types being rigid (e.g. polystyrene boards), semi-rigid (e.g. mineral wool ‘batts’) and soft, such as quilt insulation that can be stuffed into voids in studwork walls and between rafters. There are also loose-fill materials like cellulose and polystyrene beads that can be blown into lofts or cavities using special hoses (get this done by a professional with the right kit to install it).”

• Insulation in batts and rolls are ideal for floors, ceilings, partitions and unfinished walls, batt and rolled insulation can fit between studs, joists and beams, and is effective behind and around electrical boxes, wires and pipes. 
• Slabs can be installed inside walls, outside walls, under floors, above ceilings and in roof spaces.
• Boards are good for roofs, walls, floors and ceilings. 
• Loose-fill insulation is particularly useful for retro-fitting if you don’t want to take down walls etc. This type of insulation can be blown in through holes and gaps to fill cavity walls and roof spaces. 
• Spray foam insulation can be used in roofs, lofts, walls and floors and is effective in awkward spaces. 

What are R-values?

“When choosing the right insulation for your project, there are two key considerations — the R-value (or thermal performance) you need to achieve, and the application (where you need to insulate),” explains James. “The R-value tells you what you really want to know — how good a material is at resisting heat seeping through it, its ‘thermal resistance’,” explains Ian Rock. “Unlike thermal conductivity, R values depend on the material’s thickness.”

For example, to meet the notional U value of 0.18W/m2K for external wall insulation using mineral wool you could use 175mm of ROCKWOOL’s full fill cavity batt stone wool insulation.  “For masonry construction it will need to be 100mm thermal block inner skin and 90mm PIR in the cavity and brick outer skin,” says Tim.

“Once you have these worked out, the right product will depend on a number of other factors, including your desired acoustic performance, level of fire resilience, durability and sustainability, and the project budget,” continues James.

“To insulate your loft, for example, you would typically use rolls or batts. Mineral wool, sheep’s wool or wood fibre all come in suitable products, but their R-values vary, so you may need different thicknesses of each product. You will then want to weigh the thermal performance up against your other tick-boxes —does it also need to provide acoustic insulation? Or is it important to have the most sustainable option? And finally, does this all come within your budget?” 

What is the cheapest type of insulation?

“The cost of insulating your project will depend greatly on the required R-value and the space you need to insulate,” says James. “Once you have this information, you should be able to work out the most cost-effective way to insulate the area. 

“Cost should always be considered alongside performance — the insulation needs to be reliable and safe and create a comfortable indoor environment. A durable insulation material that provides a good combination of thermal, acoustic and fire performance is likely to be the most cost-effective option.”

Which insulation type lasts the longest?

“Durable insulation can mean many things, such as how the product maintains its thermal performance, whether it slumps over time, or how fire resilient it is,” explains James. “So it’s important you find the right insulation for your requirements. Eurima, the European Insulation Manufacturers Association, found in a study that the thermal performance of mineral wool doesn’t degrade over time. And, if installed in accordance with the manufacturer’s instructions, mineral wool delivers on performance even after 50 years of service.”

What are the building regulations for insulation?

The latest edition of the Building Regulations includes changes to Part L, which sets out heat loss targets for elements of the build. “As you might reasonably expect, most heat loss occurs through walls and roofs, but all parts of the design’s thermal envelope have to meet minimum U value targets,” says Ian Rock. “The U values tell you the maximum rate of heat loss (in Watts) that’s allowed to leak out of your home per square metre of wall or roof etc. The lower the figure the better, so for example, 0.28W/m2 K is better than 0.30W/m2K.”

Most self-builders go above and beyond when meeting the heat loss targets set out by the Regs to  build a highly insulated home that will pay dividends later with savings on energy bills. Some meet Passivhaus standards , which go far beyond the values stipulated in the Regs. 

“The updated Building Regulation U values shown below are the ‘notional’ targets, which means that achieving them will therefore meet the specified standards,” explains Tim Pullen. 

How much insulation do I need?

"The amount of insulation needed depends on the type of project it’s being used for, and calculating this amount is often a task for whoever is carrying out the work. If, for example, you were building a home, then you would typically employ the services of an architect or a specialist contractor who would calculate the quantity required," says James Francis from ROCKWOOL® UK.

"In situations where a contractor isn’t being used, for example on a home renovation being carried out solely by the homeowner, there are resources available to help calculate the amount of insulation needed. Builders’ merchants can also be a knowledgeable resource to get valuable advice on materials needed.

"When deciding and calculating insulation specification, solutions that deliver additional benefits beyond thermal performance should be considered. For housebuilders and renovators, stone wool insulation is one of the most efficient and effective ways of simultaneously addressing thermal, acoustic and fire protection.

"A number of factors would need to be taken into consideration when calculating the amount of insulation required. Typically, the calculations depend on the desired U value target – the amount of insulation required to deliver the appropriate thermal performance – that would need to be met as per Part L of the Building Regulations [=(as per the table above).

ROCKWOOL has a free online U value calculator tool which demonstrates the overall performance of a wall construction, floor or roof featuring ROCKWOOL insulation.”

How do you retrofit insulation?

When it comes to how to insulate old homes, the main thing to consider is continuity. If the budget is pretty tight, then it is better to install less insulation on each element – roof, wall and floor – than to blow all the budget on just one element. This approach won’t necessarily cut the cost as much as we might hope because the labour cost will remain largely the same, however much insulation is being installed. 

One way of looking at it is that when it’s cold, just putting on a pair of gloves only keeps your hands warm; wrap your whole body up and you reap the benefits from head to toe. 

The question is often asked if an extension needs the same level of thermal efficiency as a new build house. Building regulations do allow for slightly lower levels but designing in a higher level of insulation and air tightness will only help the energy efficiency of the house as a whole.

Who should order the insulation and when?

"If a project is using the services of a builder or contractor, then typically these companies would order and purchase the insulation as part of all of the materials needed on site," says James. "For those building or renovating their home without the use of contractors, a variety of insulation options are available throughout the UK from builders’ merchants and retailers.

"The delivery of project materials depends on a variety of factors, such as space on site and which stage of the overall project the insulation will be installed. Most insulation is required at a fairly early stage of the construction process, so contractors and/or project managers should ensure that they leave adequate time for ordering and delivery so as not to hold up other works. 

"It’s also important to consider the storage of insulation, making sure that there is somewhere dry for it to be kept before it is installed."

Tim Pullen

Tim is an expert in sustainable building methods and energy efficiency in residential homes and writes on the subject for magazines and national newspapers. He is the author of The Sustainable Building Bible, Simply Sustainable Homes and Anaerobic Digestion - Making Biogas - Making Energy: The Earthscan Expert Guide.

His interest in renewable energy and sustainability was first inspired by visits to the Royal Festival Hall heat pump and the Edmonton heat-from-waste projects. In 1979 this initial burst of enthusiasm lead to him trying (and failing) to build a biogas digester to convert pig manure into fuel, at a Kent oast-house, his first conversion project.

Moving in 2002 to a small-holding in South Wales, providing as it did access to a wider range of natural resources, fanned his enthusiasm for sustainability. He went on to install renewable technology at the property, including biomass boiler and wind turbine.

He formally ran energy efficiency consultancy WeatherWorks and was a speaker and expert at the Homebuilding & Renovating Shows across the country.