In an era of increasing environmental awareness and the rising cost of living, the UK government continues to discuss the topic of Energy Performance Certificate (EPC) rating for both social and privately rented housing, with a focus being on promoting the improvement of the efficiency of UK housing to a rating of C or higher. 

The EPC certificate is a rating of a property’s energy efficiency on a scale from A (most efficient) to G (least efficient), following the government’s SAP (Standard Assessment Procedure) points system:

  • EPC rating A = 92-100 SAP points 
  • EPC rating B = 81-91 SAP points 
  • EPC rating C = 69-80 SAP points 
  • EPC rating D = 55-68 SAP points 
  • EPC rating E = 39-54 SAP points 
  • EPC rating F = 21-38 SAP points 
  • EPC rating G = 1-20 SAP points

An EPC provides estimated energy costs and recommendations for improving Energy Performance. Higher EPC ratings of A to C indicate lower energy bills and carbon emissions and can bring about many benefits for the property itself, including an increase in value by up to 19.6%, and can even result in a declined mortgage application from some lenders.

Despite initial plans of a 2025 deadline proposed being scrapped in late September 2023 by PM Rishi Sunak in an attempt to reduce the financial burden on the public during trying times (the current deadline is 2028), it would be reasonable to anticipate that the Minimum Energy Efficiency Standards rules could still change in the future.

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The Importance of the EPC

For buyers and renters, the EPC rating provides an easy way to compare the energy efficiency of potential energy costs of different properties. According to the Mortgage Advice Bureau, around 71% of home buyers consider a home’s EPC rating an important factor in the decision-making process, and 59% of home buyers are willing to pay more for a property with a high EPC rating, where at least 75% of its energy comes from renewable sources. 

For sellers and landlords, a higher EPC rating from band D to C can add 3% value, and a valid and high EPC rating makes a property more attractive to buyers and tenants. Additionally, the higher the rating of the home, the more energy-efficient it is, and as the UK government is pushing for improved energy efficiency to meet net zero emissions targets, the EPC rating is something to strive for. 

This is where various upgrades to a property can make a massive difference including insulation, heating, and of course, glazing. However, such changes would pose difficulties to landlords, local authorities, and housing associations as they look to improve older properties to meet these standards. Considering as of December 2023 around 8 million homes (58%) in England were rated below a C, there is certainly an argument to be made for efforts to begin now to work towards this.

Factors to Consider to Ensure Compliance With EPC Ratings

The initial step is a simple one: to get an EPC. EPCs are only valid for 10 years, and to get a new EPC you will need to book a domestic energy assessment, which involves collecting detailed information about the property including dimensions, age, construction materials, insulation levels, lighting, hot water systems, heating, etc. 

This is carried out by professionals known as Domestic Energy Assessors (DEAs); the data they collect is then entered into government-approved software that calculates the property’s Energy Performance rating resulting in an EPC showing the property’s energy rating, estimated energy costs, and recommendations for cost-effective improvements. An EPC is always a legal requirement whenever a residential property is constructed, sold, or rented out.

What Affects an EPC Rating?

The two key factors are: 

  • The amount of energy used per m2.
  • The level of CO2 emissions (in tonnes per year). 

Both of these are influenced by a range of factors including: 

  • The use of different areas of the building.
  • The energy used to heat, cool, and ventilate a property. 
  • The property’s orientation (for example, a mid-terrace house performs better than a house of the same age but is detached).
  • The type of boiler in the property.
  • The levels of insulation, including, single, double, and secondary glazing.

How can Secondary Glazing help?

Secondary glazing is an effective solution for improving energy efficiency and thermal performance. It involves installing an additional, independent window on the interior side of existing windows, creating a “double-glazed-like” solution without changing the external windows. 

Here is why secondary glazing is worth considering:

Enhanced Insulation

By adding a secondary layer of glazing, homeowners can improve insulation and reduce heat loss through windows. This additional layer acts as a barrier, trapping air between the panes and creating an insulating pocket. This extra barrier significantly reduces heat loss through windows and can improve the U-value (the measure of the rate of heat transfer or thermal transmittance through a building material or element) by up to 69% in comparison to single glazing. 

A typical U-value for secondary glazing can range between 1.7 to 2.7 W/m²K compared to 5.2 to 5.8 W/m²K for single glazing and 2.6 to 2.8 W/m²K for standard double glazing with an air cavity. As a result, heat transfer is significantly reduced, keeping the home warmer in winter and cooler in summer.

Noise Reduction

Secondary glazing also offers excellent sound insulation. The extra layer of glazing helps to reduce outside noise, making it ideal for homes located near busy roads, airports, or other sources of high noise levels. 

As secondary glazing units are sealed with efficient gaskets, this minimises air leakage, reducing noise levels because of the lack of transference. By creating an acoustic barrier, secondary glazing enhances overall comfort and tranquillity within the home. Please speak to a professional company as to what type of glass will give you the best results.

Preservation of Historic Windows

For homeowners with period or listed properties, preserving the original windows is often a priority. Secondary glazing provides a non-intrusive solution as it can be installed internally, allowing the primary windows to remain intact ensuring the architectural integrity of the building is preserved while still reaping the benefits of enhanced energy efficiency. 

For large or irregularly shaped historic windows, secondary glazing is often a more cost-effective solution than full window replacement and as a “retrofit” solution, this can rapidly improve insulation levels and EPC ratings without extensive renovation work or altering the original windows. This is particularly important in period properties or if it’s classed as a Listed Building.

Improved Security

In addition to energy-saving benefits, secondary glazing enhances home security. The extra layer of glazing acts as an additional barrier against intruders, making it more difficult for them to break in. 

This added security measure provides peace of mind for homeowners, especially in areas prone to burglary or vandalism. Please speak to a professional company as to what type of glass will give you the best results.

Condensation Control

Secondary glazing creates an insulating air gap between the existing window and the additional glazing layer which traps the air, minimising heat transfer and reducing the temperature difference between the inside and the outside surfaces of the window, this helps control condensation and prevent moisture build-up, reducing the risk of mould and dampness. 

Overall, secondary glazing improves thermal efficiency by maintaining more consistent and warmer interior glass surface temperatures. As warmer glass surfaces are less prone to condensation build-up, this contributes to a higher overall EPC rating.

Is Secondary Glazing a More Cost-Effective Solution to Consider? 

Very simply, yes

Many landlords, homeowners, and social-housing associations make the ill-advised choice to prioritise the upgrading of boilers and installation of heat pumps to tackle the need for greater efficiency, over the general thermal insulation of homes. These changes come at higher upfront costs and could prove inefficient as, without improving the thermal insulation of the homes, these new heating systems have to work twice as hard to keep warmth in a poorly insulated building. 

It was reported in February 2024 that 71% of UK homes have cavity insulation and 67% have loft insulation, insulating windows becomes the logical next step in continuous efforts to prevent heat loss. Secondary glazing emerges as an important option for a simple and cost-effective solution to this challenge, improving energy efficiency without requiring expensive window replacements.


As the conversations continue over the efficiency of UK homes, the time for action to tackle this issue is fast approaching. For any homeowners looking to sell, landlords looking to lease, or housing associations during their day-to-day work finding effective, affordable, and sustainable solutions for this challenge is key. Secondary glazing stands out across all these metrics.

Ready to explore improving your EPC rating and be prepared for future deadlines? Give City Sound Glazing a call on 0208 523 3210 to discuss our range of options and find out how we can help you improve the efficiency of your home(s), reduce your energy bills, and provide a more comfortable living for you and/or your tenants.