Solid wall insulation
Solid wall insulation
What is solid wall insulation?
Solid wall insulation is a retrofit solution designed to reduce heat loss through solid external walls, which are common in older UK homes built before the 1920s. Unlike homes with cavity walls, solid walls have no gap to fill, meaning heat escapes rapidly through the building fabric. Insulating these walls can make homes warmer, more comfortable, and cheaper to run, while reducing carbon emissions and boosting energy efficiency.
There are two main ways to insulate solid walls:
- External wall insulation (EWI) installs insulation to the outside of the property, covering the wall with insulating boards and a protective finish.
- Internal wall insulation (IWI) adds insulation to the inside face of external walls, creating a thermal barrier within the home.
Both aim to retain heat inside, but they differ in process, level of disruption, appearance, cost, and suitability.
How it works
Insulation works by slowing the transfer of heat through the wall. In a typical solid-walled home without insulation, up to 45% of heat can be lost through the walls. Adding insulation, whether inside or outside, traps more heat within the living space, meaning your heating system needs to run less to maintain comfort.
External wall insulation
External wall insulation involves fixing a layer of insulating material to your home’s exterior, then protecting it with a render or brick slip finish. It creates a continuous thermal layer that wraps the building, helping to eliminate thermal bridges and improve airtightness.
Internal wall insulation
Internal wall insulation is fitted on the inside of the external walls, typically beneath plasterboard or insulated panels. This reduces heat loss and can improve acoustic performance, but can slightly reduce internal space and may require moving fixtures or fittings.
See how we’ve helped some local homes around Norfolk
See how we’ve helped homeowners across Norfolk improve energy efficiency through real home projects. Discover practical upgrades that reduce heat loss, lower energy bills, and improve comfort, with solutions tailored to each property and designed to deliver reliable, long-term results for everyday living.
External wall insulation (EWI)
What is it?
External wall insulation fixes insulating boards to the outside of your home and covers them with a weather-resistant finish, such as render or cladding.
Things to consider
- Typically more expensive than internal insulation.
- May require scaffolding and careful planning of external features.
- In conservation areas or on listed buildings, external changes may need special approval, even though planning permission is often not required.
Internal wall insulation (IWI)
What is it?
Internal wall insulation adds an insulating layer to the inside of external walls. Materials can include rigid boards, insulating plaster, or stud walls with insulation infill.
Things to consider
- Can be disruptive inside the home and may require removal of skirting boards, radiators, or electrical fixtures.
- Internal space is reduced slightly due to the added insulation layer.
- Careful moisture management is needed to prevent condensation issues, especially in older solid wall properties. Using insulation made from natural materials such as wood fibre is likely to be better for the building, though it may not be essential.
Main benefits of solid wall insulation
Lower bills and energy use
Solid wall insulation significantly reduces heat loss through external walls, helping your home retain warmth for longer and reducing the amount of energy needed for heating.
Improved comfort all year round
Insulated walls help maintain more stable indoor temperatures, making homes warmer in winter and reducing overheating in summer.
Reduced carbon emissions
By lowering overall energy demand, solid wall insulation helps cut carbon emissions and supports the transition to low-carbon heating and energy efficiency.
Improved noise reduction
Adding insulation to external walls can help reduce external noise, creating a quieter and more comfortable indoor environment, particularly in urban or roadside locations.
Protection for the building fabric
External wall insulation can improve weather resistance and protect masonry from exposure, while internal insulation can help regulate internal wall temperatures when correctly designed.
Potential property value increase
Improving wall insulation enhances overall energy performance, which can increase property appeal, future-proof the home, and support higher energy efficiency ratings.
Choosing between external and internal insulation – what you need to know
Which option is right for your property depends on your priorities, home construction, and planning requirements:
- External insulation is often preferable where you want to preserve internal space and minimise disruption, or improve the look of your home.
- Internal insulation can be more suitable when exterior changes are restricted (e.g. conservation areas) or where external access is limited.
A professional assessment is essential, as factors such as wall material, moisture characteristics, existing wall condition, and ventilation all influence the optimal solution.
What to expect during installation
External insulation
Installation typically takes several days to a few weeks, depending on property size and finish choice. A survey identifies any remedial work needed before insulation is fixed, boards are applied, mesh and render are added, and final finishes are applied.
Internal insulation
Internal works involve covering wall surfaces, installing insulation panels or stud walls, and finishing with plasterboard and decoration. You may need to temporarily relocate furniture and remove some fixtures.
In both cases, choosing accredited installers with experience in solid wall retrofit ensures quality, reduced risks of moisture problems, and long-term performance.
Grants and support available
For Insulation, you may be able to get funding or a more cost-effective installation through the following schemes:
Solid wall insulation FAQs
Yes. Solid wall insulation reduces heat escaping through external walls, which can make rooms feel noticeably warmer and more comfortable. Many homeowners notice fewer cold walls and more stable indoor temperatures throughout the day.
Yes. Solid wall insulation is specifically designed for homes with solid brick or stone walls, which are common in properties built before the 1920s. A survey will assess the wall construction and determine the most appropriate approach.
Internal wall insulation adds a layer of insulation to the inside face of external walls. This can slightly reduce internal room space, but the impact is usually small and balanced by improved comfort and energy efficiency.
External wall insulation covers the outside of the property with insulating boards and a protective finish such as render or cladding. This can refresh the appearance of the building while also improving energy performance.
The level of disruption depends on the insulation type. External insulation is installed outside the home and typically causes less internal disruption, while internal insulation may require work to walls, fixtures and decorations.
A professional survey will assess the construction of your walls and current insulation levels. Homes with solid brick or stone walls and poor thermal performance may benefit most from solid wall insulation.
Who can apply
Anyone can improve the energy efficiency of their home. If you’re looking for funding or support, eligibility can vary depending on where you live and income. Visit our eligibility page to find the guidance and schemes available in your area
Our partners
Home Energy Hub Norfolk is a collaboration of all Norfolk Councils. This website aims to provide residents with clear, trusted information to help them explore energy efficiency improvements and understand available support.
