Solid wall insulation

If you live in a home with solid walls, 45% of your heat is escaping through the walls which is costing you money.  Insulating the walls will dramatically prevent heat loss in the winter and greatly reduce your heating bills.

Solid walls can be insulated either from the outside (external) or the inside (internal).

Does your home have solid walls?

Solid walls are mainly made of brick or stone and are found in most houses built before 1919.

The easiest way to tell is from the pattern of the bricks on the outside of your house. If your home has solid walls, the bricks will tend to be placed head-on and lengthways in an alternating pattern like this.

If the brickwork has been covered, you may be able to tell a solid wall by measuring its thickness. Go to a window or door on one of your outer walls, and take a measurement there. 

  • if a brick wall is more than 260mm thick then it is probably a cavity wall
  • a narrower wall is probably a solid wall. Stone walls may be thicker still but are usually solid

If you live in a house that has a non-traditional construction such as a concrete, steel or timber-framed building, you will need a specialist installer with experience in insulating your building type to advise you on your options.

External wall insulation

External Wall Insulation (EWI) involves fixing a layer of insulation material to the wall, then covering it with a special type of render or cladding.  The finish is usually a textured render, pebble-dash or sometimes a brick slip or a brick effect render finish could be used.

External solid wall insulation requires a specialist approved installer. To find one in your area, visit National Insulation Association website.

Advantages of External Wall Insulation

  • can be applied with minimal disruption to the household and its occupants
  • no internal access is required
  • does not reduce the floor area (living space) of the property
  • improves the appearance of the property – potentially increasing the property’s value
  • improves weatherproofing and sound resistance
  • can make the building more airtight, reducing drafts and heat loss
  • increases the life of the existing property by protecting the existing substrate from the weather
  • reduces condensation on internal walls and can help prevent damp (but will not solve rising or penetration damp)

* figures provided by Energy Saving Trust. Costs may vary significantly depending on level of work required.

  Detached Semi-detached Mid terrace Bungalow Flat
Fuel bill savings (£/year) £355 £225 £145 £150 £105
Carbon dioxide savings (kgCO2/year) 1,540 kg 930 kg 590 kg 620 kg 425 kg


Typical installation costs 

External wall insulation: £10,000

Internal wall insulation: £8,000

Internal Wall Insulation

Internal Wall Insulation (IWI) is applied to the internal walls of a building. It is done by fitting rigid boards to the wall, or by building a stud wall filled in with insulation material such as mineral wool fibre.

  • Rigid insulation boards come in varying thicknesses depending on the price. The cheaper ones are thicker so you will lose some floor space for each wall. The highest energy savings are made with the rigid insulation boards.
  • Flexible insulation sheets are cheaper, come in rolls and hung like wallpaper. These are thinner so take less space but are not as efficient.

Key points:

  • 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)
  • can be disruptive but can be done on a room by room basis
  • 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 Aftercare

Using ladders

When using ladders, the ladders should not be directly rested on the render coating as this may cause damage even if protective ends are fitted to the ladders.  If ladders are used, the system designer recommends using a load spreading plate to distribute the weight over the rending coating.

New fittings

Should a new fixing point be required after the application of the system, the system designer recommends the following:

  • For new fittings less than 5kg in weight use SPS Envirowall spiral plugs (ESPDU). The fixings can be installed using hand tools but you may need to drill a 3mm pilot hole first.  A mastic bead should be used on the final thread of the spiral screw to seal the fixing.  A traditional external grade screw can then be used for fixing the new external fixture back to the spiral screw head.
  • For new fittings greater than 5kg in weight, the system designer recommends the use of Fischer Thermax fixings that are fixed back through the insulation to the main building substrate.  These are purpose built fixings that are designed for cladding systems and have a high resistance to flexing.

These can be purchased direct from the system designer SPS Envirowall.

Plants and shrubs

It is advisable to avoid planting climbing plants such as Ivy close to the wall as these can be very destructive over time to the render surface.

Mastic seals

As part of the installation, our contractor has applied mastic sealing around windows and doors.  Mastic sealing does not have the same life expectancy as the insulation system and should be renewed periodically where appropriate.

For more information on maintenance of the system click here to read SPS Envirowall Maintenance and Repair Manual