Conservation of Traditional Thatch

Traditional thatching materials in England

Although many plants have been used for thatching in England, research carried out by Historic England, (Letts, J, 1999 and Moir, J, 1999) shows that from medieval times cultivated cereal straw (particularly wheat and to a lesser degree rye) was the predominant thatching material in lowland areas. Across most of lowland England, harvested straw was flailed to remove the grain, which slightly crushed parts of the stems; this material is now known as long straw and was the predominant thatching material for centuries. In parts of the South West, the grain was removed more carefully without crushing the stem, and the straw was combed to remove the leaf and produce what we now call combed wheat reed.

In the Norfolk Broads (following the end of peat extraction for fuel) and some estuarine and fenland areas, reed beds were managed to produce water reed for thatching. In the late 19th and early 20th centuries, the Arts and Crafts movement popularised water reed, and it was used on a small number of architect-designed buildings outside its traditional areas of production and use.

In some coastal, heathland, and upland areas of England, the use of local wild plants such as marram grass, sedge, bulrush, bracken, heather, and gorse persisted much longer than in lowland areas, but had almost ceased by the mid-20th century.

After the Second World War, new methods and materials began to be imported from other areas and even other countries, and the centuries-old localised traditions began to be diluted (Cox, J and Letts, J, 2000).

The heritage values of traditional thatch

Thatch makes a major contribution to the significance of historic buildings. The National Planning Policy Framework (NPPF) defines significance as "the value of a heritage asset to this and future generations because of its heritage interest". In the case of thatch, such interest may be:

Architectural

Thatch is clearly a major component of the architectural interest of a building; indeed, it is often the defining feature of any building on which it is used. Architectural interest can arise either from conscious design or fortuitously from the use of local materials, techniques and building typologies. The architectural value of thatch extends beyond the immediate building because it makes a major contribution to the appearance of villages and the countryside. Furthermore, the materials traditionally used for thatching and the way that thatched roofs are constructed and detailed vary in different parts of England, reflecting regional differences in climate, topography, geology, and historical development; this has resulted in regionally distinctive forms and styles of thatched roofs, creating a strong sense of place.

Archaeological

The significance of thatch derives from much more than just its visual qualities. Where a roof retains an historic base coat or remnants of previous coats of thatch (as is often the case with straw-thatched roofs), these archaeological remains have the potential to yield evidence of past thatching materials, fixings and techniques. Through the presence of different types of cereal straw and even weeds, it can also tell us much about the past agriculture and wider environment of a locality; it may even indicate what type of bread people ate in the past! Medieval smoke-blackened thatch is the ‘jewel in the crown’, but each layer of historic thatch is valuable and every effort should be made to safeguard it or, if its removal is justified, to record it.

Historical

Survival of a traditional thatched roof also illustrates other aspects of life in the past; it reflects the building’s status and the attitudes and values that society has attributed to thatch. It also represents the continuity of one of the most iconic of English building crafts. In the case of straw-thatched roofs, periodic renewal of the weathering coat by sparing a new layer of long straw or combed wheat reed onto the surface is a method that has stood the test of time for many centuries, to the point where it has become part of the historical value of the roof in terms of both the continuity of practice and the archaeological record.

Authenticity

Underpinning these heritage values is another quality: authenticity. Authenticity refers to things being genuine rather than imitation or fake. This was understood by an Inspector considering an appeal against refusal of consent for a change of thatching material from combed wheat reed to water reed: “one of the important purposes of listed building protection is to help distinguish the genuine article from imitation.” (The Thatched Cottage, East Boldre, New Forest).

It would not normally be considered good conservation practice to repair, say, 16th-century hand-modelled decorative plasterwork by inserting modern cast plaster elements, for example. Although the aesthetic result might be superficially similar to the original, the authenticity of the element will have been harmed, and the result is an imitation or pastiche. Similarly, when it comes to re-thatching, using authentic materials and methods not only conserves appearance but sustains significance derived from long-established traditional practices.

Rarity

As new materials and methods of thatching are increasingly used, authentic traditional thatched roofs are becoming rarer. In appeal decisions in recent years, Inspectors have concluded that this makes those remaining roofs all the more important to preserve. (Mulberry Cottage, Great Horwood, Aylesbury Vale; The Thatched Cottage, East Boldre, New Forest).

Repairing a thatched roof

Repair options

Patch repair

In the past, the life of a thatched roof was maximised through patch repair. This can extend the period between complete spar coatings or re-thatching by several years.

Patching does not require such large amounts of straw or reed as full spar coating or re-thatching. Since combed wheat reed or long straw can be repaired with shorter straw than that needed for thatching, patching makes good use of straw that might otherwise be wasted. This is particularly helpful in years when thatching straw is in short supply or when a very dry year means the straw has not grown very long.

Patching does not necessarily require a full scaffold; it can often be done from a tower scaffold.

Nowadays, many owners prefer the look of a new coat of thatch and opt for full recoating when, in fact, the roof could be repaired.

Flush ridge

A flush ridge requires less straw and is quicker to fix than a raised block ridge, so saves money on both material and labour costs. A flush ridge lasts as long as a block ridge and was the traditional type of ridge on the vast majority of historic thatched buildings in England.

Coping with shortages of thatching straw

From time to time, poor wheat harvests result in a shortage of thatching straw. Historic England has worked with practising thatchers and conservation specialists to develop possible measures to cope when thatching straw is in short supply. Focussing on essential patch repair (rather than full re-thatching) and flush ridging are the best ways of making the most of available materials, but rick coating and tarpaulins may be alternative temporary solutions.

Rick coating

Roofs with more extensive wear that cannot be patched easily can be protected with a thin coat of combed wheat reed or long straw with surface fixings (variously referred to as a rick-coat, stack-coat or step-coat, and derived from the practice of protecting ricks or stacks of straw with a thin coat of thatch following harvest and before threshing). Historic images show that rick-coating was often used on buildings in the past. It uses much less material than spar-coating and can also be done with shorter straw without affecting the longevity of the new coat. And while a thin rick-coat might last only three years or so, a thicker coat can last up to about ten. Repair can often be timed to coincide with re-ridging of the roof, so that the same means of access can be used.

Tarpaulins

If there is serious extensive deterioration, the best way to protect thatch temporarily is with tarpaulins or strong plastic sheeting. On roofs that are netted, fitting the tarpaulin under the wire netting will ensure it is held securely at the eaves and verges, and will reduce wind lift. On roofs that are not netted, chicken wire or other forms of garden or cargo netting could be installed over the top to hold the covering securely.

It is best to apply tarpaulins following a period of dry weather, but this is not always possible. In some cases, it may be helpful to remove areas of sodden thatch and even backfill the damaged area before fitting the covering. Provided the thatch has not rotted right through to the underlying roof timbers or ceilings, fitting a tarpaulin is unlikely to cause further damage to the roof structure.

Conservation issues when considering a change of thatch material

When thatching straw is in short supply after a poor harvest, there may be pressure to use alternative materials for re-thatching straw-thatched roofs. From a conservation perspective, there are a number of issues that need to be considered when deciding whether to use a different thatching material on a listed building.

The National Planning Policy Framework defines conservation as ‘the process of managing change to a heritage asset in a way that sustains, and where appropriate, enhances its significance’ (Annex 2). A prerequisite to determining an application for listed building consent for a change of material, therefore, is to understand the building’s significance. Our guidance on the heritage values of traditional thatch will help with this.

We provide advice about maintaining significance when considering proposals for change in our 'Historic England Advice Note 2: Making Changes to Heritage Assets'. Because of the important contribution that traditional materials make to the special architectural and historic interest of a listed building, we recommend repair using “materials to match the original in substance, texture, quality and colour” as this helps to “maintain authenticity, ensures the repair is technically and visually compatible, minimises the use of new resources and reduces waste”. Conversely, replacing original materials with other materials “may harm significance and will … need clear justification”. In particular, “justification will be needed for changes from one type of thatch, slate or tile to another, or for changes in the way the material is processed, applied and detailed” (paragraphs 11 and 12).

In accordance with policies in the NPPF, any harm to significance will “require clear and convincing justification” (paragraph 194) and must be “weighed against the public benefits of the proposal” (paragraph 196).

If combed wheat reed or long straw is the traditional type of thatch in the area, changing to water reed could well harm the significance of a listed building, and will need listed building consent. To avoid this, when considering whether to use water reed to spar-coat or re-thatch an existing combed wheat reed or long straw roof, we suggest that you consider the following questions:

1. Does the building or area where the building is located have a tradition of combed wheat reed or long straw thatching?
2. Does the thatching material currently on the roof contribute to the heritage values of the building (taking into account issues of authenticity, as well as appearance and style)?

If the answer to the above questions is ‘yes’, re-thatching with an alternative material such as water reed (or combed wheat reed in place of long straw) will harm the significance of the building and may also have an impact on local distinctiveness. To sustain the significance of the building, it is therefore important to seek an alternative to spar-coating or re-thatching with a different material. In this case, you should consider the following:

3. Could re-thatching of any particular elevation be safely delayed for several months (until such time as straw from the following year’s harvest becomes available)?
4. Could the roof be patch repaired with straw?
5. Could the roof be repaired temporarily with a rick-coat (stack-coat or step-coat) of straw instead of a full spar coat?
6. Could the roof be temporarily protected with a tarpaulin or other waterproof sheeting?

[Local authorities may wish to obtain advice from an independent thatching consultant to help answer these questions. In the case of Grade I and II* buildings, or where complete stripping of an historic combed wheat reed or long straw roof is proposed, Historic England may also be able to advise a planning authority on proposals.]

If the answer to at least one of questions 3 to 6 is ‘yes’, we suggest that the harm to significance that would be caused by re- thatching the listed building with a different thatch material is unlikely to be justified. Instead, we advise you to wait until suitable authentic material is available, or carry out repairs using one of the methods described in Repair options above. Listed building consent should not normally be granted for a change of material at this time.

If you are satisfied, on advice, that the answer to each of questions 1 to 6 above is ‘no’, this will mean one of two things: you have not identified any harm to the significance of the building, or you believe that the change as proposed is justified because the need for the work is urgent and cannot be addressed by repair or temporary protection, and suitable straw cannot be obtained.

In this instance, we recommend that the work carried out should be the minimum needed to protect the building. Rather than stripping off all the thatch, for example, it may be possible to just recoat it or deal with just the worst section of the roof. In this case, a detailed specification for the work, including proposed details such as eave and verge shapes and ridge style, should be submitted as part of the application. The time period for commencement of the work should be limited to several months. In this way, if it is delayed beyond the early autumn (when straw from next harvest will become available), the option to use the authentic thatching material can be reconsidered. Local authorities may wish to grant consent on a temporary basis, rather than as a permanent change of roof covering, to avoid creating a precedent for a permanent change of thatch material. This means that at the next re-thatching the building can revert to the authentic long straw or combed wheat reed.

Finally, in cases where removal of historic layers of thatch is justified and listed building consent is granted, the harm to significance that this would cause can be partly mitigated by imposing a condition that the historic straw should be accurately identified (straw type, fixings, number of layers) and recorded before removal.

Thatching material supply: the future

Producers of thatching straw and water reed are facing many challenges such as reliance on out-of-date machinery, uncertain seasonal labour supply, and decline in demand for home-produced materials in the face of imported water reed. Historic England has been working with thatching straw growers and reed cutters to better understand the issues, identify barriers and develop solutions. We have published a report summarising the main issues and suggesting some next steps towards securing a sustainable future for traditional thatching materials. We will be supporting the sector to lobby for investment, research and incentives for traditional thatch material supply.

Learn more

• View the recording of our webinar on Conservation of traditional thatch. Thatch is the quintessential English country roof covering, contributing to the character and appearance of individual buildings as well as creating a sense of local distinctiveness. However, the conservation of traditional thatched roofs faces a number of challenges, not least the availability of suitable material for repair. This webinar looks at the materials traditionally used for thatching, how thatch contributes to the significance of historic buildings, and how to sustain that significance when maintaining and repairing historic thatched roofs.
• Read more about thatch: Traditional straw thatching in times of shortage - article in volume 167 of Context, the Journal of the Institute of Historic Building Conservation, published by Cathedral Communications Ltd in March 2021.
• Information about the history, deterioration and repair of traditional thatch is included in the Historic England volume Roofing in the Practical Building Conservation series, and advice on the general principles to take into account when considering the repair or alteration of a historic thatched roof are included in Historic England Advice Note 2, Making Changes to Heritage Assets.

Print references

Cox, J and Letts, J, 2000:  'Thatch: Thatching in England 1940 – 1994' English Heritage Research Transactions: Volume 6 (English Heritage)

Letts, J, 1999: Blackened Thatch: A Unique Source of Medieval Plant Remains from Southern England (English Heritage/University of Reading)

Moir, J and Letts, J, 1999: 'Thatch: Thatching in England 1790 – 1940' in English Heritage Research Transactions, Volume 5 (English Heritage)

Mulberry Cottage, Great Horwood, Aylesbury Vale: appeal reference APP/J0405/E/14/2213476

The Thatched Cottage, East Boldre, New Forest: appeal reference APP/B9506/E/08/2092965