Old Harrow Farm

Heritage Re-Roofing & Insulation Upgrade on a Grade II Listed Tudor Farmhouse, Kent

Download a copy of this heritage roofing case study here. 

Old Harrow Farm is a Grade II listed, jettied Tudor farmhouse; the kind of building where the first floor was built to project slightly out over the ground floor below. It’s a detail with a practical medieval origin: in the days before indoor plumbing, household waste thrown from an upstairs window would clear the wall below rather than landing back against the house. Look up at the right angle and the jetty is still there to see.

By the time the roof reached us, much of the covering was original and still fixed to the building’s old riven oak laths; a roof structure many decades, if not centuries, older than the battened roofs we work on day to day. The brief was straightforward in principle and demanding in practice: bring the insulation up to a modern standard, without altering the profile, pitch, or character of a listed building that has stood for hundreds of years.

The Challenge

Tudor and timber-framed houses like Old Harrow Farm are notoriously difficult to keep warm. Their roofs were built long before insulation was a consideration, and a roof still sitting on its original oak laths offers next to none. For the owners, that meant high heating bills and a building that struggled to hold a consistent temperature; problems that are common to historic houses of this age.

Any solution had to satisfy two requirements that don’t always sit comfortably together on a listed building:

• Performance: the insulation upgrade needed to make a genuine, measurable difference to heat loss and running costs, not a marginal one.
• Preservation: the roof’s external profile, tile coursing and overall appearance had to remain completely unchanged, as required for a Grade II listed structure.

A thicker, counter-battened insulation system would have met the first requirement but breached the second, lifting the tile line and altering the roof’s silhouette. We needed a product that could do both at once.

Our Approach

We specified TLX Gold breathable insulating membrane throughout – a product we have used extensively over recent years on exactly this kind of heritage project, for four reasons:

1. Thermal performance: TLX Gold is among the best-performing breathable membranes on the market. On a historic house like Old Harrow Farm, which is notoriously hard to heat, that translates into a meaningful reduction in heat loss through the roof and a real saving on heating bills. 
2. A consistent, warm envelope: wrapping the whole roof in a continuous layer of TLX Gold creates what is, in effect, a warm roof. The entire roof void sits at the same temperature as the rest of the building. This significantly reduces the risk of cold bridging and the condensation problems that often follow. 
3. No counter-battening required: because the membrane is fully breathable, it does not require counter-battening to maintain a ventilated airspace, unlike many alternative insulation systems. 
4. The profile stays true: with no counter-battens needed, the roof build-up stays slim. The tile line, eaves detail and overall profile of the building are completely unaffected, essential on a listed building of this age and importance.
   

With the membrane specified, the sequence of work was dictated by the building itself. The rear elevation is a catslide roof: a shallower secondary pitch dropping down from the steeper roof above it, originally built to allow a doorway underneath without the roof crowding the opening. The shallower the slide, the higher the doorway beneath it could be, a detail the Tudor builders needed because people were shorter than the Victorians who, generations later, added catslides of their own as the average build became taller.

That shallow pitch creates a practical sequencing problem: once the main catslide is tiled, the dormers set into it become very difficult to reach. So the dormers were tiled first, while access was still straightforward, before work moved out across the wider catslide. Around 5,000 second-hand clay tiles were brought in specifically for this job, carefully mixed with the existing stock so that old and new sit together with no jarring patches of colour or texture across the roofscape.

Materials, Techniques, and Progress

With the roof stripped back to its timbers, TLX Gold breathable membrane was fitted as a continuous layer across the structure, followed by new battens set out to match the original tile gauge, keeping the coursing consistent with the historic roof it replaced. As planned, the dormers were tiled before the surrounding catslide, while access remained straightforward. The vertical tile hanging on the dormer cheeks was dressed in around the window frames, and bonnet hip tiles were used to weather the dormer roofs neatly into the main pitch.

Leadwork and Chimney Detailing

Alongside the re-tiling, new leadwork was fabricated and fitted to the chimney stack and to the flat-roofed dormers on the front elevation. Each piece was hand-dressed on the bench before fitting, using traditional bossing tools to form the welts, laps and corners around the building’s many brick offsets and changes of direction.

The Results

The finished roof delivers exactly what the brief asked for:

• Warmer, more efficient – a continuous layer of TLX Gold across the whole roof brings the insulation up to a modern standard and removes the cold bridging that comes with an uninsulated historic roof, with a corresponding reduction in heating costs for the owners.
• Unaltered listed profile – with no counter-battening required, the roof’s profile, pitch and tile coursing are exactly as they were — a critical outcome for a Grade II listed building.
• Seamless tiling – around 5,000 reclaimed tiles were blended with the existing stock, so the roofscape reads as a single, continuous whole rather than a patchwork of old and new.
• Sequenced to suit the building – the dormers, hips and chimney stack were re-leaded and re-tiled in sequence, tackling the catslide’s tricky access on its own terms rather than fighting it.

Heritage and Conservation Roofing Expertise

Old Harrow Farm is a good example of the judgement a project like this demands: choosing a membrane that solves a genuine thermal problem without compromising a listed building’s character, then sequencing the work around a centuries-old roof’s own quirks rather than against them. It’s the kind of project where traditional skills, an eye for materials, and a proper understanding of how old buildings behave all matter as much as the tiling itself.

OUR SPECIALISMS:

• Kent Peg Tiling
• Traditional Slate Roofing
• Hydraulic Lime Mortar & Pointing
• Listed & Period Building Roof Repairs
• Breathable Insulation Upgrades for Heritage Roofs
• Ecclesiastical & Church Roofing (specialist insurance held, up to 20m)
• Oast House & Agricultural Heritage Buildings

Contact us today to find out more about our heritage roofing and conservation services, and how we combine traditional craftsmanship with modern materials on listed and period buildings across the South East.