The flexibility and natural composition of wood fibre makes it highly compatible with uneven substrates and traditional construction methods.
We are proud to have contributed to Calverley Old Hall, a project shortlisted for the RIBA Yorkshire Awards 2026, highlighting excellence in heritage restoration and design.
The Landmarks Trust History Album Volume II: Repair & ConversionCalverley Old Hall is one of the most historically significant surviving medieval manor houses in the north of England. The building, with origins dating back to the 14th century, has undergone a major programme of repair and conversion to bring it back into long-term use under the stewardship of the Landmark Trust.
Following decades of alteration, subdivision and deterioration, the project focused on carefully restoring the building fabric while upgrading performance in line with modern expectations. The scheme included re-roofing, structural repair, and sensitive internal upgrades to ensure the building remains usable, comfortable and durable for future generations.
Working with historic fabric of this nature presents a number of key challenges:
• Highly variable and irregular solid masonry construction
• Significant moisture loading and historic water ingress
• The need to retain and protect original timber elements
• Requirement for full vapour permeability throughout the build-up
• Balancing thermal improvement with conservation best practice
Like many heritage buildings, Calverley Old Hall relies on its ability to absorb, buffer and release moisture naturally. Introducing impermeable materials would risk trapping moisture within the structure, leading to decay and long-term failure.
Unity Lime supported the project through the supply and technical guidance of breathable materials, helping ensure compatibility with the existing structure.
Our involvement focused on:
• Supplying vapour-open insulation and lime-based materials
• Advising on appropriate build-ups to maintain drying potential
• Supporting specification decisions in line with conservation principles
• Ensuring all materials contributed to a fully breathable system
This approach aligns with best practice in heritage retrofit, where the priority is not just thermal performance, but long-term fabric health.
1. Vapour-Open Insulation
Natural insulation materials were selected to work in harmony with the existing structure, allowing moisture to migrate safely through the wall build-up.
Key benefits:
• High vapour permeability
• Capillary-active behaviour
• Reduction in interstitial condensation risk
• Improved summer comfort through thermal mass and phase shift
2. Lime-Based Plasters and Renders
Lime mortars and plasters were used throughout to ensure compatibility with historic masonry.
Advantages include:
• Excellent moisture buffering
• Flexibility to accommodate movement
• Low embodied carbon compared to cement-based alternatives
• Full reversibility in line with conservation principles
3. Airtightness Without Compromise
Carefully considered airtightness detailing was incorporated without introducing vapour barriers that could restrict drying.
This ensures:
• Improved energy performance
• Reduced uncontrolled air leakage
• Continued breathability of the building fabric
Moisture Strategy: The Key to Longevity
A central principle of the project was maintaining a safe moisture balance.
Rather than attempting to block moisture, the design allows the structure to:
• Absorb moisture during periods of high humidity
• Redistribute it through capillary action
• Release it back to the environment when conditions allow
This is critical in historic buildings, where moisture movement is unavoidable and must be managed rather than prevented.
The completed project successfully delivers:
• A fully functional and habitable historic building
• Enhanced thermal performance without compromising fabric
• Improved internal comfort year-round
• Long-term protection of heritage materials
The building has now been brought back into use as a Landmark Trust property, ensuring its continued occupation and maintenance into the future.
Projects like Calverley Old Hall demonstrate that:
• Breathable construction is essential for heritage buildings
• Modern performance standards can be achieved without cement-based systems
• Natural materials offer a robust, long-term solution
• Correct specification is critical to avoid unintended moisture risks
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