What is solid wall insulation?
Solid wall insulation adds a thermal layer to homes with solid brick or stone walls, helping cut heat loss and make properties more energy efficient. Since these homes lack an insulating cavity, you can insulate solid walls either internally with plasterboard or rigid boards or externally using insulation boards finished with render or cladding. This upgrade is vital for pre-1920s homes that lose more heat than newer cavity-walled buildings.
Solid walls vs cavity walls
Solid walls are built from a single layer of brick or stone, so they let more heat escape than cavity walls, which use two layers with a gap between. If your home was constructed before the 1920s, it likely has solid walls, meaning adding the right insulation is crucial if you want cosier rooms and lower bills.
Why solid walls need extra insulation
Up to 35% of heat loss occurs through poorly insulated solid walls, affecting your heating costs and comfort. By installing insulation, you keep heat indoors in winter and avoid uncomfortable cold spots, draughts, condensation, and even long-term damp issues. Landlords benefit by raising EPC ratings and meeting regulations, while eco-focused homeowners reduce carbon emissions and support sustainability targets.
Types of solid wall insulation
Internal solid wall insulation
Internal insulation uses insulated plasterboard or rigid boards fitted inside, often combined with a stud wall and insulation batts. It’s cheaper and possible on a room-by-room basis, making it ideal for phased upgrades. You’ll lose a little internal floor space, but you can often use rooms straight away once work is complete.
External solid wall insulation
External insulation fixes rigid insulation boards to the building’s exterior, then covers them with protective render or decorative cladding. This method solves external weathering, improves kerb appeal, and doesn’t affect internal living space, but is usually more expensive and sometimes limited (e.g., in conservation areas or for listed buildings).
Pros & cons of each method
Internal insulation costs less and takes less time, but reduces room size a bit and leaves external weathering problems. External insulation upgrades the look of your home, avoids losing space, and shields the structure, but is pricier and sometimes needs planning permission, especially for homes in conservation areas.
Benefits of solid wall insulation
Reduced heat loss & energy bills
Insulating solid walls can slash annual heating bills by £300–£500 for a typical family home. This pays back the investment over time and increases property value for owners and investors.
Comfort & noise reduction
Adding insulation keeps rooms warmer, eliminates chilly corners and improves soundproofing. It is particularly handy if your home is by a busy road or you have noisy neighbours.
Sustainability & eco-friendly options
By reducing energy demand, you dramatically lower your home’s carbon footprint. Eco-friendly materials such as mineral wool and wood fibre add breathability and sustainability, supporting green mortgages and climate goals.
Solid wall insulation costs
Average installation costs
Expect internal insulation to cost £60–£100 per m², and external insulation from £90–£150 per m², depending on board type and finish. For a typical three-bed semi, budget £8,000–£15,000 for external insulation or £4,000–£8,000 for internal.
Running cost savings over time
Thanks to annual bill savings (£300–£500), payback typically takes ten to 15 years, especially if you access grant support (which can cut upfront costs sharply). Properties see long-term value, lower running costs, and higher energy performance certificates.
Government grants & funding
Eligible homeowners and landlords can benefit from schemes like ECO4 and local council grants, which may pay for part or all of the installation. These improvements improve housing stock and help meet national energy targets.
How to install solid wall insulation
DIY vs professional installation
DIY internal insulation is possible (with plasterboard systems), but professionals ensure proper fitting, solve moisture and ventilation issues, and provide guarantees. External insulation should only be fitted by qualified installers for compliance and safety.
Step-by-step installation process
- Survey walls for damp and structure.
- Prepare surfaces (clean, repair cracks).
- Install insulation boards or batts, floor to ceiling.
- Fit a vapour barrier where needed to minimise condensation.
- Add plasterboard (internal) or mesh/reinforcement and render/cladding (external).
- Finish surfaces with paint or decorative layers.
Common mistakes to avoid
Never insulate damp or damaged walls. Skipping vapour barriers or leaving gaps can lead to both damp and poor performance. Always ventilate and seek advice if unsure, especially for historic or hard-to-heat homes.
Choosing the right solid wall insulation
Best materials
Choose mineral wool for breathability and fire safety, PIR or phenolic boards for high insulation with thinner layers, and EPS when cost is a major factor. Consider more advanced options like vacuum-insulated panels or aerogel for tight spaces or when top performance is critical, but be aware of their higher costs.
Thickness & performance
Thicker insulation means better U-values (lower heat loss), but some boards (like PIR) deliver the same performance with less thickness. Always confirm you’re meeting or exceeding building regulations for your upgrade.
Factors to consider
Balance cost, living space, listed status, and the potential for hidden damp or structural problems. Specialist advice can help you choose breathable systems and avoid pitfalls.
Solid wall insulation FAQs
How long does it take to install?
Most internal jobs are completed in one to two weeks. Meanwhile, external work can take a little longer, depending on property size and weather.
Can I insulate a listed building?
Listed buildings and conservation area homes face restrictions, making planning permission and specialist input essential. Breathable, reversible systems may be required.
What’s the payback period?
Generally, expect ten to 15 years for payback, though this may be faster with grants or high energy bills. Long-term, the savings and comfort are ongoing.
Final thoughts
Solid wall insulation is a standout upgrade for draughty homes, landlords aiming for higher EPC ratings, or anyone wanting lower energy costs and more sustainable, comfortable living.
Whether internal or external, you’ll enjoy greater warmth, quiet, and confidence if your home is prepared for the years ahead.
Ready to take action? Nationally certified installers like those at ecoinsulation.co.uk can deliver expert advice, quotes, and fast installation, giving you all the benefits, savings, and peace of mind you’re looking for.