BWF COLUMN: Plastic Windows in a Grade II Listed Property: an unusual case

In this article, Kevin Underwood, BWF Technical Director, explores a case where plastic windows and doors were approved for installation in a Grade II listed building after a successful appeal. Although initially rejected by the Local Planning Authority, the decision was overturned due to prior alterations that had already compromised the building’s historic character

Kevin Underwood, BWF Technical Director

A BWF member recently contacted us to raise concerns about plastic windows and doors being installed in a Grade II ‌listed property, questioning how this was allowed to ‌take place.

We frequently receive enquiries from members seeking advice on listed properties and conservation areas. Often, joiners aim to help property owners improve thermal efficiency by offering double-glazed units featuring simulated or traditional bars glazed with narrow cavity units. A common complaint is the inconsistency of decisions from planning authorities. Our advice is that each case must be evaluated individually.

Background

The case involved a late 18th-century Grade II listed property outside a conservation area. The Local Planning Authority (LPA) initially rejected the Listed Building Consent application, arguing that the use of plastic windows and doors failed to preserve or enhance the property’s character, contrary to the Local Development Plan and Section 16 of the National Planning Policy Framework on conserving and enhancing the historic environment.

The Local Development Plan stipulated that any alterations to a listed building must not adversely affect its architectural or historic character, appearance, or setting. Proposals should respect the building’s unique details, such as form, design, scale, construction methods and materials, all of which contribute to its character.

Decision overturned

The property had undergone significant alterations in the late 20th century – after being listed – including the replacement of all original doors and windows. The existing windows were timber-framed, double-glazed pivot designs in a mock sash style, which didn’t replicate the original sash windows’ appearance or function.

The owner applied to replace these windows and doors with plastic sash equivalents, but the LPA rejected the proposal. While the Georgian design was deemed acceptable, the materials were considered inappropriate for a heritage property. The LPA also raised concerns that the proposed sash horns weren’t an original feature of late 18th-century sash windows, and the simulated glazing bars didn’t replicate authentic through glazing bars typically found in timber-framed Georgian windows.

However, an appeal was filed, and just over a year later, the decision was overturned by an Inspector appointed by the Secretary of State. The Inspector allowed the plastic windows and doors to be installed, focusing on whether the works would preserve the Grade II listed building and its architectural or historic features.

An example of how heritage timber windows can be used to enhance a building

Sympathetic & in keeping

The Inspector determined that despite the late 20th-century timber windows and doors, the building retained its historic authenticity typical of its type and period, with an imposing form, pleasing proportions and characteristic patterns of openings.

Citing Historic England’s guidance, the Inspector noted that while traditional windows contribute significantly to the character of historic buildings, replacements that don’t follow historic patterns are unlikely to enhance a property’s significance. In this case, the existing windows and doors weren’t part of the historic fabric and did not contribute to the building’s significance.

The proposed replacements – white PVC-U double-glazed sash windows in a six-over-six configuration and black gloss composite entrance doors – were considered to be sympathetic to the building’s historic design and proportions. While the Inspector acknowledged the

Council’s preference for timber, they noted that the replacements were of a more appropriate historic pattern than the existing windows.

An unusual case

The Inspector accepted the inclusion of simulated glazing bars attached to the glass, accompanied by back-to-back spacer bars inside the double- glazed unit, which created the appearance of separate panes. Although the proposed units were 24mm double glazing, the Inspector noted that the existing windows were also double-glazed.

While the LPA referred to the refined delicacy of original sash windows from the late 18th and early 19th centuries, these had long since been removed. When compared to the existing replacements, the new windows and doors were not considered bulky or cumbersome.

The Inspector concluded that the proposed works wouldn’t diminish the building’s traditional appearance, architectural form, or remaining historic fabric. Therefore, the proposal met the requirements of the National Planning Policy Framework, the Local Development Plan, and relevant legislation, allowing the appeal subject to approval of specific design and installation details by the LPA.

This case is unusual because the Inspector reversed the LPA’s decision, partly due to the fact that the original sash windows – described in the building’s listing – had already been replaced with non-traditional products, possibly without Listed Building Consent. The Inspector evaluated the proposal in comparison to the current features, rather than the original historic ones, which no longer existed.

For further information, visit www.bwf.org.uk.