Ventrolla restores National Trust heritage sash windows

Preserving original windows is an important part of maintaining the character and integrity of historic buildings. At Canons Ashby, a Grade I listed National Trust property in Northamptonshire, specialist restoration was required to protect the original timber sash windows while improving their performance for years to come.

Ventrolla was appointed to restore 16 sash windows across the ground and first floors of the property’s front elevation. The project combined traditional repair techniques with discreet performance improvements, with careful consideration given to the building’s historic fabric, delicate interiors and continued use by visitors.

Restoring Original Sash Windows at Canons Ashby

Canons Ashby House is renowned for its Elizabethan architecture and centuries of history. As a Grade I listed property, preserving its original features was central to the restoration works.

Rather than replacing the existing windows, Ventrolla took a restoration-first approach, retaining as much original material as possible while addressing areas of deterioration and improving the windows’ operation.

The restoration included:

• Repairing and restoring rotten timber.
• Replacing deteriorated window sills.
• Re-glazing the existing windows.
• Installing new parting beads.
• Draught-proofing the sash perimeters.
• Upgrading sash cords and reweighting the sashes.
• Reusing the original window hardware wherever possible.

Removing rotten timber helped protect the longevity of the original windows, while upgrading the sash cords and reweighting the sashes restored their operational integrity.

By retaining the original hardware and prioritising repairs over wholesale replacement, the team helped preserve the character and detailing of the historic windows.

A Careful Approach to Conservation

Working within a historic property requires more than specialist joinery skills. The restoration process must also account for the building’s surroundings, its historic fabric and the potential impact of construction work on its interiors.

At Canons Ashby, sensitive historic artefacts and delicate interior finishes required particular care. Changes in temperature and moisture levels, as well as dust and debris, needed to be carefully managed throughout the project.

Ventrolla adopted a phased, methodical approach to the repairs, introducing protective measures to safeguard the interiors and help maintain a stable environment as the work progressed.

The team also sought to minimise disruption to visitors. Mobile towers were used to provide access to the windows, avoiding the need for fixed scaffolding at the historic site and allowing the restoration to proceed with consideration for the property’s day-to-day operation.

Improving Performance While Preserving Historic Character

An important part of the project was improving the performance of the original sash windows without compromising their historic significance.

Ventrolla incorporated its Perimeter Sealing System (VPSS) around the sash perimeters rather than the full window frames. This tailored approach supported draught reduction while respecting the conservation requirements of the building.

The VPSS is designed to reduce unwanted air movement around traditional sash windows, helping improve comfort while retaining the original windows and their appearance.

At Canons Ashby, the decision to limit the application to the sash perimeters reflected the need to balance performance improvements with the specific requirements of this Grade I listed property.

This demonstrates the importance of adapting restoration techniques to suit each building, rather than applying a standard solution across every project.

Extending the Life of Original Timber Windows

The completed works addressed areas of timber deterioration, improved the operation of the sashes and introduced discreet draught-proofing measures.

Removing rotten timber helps reduce the risk of further deterioration, while repairs to the sills, glazing and parting beads support the continued performance of the windows. The upgraded sash cords and reweighted sashes also help restore smooth operation.

Together, these improvements help extend the useful life of the original windows while enhancing comfort for visitors to the property.

The project reflects the value of a restoration-first approach to heritage buildings, where preserving original materials and making carefully considered improvements can offer an alternative to unnecessary replacement.

Preserving Britain’s Architectural Heritage

For Ventrolla, the Canons Ashby project highlights the specialist knowledge and attention to detail required when working on nationally significant historic buildings.

Mark Flanagan, Managing Director of Ventrolla, said:

“Working on a site as historically significant as Canons Ashby is an honour. Our goal here was to ensure that we retained the historic character of these beautiful sash windows whilst also meeting the necessary standards for performance and comfort.

“When working on a Grade I listed building such as Canons Ashby, there are incredibly strict guidelines in place to ensure the history of the building is respected. The project really showcases our specialist skills and time-honoured techniques, and we’re very proud to be able to contribute to the preservation of the UK’s heritage.”

The restoration demonstrates how traditional craftsmanship, careful planning and considered performance improvements can work together to protect historic windows for future generations.

By retaining original features and addressing deterioration at its source, Ventrolla continues to support the long-term care of the UK’s historic buildings, helping preserve their architectural character while making them more comfortable for those who experience them today.