This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
In country districts the roofs of cottages and outbuildings are frequently covered with thatch. This consists of layers of straw - wheaten lasts twice as long as oaten - about 15 in. in thickness, tied down to laths with withes of straw or with string. Thatch is an excellent non-conductor of heat, and consequently buildings thus roofed are both cooler in summer and warmer in winter than others, and no better roof covering for a dairy can be found. Thatch is, however, highly combustible, and as it harbours vermin and is soon damaged, it is not really an economical material, though the first cost is small. A load of straw will do 1 1/2 "squares" of roofing, or 150 superficial feet. First class thatching is an art not readily acquired. While really good thatching will stand for 20 years, average work will not endure 10.
The operation may be briefly described as follows. For renewing an old thatch the best and cheapest material is "stubble " (the lower and stiffer half of wheaten straw); but for new thatch, stubble is not long enough alone, and must be used with straw, or be replaced entirely by straw. The material is thoroughly soaked with water, and then straightened out with the hands so as to arrange the straws all in one direction, termed "drawing." When a double handful (called a "yelven") has been thus prepared, it is laid aside, until a sufficient number are ready to fill a "jack " (large forked stick), in which they are placed just so much out of the parallel as to be easily separated. A small hook in the jack permits it to be hung from the thatcher's ladder.
Commencing at the eaves and working upwards to the ridge, he proceeds to lay a strip of thatch on the opposite side of the ladder from that carrying the jack. The strip laid (technically a "stelch") is of convenient width for the workman's reach; it will be of equal breadth throughout if the section of roof is square, or taper gradually upwards if the area is triangular. The thatcher commences by forming the eaves at the bottom of the stelch, and fastens this portion securely before proceeding to the next yelven. The mode of fastening varies : in renewing old thatch, the new material is secured by thrusting the upper ends into the old thatch by a wooden spur; in new thatching, the straw is bound to the rafters and laths with tar cording, passed, by means of a huge needle, through the straw near the upper end of the yelven, where it will be covered by the next instalment. Each succeeding addition as the work advances towards the ridge is made to overlap the preceding one, all except the lower end, and is secured by the tar cording.
When the whole stelch is finished from eaves to ridge, the thatch is combed straight by a short-toothed wooden rake. Every succeeding stelch must be so united to its predecessor that no gap or weak part is left to mark their junction, or such a spot will never be watertight. The security of the thatch is further ensured by furnishing it with a series of buckles and runners on the outside. Buckles are a kind of huge wooden hairpin, made by splitting withes, shaving the middle somewhat thinner than the remainder, twisting it 2 or 3 times, bending it end to end, cutting it to a length of 12-18 in., and pointing the ends. Runners are simply long strips of split withe, laid in horizontal bands on the thatch, and held by the buckles, which are thrust upwards into the thatch, as shown at Fig. 1344: a, thatch; b, laths; c, rafters; d, tar cording; e, buckles; f, runners.
The buckles are placed at 6 to 12 in. apart, and 2 series of buckles and runners are generally adopted, an upper series just below the ridge, and a lower just above the eaves, with additional series whenever there is exposure to strong winds. The eaves are trimmed off evenly with shears. The best method of finishing off at the ridge is by a kind of plaiting of the straw, not easily described. A simpler substitute is to plaster with road-dirt, and plant a weed such as houseleek or stonecrop in the soil.
In the western counties of England, the word straw is applied only to the stems of barley and oats; wheaten straw, after it has been deprived of leaves by a rough combing, is tied in small bundles called "niches," and known as "reed." In thatching, the butt end of the reed is laid outwards and the head inwards; and the finished thatch on buildings (but not on ricks) is shaved over with a sharp sickle. Long strong reeds found in the marshes, such as Slapton Lea, are cut at certain seasons and stacked in bundles for similar application.
Byrne describes thatching as generally made of wheaten straw, laid on lathing and rafters, which may bo of the same strength and placed the same distance apart as fur a common slated roof; but in country places, where thatching is mostly used, the rafters are generally formed of the branches of trees of 3-6 in. in diameter; the slighter they are, the better, provided they are sufficiently strong, as the lighter the roof, the less strain there is on the walls: of course, if the rafters are stout, they should be placed farther apart than slight rafters; and if the rafters are far apart, the lathing must be stronger, otherwise the thatching will bag, or lie in hollows between the rafters. The straw is laid on the lathing in small bundles called "hellams," until it attains a thickness of 12-16 in.; it is fastened to the rafters with young twigs and rope-yarn. A good pitch for a thatched roof is 45°, or, as it is technically called, a true pitch: if the pitch is made less, the rain will not run off freely; and if a greater pitch than 45° is used, the straw is found to slip down from its fastenings.