What is a wall insulation board?

A wall insulation board is a solid panel designed to improve a building’s thermal efficiency by reducing heat loss through walls. These boards are made from various insulating materials, each with distinct properties, including thermal performance, fire resistance, and moisture control.

How it works

Wall insulation boards are designed to slow the movement of heat between the inside and outside of your home. By fitting these panels internally or externally, you can cut heat loss by up to 35%, reduce carbon emissions, improve EPC ratings, and enjoy more consistent, comfortable indoor temperatures, whether you’re a homeowner, landlord, or builder.

Common applications 

Wall insulation boards are widely used to upgrade energy efficiency in homes, apartments, commercial buildings, and social housing. You can install them inside on stud walls, fix them externally with render or cladding, or use them in cavity walls for systems that allow it, making them suitable for eco retrofits, new builds, or large-scale property upgrades.

Types of wall insulation boards

There are several types of wall insulation boards available, each suited to different needs and applications.

PIR insulation boards

Polyisocyanurate (PIR) insulation boards are a top choice for both internal and external walls due to their high thermal efficiency and slim profile. They’re ideal when you want excellent insulation performance without losing much living space, making them perfect for upgrades, rental properties, and compliance with modern building regs.

EPS/polystyrene boards

Expanded polystyrene (EPS) boards are lightweight and affordable, often specified for external wall insulation as part of smooth or textured render systems. They’re easy to handle, moisture-resistant, and compatible with most UK wall types, making them popular for large developments or cost-sensitive builds.

Phenolic insulation boards

Phenolic boards deliver superior insulation in the thinnest possible layers, which is key when you’re aiming for the lowest U-values (how successfully a material insulates) and minimum wall build-up. They’re especially well-suited for properties where space or performance takes priority, such as social housing or high-performance new builds.

Mineral wool boards

Mineral wool boards combine fire resistance, breathability, and acoustic insulation. They’re especially sought after for external wall systems in high-rise flats, public buildings, or anywhere fire regulations demand top-tier safety materials.

Best options for internal vs. external walls

For internal walls, PIR or phenolic boards are typically the best choice due to their slim profile and high insulation performance. For external walls, choose EPS for cost-effective upgrades, or mineral wool for buildings requiring superior soundproofing and fire safety, especially for government or public housing projects.

Benefits of wall insulation boards

Wall insulation boards come with a range of advantages that make them a smart investment for homeowners, landlords, and developers.

Energy efficiency & heat retention

Wall insulation boards dramatically slow heat loss through the walls, making your property warmer, cutting bills, and boosting your EPC rating for improved resale or rental value.

Noise reduction

Boards such as mineral wool and composite panels can significantly reduce noise transfer between rooms and from outdoors, improving living conditions for tenants and homeowners.

Fire resistance & safety

If fire safety is a priority, mineral wool and phenolic boards provide non-combustible options, crucial for conversions, flats, or contractor-led renovations in line with regulatory standards.

Cost savings

The upfront investment pays back quickly through lower annual heating bills, better energy performance, and increased market appeal, ideal for long-term landlords, property investors, and eco-conscious consumers.

How to choose the right insulation board

To choose the best board for your project, start with your property type, planned wall upgrade (internal or external), and performance targets:

• Check the required U-value and board thickness for compliance.
• Look for moisture and damp resistance if your walls are prone to condensation.
• Compare costs: EPS offers the best value, PIR and phenolic deliver higher performance at a higher price.
• For sustainability, mineral wool and recycled EPS boards are strong eco choices, great for those focused on green credentials.

Installation of wall insulation boards

Tools & preparation

You’ll need a sharp saw or utility knife for cutting; mechanical fixings or adhesives; protective clothing (including gloves, mask, and eye protection); and finishing materials designed for insulation (plasterboard, render, or cladding).

Step-by-step guide

1. Measure and cut the boards to size.
2. Fix boards to the wall with adhesive or mechanical fixings.
3. Seal joints to prevent thermal bridging.
4. Apply the chosen finish (render, plaster, or cladding).

Professional vs. DIY installation

While small DIY projects are possible, professional installation guarantees compliance with building regulations, best energy savings, and correct damp-proofing. This is especially important for landlords and housing associations meeting modern standards.

Wall insulation board prices

Average cost per m²

The average cost of wall insulation boards ranges from £10–£40 per m², depending on the material.

Cost by material type

• EPS: £10–£15 per m². 
• PIR: £20–£30 per m².
• Phenolic: £25–£35 per m².
• Mineral wool: £20–£40 per m².

Long-term savings

Properly installed boards are estimated to cut energy bills by up to 35% and can save hundreds of pounds each year, depending on property size, fuel type, and current insulation. This makes them a smart choice for anyone keen to lower costs and add value.

Where to buy wall insulation boards

The easiest way to buy wall insulation boards is online or via specialist insulation suppliers. For the best value, impartial advice, and certified installation, consider getting a quote from trusted professionals, helpful for homeowners and landlords looking to future-proof their property.

Visit EcoInsulation.co.uk to compare products, get tailored recommendations, and arrange professional installation.

FAQs about wall insulation boards

Which thickness is best for cavity walls?

Typically, 50–100mm boards are used, but the exact thickness depends on the required U-value and cavity size.

Can I install insulation boards on old walls?

You can install insulation boards on older walls, but bear in mind that older solid walls may require additional preparation to prevent damp and ensure boards adhere properly.

Are insulation boards eco-friendly?

Some boards, such as mineral wool or recycled EPS, are eco-friendly, while others, like PIR and phenolic, have higher embodied energy but offer long-term energy savings.

Final thoughts

Wall insulation boards offer years of comfort, savings, and enhanced property value. Whether you’re upgrading a family home, developing rental stock, or aiming for government efficiency targets, there’s a board to match your project. 

If your home feels draughty or your heating bills seem higher than they should be, your walls may be responsible. In an uninsulated property, about 25–35% of heat can escape straight through external walls, making your heating work overtime and costing you more than necessary. 

If your home was built after the 1920s, chances are it features cavity walls that are perfect candidates for insulation. 

Cavity wall insulation is one of the simplest, quickest, and most cost-effective ways to make your home warmer, reduce energy waste and bring down annual bills. Unlike external wall insulation, the process involves filling the gap or cavity between your home’s inner and outer walls with an insulating material, effectively slowing the transfer of heat. 

Cavity wall insulation costs

Average installation costs per property type

The cost of cavity wall insulation in the UK varies depending on property size, insulation material, and installer rates. On average, most homeowners can expect to pay:

• Detached house: £2,700–£4,600.
• Semi-detached house: £1,500–£2,700.
• Terraced house: £950–£1,800.
• Flat or maisonette: £950–£1,400.

These prices generally include all materials, labour, and a guarantee (commonly 20–25 years). The price may be marginally higher if any old insulation needs removing or if your property is in London or the South East, where labour is more expensive.

DIY vs professional installation costs

DIY cavity wall insulation isn’t generally recommended. Professional installers use specialised equipment to drill small holes in external brickwork and inject insulation throughout the cavity under controlled pressure. Doing this yourself can result in cold spots, damp problems or incomplete installation, and you could end up having to pay a professional to sort it out. 

Professional installation costs usually range from £13 to £30 per m², depending on the insulation material. While that’s higher than DIY kit costs, you benefit from total coverage, professional guarantees, and compliance with building regulations.

Payback period and long-term savings

A properly insulated home can save anywhere from £110 a year (flats) to £405 a year (detached homes) on heating. With a typical lifespan of 25 years or longer, payback periods are often between three and 10 years, one of the fastest for any insulation upgrade. If you qualify for grants, the payback starts immediately, and your home is warmer from day one.

Types of cavity wall insulation materials

Mineral wool/glass wool

Mineral wool is blown into the cavity, providing thermal and acoustic benefits. It is fire resistant, breathable, and widely used across the UK, especially for older homes.

Polystyrene beads

Polystyrene beads (sometimes coated with adhesive) are injected into the cavity, filling gaps thoroughly and working well around structural obstructions. They deliver excellent thermal efficiency, are lightweight, moisture-resistant, and ideal for exposed or complex wall structures.

Urea formaldehyde foam (older method)

Although it was common decades ago, foam insulation is rarely installed nowadays due to shrinkage and moisture issues. If your home has historic foam insulation, professional checks are advisable.

Which insulation material is best?

For most homes, mineral wool and polystyrene beads are the top choices. Mineral wool is cost-effective and durable; beads offer better moisture resistance for exposed sites. Your installer will advise the best fit for your property, taking into account cavity size, exposure, and budget.

How cavity wall insulation is installed

Professional installation process (step-by-step)

1. Survey: An expert checks the suitability of your walls (cavity width, existing insulation, exposure).
2. Drilling holes: Small holes are drilled in exterior brickwork at intervals.
3. Injecting insulation: Chosen material is pressure-blown or injected to fill the cavity evenly.
4. Sealing holes: Mortar is used to refill the holes, blending with the existing brickwork.
5. Final check: The installers confirm that the cavity is fully insulated and issue a guarantee certificate.

How long does it take?

For the typical family home, installation is completed in two to four hours, with minimal disruption since all work is performed from outside. Larger properties may take a full day. Once it’s complete, you can usually carry on living as normal, only in a warmer home.

Can you DIY cavity wall insulation?

DIY kits exist but aren’t recommended due to technical demands and potential risks. Only professionals have the right tools to ensure every part of the cavity is filled and to offer a warranty. If you’re planning to sell or rent your home, professional certification is vital.

People also ask

How do I know if my house has cavity wall insulation?

Most homes built from the 1920s to the 1990s feature cavity walls. A uniform brickwork pattern is one clue; for confirmation, check for filled drill holes at intervals on exterior walls or book a borescope inspection.

What is the difference between cavity and solid wall insulation?

Cavity wall insulation fills the gap between two walls; solid wall insulation is added inside or outside homes without a cavity (usually older properties). Solid wall solutions are typically more expensive and disruptive.

Is cavity wall insulation worth it?

Absolutely. It is one of the lowest-cost energy upgrades, pays back quickly, and often makes homes cosier, quieter, and more valuable on the market. It can also help you meet the legally required Minimum Energy Efficiency Standards as a landlord.

Does cavity wall insulation make your house warmer?

By dramatically reducing lost heat, cavity wall insulation keeps rooms comfortable in winter and cooler in summer. Fewer cold spots and draughts are common benefits.

How much does cavity wall insulation cost for a 3-bed house?

For a typical 3-bed semi, you could expect costs between £1,500 and £2,700, depending on location and wall size.

Is cavity wall insulation free?

Many homeowners qualify for support under government grants like ECO4 or the Great British Insulation Scheme, especially if the property has a low EPC rating or occupants receive certain benefits. Professional installers such as Eco Insulation can check eligibility and arrange funded installation.

Cavity wall insulation remains a quick, affordable, and high-impact way to cut bills and improve home comfort.