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Retrofit vs New Build: The Best External Wall Insulation Approach in the UK

Last modified: 05.12.2025
Retrofit vs New Build: The Best External Wall Insulation Approach in the UK

Retrofit vs New-Build: The Best External Wall Insulation Approach in the UK 

Homes and buildings are losing heat every single day…and someone always pays for it. 

Let that sink in.  

External wall insulation is one of the easiest ways to stop the waste, and you will feel the difference immediately. It simply comes down to one key question for homeowners and developers alike: should you retrofit with EWI, or integrate insulation into new-build from the start?  

It’s easy to get lost in all the options, but we’re here to seal the facts and guide you through!  

 

Retrofit external wall insulation(EWI) is added to homes that have already been built, especially older properties that love leaking heat. It’s truly one of the simplest ways to improve energy efficiency, lower heating bills, and boost your EPC rating.  

 

It’s best for:  

  • Solid-wall or uninsulated homes - the ones that let your hard-earned warmth sneak out the back door.   

  • Cold rooms, damp issues, or mould - those corners that feel like they have their own microclimate.  

  • Homes needing EPC improvements - perfect for climbing the energy rating ladder (and not looking bad on paper).  

  • Renovation or energy upgrade projects - give your home the upgrade it’s been crying out for (it’s been patient enough).  

 

Benefits:  

  • Transforms your chilly house into a cozy haven - finally, somewhere you can actually enjoy the heating.  

  • Keep the heat where it belongs - inside, not sneaking out through the walls.  

  • Improves indoor air quality and reduces condensation - breathe easier, without any damp drama.  

  • PAS 2035 compliant - meets the latest retrofit standards, hassle-free.  

  • Compatible with EWI PRO systems - reliable, tested and works as it should.  

 

New-build insulation is planned from the start of construction, which makes it easier to integrate thicker insulation and achieve excellent airtightness. 

 

It’s best for:  

  • Developers  

  • Self-build projects  

  • Energy-efficient new homes  

 

Benefits: 

  • Enables very low U-values, keeping heat in and cold out.  

  • Easier to apply insulation evenly and consistently because you will be working with fresh, new and straight walls.  

  • Helps meet part L regulations as it reduces a properties carbon emission and improves the buildings thermal performance.  

 

New-Build EWI builds performance into the structure of the property.  

 

  • Retrofit EWI: Generally, more expensive than new build EWI, mainly due to the Value Added Tax differences however, the investment usually yields long-term benefits.  

  • New Build EWI: New builds may cost more upfront; however, they are more cost-effective than retrofit EWI, as this is due to the absence of hidden costs and seamless integration into the construction process.  

  • Retrofit: Expect some scaffolding, a lot of noise and prep work, which would be very disruptive to occupants or neighbours. Labourers do tend to work in different stages in order to minimise the disruption.  

  • New-build: Very little disruption due to the insulation being applied before anyone moves in.  

  • Retrofit: Highly energy-efficient and reduces a beating heat loss; however, it is limited by the building's existing condition.  

  • New-build: Due to the external wall insulation being installed from the start to meet current energy standards.  

 

A recent new-build project in Averley used an EPS system specified by EWI Pro to achieve a U-value of 0.13 W/m²K on timber-frame homes. The development of seven exquisite, energy-efficient properties with Silicone Render was the result of this project. Read the full case study here.  

A major refurbishment project in Liverpool used an EWI Pro Mineral Wall System to improve fire safety and achieve a U-value of 0.13 W/m²K on a large apartment block. The retrofit followed a previous fire event in the area, making fire resistance and thermal performance key priorities. Read the full case study here. 

 

  • If you want to cut heating bills  

  • If you want a better EPC rating  

  • If you own an older or inefficient home  

  • If you want insulation integrated into the building fabric  

  • If you are building from scratch  

  • If you want the lowest possible U-values  

 

Both approaches can deliver excellent results, especially with high-quality materials from EWI Store and trusted system design from EWI Pro.  

 

Whether you’re constructing a new property or improving an older one, external wall insulation is one of the most reliable ways to reduce bills, boost energy efficiency and create a more comfortable living environment. With EWI Stores ' certified range of materials and EWI Pro’s expertise systems, retrofit and new-build will deliver long-lasting results you can rely on.  

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