Logo STONE ROOFING ASSOCIATION
Home > Start > Contents > Glossary of Stone Roofing Terms
.
GLOSSARY OF STONE ROOFING TERMS
  • Backer: narrow slates laid roughly centrally over a wide slate to accommodate the increasing number of slates in each course as work progresses up the roof.
  • Batten: sawn wooden support for hanging or nailing stone slates. Synonym: lath. In this website, the word lath is reserved for split supports. 
  • Random slating
    The terminology of random slating.
  • Bedding of rocks: a plane parallel to the surface of deposition of a rock. The plane along which stone slates often, but not invariably, split; 
  • Bedding of slating: use of mortar in spots or fillets to prevent stone slates from rocking. In some areas, it is used to improve weather tightness 
  • Breeze: a mixture of clinker and lime or cement. When used to bed slates it could be crushed down to fill any gaps without excessive separation of the slates. 
  • Cleavage: slatey cleavage is developed in fine grained rocks following metamorphism. Under the influence of pressure and heat the pre-existing platey minerals are partially recrystallised and aligned perpendicular to the pressure. Slates cleave parallel to the platey minerals. 
  • Clive: (Collyweston) setting a log cracked by frost on edge and gently tapping with a special (cliving) hammer, turning to each edge until splitting is completed.
  • Cusome: the eaves detail in Cotswold slating where the under-eaves slate is supported over the wall head on stone packing and with its head placed under the first batten or lath.
  • Diamond pattern slating: a roofing system using 'diamond' shaped pieces of stone hung from one corner. The shape is actually hexagonal to avoid three layers where adjacent slates and courses meet. An ancient method found on many Roman sites and still to be seen in Dumfries. 
  • Diamond pattern
  • Diminishing: the system whereby slates are sorted by length and laid with the longest at the eaves, diminishing to the smallest at the ridge. It is essential that the minimum head lap is maintained when there is a change of slate length between two courses. This also ensures that each successive margin is the same size or smaller than those below (see pigs). 
  • Double lap: stone slates laid so that each course overlaps the course next but one below. In some regions and in some special applications, triple lap slating (where each course overlaps the course next but two below) is adopted.
  • Dressing: the process of shaping the stone slate and producing the edge detail using either a chisel-edged hammer or a bladed tool. Regional differences exist for the edge detail which may be square or beveled. Synonyms: trimming, fettling (Yorks, Lancs). 
  • Eaves, of stone slates: the short course laid at the eaves under the first full course. The method of placing and supporting the eaves stone slates varies regionally. Synonyms: under eave(s), cussome (Cotswolds). 
  • Facies: the characteristics of a sedimentary environment: rock type, mineral and fossil content, sedimentary and bedding structures. 
  • Fissile: rock which can be split along bedding planes. 
  • Fixings: nails or pegs. 
  • Gallet: small pieces of stone slate or metamorphic slate bedded in lime mortar at the head of a slate to support the slate above. Synonym: shale. 
  • Gauge: the spacing of laths or battens up the roof slope. In stone slating, the gauge is always variable. 
  • Head: the top edge of a stone slate as laid. 
  • Head lap: in double lap slating (the normal method), the amount by which a stone slate overlaps the stone slate in the course next but one below. In single lap slating such as diamond pattern it is the amount by which each slate overlaps the one immediately below. 
  • Head and side laps
  • Heap: (Collyweston) a quantity of dressed slates of all sizes on the ground. A heap should produce about two squares of slating laid on the roof and is made up of -
    • 7 hundreds (840 slates) plus 13 large ones
    • each hundred is 40 cases (120 slates) and 
    • each case is 3 slates 
  • Lath: split wooden support for hanging stone slates. Synonym: batten. In this guide, the word batten is reserved for sawn supports. 
  • Log: (Collyweston) a lump of stone of no defined size quarried for the purpose of making slates.
  • Margin: strictly the area, but more commonly the length, of the exposed part of the slate. 
  • Metamorphism: the process, involving heat, pressure or both, which changes the direction in which sedimentary rocks split. Metamorphic rocks such as true slates split along cleavage planes which are unrelated to their original bedding. Sometimes the cleavage and bedding are parallel. True slates are formed by low grade metamorphism - not much heat or pressure involved. Higher grades of metamorphism produce rocks with larger mineral crystals which can be seen without magnification. Examples include schists, quartzite and gneiss. Generally such rocks cannot be split thin enough to use for roofing, but some examples do exist. 
  • Mossing: use of moss or other vegetable material to windproof the joints and gaps between stone slates. 
  • Mossing iron: tool used to force moss etc. between slates. 
  • Overburden:  in quarrying: useless material which overlies a bed of useful material .
  • Parting: (Collyweston) a set of slates of the same length.
  • Pendle: generally a quarrying term for any fissile rock. For Cotswolds stone slates it is used specifically for rock which is split by frosting. 
  • Pig: a course with a longer margin than the course(s) below resulting from poor setting out and a failure to maintain an adequate head lap. 
  • Pitch: the angle of the rafters to the horizontal. The pitch of the stone slates will be significantly less because they are resting on each other, but this is taken into account by the traditional rafter pitch and lap relationship for the slate and the locality. 
  • Pointing: use of mortar to fill the vertical joints and to seal the tail gap of stone slating. Pointing may show (undesirable) or be raked or held back. Often associated with bedding. 
  • Presents: stone slates formed by natural weathering in near surface deposits. They are often thicker than hand-split stone slates produced from deeper layers (Cotswolds). 
  • Pied: (Collyweston) a method of storing logs during the summer to prevent drying out.
  • Pit: a mine or quarry for the extraction of stone or slates.
  • Random, of stone slate: variable length and width; 
  • Random, of roofing: slates laid with reducing length up the roof slope and the widths selected and placed so that they provide at least the minimum side lap over the slates in the course below. 
  • Regularly (of diminishing or random slating): the system whereby each successive margin is the same size or smaller than those below. It does not mean that there are an equal number of courses of each margin size. 
  • Sedimentary: rocks which have been formed from other rocks which have been broken down by weathering, or rocks formed by biological or chemical actions. If they can be split to make roofing (fissile) it will be along bedding planes. See metamorphism. 
  • Shadow: a thin piece of slate used in the Horsham district to improve the weather resistance of the roofs when, because of a shortage of stone slate, the head lap is reduced to less than the normal minimum. Originally the shadow was a thin piece of  Horsham stone but it is now normally a Welsh slate. It was always used in conjunction with mortar bedding and pointing. Technically this is an undesirable method, however it has been in use for about 100 years and appears to work satisfactorily. 
  • Shale: small pieces of stone slate or metamorphic slate bedded in lime mortar at the head of a slate to support the slate above. Synonym: gallet. 
  • Shoulder: (v) to remove the top corners of a stone slate; (n) the top corners of stone slates. Excessive shouldering can result in a leaking roof. 
  • Side lap: the lateral amount by which a slate overlaps the slate in the course below. 
  • Slate: People have different preferences for terms to describe sandstone, limestone and similar non-metamorphic roofing products. The most frequently encountered, traditional and colloquial terms are stone slates or grey slates but they are also called flags, flagstones, thackstones, stone tiles, sclaites or grey sclaites (in Scotland), slats or slatts. Each of these terms is used to distinguish them from metamorphic, Welsh or 'blue' slates. The objection to the term stone slate is that sandstones and limestones are not, petrographically, slates. That is, they have not been metamorphosed and consequently they split along bedding rather than cleavage planes. This is certainly true and some geologists prefer the retronym tilestone to distinguish them from real slates. However the term slate, meaning any 'flat rectangular' roofing product has historical precedence, since it predates the science of geology by hundreds of years and is the term in common use. In this website we use 'stone slates' for preference but in geological pages 'tilestones' will be encountered and don't be surprised if you find any of the other synonyms. If this is confusing, the easiest thing to remember is that metamorphic slates will always be called ......... metamorphic slates! Anything else isn't. 
  • Sprocket: the lower pitch of the roof slope at the eaves; the additional piece of rafter fixed to the main rafter to give the tilt at the eaves. The sprocket can arise naturally due to the rafter footing on the inner face of the wall or can be deliberately constructed to carry the eaves away from the outer face.
  • Square: one hundred square feet of slating laid on the roof.
  • Tail: the bottom edge of a stone slate as laid. 
  • Tiering: see torching. 
  • Tilt: the lift provided to the tail of the eaves course to ensure that successive courses lie correctly without gaps at the tail. On the main areas of the roof slope, the tail of each stone slate rests on two thicknesses of stone slate in the course next but one below. At the eaves, the first full course  rests on only one thickness - the eaves slate. Essentially, the tilt replaces the missing thickness. 
  • Torching: lime and hair mortar applied to the underside of stone slates to render them wind proof. Synonym: tiering; 
  • Torching: half torching: application of lime and hair mortar between the top edge of the lath or batten and the underside of the slates. Synonym: single torching; 
  • Torching: full torching: application of lime and hair mortar between the top and bottom edges of the laths or battens and the underside of the slates; 
  • Torching: single torching: see half torching. 
  • Unweathered, of stone slates: rock which is too deep to have been subjected to weathering and consequently has to be split by mechanical action or frosting after extraction. 
  • Weathering (of rocks): the process by which rocks are broken down and decomposed by the action of external agencies such as wind, rain, temperature changes, plants and bacteria. In the development of weathered stone slates, it is often very thin clay or mica beds which are weathered out;
  • Weathering (of stone roofing): the processes of mineralogical change, particle deposition and plant growth which change the apppearance of slates on the roof.
  • Weathering (of a roof): the arrangement of the parts of a roof covering - the slates, soakers, flashings, mortar fillets etc - which prevent water getting into the roof.
  • Home
    Contents
    Start