Webinar on 'Conservation of Traditional Thatch'

Conservation of Traditional Thatch 

Speakers: Alison Henry, Catherine Marlow and Keith Quantrill 

Alison [00:04] Lovely. Thank you, Alice. And good afternoon, everyone, and welcome to Technical Tuesday. I hope you're keeping well and warm. My name's Alison Henry, and I'm head of Building Conservation in the Technical Conservation team at Historic England. Before that, I was a conservation officer in Somerset, which has a strong tradition of thatching, so I've had a long-standing interest in the topic, and I now lead our research on thatch. And I'm very pleased to welcome my co-presenters, Catherine Marlow and Keith Quantrill, and I'll let them introduce themselves. Catherine. 

Catherine [00:50] Hello. My name's Catherine Marlow. I'm an inspector of historic buildings and areas for Historic England in the South West. I've been working in historic building conservation for over 20 years, primarily in the South West. 

Alison [01:03] Thanks, Catherine. And Keith. 

Keith [01:05] Sorry, I'm jumping in there before you. I'm Keith Quantrill, an independent thatching consultant and a thatcher by trade. I started thatching back in 1972 at the tender age of 15 and have been involved in the craft ever since. For the last 17 years, I've worked as a consultant, and amongst other things, and with my client base, I look after around 200 thatch buildings, some dating back to the 14th century. 

Alison [01:34] Thanks, Keith. Before we make a proper start, I'd just like to let you know a bit about the Technical Conservation team. Sorry, I've got something funny going on here. No, that's OK. So we're a group of technical specialists, including conservators, scientists and engineers, and we undertake research and provide advice and guidance on technical conservation issues. And Alice is going to paste those links into the chat for you to copy. The first one takes you to the main technical advice page on the website, where you can find all our technical advice. And then all our research reports and PDF guidance documents are also free to download from our website. 

And the second link takes you to that little catalogue on the right, where they're all listed, and I think Alice is going to put a poll on the screen. We also thought you might find it helpful if we emailed you each time we produce a new technical advice note or new web guidance. So if you would like to be added to the mailing list, just click 'Yes' and we'll send you the monthly updates. Be assured this is just technical conservation update. You won't get inundated with lots of extra emails. 

OK, so that seems to have stabilised, so thank you. That's great. So we're going to crack on now, and I'm going to hand you over to Catherine. 

Catherine [03:04] Thanks, Alison. The first thing we're going to do is have a look at some statistics. The percentage of all buildings in England that are listed is only 2%, and the percentage of listed buildings that are thatched varies. It's hard to be precise because some of the list entries cover more than one building, but we think that the county with the highest density is Devon, with about 23%. It has a total of about 4,700 listed thatched buildings, but it's less than 10% in most other counties. Only nine counties have more than 1,000 listed thatched buildings, and we think that the total in the country is just over 26,000. Of course, there are also thatched roofs that are unlisted, but we're focusing on the listed ones today, as those are the ones where we've got legislation to help conserve them, but bearing in mind that much of the discussion today will equally apply to unlisted buildings. 

So in summary, we're trying to conserve a relatively small number of traditional thatched roofs. Obviously, over time, this number decreases through accidental loss, such as fire or through the decisions that thatchers, owners or local planning authorities make. Since the 1800s, we think that about 90% of all thatched roofs in England have now gone, and that's why we're here today, to promote their conservation and importance as part of England's unique buildings tradition. 

So the seminar today is going to look at these topics shown on the slide. We know that many of you attending today may work for local planning authorities or maybe agents submitting applications to local authorities. So this webinar will hopefully give you some help in considering how you would approach that situation. We can't go into too much detail today. Thatch obviously is a really vast and complex topic, but we're trying to give you an overview of the issues, and we'll refer you to some more detailed sources of information as we go along through the session. 

I know the risk of fire in thatch is an important topic as well, but we're not going to cover that today as we did a previous webinar on that last year, and we are a bit restricted on time today. So if you'd like to view the recording of that, it is available on the Technical Tuesday web page. So let's start. What is traditional thatch, and how can you find out more about it? Over to Alison. 

Alison [05:28] OK. Thanks, Catherine. Well, to answer that question, we need to think about what evidence we've got for how thatching was carried out in the past. There are various documentary sources, such as paintings and old photographs, that give us a snapshot of how thatched buildings used to look. And sometimes, they'll also tell us something about the materials that we used. For example, the top right photo there shows water reed being harvested for thatching on the Norfolk Broads in 1887, and you can find photos like this in online archives such as the Historic England archive and various commercial ones such as the Francis Frith collection and, of course, in local record offices. 

Keith [06:10] If I could jump in there as well, I also find vintage postcards are a really good source of photographs of old thatched buildings. You can often find these on eBay and either purchase them or take a screenshot, but do be mindful of any possible copyright. 

Alison [06:28] Yeah, that's a good tip, Keith. Thanks. And as well as images, there are also various contemporary written sources that can provide information on thatch and thatching – so things like old travel guides and estate or farm surveys. Also, there's a series of reports on the agriculture in individual counties that was commissioned by the board of agriculture between about 1794 and 1815, and these give an insight into what crops were being grown, how they were processed and what they were used for. So these are really useful. 

And then there's the evidence from the thatched buildings themselves, or the archaeological evidence. So although the outer-most coat on a thatched roof is always going to be comparatively recent, on straw thatch, where the tradition is to fix a new layer of thatch over the remains of previous coats. The topcoat might overlie successive layers of much older thatch, and there might be some really old material in the lowest layers. And in a few roofs, the original medieval base coats might even survive. 

Now, these date from a time before houses had chimneys, when you would have an open fire in the middle of the room, and the smoke just had to find its way out as best it could, via vents in the roof or the walls, leaving a black soot-encrusted layer on the underside of the timbers and thatch. In some cases, these historic layers have been carefully excavated to show what materials and fixings were used at different times, so we can learn a lot about ancient thatch this way. And, Keith, I think this is something you have come across. 

Keith [08:08] Yes, I certainly have. You find most of the recorded surviving smoke-blacken thatches seem to be in the South West, but I have also come across a few roofs elsewhere, although these are pretty rare, so if anyone sees one, these are very important, and ideally the location should be recorded. In addition to this multi-coat roof, the base coats that are three or four hundred years older are just as significant as medieval smoke-blackened thatch. 

Alison [08:39] Yeah, that's true. Thanks. So I'm afraid we don't have time to go into this in more detail at the moment, because that would be a webinar in itself, but if you want to read more about the history of traditional thatch, then there are three Historic England research publications that provide a lot more detail, and Alice is copying those details into the chat for you so you can copy and paste them. And there's also an excellent publication by Devon County Council, and it's just a pity that there isn't such a well-researched publication in every thatch county. 

But what the research shows is that many types of plants with long stems have been used for thatch in the past. Many of these were wild plants, such as heather, broom, reeds and rushes, and they made use of whatever grew locally. But by medieval times, cultivated cereal straw had become the predominant thatching material in lowland areas of England. And I'm going to hand over to Keith now to tell us a bit more about traditional thatching materials. Keith. 

Keith [09:43] Thank you. As Alison said, by medieval times, many thatching materials were cereal straw as was-- This was mainly winter wheat, and to a lesser degree rye was also used, but this declined dramatically through the medieval period, although you do often find mixed wheat and rye in old basecoats, even up to the 19th century. Most thatching straw today is produced from older varieties of wheat that have far longer stems than modern straws. 

In the 1980s, some thatchers started to use a hybrid of durum wheat and rye called triticale, as this was a sufficient hide for thatching purposes. Nowadays, this material is sometimes just referred to as wheat straw but, in fact, is a standalone material, much like oats, barley and rye. And it's actually classified as an individual variety on the Defra Classification. 

Straw was originally harvested by hand by using a scythe, but with the dawn of the industrial revolution, this process soon became mechanised, and straw is now harvested using a reaper-binder, as you'll see in the image. The straw is then stooked in rows to further ripen in the field. 

In most areas of England, straw was generally threshed on the ground, using a wooden-jointed stick woof flail. This loosens the grain from the ear. The process also slightly crushes the stems. Removing the flailed straw with a pitchfork to reveal the grain also jumbled the straw further. Since the 19th century, the threshing process became more mechanised and is now done using a durum thresher. Sorry. This combs and ties the material into loose bundles. These are sometimes called boultings, and this makes them easier to handle and stack and move for transportation. 

To prepare the jumbled straw for thatching, the stems have to be realigned, and this is done by cutting open the individual bundles, or trusses, and shaking the straw into what is known as a bed. The straw is whetted, and handfuls are then drawn from the bottom of the heap and placed on the floor to form flattish bundles of around 60 cm wide, or 2 feet in old money, and these are known yelms. Yelm [indistinct] parallel with the majority of the butts at one end. Some of the ears of heads will be found on either end of the yelm, so when the straw is applied to the roof, a mixture of ears and butts are visible on the surface, as shown in the image on the right. The material, and critically, the process are what defines long straw. 

Alison [12:56] Well, that's long straw, but here in Devon, where I'm based, we don't see long straw on roofs at all. 

Keith [13:03] No, that's right. Really, the South West is sort of a bit of a special case to some degree. Because of the climate and the topography, cereal crops could be grown, so processing was done more carefully in order to reduce the waste as much as possible. So from at least the 18th century, threshing was done by lashing the ears over a wooden trestle called a brushing horse, or even a barrel or a door turned on its side, and in some cases even cutting off the ears. Either way, the threshing process meant that the stems of straw remained uncrushed with all the butts at one end. The straw was then combed used a spike set in the end of the brushing horse or some other spiked tool to remove the weeds and leaf. 

Combing was mechanised in the 19th century by fitting a combing device to the threshing machine. Once the grain is dislodged, the aligned stems with all the butts at one end are tied into bundles, or nitches is the local word them. The process of extracting the grain and combing out the straw leaves us with a material known as combed wheat reed. 

Alison [14:13] OK, that's great, Keith. So that's covered straw thatch, but what about water reed? 

Keith [14:19] Interestingly, well, following the decline of peat extraction, well-managed reed beds emerged in areas such as north Cambridgeshire up into the Lincolnshire Fens and, of course, the Norfolk Broads. Water reed was also found in limited pockets in other areas but was generally cut from estuaries, such as in Hampshire, Dorset and Devon. 

Alison [14:41] Yeah, and of course, in lots of places, you get water reed growing along ditches and streams, and it might be tempting to think that it would've been used for thatching in those places too, but I remember that the research published in our research transactions that I mentioned earlier calculated that it would take almost nine miles of drainage ditch to produce enough water reed to thatch one small cottage, so that really doesn't sound like a very viable supply for most people. 

Keith [15:09] No, exactly, and the other thing to bear in mind is that water reed was also in demand for other building uses, particularly as a support for lime and earth plaster, so it would be very unlikely that there would be sufficient residual material available in any quantity anyway that was needed to thatch buildings outside of the areas I've just mentioned. And as a side, not all water reed is suitable for thatching. However, in the areas where water reed was abundant and well managed, it's been long established as a thatching material. Water reed was also popularised by the arts and crafts movement in the 19th and 20th century, and this saw water reed being exported to other areas that would not previously have seen this particular material, and you'll see it in the bottom right-hand image on an arts and craft church in Herefordshire. 

Alison [16:15] So that describes the materials, Keith, but how were these materials then fixed to the roof? 

Keith [16:22] Well, the very first coat, which we often refer to as the basecoat, so the first coat of thatch was traditionally held in place with wooden rods of hazel willow. The rods were often referred to as sways, which you'll hear lots of colloquial terms for different parts of thatching, and these were tied to the raft of the underlying roof structure. On early roofs, the tying material consisted of brambles, thin twisted rods of hazel or willow, much as you'd see in basket making, as well as straw and rush ropes and also honeysuckle, or old man's beard as it's sometimes known. 

Later on, hemp twine became commonplace as a tying material, with a number of patents being lodged around the late 1970s-- sorry, the late 1700s. With straw thatch, every subsequent layer then took place on top of the existing old coats, with the new weathering coat being held in place with wooden sways, or more commonly, twisted straw bonds along each course. These are then fixed into the underlying old thatch using pointed wooden pegs of split hazel or willow. The pegs are widely referred to as spars, hence the term spar coating, although spars do have a number of other names around the country. 

Once in place, the surface of the long-straw roof is-- the thatch is finished with a side rake to take out any twisted straw leaf, general rubbish, and then the roof is then finally clipped over with dagging shears, or sheep shears as you probably know them as, to give it a clean neat finish, allowing the water to run off evenly over the entire roof. And then finally, eaves and gables are pegged and cut square. 

Fixing a combed wheat reed is very similar to, if not identical, to long straw. However, combed wheat reed does differ greatly from long straw in one key area, and that is the fact that [indistinct] is all butts at one end and can be dressed into place with a tool known as a leggett or a drift. Some people with the eaves and the gables traditionally cut with a sharp undercut angle. Shearing hooks were also used at one time, and this was to give the surface of the roof and nice, clean, sharp finish to it. 

With water reed, this is traditionally fixed directly to the roof frame, and being too hard to shear or cut is simply dressed into place with a leggett to give a final finished profile. The early fixings for water reed were often of rush ropes, and this material was used because it grew in the same environment as the reeds, but later on, tarred twine then followed after the late 1700s and then into the early 1800s, and then still spikes were used and today many people use screw and wire fixings. A point to note is that all thatched roofs in one way or another are fixed directly to the roof frame, either round the rafters or directly into the rafters themselves, very much unlike other historic roofing materials that are hung onto the roof. 

Alison [19:52] OK, thanks, Keith. Well, that's give us a really good overview of the main thatching materials used in the past. But what about the style and detailing of traditional thatch. There seem to be some very strong regional variations. 

Keith [20:06] Yes, absolutely. For example, one of the most distinctive details of long-straw thatch are the surface fixings at the eaves and the gables, and you'll see those in the left-hand image in front of you. Split rods, or liggers as they are sometimes called, are sparred into place, filling the straw down firmly so it's enabled to be cut. Without the tightly packed eaves and gables, these areas of the roof would be vulnerable to wind and vermin damage, so it's a classic case of form following function. In parts of East Anglia, you also see what they called rolled gables, and the image at the centre of the screen gives you an example of a rolled gable. 

In traditional combed wheat reed areas verges around it and then undercut to give this distinctive appearance and do not normally have surface [indistinct]. Water reed roofs are distinctive in their own right because they are normal of a single coat, have a flatter appearance and the eaves and gables are always dressed square. 

Right, we've got another slide now. There's also regional variations in ridging detail. On straw thatch, the ridge would be of the same material as the coat work. Water reed being stiffer, it's too ridged to use as a ridging material, so you'll find straw and sedge use, sedge in particular because it grew in the same environment as the water reed. There are two main types of ridge. There's a butt-up ridge or a wrap-over ridge. 

The rope ridge of the South West has all but disappeared even in my lifetime, so the flush butt-up ridge of the South West that we're seeing now also has a very distinctive pinnacle at one end, but again this is rapidly disappearing, being replaced by block-cut wrap-over ridges, more familiar to the eastern and home counties. And even in these areas, what was once the traditional flush ridge, a wrap-over flush ridge, has now given way to the decorative block-cut ridge that we see on the majority of buildings now. 

Alison [22:37] So, Keith, those ornate block ridges obviously look very different to the clean lines of the traditional simple flush ridges. Do they last any longer? 

Keith [22:48] Well, having been in the trade an awful long time, it's been my experience that providing they are well executed the life expectancy is very similar between both types of ridge. As we saw in the previous slide of the Herefordshire church, the arts and crafts movement had a huge influence on the detailing of water reed roofs. It would also be true to say that the loss of simple traditional flush ridges can at least in part be attributed to this movement, with the emphasis being on appearance over function. 

Now, thatch can often wear unevenly, for example, beneath chimneys and in valleys, so traditionally it was repaired by patching when and where needed. In fact, in my early days as a thatcher, much of our time was taken up by ridging and repairing coat work. After all, the purpose of the roof was to keep the building dry, not for its appearance, and therefore, patching repairing made economical and common sense, so why would do and spend more money than you needed to? 

It's also common for one side of the roof, often the south elevation, to wear more rapidly than the other, so when we did undertake full coat work replacement, it was often only half the roof, and this was completed as part of the replacing the ridge, the other half of the roof being rethatched when the ridge needed replacing again in about 15 years’ time. You can start to see the economic benefit of repairing and maintaining a roof in this manner, and only once the thatch had weathered back close to or beyond the fixings, in some cases, over the majority of the roof, would we ever consider replacing the new coat work. 

Also, historically, eaves and gables were not stripped out completely. They weren't stripped out each time we did a rethatch, so it would always be possible to see the different layers of old thatch and gauge its sort of history in these particular areas. But for some reason, there's seems to be a change for preference of wholesale stripping and renewing of eaves and gables, and this is often based solely on appearances, or for appearance's sake. 

The method of patching and periodic renewal of the weathering coats stood the test of time for many centuries, and this continuity of craft practice contributes greatly to the historic interest of traditional thatch roofs. Water reed roofs were repaired by patching, much in the same way as straw roofs and combed wheat reed roofs, but the evidence suggests that when the weathering coat really did reach the end of its life, it was repaired by stripping it away completely and thatching back to the rafters, and tying on of new coats was therefore not really was-- tying on of the single coat was generally the tradition, and you didn't get this build-up of historic layers. 

However, base coats and water reed can still sometimes be found under spar coats of long straw, and often the water reed is a very early example of water reed thatching and therefore is, in itself, of historic interest. Overall, the methods of thatching remained pretty much the same from the medieval times up until the 20th century, the techniques handed down from master to apprentice. And the methods often reflect the local available material, which historically is far more diverse than it is today, but I think that's another subject to refer to a different webinar. 

With the exception of the arts and craft movement after the Second World War, there was much more importance importing materials and styles from one region to another. For example, combed wheat reed being introduced into long straw areas and water reed being used far beyond its traditional boundaries.  

Alison [27:09] OK, Keith. That's fantastic, really interesting resumé of the history of traditional materials, but I think that change in context of thatch through the 20th century is really important because it does create some issues for the conservation of traditional thatch, and of course, we've seen the same thing in other aspects of the building trades, with new materials and methods being introduced in the last century. And this is one of the main challenges, I think, of building conservation. 

Anyway, now we know what traditional thatch is, I'm going to hand over to Catherine to explain why it's important and why we should care about it. 

Catherine [27:53] Thanks, Alison. Well, most buildings are valued because they have a use and a function as homes or offices, factories, places of worship and so on, but historic buildings have other values in addition to that. This quote from Historic England's conservation principles emphasises that heritage assets have more value than just their function. And also the historic environment planning practice guidance, or PPG, explains that part of the public value of heritage assets is the contribution that they can make to understanding and interpreting our past. 

As many of you will be aware, the values of heritage assets as defined in the national planning policy framework, or NPPF, and the historic environment PPG, stemmed from their archaeological, architectural, artistic and historic interest. So let's have a look at these in slightly more detail in relation to thatch. 

So what is architectural value? It could be the vernacular architecture that has developed over many hundreds of years that is based on the local materials available, the local geology, the craft and agricultural traditions of an area and the social positions of the people who live there, and that's to say fortuitous design. And with thatch, it's quite obvious that it contributes so much to the form and character of the building. So on the left here, we can see a stone cob and thatch building, which represents that kind of fortuitous architectural value really well. 

And on the right-hand side, you can see a very clearly designed building, a church, and it's making a statement about its status and the style of the designer or the person who's commissioned it and is using thatch in a decorative way. This isn't the easiest material to use in this situation. It is a conscious choice, and this is particularly typical again of the arts and crafts movement. 

Architectural values can also be demonstrated through regional variation, with the appearance, form and layout of buildings contributing to local distinctiveness, and this in turn creating a sense of place. For example, you can see the difference between these two buildings. The one on the left is from the South West, and the one on the right is from the South East. They are very different, but both are characteristic of the thatching traditions of their area, and they also contribute of their character and appearance of their villages in which they lie and the wider landscape, again creating that level of local distinctiveness. 

Moving on to archaeological values. In terms of archaeological value, multi-layered thatch has huge potential. The layers of thatch, as Alison has said previously, can tell us about agriculture, past thatching methods and can even give information on pollen and the insects that were prevalent at different times in the past. So the smoke-blackened thatch in the picture on the left will data perhaps to medieval times, and the multiple layers of thatch on the right have built up over many generations of thatching. If you think that between each thatching there may have been a gap of between 20 to 30 years, this is the thatched roof equivalent of archaeological stratigraphy. 

Thatch also has historic value because of the way that it illustrates aspects of past lives. It provides evidence of craftmanship and thatching techniques and of how buildings were maintained, and the layers of historic thatched roof can even chart the changes in diet, from rye to wheat bread, as the staple food of peasants in the middle ages. 

Alison [31:36] OK. Thanks, Catherine. So those are the heritage values referred to in the NPPF, but there are other criteria that we can use to assess the importance of historic thatch. One of these is rarity. On the whole, the rarer something is, the more we tend to value it, and thatch is no exception. And as Catherine mentioned earlier, traditional thatch has been under threat for all sorts of reasons, and the number of thatched roofs have declined. So the ones remaining are becoming rarer. 

A few years ago, we helped to fund a survey of thatched buildings in Buckinghamshire. There were 904 listed thatched buildings in the county at that time, and virtually all of them would originally have been thatched in long straw, but by the time of our survey, only 31, or less than 3.5% still had an authentic long straw roof. The rest had changed to other types of thatch. 

And then shortly after that survey, we were involved in an appeal relating to a listed long straw thatch building in Buckinghamshire. The proposal was to use a sort of hybrid type of thatching material consisting of combed wheat reed jumbled up so that some ears showed up on the surface of the roof to imitate long straw. But in the inspector’s decision letter, she referred to the Buckinghamshire survey and the fact that, as well as being rare in the county, this house was the only authentic listed long straw building in the village and concluded that this made its genuine long straw roof all the more important to preserve. 

And we've seen similar conclusions in other cases. For example, in another appeal relating to a cottage in the New Forest, the inspector said that the fact that so many combed wheat reed roofs have been replaced by water reed only goes to make those roofs remaining unaltered all the more rare. And Alice is going to copy those – oh, she's already done it; thank you – those appeal decisions, or appeal references, so if you want to read those decisions in full, you can. 

But there's another issue to consider as well, and that's the issue of authenticity. So authenticity is about things being genuine or the real thing, rather than imitation or fake, and it underpins the heritage values that we mentioned earlier. In the appeal relating to a cottage relating to a cottage in the New Forest that I mentioned a moment ago, the inspector said that one of the important purposes of listed building protection is to help distinguish the genuine article from imitation. 

So here we have a thatched medieval longhouse on Dartmoor, or rather we have something that looks like a thatched medieval longhouse on Dartmoor, but it was actually built less than 20 years ago. The walls are rendered concrete blocks, and the roof is water reed thatched, which is not the traditional thatching material for Dartmoor. It's got underfloor heating and double glazing, and as the owner commented in a newspaper article, this means no drafts, no damp and no grade II listing.  

So this building has values at many levels. It looks lovely, it's a cosy house – and no doubt a much-loved home – and, of course, it has high financial value, but it does not have heritage values. It's not historic building and it's not traditional thatch. So heritage values run much deeper than simply appearance, and of course, if they didn't, then based on its appearance, we'd have to list this house because it looks like a medieval longhouse. And this is really important to recognise when we come to consider how best to conserve heritage assets, because it is about much more than just how things look. 

And I think we really value authenticity in art and antiques, and we tend to use somewhat pejorative terms for things that are not genuine. So we call them fake or repo or pastiche or even forgery. And there have been many attempts to forge copies of the Mona Lisa. Some of these are so skilfully done that a layman probably couldn't tell the difference, and only an expert would be able to identify the one true version, but that doesn't mean that those fakes are as precious as the original, and it doesn't make the original and less valuable. 

So the same could be said for, say, a water reed roof in place of a traditional combed wheat reed roof. It may be hard to visually distinguish between them, but the authentic material has very different values. And I think that this concept of authenticity lies at the heart of what is important about many historic buildings, and it's one of the things that we seek to maintain through conservation, and conservation is not about protecting pastiches or creating fakes. 

So hopefully, that explains the heritage values of traditional thatch, and now I'm going to hand back to Catherine to explain how we can sustain these values when repairing thatched buildings. 

Catherine [36:49] Thanks, Alison. Just going back to basics for a moment, I wanted to remind everyone of the documents and guidance that we have to refer to when we consider this issue. We have the NPPF, as mentioned earlier, and the National Environment Planning Policy Guidance-- sorry, the Historic Environment Planning Policy Guidance, which is not perhaps used as much as it could be, so I would refer you to it. Historic England has also published conservation principles, policies and guidance, as well as advice notes on making changes to heritage assets, and Alice is copying details of those into the chat for you. So there's a lot to help support you in how to sustain significance and what that means. 

Here's a quote from the NPPF, that 'Conservation is a process of managing change in ways that will best sustain significance'. And that second part of the statement is particularly important in decision-making, as it emphasises that yes, buildings evolve and change, but this needs to be done in ways that conserve the special interest of the building. 

The starting point for traditional repairs in building conservation, on the whole, is like-for-like repair, and this is a long-standing principle that I'm sure many of you are perfectly au fait with. So this is using the same materials and methods as in the past, and this is something that we would certainly apply to, for example, window repair or plaster replacement, and thatch should be treated in the same way.  

And this, of course, helps to maintain that authenticity of the building and the continuation, also, of those craft practices. 

Alison [38:24] Yeah, and I'd just like to expand on that idea of authenticity in repair. So we've got some good appeal decisions to support this. At Park Cottage in Wiltshire, the inspector determined that the use of water reed to spar coat over the existing combed wheat reed roof would not make an appropriate contribution to the evolution of this vernacular building but would be significantly detrimental to its authenticity. And then, similarly, at Mulberry Cottage in Buckinghamshire, another appeal that we were involved with, the inspector considered that the type of thatch proposed there was not the genuine article and that therefore, the authenticity of the building, and thus its significance, would be unacceptably eroded. 

And then finally, at Diamonds on Dartmoor in Devon, the inspector determined that the use of water reed instead of combed wheat reed would be no more than a superficial replica of the authentic product. So I think these appeals really help to support the case that we made earlier that conservation is about much more than just appearance. So now we're going to move on and look at the process for making changes to listed thatch roofs, and I'll hand you back to Catherine. 

Catherine [39:41] Thanks. OK, for those of you who deal with listed building consent applications, or indeed, submit them to local planning authorities, you will know that the NPPF requires that the significance of the building is described, and then an assessment is made by the planning authority on how that significance might be affected by the works. In order to do that Assessment of Significance for an application about thatch, you need to know about the thatching tradition of the area and whether this building is a typical example. 

It would also be useful to understand how many of the listed buildings in the region are thatched, and you can find that information using the search function in the National Heritage List for England, and this will give you an idea of the rarity of the thatch. You'll need to know what is currently on the roof and when the roof was last rethatched. Was it stripped right back to the rafters, or was a standard spar coat put across the whole roof? 

Keith [40:41] I just want to jump in there as well if I can. You can't always rely on what the owner, or sometimes even the thatcher, will tell you, as they don't always know. And you really need to inspect inside the roof space to look at the fixings, which will give you an indication of the date of the basecoat and condition, and you may need to take samples of the weathering coat to find out whether it is actually wheat reed or triticale. 

Catherine [41:09] Thanks, Keith. Those are all good points. Going on to assessment of the proposal, the local authority has to assess the impact of the proposal on the significance of the building, and just like for any other listed building consent application, you do need a specification. It is very hard to work out if there's going to be harm caused if you don't know what's actually going to happen to the building. So what level of thatch removal will take place? What is the current condition of the roof? Will the eaves be stripped out? What materials are proposed for rethatching? What thickness will the coat be? What will the fixings be? And what type of ridge is proposed? What's going to happen at the ridges? Et cetera. 

This is not an unreasonable amount of information to request. It is comparable to what might be asked for, for example, replacement windows or any other works. It is, however, quite common to see applications for thatched roofs saying very basic phrases like, 'Rethatched roof using spar coat in reed'. Is that really enough information? 

Keith [42:14] Yeah, I'd kind of agree with Catherine. I see this all the time with clients that receive a couple of lines in a quotation with a £40,000–£50,000 price tag at the bottom of the page. One wouldn't accept that for any other type of building work, and don't forget you also need to understand the potential impact of rethatching on other parts of the building such as the roof structure and the ceilings, and this can't be covered in a two-line description in a quote. 

An example – if you take a look at this slide, I'm sure the owners of this grade II* listed building or the conservation officer might have queried what was proposed if it had been written down in a specification. Here we have bamboo garden canes for the [layers?], and we have sawn [lars] for the cross patterns in place of what should be hazel rods and split hazel cross stitch, so you really can't take anything for granted, so don't be afraid to ask questions if you're not sure of exactly what's being proposed. 

Alison [43:23] Thanks, Keith. I've seen a number of applications where the applicant says that the existing thatch has failed and they want to replace with a different type of thatch that is perceived as more durable, but again, I think you need to scratch the surface here and ask if a few questions. Firstly, has the roof actually failed, and if so, what are the reasons for this? It may be because the building is in a difficult microclimate, and that thatch on this roof never lasts very long, or it might be because of poor workmanship. It won't always be directly because of the material used. 

And it's really important to understand exactly what material has been used, especially if it's claimed to be combed wheat reed, because it might actually be triticale, and as Keith mentioned above, many thatchers use the term combed wheat reed to refer to triticale too, but there could well be differences in their potential performance. 

Keith [44:18] Yes, I would suggest that when a building has been thatched in the same material for the last, say, 300 years, it raises questions if the roof now suddenly starts to fail in a short period of time. Really, the whole question on thatch durability is very poorly understood. A lot of people refer-- with, sort of, time frames, a lot of people refer to what's quoted in The Thatcher's Craft, which was actually published in 1960, but at this time, just after the war when the quality of thatching straw was not at its best, you may now-- it didn't really last-- it altered really, sort of, what durability you do actually get. For example, long straw, we have good examples of long straw that last far longer than the averages set out in The Thatcher's Craft. Also, the figures quoted for water reed really only apply to East Anglia, because at that time, that was the only place that water reed really was widely used. But if you use it in – the water reed this is – if you use it in a warmer, wetter climate, it won't necessarily last as long as it would do, say, in East Anglia on dryer area. 

Many factors affect thatch durability as well. As Alison mentioned, there is a microclimate around the buildings, in each individual building, and also things like trees, which will grow large over decades. They'll also impact on the microclimate around the building, so it isn't always just about material. And it's also true to say that we've seen cases of [indistinct] [triticale?], all types of thatch, including water reed, and cases where all types of thatch also have a very long life expectancy. And as a footnote, I'd just add that The Thatcher's Craft is still a good reference book for regional style material and application, although it doesn't cover spar-coating. 

Alison [46:27] OK. Thanks, Keith. And of course, another reason for wanting to change the type of thatch is during periods of material shortage, and at the moment we've got a shortage of combed wheat reed and long straw in some areas because of a poor harvest last year. So, Keith, what's your advice on this? 

Keith [46:46] Well, firstly, I'd just like to say shortages are nothing new. There have always been good years and bad years and sometimes runs of bad years, as a matter of fact. And thatchers have always adapted and adopted-- For example, if the thatch is only found in a few small areas, it's highly likely it can be patch-repaired, as was common practice in the past. Or perhaps only one side needs renewing, and the other side could be done at a later date, possibly when the ridge needs renewing again. 

Another option to consider is rick-coating. This is sometimes called step-coating or various other names around the country, and this can be quite cost-effective as well. If the roof is in a pretty bad state of repair all over, it might then make more sense to protect it with a tar polling until supplies of the correct material is available. If fact, I now have a roof in Cambridgeshire that has been sheeted for the last ten years. A lot of people do, however, worry that sheeting over a roof will cause further deterioration to the roof, but unless there's saturated thatch in contact with the timbers or the ceiling, this is unlikely to be the case. However, were this to be the case, the wet material could be removed and if needs be the area filled up with any dry material fixed temporarily in place until such time as the roof can be prepared properly. 

Catherine [48:25] Thanks, Keith. That gives a really good background to the values of thatched roofs and all the kinds of questions you might ask about an application. Presuming that you have all the information you need to assess the significance of the building and to understand what it proposed, you'll then need to assess if harm was caused. We think that given the multiple appeal decisions that we've seen over the past few years, we can be confident that substantial harm, as described in the NPPF, is likely to be this: stripping the roof entirely and removing all historic thatch. Obviously, each case needs to be considered on its own merits, but that seems to be what inspectors are concluding. 

I did just want to remind you of this paragraph relating to substantial harm in the NPPF. It says that local planning authorities should refuse consent unless it can be demonstrated that there's substantial harm or a loss is necessary to achieve substantial public benefits that outweigh that harm or loss or that all of a number of other criteria relating to the viable use of the building apply. And I'd refer you to the NPPF 195 for that list of criteria, and the critical word there is 'all'. So you can see that in a situation where you think that substantial is going to take place, and that is a very high bar, then there are strict tests that must be met to justify that harm being caused. 

Much more common might be less-than-substantial harm. Again, from the appeals we have seen over recent years and which Alison has already mentioned, we think that recoating in a different material would cause harm to the significance of the building but that the harm would be less than substantial. So the NPPF says, 'Where harm is caused, it should be weighed against any public benefits'. 

So let's have a think about what public benefits might be put forward as a justification for harmful work. All of these suggestions have been put forward in various appeals as public benefits, but in each instance, the inspectors involved did not consider that a change of thatching material was required to achieve these benefits. And this was usually because the same result could be achieved by using the traditional thatching material. And in the instance of lower cost, we have several appeal decisions where it was determined that this is a private to the owner and is not a public benefit. 

So what is a public benefit? Well, it's conserving the heritage values of the building, as we discussed earlier. And that brings us back to the statement in the Planning Practice Guidance that I mentioned earlier that part of the public value of heritage assets is the contribution that they can make to understanding and interpreting our past. 

Alison [51:19] OK. Thanks, Catherine. And just to conclude this discussion of the listed building consent process, I think it's worth noting paragraph 193 of the NPPF, which says that 'When considering the impact of a proposed development on the significance of a designated heritage asset, great weight should be given to the asset's conservation'. And that's irrespective of whether any potential or harm is substantial, less than substantial or even total loss. 

So I think we have a really strong mandate for the conservation of traditional thatch, remembering that inherent in the definition of conservation is the need to sustain significance and that significance, as I hope we've shown, is about more than simply appearance. The archaeological and historic values are just as important. But unfortunately, I don't think legislation is enough to secure for traditional thatch. We need an assured supply of the right materials as well as craftsmen skilled in applying them in the traditional ways.  

And although at the moment, there is a short-term shortage of thatching straw, I think the problems with supply run much deeper than that. Straw growers are battling with anti-machinery, very uncertain season or labour supplies and the vagaries of the English weather, and of course, they hardly feel encouraged in their efforts when they hear about straw roofs being allowed to change to water reed. And it's worth remembering that every roof that changes from long straw or combed wheat reed is a nail in the coffin of traditional straw thatching, because once changed, I think it's highly unlikely that those roofs will ever revert back to the authentic material, so demand for thatching straw drops even further. 

And water reed has its own issues around supply, which we haven't really got time to go into today, and we've not said an awful lot about traditional fixings, but there are challenges there, too. So I think we're in danger of reaching a tipping point beyond which the production of home-grown thatching materials will become pretty much unviable, and I think it will be really ironic if the most iconic of English craft traditions ends up being completely dependent on imported materials. And we are seeing that with some other traditional building materials, such as slate and stone slate being imported from India and Canada and hydraulic lime from France, Germany and Portugal. 

So to help with the challenges of supply, Historic England has been working with the National Thatching Straw Growers Association on some straw growing trials in East Anglia to look at different traditional thatching straw wheats and understand more about their cultivation. And we're now monitoring trial roofs, thatched with the straw produced, and as part of this research, we've funded what I suspect is the world's only thatched shipping container, but this will allow us to monitor the thatch for 25 years and learn more about thatch durability. And then starting later this year, we're going to be doing some more research into the challenges of supply, and we'll be working with the thatching industry to lobby for investment, research and incentives for traditional thatch material supply. 

So I hope that's given you a helpful overview of traditional thatch and some of the challenges it faces as well as some of the ways that we can conserve it, and I think Alice is going to put a link up there, which is a link to our thatch advice webpage, where you can access various other resources, including a report on the straw growing trials. I don't know if you can see, but on mine, Alice, it's not quite scroll down far enough, but perhaps that will become apparent. That's it. OK, thank you. 

And we'll also be updating our web guidance on the straw shortage in due course, so now I think we've got just probably a few minutes for some questions, so I'm going to hand you back to Alice to compare the questions. Thanks. 

Alice [55:38] Hi there. Thank you, Alison. Thank you, Catherine and Keith. Really interesting talk. So as Alison said, we have a few minutes for some of the questions that I've gathered from the chat box, so thank you everybody who's put in a question. So we're going to start with John's question: 'When reverting from back to wheat from 21st-century water reed, is there any problem in sparring wheat to a water reed basecoat?' 

Alison [56:03] I think that's probably a question for Keith. Are you able to answer that? Throw you in there. 

Keith [56:08] Yeah, let's not pick that one up. No, not at all. Absolutely no problem whatsoever. In fact, water reed makes a very good base for spar-coating onto, and in fact, if you have a very fragile multi-layered roof, a very thin coat of water reed can give you a firm fixing to avoid having to strip too much of the old straw base coat out. So as a medium for thatching into, water reed is incredibly good. 

Alison [56:39] Thank you. 

Alice [56:45] Great. Another question from Kailey: 'We seem to be going through a phase in the Broads of thatch (water reed) that hasn't lasted as long as owners may have hoped. I have heard that there was a period where the reed may not have been of a high quality or been imported from elsewhere, which may have affected the quality. Is this an issue you have come across? What would you recommend to owners who are concerned that a rethatch won't last as long as they would like and therefore, unfortunately, looking at alternative options?' 

Alison [57:17] Keith, I think that's another one for you. You're probably more familiar with water reed than Catherine and I. 

Keith [57:22] Yeah, it's quite an interesting question, really. I think there may be lots of elements going on with it within the problem that the questionner asked. High demand for water reed has possibly pushed people into cutting water reed beds, which historically weren't cut for thatching, so that could be one issue. I think it's very difficult to really be able to put any real concrete answer to the question of durability. 

I'm not sure what the questionner's asking about an alternative material, because other than water reed, unless you go back to straw, I think that's a-- it'd be a big ask to change a roof from water reed to slates or tiles because they really would not fit with a wall that's been discussed today. Sorry, I don't know whether that really answers the question fully. 

Alison [58:30] It seemed like a good answer to me. 

Alice [58:30] Thanks, Keith. Yes, me too. Just looking at the time. I think we have room for two short ones, so I'll start with a quick one. Keith, I think this is for you: 'You mentioned a book to show some regional differences. I was wondering if you could tell us what that was.' 

Keith [58:48] That would be The Thatcher's Craft, which is a very well-established publication and well respected within the industry. The only question mark-- The only reason I raised it in the actual talk was the life expectancies may not really be up to date. The actual styles and methods and processes are very well demonstrated in that publication, so always worth a look at that. 

Alice [59:16] Great, thank you for giving us a bit [indistinct] over that. And then I have time for one last question before we wrap up, and it is from Jessica: 'What about the argument that the appropriate materials can't be sourced?' 

Alison [59:32] I think I can probably sort of answer that. [crosstalk] I was going to say I think it would depend on what are the appropriate materials and is the question, can it just not be sourced just now? In which case you do something like Keith explained earlier, to tide you over, either patching or some other form of sort of protection. I think Jessica, knowing where you're speaking from up in Scotland, I think the issues might be a little bit different in that you probably are trying to deal with buildings where some of the more obscure thatching materials are really not being produced, so maybe things like marrow and grass and heather are probably, I think-- the only thing there is to try and sort of open a debate with producers and land owners and so on and try and persuade them of the merits of using these traditional really sustainable materials, and it would be great to see some of them making a comeback. 

Alice [01:00:28] Right, thank you, Alison, Catherine and Keith. Thank you again and thank you to our audience. Unfortunately--