Internal wall insulation is one of the best home improvement options you can choose for your property. Not only does it ensure your home is cooler in summer and warmer in winter, but it also ensures that the energy you generate is used more effectively, resulting in lower energy bills.
But what are the costs of internal wall insulation? In this article, we will break down the different types of internal wall insulation available, as well as all associated costs, so you can make an informed choice about the value of your next home improvement investment.
Type of internal wall insulation material and their costs
Different wall types and conditions require differing insulation materials and solutions, not to mention some homeowners may prefer one over the other for reasons aside from insulation.
Rigid Insulation Boards
Rigid insulation boards are, as the name implies, solid panels of insulation material. It comes in three different types of material, which we will detail.
As a note, R-value is a term used to denote a measure of thermal performance (how well the material bars heat transferring through it). R-value typically ranges from the lowest acceptable value, R-13, to the very high R-60.
Expanded Polystyrene (EPS)
EPS is a lightweight and rigid cellular plastic foam, made up of beads that have been heated with steam, causing them to expand up to 50 times their original size. Moulded into blocks or boards, they create a closed-cell structure that traps air and provides high thermal insulation.
Pros:
- Cost-effective – EPS is considered the most budget-friendly of all rigid insulation boards and is especially loved for large-scale projects.
- Thermal performance – EPS has a good r-value of 3.15 per inch. This helps protect against heat loss and improve energy efficiency within buildings.
- Lightweight – EPS boards are easy to cut, shape and install.
- Versatile – EPS has applications in walls, floor space, roofs and even beneath concrete.
Cons:
- Less Breathability – The structure of EPS is a closed-cell structure, meaning moisture can build up when in some conditions damp issues can form (such as older properties).
- Lower moisture resistance – Whilst EPS is often referred to as a closed-cell structure, in actuality, they’re only semi-closed. This lacks moisture resistance and makes moisture penetration a possibility. This can weaken the structure of EPS and reduce the amount of air pockets, thereby also lowering insulation abilities.
Cost:
- 25mm – £5 – £8
- 50mm – £8 – £12
- 100mm – £15 – £20
Extruded Polystyrene (XPS)
Polystyrene pellets are combined with a blowing agent alongside other additives and melted through a die under high pressure. This creates a continuous sheet of foam with a uniform cell structure.
Pros:
- Higher Insulation Value (R-Value) – XPS has high insulation values per inch in comparison to EPS, with it typically being around 5.0 per inch. It offers better thermal resistance with a slimmer profile.
- High moisture resistance – XPS has a closed-cell structure, meaning there’s not much chance of moisture penetration. This makes your internal wall insulation highly resistant to moisture, maintaining its thermal resistance for the full lifespan.
- Enhanced durability and compressive strength – XPS is dense and rigid, even more so than EPS. This offers better resistance against wear and tear or in the case of internal walls, compression and impact.
- Dimensional stability – XPS keeps its shape and size regardless of the temperatures and humidity levels in the area.
- Chemical resistance – XPS is resistant to most chemicals and solvents found in construction, it has structural resistance against agents that could trigger deterioration.
Cons:
- Higher cost – XPS, due to its more involved manufacturing process and superior performance, is more expensive than its EPS counterparts.
- Lower breathability – XPS has a closed-cell structure and is highly moisture resistant, making it less breathable. This could mean that if moisture is trapped, it could grow mildew. That being said, little damage will come to the insulation itself.
Costs:
- 25mm – £10 – £15
- 50mm – £15 – £22
- 100mm – £25 – £35
Polyisocyanurate (PIR)
Polyisocyanurate is a premium choice for various insulation applications due to its high level of thermal, fire and moisture resistance, taking up little space overall.
Pros:
- Thermal performance – PIR boards typically boast between R-5.5 to R-6.7 per inch. With this exceptional performance, they allow for thinner layers to achieve the same levels of energy efficiency as thicker layers of insulation materials.
- Excellent fire resistance – These are the ultimate boards for fire safety. PIR resists burning and melting at high temperatures, which is not the case for the other two rigid board materials. This means that in terms of a fire, the boards will maintain their structure, aiding in preventing building collapse and slowing the fire’s spread.
- Moisture resistance – Like XPS, EPS’ rigid structure is closed-cell, meaning it blocks moisture from seeping inside of it. It’s effectively a wall against moisture, making it suitable for a damp wall.
Cons:
- Less breathability – Like other closed-cell foams, PIR’s material cannot “breathe”, meaning moisture can build up behind the boards. Ensure proper ventilation to counteract this.
- Potential for thermal bridging – The foil facings that are commonly used on PIR boards mean thermal bridges can be created if the board isn’t installed correctly. Ensure those that install internal wall insulation within your home are certified, trusted, and offer a warranty.
Cost:
- 25mm – £12 – £18
- 50mm – £20 – £30
- 100mm – £35 – £50
Insulated Plasterboard
Insulated plasterboard is made up of standard gypsum plasterboard with a backing layer of either EPS or PIR. The two components are bonded, creating a singular product that boasts ease of installation.
Pros
- Easy Installation Process – Since the insulation is already bonded to the plasterboard, eliminating the need for any further installation steps whilst installing internal wall insulation.
- Space saving – Insulated plasterboard is thin compared to most insulation materials and measures, ensuring that your wall insulation will go ahead even when space is at an absolute premium.
- Improved Thermal Performance – It’s hard to pin down a specific R-value for insulated plasterboard due to the different material makeup of each, we recommend taking a look at the specific manufacturer guidelines.
- Sound insulation – Plasterboard can also provide a barrier to sound, reducing noise transmission travelling between rooms.
Cons
- Breathability – Some insulated plasterboards come with some breathable materials and others do not. For breathable types, look to common building materials such as stone, brick, wood etc. EPS-backed insulated plasterboard is a non-breathable type.
- Limited Thickness Options – The maximum thickness of an insulated plasterboard is generally less than that of other insulation measures, limiting their versatility.
- Specific Fixings – Installing internal wall insulation of this type is more involved and complicated than rigid boards, as they require longer screws to not damage the insulation layer during installation.
EPS Insulated Plasterboard Costs
- 25mm EPS: £12 – £18 per m²
- 37.5mm EPS: £15 – £22 per m²
- 50mm EPS: £18 – £25 per m²
- 75mm EPS: £22 – £30 per m²
PIR Insulated Plasterboard Costs
- 25mm PIR: £15 – £22 per m²
- 37.5mm PIR: £20 – £30 per m²
- 50mm PIR: £25 – £38 per m²
- 75mm PIR: £30 – £45 per m²
Wood Fibre Insulation
Wood fibre insulation is made up of wood chips or shredded wood waste. This is a good alternative to conventional insulation materials for those who want to promote environmental benefits.
Pros
- Natural and Breathable – Synthetic insulation materials such as EPS or XPS act as barriers to moisture due to their closed-cell structure, but wood fibre is porous. This allows them to breathe, regulating humidity levels and reducing condensation, mould growth etc.
- Thermal Performance – Wood fibre is naturally high in insulation, with a r value of around 3.5 per inch.
- Sustainable and Environmentally Friendly – Wood fibre is harvested through sustainable means – either through natural, managed forests or recycled wood waste.
- Sound Insulation – The dense and fibrous nature of wood’s structure does an effective job of blocking sound. With wood fibre, you can expect to achieve sound reductions of between 35 and 55 dB.
Cons
- Professional Installation – Whilst we would always recommend that a professional carry out the installation process to get the maximum longevity and value of your insulation materials, wood fibre has special handling and installation requirements that call for a professional’s expertise.
- Bulkier – Wood fibre insulation boards are heavy as far as insulation materials go, requiring care, strength and stamina to install insulation of this type.
Costs
- Rigid boards: £10-£30 per square meter
- Flexible rolls: £5-£15 per square meter
- Loose-fill: £8-£12 per bag (typically covering 1-2 square meters)
To insulate internal wall(s) – factors that affect price
There are many factors influencing the cost of your internal wall insulation, but one of the biggest, by far, is the type of wall and the insulation material required to achieve high thermal performance. The types of walls you have differ not just in the material it’s made of, but rather the structure, which may limit or expand options.
Cavity Wall Insulation
Cavity walls are aptly named, as they are two walls with space in between. This was done so air could act as an intermediate internal wall insulation method in and of itself, but over time, this effect diminishes.
A cavity wall insulation project is carried out using blown-in insulation materials (mineral wool insulation and/or EPS beads) via small holes drilled into the cavity wall.
Average costs are:
- £350-£850 for a mid-terraced house
- £450-£1,000 for a semi-detached house
- £700-£1,500 for a detached house
Solid Wall Insulation
Solid walls are typically stone walls that are made up of a single layer of hard material:
- Solid Stone Wall
- Solid Brick Walls
- Solid Concrete Walls
Insulating solid walls is harder than cavity walls, which are relatively simplistic and quick. As a result, how solid walls are insulated tends to be more expensive.
In this case, insulating interior walls can be done by affixing insulation boards (EPS, XRS, PIR), wood fibre, and insulated plasterboard affixed to solid walls’ interiors. Many believe that mineral wool is an option, but that is reserved for external solid wall insulation.
The average costs of internal wall insulation of this kind are:
- Semi-detached house – £1,800 – £3,000
- Detached house – £2,500 – £4,000
- Large detached house – £3,500+
Timber Frame Walls
A timber frame wall is a type of stud wall, which refers to the walls constructed with the framework consisting of vertical studs. Insulation methods may be as straightforward as cavity walls or as limiting as solid walls depending on how accessible said cavities are. Accessibility will also be reflected in the price, as additional costs will be levied if the installers have to open up the wall manually to have the stud wall filled using blow-in materials. Alternatively, rigid boards can also be applied as internal insulation.
The average costs:
- Small terraced– £10-£15
- Mid-terraced – £12-£18
- Semi-detached – £15-£20
- Detached – £18-£25
Conclusion – Is Internal Wall Insulation worth the investment?
The short answer is – yes.
As for the long answer:
- Reduced Heating Bills – Internal wall insulation allows you to make immediate returns on your costs through how much it saves on heating. Heat loss is minimised, energy efficiency is increased, and your home is cheaper and more comfortable.
- Increased Property Value – Proper internal wall insulation means the running costs of the property are low from the start, enhancing its overall value.
- Reduction in Condensation/Dampness – Damp-proof materials creating a continuous vapour barrier within your internal insulation protects your home from all types of moisture damage, including microbes and other harmful allergens.
- And more!
Here at FreeInsulationScheme, we are able to help people access any available funding, which can sometimes mean households getting their home insulated for free. Check if you qualify today.
