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Solid Wall Insulation

Insulating your solid walls could cut your heating costs considerably, because solid walls let through twice as much heat as cavity walls do. The good news is they can be insulated.

If your home was built before 1919, its external walls are probably solid rather than cavity walls. Cavity walls are made of two layers with a small gap or ‘cavity’ between them. Solid walls have no gap, so they let more heat through.

Another way to tell is by measuring the width of the wall. Look at an external wall window or door and if the brick wall is less than 260mm, then it is likely a solid wall, while if it is greater, it is probably a cavity wall.

If you live in a house that is not made from bricks, such as a steel or timber-framed building, insulating will be different.

Solid wall insulation

Solid walls can be insulated – either from the inside or the outside. This will cost more than insulating a standard cavity wall, but the savings on your heating bills will be bigger too.

How much could you save by insulating your solid walls?

England, Scotland and Wales 



Semi detached

Mid terrace



Fuel bill savings (£/year)






Carbon dioxide savings (kgCO2/year)

1,900 kg

1,100 kg

720 kg

 740 kg

610 kg

Typical installation costs*

External wall insulation: £5,000 to £18,000
Internal wall insulation: £3,000 to £14,000

Estimates based on insulating a gas-heated home. *Costs may vary significantly depending on level of work required.

You might be able to reduce these costs by carrying out the work at the same time as other home improvements or by not tackling all the house at once.

Internal or external insulation?

Internal wall insulation is done by fitting rigid insulation boards to the wall, or by building a stud wall filled in with insulation material such as mineral wool fibre.

External wall insulation involves fixing a layer of insulation material to the wall, then covering it with a special type of render (plasterwork) or cladding. The finish can be smooth, textured, painted, tiled, panelled, pebble-dashed, or finished with brick slips.

There are advantages and disadvantages to both.

Internal wall insulation:

  • is generally cheaper to install than external wall insulation
  • will slightly reduce the floor area of any rooms in which it is applied (the thickness of the insulation is around 100mm)
  • is disruptive, but can be done room by room
  • requires skirting boards, door frames and external fittings to be removed and reattached
  • can make it hard to fix heavy items to inside walls – although special fixings are available
  • needs any problems with penetrating or rising damp to be fixed first.

External wall insulation:

  • can be applied without disruption to the household
  • does not reduce the floor area of your home
  • renews the appearance of outer walls
  • improves weatherproofing and sound resistance.
  • fills cracks and gaps in the brickwork, which will reduce draughts
  • increases the life of your walls by protecting the brickwork
  • reduces condensation on internal walls and can help prevent damp (but will not solve rising or penetration damp)
  • is best installed at the same time as external refurbishment work to reduce the cost
  • may need planning permission - check with your local council
  • requires good access to the outer walls
  • is not recommended if the outer walls are structurally unsound and cannot be repaired.

Keeping the costs of installing solid wall insulation down

The costs we reference for installing solid wall insulation are for paying a company to come in, insulate your whole house in one go, fully redecorate and replace everything just as it was. Some people want exactly this, but it does cost a lot of money. If you're looking to spend less, it is adviseable to insulate a wall when you are having other building or decorating work done. Fitting the insulation work in with your other home improvements not only saves money on the job, it also spreads the cost of the insulation as you improve your home's rooms.

External insulation will also cost less if you do it when you're having other work done to the outside. If you're having a new roof, or painting the windows, or even having solar PV panels fitted, then you will probably have scaffolding up already, which can save a bit on the costs. If you have rendered walls with damaged render, or brick walls that need re-pointing, external insulation may not cost you much more than you would need to pay for the repairs.

Moisture movement and ventilation

In traditionally built properties with solid walls, it is recommended to use breathable (also known as vapour permeable) solid wall insulation materials as these allow continuous movement of air (vapour) and this helps reduce the possibility of moisture build up.

If you are planning on installing non-breathable (also known as vapour impermeable) solid wall insulation materials in a traditionally built property then we recommend you ask the installer what consideration needs to be given, if anything, to avoid the build-up of moisture in your home.

Remember to check with your installer that the installation is covered by the SWIGA guarantee  which gives 25 years cover for defective materials, design or workmanship or by other appropriate guarantees such as Kinnell ECO Guarantee  (which covers most of natural building technologies). Also check with your installer that the products/materials are BBA certified.

How Th!nk Energy can help with your Solid Wall Insulation.

In the past owners of older properties were unable to install adequate insulation as these properties often had solid walls which were unsuitable for cavity wall insulation.
The good news is that a variety of new systems have been developed which can overcome this problem. In extensive research it has been shown that a home can lose up to 45% of its warmth through uninsulated solid walls.

Here at Th!nk Energy we are a local Yorkshire firm who can offer you the latest state of the art systems to provide superior insulation solutions for solid walls. 
There are essentially two different ways of insulating a solid wall - external wall insulation and internal wall insulation.

External Wall Insulation

Think Energy's External Solid Wall offerings are Knauf Thermoshell EWI and the JUB EPS System.

The below Diagram is showing a wall cross section of the JUB EPS System


At Th!nk Energy we can offer our customers the latest Thermoshell external wall insulation ( EWI). This insulation has been developed by Knauf and is the latest innovation in EWI. Once fitted to the exterior of the property this insulation has many advantages;

  • Warmer in winter but cooler in summer
  • Extends life of building
  • Visually improves appearance of building
  • Increases the value of the property
  • Uses rock mineral wool which allows the building to breathe- eliminating problem of damp     caused by condensation
  • Water repellent
  • Comes in an extensive range of colours and finishes
  • Low maintenance
  • Reduces external noise
  • Non- combustible having a Euroclass A1 reaction to fire rating

Knauf offer a wide range of different finishes from mineral renders, silicone, silicate and Nano through to dashing renders. They also offer an extensive choice of colours as can be seen in their brochure. Please click here to access their brochure showing the colours available.

We also supply Jubizol Thermal Insulation systems which have many of the above advantages. The Jubizol range is produced by JUB, a company with over 45 years of experience in developing EWI systems, for more info on the Jub range please click here.

JUB offer 5 different types of EWI systems:- Standard, Comfort, Premium, Nature and Strong. These systems are specifically designed for buildings which have different requirements. They vary in price but all offer the customer reduced heating costs of up to 40%.

Internal Solid Wall Insulation 

Some properties may not be suitable for the installation of External Solid Wall Insulation, in this case Internal Solid Wall Insulation( IWI) may be the solution. Although EWI is generally preferred as it causes less disruption to install IWI can be just as effective in saving money and lowering the carbon footprint of a property.

Think Energy's Internal Solid Wall offerings are Knauf Thermoshell and British Gypsum Drilyner & British Gypsum Gypliner.

Further info please the attached case studies: British Gypsum Whitley Bay Case Study Isover Internal Wall Insulation: Bolton Home Case Study 

Kauf have developed their Thermoshell internal solid wall insulation specifically for properties which have 'hard to treat' solid external walls. This system allows homeowners to improve the thermal performance of their homes without affecting the external appearance. 

This system has many advantages;

  • Lower cost
  • Easier to maintain
  • No scaffolding required
  • External appearance unaffected (useful in conservation areas)
  • Materials readily available
  • Can be installed a room at a time 
  • Installation not delayed by bad weather

For more information about Knauf Thermoshell Internal Wall insulation please click here.

The following brochure contains more technical information should you require it: Knuaf BBA certificate.

Both Internal Solid Wall Insulation and External Solid Wall Insulation are energy saving measures recognised under the government's 'Green Deal 'scheme and you may be entitled to help with the cost of installation. Here at Th!nk Energy we are an accredited Green Deal business and we can guide you through the process of applying for any available grants.


..Or call us on 01924 272 996