Preserving the character and historical charm of period properties in the UK is a delicate balancing act. On one hand, homeowners aim to improve the energy efficiency of their homes, while on the other, they must adhere to stringent planning constraints. The choice of glass is a pivotal aspect of this renovation process, and something that is always problematic area to address when replacing external timber windows and doors, we have already discussed replacing heritage windows in a recent blog which you can read here.

In this blog, we’ll delve into the three main types of glass used within the UK: Heritage Slim Double Glazed Units, Vacuum Glass, and Regular Double Glazing. We’ll explore their advantages and drawbacks in the context of period properties and listed buildings.

  1. Heritage Slim Double Glazed Units

Heritage Slim Double Glazed Units are a sophisticated solution for homeowners who are committed to preserving the aesthetics of period properties. These units combine the beauty of traditional single glazing with modern thermal efficiency. The main advantages and challenges of this type of glass are as follows:


A. Aesthetic Appeal: Heritage Slim Double Glazed Units are specifically designed to match the appearance of single glazing commonly found in older properties. This ensures that the character and charm of the building remain intact. they had a reduced height sight line over regular double glazed units which allows us to keep the narrow elegant proportions of original sashes and glazing bars.

B. Improved Thermal Efficiency: These units consist of slim double glazing with advanced insulating technology, providing better thermal performance without compromising the window’s slim sight lines. the thermal value of these units can also be increased by introducing different gasses such as Argon and Krypton.


A. Cost: Heritage Slim Double Glazed Units can be more expensive than other glazing options due to their specialized design and installation requirements.

B. Limited Performance: While these units offer improved thermal efficiency compared to single glazing, they may not be as energy-efficient as more modern glazing options like vacuum glass or regular double glazing. the narrow cavity of only 4mm is always going to compromised over a modern 14/20 mm cavity, although this can be improved with the addition of Krypton glass this does come with a significant uplift in cost, and will still only give a typical U-Value of 1.2 – 1.9 W/m2k. more information from our preferred supplier can be found here.

  1. Vacuum Glass

Vacuum glass is a cutting-edge glazing option that leverages advanced technology to provide exceptional thermal performance without compromising the aesthetics of a period property. further technical information can be found here for  Here’s a closer look at the benefits and challenges of using vacuum glass:


A. Exceptional Insulation: Vacuum glass consists of two panes of glass with a vacuum-sealed gap in between. This design virtually eliminates heat transfer, making it one of the most thermally efficient options available with an overall thickness of only 8.3mm and a U-value of 0.4 W/m2k, these proportions make the units ideal for installing in traditional proportioned sashes, with a thermal performance that exceeds regular triple glazed units.

B. Minimal Sight line Disruption: Vacuum glass is designed to maintain the slender sight lines of traditional single glazing, ensuring that the appearance of the period property remains authentic.


A. High Initial Cost: Vacuum glass is among the pricier options for glazing, making it a substantial investment for homeowners looking to improve energy efficiency.

B. Limited Availability: While vacuum glass is gaining popularity, it may not be as readily available as other types of glazing in the UK. although this is improving with the  two leading suppliers of Landvac and Fineo now operating a regular supply chain in to the UK, this does however come with a longer lead time for order, typically around 12-14 weeks.

  1. Regular Double Glazing

Regular double glazing, while less tailored to period properties, offers a balance between cost-effectiveness and thermal efficiency. It involves the use of two panes of glass with a sealed space in between, filled with air or an inert gas. Here are the pros and cons of using regular double glazing in heritage buildings:


A. Cost-Effective: Regular double glazing is more budget-friendly than Heritage Slim Double Glazed Units and vacuum glass, making it a practical choice for many homeowners.

B. Improved Thermal Efficiency: While not as thermally efficient as vacuum glass, regular double glazing significantly reduces heat loss compared to single glazing.


A. Sight line Disruption: Standard double glazing has thicker sight lines compared to vacuum glass and Heritage Slim Double Glazed Units, which can alter the appearance of the windows in period properties.

B. Planning Constraints: In some cases, planning authorities may have restrictions on using regular double glazing in listed buildings. It’s essential to consult with the local planning office to ensure compliance.

Balancing Efficiency and Aesthetics

Preserving the heritage and aesthetics of period properties in the UK is paramount, but so is improving their energy efficiency. To navigate the challenges, homeowners and property developers should consider several key strategies:

  1. Consult with Conservation Officers: When working on a listed building or within a conservation area, it’s essential to consult with local conservation officers who can provide guidance on appropriate materials and designs.
  2. Choose Wisely: Assess the specific needs of your property. If maintaining historical accuracy is a top priority, Heritage Slim Double Glazed Units or vacuum glass may be the best choices. For those with more flexibility and budget considerations, regular double glazing can provide a good balance of efficiency and cost.
  3. Seek Professional Advice: It’s crucial to engage the services of experienced architects, designers, and contractors who specialize in period properties. They can provide insights into the best glazing options for your unique situation.
  4. Explore Secondary Glazing: In some cases, secondary glazing can be an effective compromise. It involves adding an additional glazing layer to existing windows, providing improved thermal efficiency without altering the primary windows.


Revitalizing period properties in the UK while complying with planning constraints can be a complex process. The choice of glazing is a vital part of this journey, impacting both energy efficiency and the preservation of historical aesthetics. By carefully considering the advantages and challenges of Heritage Slim Double Glazed Units, Vacuum Glass, and Regular Double Glazing, homeowners and property developers can make informed decisions that honor the past while embracing a more sustainable future for these architectural treasures.

Although we obviously appreciate the importance of people respecting and preserving the heritage features of their homes when replacing external doors and windows, we do also feel that there needs to be some form of comprise from conservation consultants in the consideration of the thermal performance of external joinery products. like a lot of things in life there often needs to be some form of compromise somewhere, and we feel that the slightly sterile look of Vacuum glazing is a small price to pay for the increased thermal performance of this glass, and its slim proportions allow us manufacture doors and windows that are exact reproductions of their original designs. but with that been said we would always recommend that you gain all the correct permissions and consents before replacing your existing period property windows, if you would like to discuss this further then please contact us




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