Case Study: Low-pitch challenge resolved on Grade II renovation at Howgill House
20 February 2026A sensitive renovation in the Yorkshire Dales National Park has highlighted the importance of balancing historic character with modern performance standards, particularly where roofing constraints are involved.
Meeting listed building requirements
Howgill House, a Grade II listed farmhouse in Dent, Cumbria, had stood semi-derelict for several years. The property had only basic services and was suffering from significant deterioration, including major roof leaks that threatened the long-term integrity of the structure. The refurbishment project, overseen by Mark Deverill of HM Architecture, set out to bring the building back up to modern standards while preserving its historic appearance.
Located within the Yorkshire Dales National Park, the building sits prominently within the village context. As a listed property, any intervention required a careful, conservation-led approach, ensuring that the original roof form and external materials were respected.
Given the building’s listed status and its prominent setting within the National Park, retaining the existing roof profile was essential. Materials and detailing needed to remain in keeping with the original structure, with a like-for-like approach adopted across the majority of the roof.
However, while the main building benefited from a steep roof pitch suitable for traditional slate reinstatement, a smaller extension presented a significant challenge. Its pitch at 18 degrees fell below that recommended under British Standards and good building practice for slate or stone roofing.
Resolving the low-pitch constraint
Altering the roofline was not an option, and introducing a flat roof would have conflicted with the traditional form of the farmhouse. The design team therefore required a solution that would allow the original slates to be reinstated while ensuring long-term weathertightness at a lower pitch.
“We had to work entirely within the existing roof form of the building,” explains Mark Deverill. “On a listed property, preserving the external appearance is critical.”
To address the technical constraint, the team incorporated a low-pitch sub-roof system beneath the reinstated slate covering. The system provides a secondary weatherproof barrier below the primary roof finish, allowing the traditional material to remain visible while enhancing resilience against wind-driven rain and snow ingress.
Although familiar with Onduline’s wider roofing products, ISOLINE LOW LINE was new to the project team. Early engagement with the manufacturer ensured appropriate detailing and installation guidance.
“On a heritage scheme, there’s very little margin for error,” adds Mark. “Having clarity around detailing and performance was essential. The solution gave us confidence that the lower pitch area would perform as required without visually altering the roof or departing from our slate specification.”
Delivering long-term performance
Installed beneath the slate covering on the extension, the sub-roof system now provides enhanced protection in what can be an exposed Cumbrian location. By introducing a dependable secondary line of defence, the design addresses the leak issues that had previously contributed to the property’s decline.
Works began in October and are due for completion in July, by which time Howgill House will once again be a fully habitable rural dwelling, complete with upgraded services and improved thermal performance, achieved in a manner that remains consistent with the original structure.
For architects, conservation officers and contractors working on historic buildings, the project illustrates a familiar challenge - reconciling modern minimum pitch requirements with traditional roof forms. By carefully integrating contemporary sub-roof technology beneath heritage materials, it is possible to safeguard both performance and authenticity.
At Howgill House, a once-vulnerable roof has been transformed into a robust and conservation-sensitive solution that supports the building’s long-term future.
For more information on Onduline’s ISOLINE® LOW LINE roofing system, visit the ISOLINE product page.
