Introduction
With energy prices rising and the need to reduce carbon emissions, insulating our homes has never been more important. Walls account for up to 35 per cent of heat loss in uninsulated properties. Choosing the right insulation can dramatically reduce heating bills, improve comfort and protect against damp and condensation. This guide compares external wall insulation (EWI) and internal wall insulation (IWI), explains their benefits and limitations, and offers practical advice for homeowners in London, Surrey and Berkshire.
Understanding wall insulation
Wall insulation reduces the rate at which heat escapes from a building, keeping interiors warmer in winter and cooler in summer. In the UK, many older properties have solid walls with no cavity, making them thermally inefficient. Even cavity-wall homes can benefit from additional insulation. EWI and IWI are two methods to retrofit insulation to existing walls. Both involve fitting insulation boards or batts, but they differ in where they’re installed and how they impact the building’s appearance and space.
External wall insulation explained
EWI entails fixing insulation boards to the outside of the walls and covering them with a protective render or cladding. Materials include expanded polystyrene (EPS), mineral wool or phenolic boards. The insulation is held in place with adhesive and mechanical fixings, then reinforced mesh and base coats are applied before finishing with render.
Benefits of EWI:
- Energy savings: By wrapping the entire building, EWI eliminates cold bridges and drafts. Homes retain heat more efficiently, lowering heating requirements and carbon emissions.
- Enhanced appearance: A new render or cladding finish can modernise tired facades and add kerb appeal. Colour-through renders such as monocouche offer a wide range of textures and finishes.
- Condensation prevention: External insulation keeps the wall mass warm, reducing the risk of condensation on interior surfaces and mould growth.
- Protection: EWI shields external walls from the elements, prolonging the life of the masonry and reducing maintenance.
Considerations: EWI can alter the appearance of the property, which may not be acceptable in conservation areas. It can also add several centimetres to the wall thickness, requiring adjustments to window sills and roof eaves. Scaffolding increases installation costs, and any existing render must be removed or prepared properly.
Internal wall insulation explained
IWI involves fixing insulation boards or batts to the inside face of external walls. Systems typically use rigid PIR boards with a vapour control layer or mineral wool studs with plasterboard. After installation, the walls are plastered or taped and jointed to create a smooth finish.
Benefits of IWI:
- Less external disruption: Because insulation is applied internally, the exterior appearance remains unchanged – ideal for listed buildings or areas with strict planning controls.
- Room-by-room approach: You can insulate individual rooms, spreading costs over time.
- Minimal impact on neighbours: There’s no need for scaffolding or external access, which is useful for terraced properties.
Considerations: IWI reduces room dimensions slightly, especially with thicker insulation levels required to meet modern standards. Electrical sockets, radiators and skirting boards must be removed and refitted. Careful detailing is required at junctions, around windows and doors, to prevent cold bridges and condensation. Proper vapour control is essential to prevent moisture build-up within the structure.
Which insulation is right for you?
The choice depends on your property type, budget and goals. EWI provides the greatest thermal improvement and avoids reducing internal floor area, but it’s more expensive and may alter the building’s look. IWI is often more affordable and less disruptive externally, but it requires meticulous installation and sacrifices some internal space. Properties in conservation areas or terraces may be restricted to IWI. Homes with decaying or badly weathered external walls can benefit from EWI as it combines insulation and a new weatherproof finish.
Other factors to consider
- Planning permission: In some cases, especially for EWI, planning permission may be required. Always check with your local authority.
- Ventilation: Adding insulation makes your home more airtight. Ensure adequate ventilation through trickle vents, mechanical systems or positive input ventilation to avoid condensation and maintain air quality.
- Whole-house approach: Loft and floor insulation, double glazing and draught proofing complement wall insulation. An energy assessment can identify the most cost-effective measures.
- Professional installation: Poorly installed insulation can cause more harm than good. Choose a qualified installer with experience in both external and internal systems. Ensure they follow industry standards, use appropriate materials and provide guarantees.
Rendering and plastering after insulation
Regardless of the insulation method, finishing is critical. With EWI, high-quality render protects the insulation from weather and impact. Options include silicone render, acrylic render and monocouche render, each offering different levels of flexibility, breathability and finish. GO2 specialises in both modern and traditional renders, ensuring insulation systems perform well and look attractive. For IWI, after the boards or studs are installed, plastering creates a smooth, durable surface ready for decorating. GO2’s plasterers achieve flawless finishes with minimal disruption, whether patching around sockets or plastering entire rooms.
Local expertise matters
Properties in London, Surrey and Berkshire vary from Georgian townhouses to post-war semis and rural cottages. Each has unique wall constructions and insulation needs. Choosing a local provider like GO2 ensures installers understand common building types and local regulations. Our team completes a detailed survey to recommend the most suitable system, explains the benefits and costs, and manages the installation from start to finish. We use high-quality materials and proven techniques to deliver long-lasting results.
Conclusion
Wall insulation is one of the most effective ways to improve energy efficiency, reduce bills and enhance comfort. Both external and internal wall insulation have merits and potential drawbacks. EWI is ideal for achieving high performance and refreshing exteriors, while IWI is suitable for preserving architectural features or working within planning constraints. Consulting a professional is the best way to decide. At GO2 Property Services, we provide honest advice and complete solutions – from insulation and rendering to plastering and damp proofing – across London, Surrey and Berkshire. Contact us today to explore how insulation can transform your home and start saving on heating costs.