Home insulation — An expert guide to types and how to choose the right insulation for your build

Whether you're undertaking a self build, renovation or extension, getting your home insulation right is an integral part of your plans.

As well as your home needing to meet certain levels when it comes to thermal performance, the environmental benefits of insulating your home well are well documented.

And of course, with rising energy bills a cause for concern amongst homeowners, understanding what types of home insulation you need, where it will be used and how to choose the best materials for your project needs to be considered in your overall plans. We dive into home insulation to help you understand more before you start.

Why home insulation is a fabric first essential

The term 'fabric first' is a commonly used term in housebuilding, but what does it mean and what part does insulation have to play in this?

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,” advises James Francis, product manager GBI at Rockwool® UK.

But what does this all mean if you’re building your own home, renovating or extending and how do you know when a home is truly constructed with a fabric first approach?

Building regulations and home insulation

Building regulations Part L sets minimum standards for what insulation you can use in different parts of your home which provides a good starting point for understanding what types you need to use, and where. Knowing the project has passed the required regulations also means you can be more confident it has been constructed with a fabric first approach.

“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 chartered surveyor, 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 regulations.

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

Ian Rock

Chartered surveyor Ian Rock MRICS is a director is Rightsurvey.co.uk and the author of eight popular Haynes House Manuals, including the Home Extension Manual, the Self Build Manual and Period Property Manual. Ian is also the founder of Zennor Consultants. In addition to providing house surveys, Zennor Consultants provide professional guidance on property refurbishment and maintenance as well as advising on the design and construction of home extensions and loft conversions, including planning and building regulations compliance.

Tim Pullen

Tim Pullen, an expert in sustainable building methods and energy efficiency in residential homes also wrote 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. He formally ran energy efficiency consultancy WeatherWorks and was a speaker and expert at the Homebuilding & Renovating Shows across the country.

Types of home insulation

If you've ever taken a look at insulation, you'll know that in the same way there are a variety of places within your home where insulation is needed, there are also a raft of different types of insulation available.

“The most familiar types of insulation are probably the big rolls of loft quilt you see in DIY stores,” says Ian Rock. “But, there are many other types of insulation, including stone wool, glass wool, sheep’s wool and wood wool,” adds James Francis.

“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.”

And while we have guides to a variety of the types available, it's important to understand some of the different ways in which insulation is made to help you choose the best type for you.

1. Foam plastic insulation

“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 insulation board 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.”

These are covered in more detail in our guide to insulation board, with the exception of the following:

• Polyurethane (PUR) insulation: PUR is 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, which is retained in the final products to improve thermal performance
• 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

In addition to boards spray foam insulation is another form of foam plastic insulation, but this is typically an open or closed-cell polyurethane liquid that is sprayed into position to form an insulating layer when set.

2. Eco insulation

When looking at more eco-friendly options, there are two different categories under the main heading of eco-insulation – natural insulation and recycled insulation.

Natural insulation doesn't require manmade chemicals in its formation and is therefore less likely to release toxins into your home. It is also more likely to be biodegradable at the end of its life and have a smaller carbon footprint.

Types of eco-insulation include:

• Sheep wool insulation
• Mineral wool insulation
• Straw bale insulation
• Hemp insulation
• Wood fibre insulation

While the guides to each different type of eco-insulation listed above contain all the key facts you need to know, one other product, cork insulation, is also worth noting.

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, meaning it’s a material that continues to be developed in use for house building.

3. Recycled insulation

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.

It's often made from recycled PET which comes from plastic bottles. However, other types include cellulose insulation (paper), a popular choice for timber-frame insulation as it can be blown into the cavities.

Cotton insulation is another type of recycled insulation which comes from 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.

Where to use different types of insulation

With each different type of insulation coming in varying forms, from boards to rolls or blown in products, knowing where to use each type will help you narrow down which type to use in your project.

Your architect may also have preferred types and methods on how to insulate your house, but understanding what types are available will help you make an informed decision.

The best solution for you will of course also 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.

“Insulation materials differ in how stiff they are too,” adds Ian Rock, which also determines their best placement as outlined below:

• Rigid boards – ideal for walls, floors, pitched roofs and ceilings. They can usually be cut to size and are relatively easy to install
• Semi-rigid boards – consider for vertical applications such as filling the void between stud work for instance, but can also be used horizontally
• Flexible or blanket insulation – comes in rolls and usually used to insulate lofts as it is soft and pliable and therefore easier to lay in cramped attic spaces. It is also 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. However, flexible rolls do tend to sag in vertical applications, meaning they need special attention to prevent sagging when in situ
• Slab insulation – can be installed inside walls, outside walls, under floors, above ceilings and in roof spaces
• Loose-fill insulation – particularly useful for retro-fitting if you don’t want to take down walls. 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 but should be installed by a reputable company

The importance of R-values

As well as understanding the importance of building regulations and U values, you also need to take into account the importance of R-values when choosing insulation.

“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 Francis.

“The R-value tells you what you really want to know," explains Ian Rock. "It tells us how good a material is at resisting heat seeping through it, which is referred to as its thermal resistance. Unlike thermal conductivity, R-values depend on the material’s thickness.”

“Once you have worked out which product will meet the guidelines set in building regulations, the right product for your project will then 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?” 

FAQs

What is the cheapest type of home insulation?

“The cost of insulating your project will depend greatly on the required R-value and the space you need to insulate,” says James Francis. “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," he stresses. "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.”

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.

"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.

"A number of factors would need to be taken into consideration when calculating the amount of insulation required," advises James. "Typically, the calculations depend on the desired U value target – the amount of insulation required to deliver the appropriate thermal performance under building regulations."

How do you retrofit insulation?

Understanding how to insulate old homes is vital when retrofitting insulation. The main thing to consider is continuity, so if the budget is pretty tight, then it is better to install less insulation on each element, than to blow all the budget on just one element.

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 insulating 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.

Keen to learn more about insulation? Take a more in-depth look at cavity wall insulation and find out how long does insulation last to make sure you have peace of mind that your home insulation choices will have the required amount of longevity.