Internal Wall Insulation System IWI

When insulating on the outside is not an option!

Wetherby’s R&D department are always on the look out for new opportunities to help expand their system portfolio and it seemed a natural progression for Internal Wall Insulation to be the next step.

Along with external wall insulation, Wetherby are now in a position to offer a ‘whole house approach’ when it comes to thermally insulating solid walled properties.

Specifically developed to meet an increasing demand to improving the energy efficiency of homes in the UK that need to maintain their external appearance, Wetherby’s new Internal Wall Insulation System is one of the most flexible and cost effective IWI solutions on the market.

Wetherby’s new system utilises a high performance rigid Phenolic insulation board, bonded to a standard 12.5mm plasterboard, available in a range of thicknesses to achieve the desired U value. The IWI system can be used in conjunction with Wetherby’s ‘External’ Wall Insulation system to create a “hybrid” solution where required.

Offering approved installers complete flexibility during installation, Wetherby’s Internal Wall Insulation System is BBA approved for use with the most diverse range of fixing techniques including dot and dab, direct fix, timber battens and metal furring.

Each fixing method provides a reliable long term energy saving benefit, especially on domestic refurbishment projects and they’re absolutely ideal for properties where no cavity exists (solid wall).

BBA Certificate Number: 19/5658

The benefits of insulating internally

  • Doesn’t affect the external appearance of a property – architectural features can remain intact.
  • Delivers better U-values and thinner solutions compared to alternative systems.
  • Offers the installer maximum flexibility and installation speed due to the tapered edge insulated plasterboard.
  • Provides reliable long term energy savings.


Anticipated Cost Savings

Type of property Installation cost Savings per year CO2 savings per year (kg)
Detached house
(four bedrooms)
Est. between £4,500 and £15,000 £460.00 1,040
Semi-detached house
(three bedrooms)
Est. between £4,500 and £15,000 £270.00 600
Mid-terrace house
(three bedrooms)
Est. between £4,500 and £15,000 £180.00 395
Detached bungalow
(two bedrooms)
Est. between £4,500 and £15,000 £180.00 410
Mid-floor flat
(two bedrooms)
Est. between £4,500 and £15,000 £150.00 345
Table notes: figures based on a typical gas-heated home with an 81% efficient gas boiler and gas tariff of 4.21p/kWh and electricity tariff of 13.52p/kWh. Figures based on a home with 80% double-glazed windows and 20% single-glazed, with main living areas heated to 21°C and other areas at 18°C. All data obtained from the Energy Saving Trust (EST).


Internal Wall Insulation Brochure



For further information on the Wetherby Internal system, contact our technical support department on 0800 107 32 99.