Restoring the Roof of Domesday Barn with Traditional Methods for Future Generations
Russell Blackaller, owner of specialist heritage roofing Heritage Roofing Southwest based in Devon, has this spring completed the re-roofing of the historic Domesday Barn and farmhouse at Wisdome Farm, South Hams. Here, he provides a fascinating account of restoring the increasingly rare vernacular scantle barn roof, tackling its numerous challenges to construct a beautiful and long-lasting roof for future generations.
Russell Blackaller has notched up extensive heritage roofing experience having worked on several historic properties on Northumbrian country estates and from there, several conservation projects in the region, and in Scotland and Wales over the past decade.
Russell was invited last year to take on the restoration of Wisdome Farm and its outbuildings. Estimated to be at least 400 years old, the Domesday Barn gets its name from a reference to its location in the Domesday Book.
The owners, who bought the farm in 2020, wanted the building’s restoration to be as traditional as possible, using authentic materials and methods.
The Domesday Barn is of stone construction with sturdy, two-storey high walls and a timber A-frame roof structure. It’s original Delabole scantle slate roof was traditionally constructed in the random style, with diminishing courses.
The project involved stripping and replacing the old roof, including its timber frame, sorting and re-using slate where possible, combined with new Delabole slate bought in by the tonne. The slate would then need grading, before being hung using split oak pegs onto split oak lathes.
Russell jumped at the chance to restore such a beautiful historic building and the Blackaller family moved back to Devon in August to start work on the barn in October 2021.
The timing of the project was critical because the roofs of Wisdome farmhouse and Domesday Barn are home to colonies of Pipestrelle and Brown Eared Horseshoe bats. The project had to be scheduled to coincide with the time of the year when the bats leave their roosts after breeding.
But this proved the first of many challenges for Russell and his team to overcome, as he explains: “The problem was, if the horseshoe bats weren’t gone when we started work, they can’t be removed so we would have to work around them. And that’s what we found – some bats were still present, so we had to postpone stripping the Barn and started with the farmhouse instead. In the end, there was just one Horseshoe bat left in the barn roof, so the ecologist blocked his route into the roof in the middle of the night while the bat was out to encourage him to move on! The roof is basically a hotel for bats and we had to finish by 30th April because that’s when the bats want to come home.”
With the last bat vacating the premises, Russell began the mammoth task of stripping the barn roof of its 12,000 existing slates.
As the roof stripping began, the primary task was to try and save and reuse as many of the original Delabole ‘scantle’ (meaning ‘small’ in the Cornish language) slates as possible.
Historically, the very large, random slate, quarried at Delabole in Cornwall from where the slate gets its name, and called ‘rag’, would be reserved for roofing well-to-do dwellings, such as manor houses. The leftover slate would be used for lesser buildings, such as barns. This small, ‘scantle’ slate, irregular in size, shape and colour necessitates a traditional method of slate roof construction unique to Cornwall and Devon, termed ‘scantle peggies’.
It is a time- and labour-intensive method of roofing as the scantle slates need pre-sorting to be laid out in courses before roofing begins to ensure a flat, close course, an effective side and head lap, evenly diminishing gauges and so a watertight roof. As Russell remarks: “Using scantle slate used to be one of the cheapest ways of roofing, but much like thatch, because it’s so labour intensive, it’s nowadays one of the most expensive roofing systems”.
In Cornwall, often in coastal areas, the traditional scantle slate roof would be hung on oak pegs on a bed of lime mortar. This creates a firm roof bedded together that can be walked on and is one of the longest lasting roofs possible.
However, as Russell explained, around Dartmoor they bring their own local approach to scantle slating: “There are only a couple of other roofs I know of that have used the traditional local method – one not far from us which used the exact same style as us: laying the slate dry and torching the underside of it with lime putty and horse hair. But it’s not torching like you see in the North, just on the backs. This is torching that really builds out to halfway down the rafter height. It looks properly skimmed when it’s finished.”
But before the first slate could be laid, the existing A-frame timber roof trusses had to be removed and this was an immense job in its own right. Each frame, comprising three sections, weighed a hefty 300 kilos. For this, Russell devised a pulley system that he and his team used to carefully lower each frame from its location to the ground without disturbing or damaging the ancient walls.
Again, another challenge to this part of the job was a bowed wall which had been compensated for with an ugly step in the original roof. Instead, Russell agreed with the joiners to accommodate the irregular wall as the new frames were made up, creating a straight roof.
The old A-frames were replaced with new green oak frames which were pegged and bolted together and placed with their feet on the walls before being pulled up into position.
The frames were then strapped with split oak lathes from North Wales, which came in lengths of 4 foot to fit the 400 centre rafters. Russell set up a jig to pre-cut them to exactly 1200 mm, so that they didn’t have to do any cutting on the roof. They were also pre-drilled so the lathes didn’t split – a significant danger at just 30 mm wide and ranging from 5mm to 15mm depth. Next, each lathe was fixed by hand to the rafters using just a hammer and nails.
Then came the sorting and grading of the slate, and as Russell explains, this too proved to have its complications: “The unevenness of the oak lathes meant careful grading of the slate was even more important. Normally we would do thin, medium, thick, but we were going to extra thin, thin, to medium, thick, extra thick, extra extra thick!
“In the end pre-grading proved a bit pointless as the lathes’ thickness didn’t just vary but undulated and bulged. As you can imagine, when you split a piece of oak it splits along the grain so we tried to make it go into the roof but we ended up putting a thick one on then a thin one to fit flat with the rafter, which meant in practice we were doing sections in different grades throughout the whole roof.”
As Russell and his team stripped the old roof, they found that around a third was in fact Welsh slate, meaning that there were not enough reusable Delabole slates to complete one whole elevation. Feeling it would be a shame to stagger or lace old and new slates, resulting in one part of the roof lasting longer than another, the decision was taken to complete the whole roof in new Delabole.
Russell says, “Although the old Delabole looked lovely, if you can’t get a whole elevation done it’s not going to look as nice as it could. And actually, although old Delabole goes back on nicely, if you have the option to do the job with new Delabole you’re then looking at creating a 100-year roof. We had that chat with the owner and pointed out that, as we were using the traditional method, it made more sense to have a roof where the whole thing would last as long as it could.
“I’m glad that we did it that way because knocking oak pegs into old slate would have taken a lot longer because old Delabole is softer, although this is the first time in my 20-year career I’ve used new Delabole.”
Russell continues: “Despite using new slate, their irregularity meant some were so thick we didn’t use them at all. With a normal roof you might be able to use them at the eaves around the kick, but with this roof, a typical scantle roof, it starts with a very big first course of rag slates about 22 inches long.
“I thought this looked odd to begin with, but when you get used to it, it looks quite impressive and robust. Practically, because the rafters are open at the eaves, if you had a small first course you would look up and you would see the lathe, plusvit would be impractical to torch. But with a big first course you only see the exposed rafters and slate, so I think that’s why it was traditionally done like this.”
Fixing the 12,000 new slates was a major challenge demanding huge labour intensity and Russell gave one of his team the job of preparing and knocking the pegs into the slates, which took nine straight weeks.
“We trialled lots of different methods for doing this. We had a pillar drill set up and a wooden jig made up with holes at the perfect depth and radius for knocking pegs in. We eventually found that the best method was having someone inside grading and pegging constantly to keep feeding us as we slated,” says Russell.
“Each peg and slate then had to be matched to its perfect position on the varied thickness of the lathe, like a giant puzzle,” Russell adds. “And once the peg was hammered in to its furthest point before it would split the slate, we trimmed the top to sit flush with the face of the slate.”
The roof itself is a steep 450 pitch, but here Russell’s experience working in Scotland proved particularly beneficial as he had used ‘brackets’ or ‘irons’ as platforms on the sarking board roofs typical there, and so used these as a working platform on the Domesday Barn roof.
In total, Russell installed 50 courses across the barn’s elevations. These ranged from the largest slates at 11 inches long (about 28cm) to about 7 inches (18cm) at the apex of the roof. That meant over 200 close mitred cuts on the hips!
Capping the roof are new clay ridge tiles with a hole between every third one giving the bats access to the ridgeline.
A similar adaption was made to the gable end slates, as there was evidence that these were also inhabited by bats in the original roof. The hips were originally just slates with mortar fillets, but Russell suggested these should be close mitred as a more authentic solution for a traditional Devonshire roof.
To finish the roof with true southwest features meant the gable slates or rangers as call in the west country, with a clipped heel just for a little extra seasoning.
Russell concludes, “The Delabole slates look absolutely beautiful. Their patina is like sea shells – when the light hits them, they sort of shimmer like mother-of-pearl or a scallop shell.”
The scantle roof project has been something of a rite of passage for Russell, as these roofs are becoming increasingly rare and a roofer might be asked to construct this type of structure once in a thousand roofing jobs. He says, “Although this job was quite a challenge, it was satisfying to come up with solutions as each issue cropped up, combining old methods with new. It just feels like every heritage job I work on, I get happier and happier with the outcome. I’m very proud of the job and the roof looks just lovely, really architecturally stunning inside and out.”
This article was originally posted on Roofing Today
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