Internal vs External Solid Wall Insulation: Which Is Best?

If you live in a home built before 1920, chances are you're sitting in a property with solid walls, haemorrhaging heat and money. Approximately 8.5 million homes across Great Britain have solid walls, and a staggering 90% of these remain uninsulated or poorly insulated. That means your home could be losing around 33% of its heat through the walls alone.

The good news? Wall insulation for solid walls can transform your chilly house into a cosy, energy-efficient home while slashing your heating bills. But with two approaches available – internal and external solid wall insulation – which is the best route to take?

Understanding Solid Wall Properties

Most solid wall homes were constructed using single-thickness brick, stone, or concrete blocks. Unlike modern cavity wall properties, there's no gap between the inner and outer walls to fill with insulation material. This construction method was standard practice until around 1920, when builders began creating cavity walls with space between two layers.

Solid wall properties present challenges for housing insulation. Without any existing thermal barrier, heat flows freely through the masonry, creating cold spots, condensation issues, and eye-watering energy bills.

Internal Solid Wall Insulation: An Overview

Internal solid wall insulation involves fitting insulating materials to the inside face of your external walls. There are several methods available, but the most common approaches include rigid insulation boards fixed directly to walls or constructing a stud wall frame filled with insulation material.

Advantages of Internal Insulation

Cost-effective solution: Internal solid wall insulation typically costs around £8,500 for a three-bedroom semi-detached home, making it significantly cheaper than external alternatives.

Maintains exterior appearance: Perfect for listed buildings, properties in conservation areas, or homes where you want to preserve the original facade. You won't need planning permission in most cases.

Room-by-room approach: Unlike external insulation, you can tackle internal solid wall insulation one room at a time, spreading costs and reducing disruption.

Quick installation: Internal work can often be completed faster since there's no need for scaffolding or weather-dependent exterior work.

Disadvantages of Internal Insulation

Reduced floor space: The insulation thickness will slightly reduce the floor area of rooms where it's applied. In smaller properties, this space loss can be significant.

Disruption: Rooms may not be usable while work is ongoing. You may need to remove furniture and kitchen units temporarily. Anything against the walls will need to be removed, including radiators, skirting boards, windowsills and plug sockets.

Thermal bridging risks: Without careful installation, cold bridges can form around window and door frames, creating condensation problems.

Fixing challenges: It can be difficult to secure heavy items to internal walls, although special fixings are available.

External Solid Wall Insulation: An Overview

External wall insulation involves applying insulating materials to the outside of your property and then covering them with protective render or cladding, creating a continuous thermal envelope around your home.

Advantages of External Insulation

Superior thermal performance: External insulation eliminates thermal bridging more effectively, resulting in improved energy efficiency.

No internal disruption: You can remain living in your home throughout installation, with minimal internal disturbance.

Protects the building fabric: The insulation shield protects your original walls from weather damage and temperature fluctuations.

Maintains internal space: Your room sizes stay the same, which is valuable in smaller properties.

Improves external appearance: Modern render systems can refresh tired-looking exteriors and may increase property values.

Disadvantages of External Insulation

Higher costs: External wall insulation costs approximately £12,000 for a typical semi-detached home, but the actual price depends on the property's size.

Planning considerations: Listed buildings and properties in conservation areas often face restrictions or require planning permission.

Weather dependency: Installation may be delayed due to adverse weather conditions.

Scaffold requirements: Installation often requires removing your existing gutters and other external pipework.

Cost Comparison and Savings

The financial picture varies significantly between internal and external approaches:

Internal solid wall insulation: Installing internal solid wall insulation in an average 3-bedroom, semi-detached house costs around £ 8,500, although this is dependent on the number of rooms being renovated.

External solid wall insulation: The cost of external wall insulation starts at around £12,000, depending on the property's size.

Both options deliver substantial energy savings.

Which Properties Suit Each Method?

Internal insulation works best for:

●      Listed buildings or properties in conservation areas where external changes aren't permitted

●      Homes where you're already planning internal renovations

●      Properties where external access is difficult or costly

●      Budget-conscious homeowners seeking a more affordable solution

External insulation suits:

●      Properties where internal space is at a premium

●      Homes requiring exterior maintenance or improvements

●      Properties where disruption to daily life must be minimised

Funding Options Through ECO4

The excellent news for eligible homeowners is that you might not need to pay the full cost yourself. The ECO4 scheme provides funding for both internal and external solid wall insulation for qualifying households.

To be eligible, you typically need to:

●      Own your home or have your landlord's permission

●      Receive certain benefits that place you in the government's Help to Heat Group

●      Live in social housing with an Energy Performance Certificate rating of D-G

The ECO4 scheme can provide these improvements completely free of charge, making wall insulation for solid walls accessible to thousands of households who would otherwise be unable to afford it.

Making Your Decision

Your choice between internal and external wall insulation for solid walls should consider:

Budget: Internal insulation offers a lower upfront cost, though external insulation may provide better long-term value.

Property constraints: Listed status, conservation area restrictions, or planning permissions may dictate your options.

Lifestyle factors: Consider how much disruption you can tolerate and whether you need to remain in the property during installation.

Long-term plans: If you're planning other renovations, timing your insulation work with these projects can reduce overall costs.

Getting Started

At Northeast Insulation Services, we're a qualified and trusted insulation contractor and can assess your property's suitability for free home insulation. We'll evaluate your home's requirements and help determine whether you qualify for funding through the scheme.

Contact Northeast Insulation Services today for a free assessment and discover how ECO4 funding could help you achieve a warmer, more efficient home.