CONSERVATION ADVICE SHEET by monkey6

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CONSERVATION ADVICE SHEET

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									C O N S E RVAT I O N ADVICE SHEET

Thatching is one of the oldest building crafts still practiced today. The roof covering remained popular all over Britain until towards the end of the mediaeval period, when effectively the first building regulation came into force, (due to a number of disastrous fires, sweeping through the narrow mediaeval streets), prohibiting the thatching of new properties within London. (Thatched properties which remained were to be coated with a whitewash plaster daub, to protect against fire). As a result, thatching was generally confined to rural areas, and remained their most practical and available material until the mid 19th century. Types of Thatch Water reed and wheat straw are the 2 main thatching materials in use today. Norfolk reed, a form of water reed is most commonly used in East Anglia. The two main varieties of wheat straw are spring and winter. Of the two, winter wheat is most suitable for thatching, commonly used in the form of combed wheat reed or long straw. Spring wheat is a poor substitute, occasionally prepared for thatching. Norfolk reed Norfolk reed is native to East Anglia, growing in wet marshy landscapes. Norfolk reed may be identified by its crisp, darker, angular appearance, following more closely the shape of the roofing timbers, exposing only the butts of the thatching material. The strength and stiffness of water reed allows the material to be dressed, by beating or pushing the reed into shape under the eaves, rather than cutting into shape. As a result the butt ends will show the original square cut of the reed undergone at harvesting, as oppose to oval butts, seen when the eaves are cut into shape. Traditionally it was unusual to see wire mesh over the whole of a Norfolk reed roof, unless in its mature years. Usually only the ridge, normally block cut and sparred was

protected with wire mesh, however today complete coverage is common. The expected extent of useful life for Norfolk reed is between 50-60 years if laid correctly using good material, unaffected by excessive nitrates, etc... Long Straw Long straw is a winter wheat, identified according to the treatment it receives after reaping and binding. The straw is fed directly into a threshing drum, frequently braking stems, retaining leaves and mixing ears and butts. Long straw can be identified by its softer, rounder looking lines often exaggerated by its thickness, built up over a number of years, removing only the decayed layer as oppose to the complete covering. However thatch around chimneys should be stripped back to the timbers to ensure there are no loose bricks or stones and the mortar is sound. It is quite common to find decayed mortar below the level of the thatch and sound above. Its ridge can either be flush or block cut. Unlike Norfolk reed, stem lengths are exposed and ears and butts are mixed. Long straw is nearly always protected from damage, by birds and rodents, with a complete covering of wire mesh. The thatch is held in place at the eaves and gables with an exposed ligger, or cross-spar pattern. The strength and stiffness of long straw will not generally permit the eaves or gables to be dressed or pushed into shape. Instead both eaves and gables will be cut into shape once laid, displaying oval butts cut at 45 degrees. The expected extent of useful life of long straw is between 15-20 years, if laid correctly, using good materials, unaffected by excessive nitrates etc... Sedge Sedge is a more flexible material, harvested every four years, producing long growths more suitable for ridging material.

Combed Wheat Reed Combed wheat reed is a variety of winter wheat, similar in appearance to water reed but is essentially a Westcountry material. The reed is put through a threshing machine, combing the stems, preparing the material so that it may be used in thatching in a similar manner to water reed. The expected extent of useful life of combed wheat reed is between 3040 years if laid correctly using good material, unaffected by excessive nitrates, etc... Repair and Maintenance The type and quality of material used together with pitch and design of roof, geography, topography and skill of the thatcher will all influence the life expectancy of the thatch. The condition of the thatch should be continuously monitored to ensure any problems are highlighted in their early stages and rectified immediately, to prevent the need for major works in between re-thatching. To ensure a thatch achieves its maximum life expectancy, the thatch should remain as dry as possible for as long as possible. Changes to climate are obviously not controllable, however, overhanging trees, which block out sunlight, should be cut back and any moss, lichen or fungal growth leading to early degradation, should be controlled. Traditionally a copper wire sparred to the ligger on a ridge helped to discourage fungal growth by spreading a dilution of carbonates and hydroxides of copper over the surface of the thatch whenever it rained. Stubborn, dense moss, entangled in the wire, may require physical removal by hand after treatment where weathering has not been successful. Other Pests The removal of straw or reed by birds

forming nestling holes may cause areas of weakness and should be repaired, covering all slopes with galvanised wire mesh 19mm (3/4 “). Rodents (rats, mice and squirrels) pose a greater threat, potentially causing extensive damage, moving under the thatch in any direction. Repair work can be expensive and will almost certainly necessitate a thatcher. On discovery appoint your local pest control expert to remove them as quickly as possible. It is possible to determine the pest by examining the lengths of straw/reed which has fallen to the ground, from the suspect area. Whole lengths indicate birds, short, chewed lengths indicate rodents. Fire There are a number of precautionary steps which should be taken to reduce the risk of fire to a minimum. Earlier methods of protecting a thatch involved a coating of limewash plaster daub, however technological advances necessitate further precautionary steps. Regular checks on the wiring throughout the house, by an expert is paramount, especially if rodents have gained access. Faulty/worn wiring, together with sparks from fires pose the greatest threats to the thatch. Working chimneys should ideally be swept biannually, or at least annually, checking parging and pointing of the chimney breast to reduce the risk of heat transfer. The insertion of chimney liners both metal or cementitious promotes the acceleration of sparks to the thatch by smoothing irregular surfaces, which upon contact would normally extinguish a spark. The rigidity of a cementitious liner will also restrict the buildings movement introducing secondary problems. Spark arresters, galvanised wire cages, extending from the top of the chimney pot may help to prevent large sparks and pieces of burning paper from falling into

the thatch. However, it is important to thoroughly clean the spark arrester, every time the chimney is swept to prevent the build up of soot. Failure to do so will create a difference in thermal temperature between stack and spark arrester, encouraging soot to stick to the arrester, increasing the risk of fire. It should be noted that the burning of softwoods will create more deposits, which are often tarlike necessitating regular sweeping. Bonfires and barbecues can pose a threat if consideration is not given to an unfavorable wind direction. It is good practice to keep several Co2 extinguishers around the house, together with an outside hose permanently connected to the mains. Fire retardant treatment Barrier protection provided by lining the roof before thatching restricts the permeability of the roof creating favorable conditions for fungal attack to roof timbers, however a balance between the preservation of the thatch and the preservation of the building in the event of a fire needs to be achieved. The threat of lightning can be diverted by erecting a metal conductor above the highest point of the roof connecting it down to earth. In the absence of gutters on a thatched roof, splash marks to the walls and soil erosion immediately adjacent to the walls is common. The introduction of a French Drain, a ditch filled with pea-shingles around the perimeter of the property, will allow moisture to evaporate and water to percolate freely away from the walls of the building. The centre of the ditch should be plumb with the eaves edge. Simple repairs to eaves, barge ends and netting may successfully be carried out by the owner; holes at eaves may be repaired by pushing appropriately sized and tied bundles into place with the aid of

a mallet. Stray ends may be trimmed using garden shears. However repairs to the surface of the thatch should be carried out by a professional. An inappropriately placed ladder can cause extensive damage before attempts to the repair area are even started. For further advice and information, please contact Andrew Gayton (Historic Buildings Officer) on tel. 01362 656 257 or E-mail: andrew.gayton@breckland.gov.uk


								
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