Solid Wall Insulation

Solid wall insulation (SWI) is a significant fabric upgrade for properties with solid walls, typical of many older properties built before the 1920s. Unlike cavity walls, solid walls lack an air gap and therefore lose more heat, making SWI a powerful way to boost energy efficiency, improve EPC ratings, and enhance tenant comfort. Both internal and external insulation options are available, each with its benefits and considerations.

For landlords, spending on solid wall insulation demonstrates a commitment to sustainability and future-proofs homes against increasingly strict energy regulations.

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Why Insulate Solid Walls?

Solid walls can account for up to 35% of heat loss in many properties. Because these walls transfer more heat to the outside, tenants often face higher heating bills and may experience cold spots and damp issues inside the property.

By insulating the solid walls—either on the inside or outside—landlords reduce heat loss, improve temperature stability, and enhance EPC ratings significantly. This upgrade may raise a property’s EPC band by one or more grades and save tenants hundreds of pounds a year on energy costs.

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Regulations and Financial Support

Solid wall insulation must comply with Building Regulations to ensure safety, moisture control, and structural integrity. The choice between internal and external insulation will depend on the property’s construction, planning permissions (especially for external works in conservation or listed areas), and tenant considerations.

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Available grants and funding:

• The Energy Company Obligation (ECO4) supports SWI upgrades for eligible properties, prioritising low-income.

• The Great British Insulation Scheme (GBIS) may provide grant aid towards solid wall insulation costs.

• Local authorities sometimes offer regional funding or council incentives.

• Eligibility is generally based on EPC rating (usually D or below), tenant income and benefit status, council tax band, and sometimes planning constraints.

• If eligible, grants can cover a significant portion of the cost depending on the type of insulation and property size.

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Types of Solid Wall Insulation

 

• Internal Wall Insulation (IWI):

IWI involves fixing insulated boards or stud partitions with insulation material to the inside of external walls. This reduces wall heat loss but slightly reduces room size. The process requires careful sealing around windows, doors, skirtings, and electrical fittings to prevent cold bridging and condensation.

• External Wall Insulation (EWI):

EWI involves fixing insulation boards to the exterior walls, then applying a weatherproof render or cladding system. EWI improves thermal performance without reducing internal space and also protects the wall fabric from weathering.

Installation typically takes several days to a few weeks depending on property size and complexity.

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Benefits to Landlords

Solid wall insulation brings substantial advantages for landlords. It improves property EPC ratings up to three bands, aiding compliance with regulations and making properties more attractive to energy-conscious tenants.

Energy bill reductions and improved comfort can help retain tenants longer and justify higher rents. By mitigating damp and cold spots, SWI reduces risk of structural damage and maintenance issues, protecting the landlord’s asset value.

Environmentally, solid wall insulation supports the nation’s net zero targets by reducing household carbon emissions substantially, demonstrating landlords’ commitment to sustainable property management.

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Common Questions and Concerns

• Is there disruption during installation? External insulation may mean limited access for a while, the use of scaffolding, and changes to the exterior of the property, while internal insulation involves temporary room loss and furniture movement. Landlords should plan accordingly.

• How long does SWI last? Both internal and external insulation systems are designed to last decades with minimum maintenance.

• What about planning permission? External insulation may require planning permission, especially in conservation areas or listed buildings. Internal insulation generally does not.

• Will room sizes be reduced? Internal insulation reduces internal floor area slightly due to added wall thickness; external insulation does not affect internal space.

• Can SWI cause condensation? Correct design and installation are essential to avoid moisture problems, particularly with internal insulation. Professional surveys address this risk.

 

Getting Started

Landlords wanting to install solid wall insulation should first arrange for a detailed survey by a qualified installer. This survey assesses structural and moisture conditions, tests wall construction, and advises on the best insulation type for the property.

Checking eligibility for government grants is important. Landlords should gather EPC reports, tenant income details, and council tax information to prepare funding applications with installer support.

After installation, landlords should update the EPC to reflect improvements and inform tenants about optimising the upgrade to enhance comfort and savings.

For retrofit recommendation, check grant eligibility and connect with qualified installers, landlords can register for eco-Landlord and take the next step toward a more energy-efficient rental property.