Solid wall insulation: A practical guide

Solid wall insulation is a key retrofit measure for improving the energy efficiency of older homes, helping to reduce heat loss, cut energy bills, lower carbon emissions, and enhance comfort. Here’s what you need to know about insulating solid walls, both internally and externally.

What is solid wall insulation?

In uninsulated homes, around a third of heat loss occurs through the walls. Solid walls, which lack a cavity, cannot be insulated using cavity wall insulation. Instead, they can be insulated by adding material to the inside or outside of the wall to retain heat more effectively.

How does solid wall insulation work?

There are two main approaches to insulating solid walls:

Internal wall insulation

• How it works: Rigid insulation boards are fitted directly to the inside wall, or a stud wall can be built and filled with insulation material like mineral wool fibre.
• Impact: Slightly reduces the floor area of the room.
• Preparation: Any existing damp issues must be addressed before installation.

External wall insulation

• Considerations: May require planning permission, depending on local regulations.
• How it works: Insulation material is attached to the outside wall, covered with plasterwork or cladding, and then decorated.
• Benefits: Improves weatherproofing, sound resistance, and protects brickwork, extending the lifespan of walls.

Ventilation and solid wall insulation

Solid walls naturally allow water vapour to move through bricks and stones. Adding insulation can change this dynamic, potentially leading to condensation on the inside of walls. To prevent this, professional installers use techniques such as:

• Breathable insulation materials
• Vapour barriers

Working with trusted professionals ensures ventilation is effectively managed, avoiding future damp issues. If you choose Cosy Homes Oxfordshire, you’ll gain access to our network of vetted contractors who will handle these details for you.

Is solid wall insulation right for your home?

Solid wall insulation is particularly suited to older properties, such as those built before 1920, which likely have solid walls. To identify your wall type:

• Measure the thickness: Walls thinner than 260mm are likely solid.
• Check the construction date: Homes built before cavity walls became standard often have solid walls.

Not sure about your walls? A whole house assessment will confirm this and provide a tailored Whole House Plan to guide your retrofit.

Costs and savings

Solid wall insulation costs more than cavity wall insulation, but it delivers greater energy and carbon savings. According to the Energy Saving Trust (April 2019 data):

• Internal wall insulation: Approx. £7,400 for a semi-detached home
• External wall insulation: Approx. £13,000 for a semi-detached home

These figures are based on 2019 estimates and may vary depending on factors such as property size, location, and installation requirements. For the most up-to-date information, visit the Energy Saving Trust’s advice on solid wall insulation.

By combining solid wall insulation with other retrofit measures through our Whole House Plan, you could reduce costs and maximise savings.

Real-life example

A few years ago, we worked on an end-terrace cottage in Hook Norton, where both internal and external wall insulation were installed alongside an Air Source Heat Pump. Read the full case study here to see how these measures transformed the property.

Take the next step

Thinking of retrofitting your home? Book a Whole House Plan with Cosy Homes Oxfordshire and call 0330 223 2742 today to get expert advice tailored to your property and lifestyle, or try our free advice tool to get more ideas about your home’s energy saving potential.