Maximising Energy Efficiency with Wall & Roof Insulation

Insulation such as external wall insulation might seem like a simple concept—it’s a material used to reduce heat loss—but it plays a crucial role in construction, especially in the UK’s cold and often windy climate. However, when selecting insulation materials, cost and thermal performance should not be the only factors considered. For those serious about lowering their energy consumption, balancing embodied and operational carbon is crucial to ensuring that today’s insulation choices reduce both immediate and long-term carbon impacts. This balance not only supports current energy efficiency but also contributes to the building’s total lifetime carbon reduction, helping mitigate the overall environmental footprint. As insulation becomes more widely used and understood, it’s important to ensure that the common knowledge surrounding it is both useful and accurate.

In the construction industry, there is often a gap between knowledge, design, and on-site implementation. If insulation isn’t properly applied or understood, its performance can be compromised. In this post, we’ll take you through the A to Z of insulation, highlighting key points to ensure it works as effectively as possible. After all, insulation is the most basic energy-saving measures and also the most cost-effective.

Why Insulation Matters: The Secret to Slashing Energy Bills

The primary role of insulation is to stop or reduce the transfer of heat from one side to the other via conduction. Conduction is the process by which energy is lost as it passes from one molecule to the next, across the material. By limiting this heat transfer, insulation helps keep buildings warmer in winter and cooler in summer, enhancing energy efficiency and making homes more comfortable while reducing heating and cooling costs. This is why the primary characteristic of a good insulant is a low U-value. The U-value measures the rate of heat transfer (W/m²K) per unit thickness, and the lower this number, the less energy is transferred through the material. Typically, insulation on the market ranges from 0.04 to 0.022 W/m²K. Consequently, insulation contributes to lowering carbon emissions, supporting environmental sustainability, and reducing heating or cooling demand in buildings.

There are many different types of insulation on the market, each with its own advantages and disadvantages. Below is a list of the main types of insulation and their common names, along with their typical U-values. The choice of insulation should be based on several factors, including the location of the insulation, the space available, cost, and its environmental impact. For comparison, some common building materials are also listed to illustrate their worse thermal performance.

Table 1: Types of Insulation:

Table 2: Common Building Materials (for comparison):

The Most Popular Insulation Materials, External wall Insulation and Beyond( Could we do better?)

Arguably, the most commonly used insulation in the construction sector today is EPS foam, more commonly known as polystyrene. EPS foam is considered one of the most cost-effective options, providing excellent heat energy blocking for your money. It typically comes in the form of white or grey, rigid boards. The most common applications include external wall insulation (often covered with a weather screen), cavity wall insulation in new builds, under concrete floor slabs, and in roofs. It is also used above and between joists for flat roofs and between rafters in pitched roofs. It is crucial that board insulation is cut neatly and accurately so that when two pieces of insulation butt together or meet a building element, there is a tight fit. I would recommend installing it with a small amount of airtight insulating expanding foam to ensure its continuity without gaps.

The downside to EPS foam, and other higher-performance petrochemical insulants such as XPS and PIR, is that they are very harmful to the environment to produce. The topic of embodied carbon is often overlooked. These petrochemical products have an extremely high environmental impact, so much so that if they are not utilised properly to reduce carbon consumption over their lifetime in a property, they could have a net negative impact.

In very low-energy homes, such as Passive Houses, the replacement of petrochemical insulants should be strongly considered, as the carbon footprint of these materials makes up a significant portion of the whole life cycle carbon footprint of the property. This includes the carbon footprint of the materials in the build plus the carbon footprint of using the building for its lifespan. We will touch on alternatives later.

Rockwool and glass wool are commonly used insulations. Generally, glass wool is slightly more environmentally friendly as it is made from recycled glass and has a smaller carbon footprint. Both materials are very cheap and are best utilised in areas with lots of space, such as attics, where they can be layered up thick. Around 400mm of glass wool is ideal and would provide an effective U-value at little cost.

When it comes to insulation, choosing the right materials is just the beginning. How insulation is installed and implemented plays a crucial role in its overall effectiveness. Poor installation can lead to a range of issues, from thermal bridging to insufficient coverage, both of which can undermine the insulation’s ability to perform as intended.

How to Install Insulation Like a Pro

Proper installation is vital for insulation to work as designed. Even the best insulation materials can fail to reach their full potential if they are not correctly fitted. Careful attention must be paid to ensuring that the insulation is securely placed, without gaps or compression, as this can reduce its thermal performance. When installing insulation in hard-to-reach areas, such as attics or behind walls, it’s important to ensure the material is evenly distributed. Professional installers typically use specialised equipment and techniques to guarantee that the insulation forms a tight, effective barrier. However, as in many industries, installers must be held accountable, and their quality of work must be checked. Mistakes are often made accidentally, which result in thermal bridges.

It is critical to avoid gaps where heat can escape. A break in the insulation, no matter how small, can compromise the energy efficiency of the entire structure. Thermal bridges can also occur around window frames, doors, and junctions between walls, ceilings, and floors. If thermal bridges are not addressed, they can significantly reduce the overall thermal efficiency of a building, creating cold spots and increasing energy consumption. Minimising thermal bridges requires careful planning during both the design and installation phases, ensuring that insulation is continuous and covers all potential weak points. A seamless layer of insulation not only enhances thermal performance but also reduces the likelihood of condensation forming within the building fabric, which can lead to damp problems over time. Consideration must always be given to the potential for trapping moisture between layers, creating issues in years to come.

Boosting Floor Insulation

Floor insulation is often overlooked in refurbishments, but it plays an important role, especially in homes with ground floors over subfloor voids. Retrofitting insulation on a ground floor can often be difficult, but always remember that something is better than nothing, and experienced designers will be able to determine the best and safest way to improve insulation.
In the case of ground floor slabs, the earth below the slab provides some level of insulation. Nonetheless, there are several key points that can improve the situation. Removing the ground floor slab may seem extreme, but this daunting task could open up a range of new possibilities. Earth can be excavated below the slab, creating space for insulation beneath a new slab. Alternatively, after excavation, a suspended floor may be preferable, removing the need for concrete entirely.
With a slab on the earth, it is the perimeter of the building that is most susceptible to heat loss, as this is the shortest distance to the outside air. In some cases, perimeter insulation can be utilised, meaning the whole slab does not need to be removed. Instead, insulation is placed only at the edges and to a deeper depth. This greatly increases the heat loss path and consequently reduces your energy use and bills. If this technique is used alongside internal floor insulation, even with a relatively slender profile, significant differences can be made.
Suspended floors with large subfloor voids or basements are more favourable for floor insulation. With good access, the floors can be insulated with less disruption. Provided some simple guidelines are followed, as much insulation as possible can be added. The insulation must remain 300mm above the ground and more if the subfloor void is susceptible to moisture ingress. Preventing moisture from entering through the walls to the insulation must also be considered, and the choice of insulation should account for moisture levels.
The subfloor void must be well-ventilated to help prevent moisture build-up. Traditional air bricks provide this function, and these must not be blocked. Other means of ventilation should be considered if necessary. If joists are to be completely surrounded by insulation, it is essential to prevent warm, moist air from the house descending into the joists and condensing, which is crucial to avoid rotting joists.

Wall Insulation Tips for Maximum Energy Savings

Walls typically make up the largest surface area of a residential property. There are no ifs or buts when it comes to insulating, but there are several methods to choose from.
External insulation is widely regarded as the easiest and most cost-effective option, if circumstances allow it. By wrapping the entire building in an insulating layer, the possibility of thermal bridging is reduced. The property must not be subject to restrictions on changes to its appearance, and suitable roof overhangs are necessary. As is often the case, EPS (expanded polystyrene) is typically used for its cost-effectiveness, but other insulations provide better thermal properties and have a lower carbon footprint. External insulation requires a waterproofing layer on the outside, which could be brick slips or cladding, but is often render in the UK. Most EWI (External Wall Insulation) installers refuse to insulate below the damp proof course (DPC) on the ground floor due to insulation being susceptible to deterioration from moisture. However, the industry has many solutions to overcome this issue. In reality, if you are serious about reducing your heating demand, more water-resistant insulation, such as XPS (extruded polystyrene) or PIR (polyisocyanurate), can be used below the DPC and below ground. A trustworthy designer or contractor should be able to detail such an insulation solution.
Internal insulation can be an effective solution where altering the building’s external appearance is not permitted, such as in heritage buildings. The same principles of installation apply as described above, but as the change in air temperature occurs within the building structure, there is more risk of interstitial condensation, which can lead to increased problems if the building structure gets damp. Consequently, the thickness of insulation is often limited to 80mm, and while thicker insulation is possible, there is an increasing need to install an intelligent vapour membrane to prevent warm, humid air from condensing in the wall. The ability of the insulation to allow the passage of water vapour is increasingly important, and natural insulation is by far the most effective. When insulating internally, extra care must be taken to prevent cold bridging where structural elements penetrate through the insulation. It is often a messy task, exposing every square centimetre of the external wall, behind cupboards, consumer units, between floors, and in dead spaces.

Cavity vs. External Wall Insulation: The Ultimate Showdown

Cavity wall insulation is a popular choice for improving the thermal efficiency of homes with cavity walls. By filling the gap between the outer and inner walls, it prevents heat from escaping. It is a relatively straightforward process for most buildings constructed after the mid-1900s, as many have thicker cavities designed to provide insulation. However, it is important to ensure that the walls are in good condition before installation, as problems such as damp or cracks can be exacerbated if insulation is added without proper preparation, particularly if the external wall can be penetrated by water. In most older properties, the cavity, if there is one, is very thin, and attempting to insulate it can be problematic. You may be overly confident in the continuity of the insulation, while there could be sections of the wall that remain uninsulated. Techniques such as thermal imaging can be used to help identify this issue. Resolve deals mainly in back to brick refurbishments, and therfore we do not recommend cavity wall insulation often, it comes with some risks around moisture transfer and is limited in its energy saving potential.

Retrofit vs New Build

The approach to insulation can differ significantly between retrofit projects and new builds. In new builds, insulation is typically planned from the design stage, making it easier to incorporate optimal insulation solutions such as continuous insulation layers and the elimination of thermal bridges. With retrofitting, the challenge is often working with existing structures, where space might be limited and there may be restrictions on altering the building’s appearance. However, retrofit insulation, whether added internally or externally, can drastically improve the energy efficiency of older homes and reduce heating bills. The key in both cases is a strategy that has been modelled and detailed thoroughly.

Eco-Friendly Wall and Roof Insulation: Top Natural Insulation Options

Natural insulation materials are experiencing a resurgence in popularity after years of being overshadowed by petrochemical-based products like EPS (expanded polystyrene). One of the key benefits of natural insulation materials is their low embodied carbon. Materials such as sheep’s wool, hemp, wood fibre, and cellulose are derived from renewable resources and often have significantly lower environmental impacts compared to synthetic options. Their production requires less energy, and they are often biodegradable at the end of their life cycle, making them a more sustainable choice for eco-conscious projects. These environmental benefits become more impactful as the energy efficiency of the building improves.

Another important advantage of natural insulation is its ability to manage moisture. Unlike closed-cell petrochemical products, natural insulations are often vapour-permeable, allowing moisture to pass through the material without becoming trapped. This helps reduce the risk of condensation and damp-related issues within the building structure, which can be critical for the long-term health of the building fabric and indoor air quality. Additionally, materials like wool can absorb and release moisture without losing their insulating properties, contributing to a healthier living environment.

Natural insulations also tend to have higher thermal mass compared to lightweight synthetic insulations, which means they can help regulate temperature more effectively by absorbing heat during the day and releasing it slowly at night. This improves overall thermal comfort and can reduce heating and cooling demand. For example, in a converted loft, EPS foam between the joists will only be able to stave off the heat from the sun for so long, resulting in a stiflingly hot attic room. Conversely, wood fibre insulation not only resists heat transfer but can also absorb heat, providing a further buffer against rising room temperatures. It then slowly releases this energy at night when temperatures drop.

While the thermal performance (U-value) of some natural materials may not be as high as petrochemical products—for example, the U-values of materials like sheep’s wool or hemp can range from 0.037 to 0.040 W/m²K, slightly higher than that of PIR or EPS—the other benefits of these products often outweigh the marginal reduction in performance. They are also much more pleasant to work with and install, and do not have the dangers of chemicals.

The cost of natural insulation materials is often higher than petrochemical alternatives. This is partly due to the smaller scale of production and higher material costs. However, for many projects, the environmental and health benefits outweigh the initial expense. As demand for sustainable building solutions grows, it is likely that the cost gap will narrow, making natural insulation an increasingly viable choice for both retrofit and new-build projects. If you’re passionate about natural insulation, blown recycled newspaper is one of the most affordable options, although it may require a thicker application to achieve the desired performance

Table 3: Carbon Footprint of Common Insulation Materials

Table 4: U-Values and Carbon Footprint of Natural Insulation Materials

How much insulation is enough?

Table 5: U-Value Standards and Required Insulation Thickness

Building Regulations Part L stipulates the minimum standard of insulation in the UK. It is widely recognised that more insulation is better. The table below shows different U-values expected from various standards. The right two columns display the range in insulation thickness depending on the standard you are aiming for and the thermal performance (U-value) of the insulation material.

Your FAQs on Insulation (Answered by Experts!)

How much does it cost to install insulation?
The insulation material is typically not considered the significant cost, but the ancillary work surrounding insulation can add up significantly. It is dependent on where the insulation is needed and how disruptive the installation will be. This is why it is recommended to carry out thorough insulation during a property renovation, as it will likely cost more if done later. However, insulating a loft space is relatively inexpensive and widely considered the most important area to insulate. A thorough job can be completed at a cost of £20 per square metre and one day’s labour for two people for a small or medium home. This may amount to approximately £1,200. External insulation is more expensive. A terraced house, with both front and rear insulation, would require more materials, a larger workforce, and scaffolding. This may range between £7,000 and £15,000. Grants are often available to help with these costs, and Resolve can guide you in finding these if you are eligible.

What is the best insulation for my home?
The best type of insulation depends on the specific needs of the home and what insulation is already present. Cavity wall insulation, loft insulation, and external wall insulation are common options. Resolve can help identify your needs and provide recommendations according to our modelling process. The choice of insulation material will depend on priorities such as saving space or minimising costs.

How long does insulation last?
Most insulation materials are designed to last the lifetime of the building, typically at least 20–30 years. However, some types of insulation may require occasional maintenance or replacement if disturbed during renovations. Cavity wall insulation is less reliable and can lead to other issues, so it should not be installed without seeking multiple professional opinions.

Does insulation prevent dampness?
While insulation helps reduce heat loss, some types, like cavity wall insulation or other plastic insulants, can contribute to dampness issues if not properly installed or paired with external insulation. Breathable insulation, such as wood fibre or wool, can buffer moisture in the walls and help reduce the effects of moisture build-up. However, they do not prevent or resolve underlying moisture issues.

Will insulation reduce noise?
Insulation can help reduce noise, particularly through walls, but the level of noise reduction depends on the type and location of the insulation. Windows and vibrations are often the main sources of sound transmission. Insulation, along with other interventions, can help mitigate noise.

Insulation is what we know best, so you dont have to.

While this article provides key information on the principles of insulating your home, it’s important to note that this may not be enough for everyone. Resolve models a building and its heat loss areas to determine, with scientific evidence, which products are most suitable for every element of your development. We can compare and contrast alternatives based on their performance, cost, and environmental impact, ensuring that your home is truly designed to your needs.

While design is crucial, we cannot overlook implementation. Resolve provides installation guidance directly to your installer or contractor to ensure high standards of workmanship. We offer design details, step-by-step guides, and photographic evidence is often requested for particularly critical elements. With our modelling and support, you can have peace of mind knowing you’re getting the best results from your once-in-a-lifetime home retrofit.