Internal Wall Insulation

Important: All installations must comply with current regulations, which may change over time.

What Is Internal Wall Insulation (IWI)?

Internal wall insulation is the process of adding an insulation material to the inside surfaces of a property's external walls. This improves the wall’s thermal performance (how much heat is transferred out the property through the walls), helping to maintain a comfortable room temperature.

It is installed alongside ventilation* to manage moisture levels in the property. This is required by building regulations because if moisture is unable to escape it can cause condensation and mould growth. Ventilation improves air flow to help remove this excess moisture, ensuring a healthy environment.

*Please see our ventilation guide for more information. Ventilation | YES Energy Solutions

Internal wall insulation is only used to insulate the external walls in your property; it will not be used on connecting walls that separate rooms. Depending on the property, it can sometimes be used in combination with external wall insulation or cavity wall insulation. This will be subject to the property’s wall types and what funding is available at the time.

Key things to know before installation:

• Someone must be present during installation (you or someone you trust).
• Disruption is expected – rooms may be unusable during work.
• Room size will reduce slightly due to insulation thickness (typically 40–100mm).
• You cannot drill or nail into insulated walls without special fittings.
• Ventilation upgrades are likely required to meet building regulations.

Common questions & misconceptions:

Will the room feel smaller?

Yes – insulation adds a thick layer to the wall, reducing floor space.

Do I need planning permission?

No – unless your property is listed. YES Energy Solutions will advise if this applies to you.

Does IWI cause damp or mould?

No – when installed correctly with proper ventilation, IWI prevents moisture build-up.

Is IWI only useful in winter?

No – insulation slows heat transfer, keeping homes cooler in summer too.

Is more insulation always better?

Not necessarily. The right amount depends on your property. The retrofit coordinator will determine this after surveys.

What are the benefits?

• Lower energy bills
• Improved comfort
• Reduced noise
• Potential increase in property value
• Typically, the life span can range from 30–50 years, depending on materials and maintenance.

Installation process

Before installation

Furniture must be moved (contractors can assist if needed).

Wallpaper will be stripped by installers.

Walls will be checked for damp/mould.

Fixtures removed: radiators, curtain poles, sockets, switches, skirting boards.

Flooring protected: carpets covered, installers wear shoe covers.

Note: Fixtures will be reinstalled after insulation is complete.

During installation

Expect dust, noise, and disruption.

Rooms may be unusable during work.

Installers will do their best to minimise disruption and maintain comfort.

Installation Steps

Insulation fitted to internal walls.

Plasterboard and plaster applied for a smooth finish.

Fixtures reinstalled.

After installation

Redecoration is not covered by grant funding.

Walls will be ready for painting or wallpapering.

Rooms may feel slightly smaller due to insulation.

Maintenance tips

• Avoid drilling or nailing into insulated walls.
• Insulation includes a vapour control layer – damaging it can trap moisture.
• Use specialised fittings if you need to hang items.
• Check for damage regularly and contact YES Energy Solutions or refer to your warranty if needed.

Handover documents you’ll receive:

• Trustmark Certificate
• Insurance-backed guarantees
• Workmanship guarantee
• Manufacturer’s warranty
• Claim of compliance
• Maintenance guide