Combed Wheat Reed Thatch - Leverton - Wiltshire

Thatching Explained

The following definitions are designed to familiarise the thatch owner with commonly used thatching terms & important elements in the construction of a thatched roof.

Be it a 'single weathering coat' of thatch laid directly onto a roof frame of rafters & battens, or a 'weathering coat' secured to a 'basecoat', all three commonly used thatching materials are laid to a depth of at least 12 inches (30 cms) and are distinctively 3-dimensional in form when compared to other roofing methods.

The life of a thatch will depend on many factors, these include pitch of roof, roof design, type and quality of material used, geography & topography. But of paramount importance is the level of thatching technique & skill employed.

There are several basic principles, that when closely adheared to and correctly executed, combine to maximize longevity.

Depth of Fixings

How far the heads of the Hazel securing spars or steel thatching crooks are buried beneath the surface. The ideal minimum depth of fixings should be 6 inches when newly thatched. Any significant reduction in depth of fixings is likely to adversly affect lifespan.

Material Pitch

Is the angle the material lays in relation to the horizontal and the ideal is the maximise pitch of material in order to maximise water shedding efficiency whilst keeping within the specification for depth of fixings.

Material Density

Relates to the compactness of material throughout both its vertical & horizontal planes. Variations in density will result in hollows and gullies forming in areas below ideal density.

Surface Density

Too great a surface density will result in capillary action drawing water into the coatwork. To little surface density will result in water penetrating the coatwork by gravity. These conditions will be greatly exaggerated when material is laying too flat (horizontal) in relation to the roof pitch.

Tension

Refers to the degree of tightness by which the material is held in a stable position on the roof. Too much tension may result in too great a surface density. Too little tension may result in material slippage.

Single Coat

Single coat of Water Reed, Wheat Reed or Long Straw, laid directly onto roof frame of rafters & battens. Laid in courses & secured to the rafters using Steel Thatching Crooks and steel or hazel rod. Ideal minimum depth of fixings - 6 inches (15 cms).

Basecoat

Permanent dense foundation of Combed Wheat Reed of Long Straw firmly secured to rafters, the purpose of which is to receive & firmly hold the pointed shafts of weathering coat securing spars. Also known as undercoat.

Weathering Coat

Outer layer of Combed Wheat Reed or Long Straw laid over & secured to the basecoat using Hazel spars. Ideal minimum depth of fixings - 6 inches. This coat is replaced when the tops of hazel securing spars become exposed on the thatch surface through natural wear. Also known as the Spar Coat, Top Coat or Casework.

Consistently correct material pitch, density & tension, together with consistently correct depth of fixings are essential factors in the durability of a thatch. It is an understanding of this relationship between adequate cover over fixings and pitch angle of material, balanced against the tension under which the material is held, which will determine a roof's longevity and not the overall thickness.