Building techniques :

Country :

D6 – Sloped Slate (schist) roofing Mediterranean Area

PRÉSENTATION Geographical Influence Definition Sloped Slate (schist) roofing - Roof with common slope from 25 % to 40 % covered with slabs of limestone, schist or slate. - The schist or slate slabs are an irregular oval, rectangular or trapezoidal shape. Dimensions are extremely variable, with lengths ranging from 10 cm to 150 cm, widths ranging from 10 cm to 80 cm, thickness, variable for the same unit, ranges from 1 cm to 6 cm. - The schist or slate slabs are either nailed on battens or wooden shingles, or stacked as a loading element, or laid with mortar on battens or wooden shingles, or sometimes on masonry. - A schist or slate slab roofing either rests on a wooden frame, or on vault masonry. - A schist or slate slab roofing appeared in the Middle Ages ; this technique, still in use, is disappearing in France and in Morocco. The slabs of schist or limestone are heavy, expensive and long to lay, and are therefore often replaced by industrial slates, tiles or plates of coated sheeting or enameled steel, which require less maintenance.

Environment In the MEDA area, sloped roofings made of limestone, schist or slate slabs are generally present in rural and mountain environment ; they are also present in urban environment in France and Greece, and in plain areas in Spain and France. This type of roofing is common, except in Spain.

Illustrations General view :

Detail close-up :

This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.

1/6

D6 Med i t e r r a n e a n S p a c e – S l o p e d S l a t e ( s c h i s t ) r o o f i n g

CONSTRUCTION PRINCIPLE Materials

Illustrations

Nature and Availability (in what form) Schist or slate slabs : Besides the many quarries throughout the territory, which are exploited for the local needs of farmers (as extra income), the main deposits used to supply the needs over extended areas. Schist banks are selected for their stratification qualities, ensuring flatness and good cleavage of schist or slate slabs. The blocks are released using a pick ; when the stratification is horizontal, the blocks are extracted through successive lines. The alternation of quartz seams and layers of mica spangles produce fiscibility, allowing for good cleavage of the schist or slate slabs using a small pickaxe (marteline), or a sledgehammer and a wedge, according to the density of the rock. Limestone roofing stones : They come from outcrops naturally breaking or splitting into thin slabs, with flat or convex faces. Before being used, the limestone slabs are stored outside for at least three winters, to test frost resistance. These schist or slate slabs are squared before laying.

Modules, Dimensions, Thickness, Dosages The schist or slate slabs have an oval, rectangular or trapezoidal irregular shape. Dimensions are extremely variable; length from 10cm to 150cm, width from 10cm to 80cm, thickness, variable for a same unit, from 1cm to 6cm. The size of schist or slate slabs decreases from the sewer to the ridge sheathing. The weight of schist or slate slabs is between 100kg and 200kg per m2 for schist, and between 200kg and 300kg per m2 for limestone. Schist or slate slabs have varied colours: silver gray, bluish, greenish or brown, according to the iron contained (brown tone ), quartz and mica (dark tone ) and of feldspar (light tone). Limestone schist are a more or less dark cream shade, according to the metal oxides contained.

Type of laying Type of laying Schist or slate slabs are either nailed on battens or wooden shingles, or stacked as a heap, or laid with mortar on wooden battens or shingles, or sometimes on vault masonry.

Associated framework A roofing with schist or slate slabs rests either on a wooden frame, or on vault masonry or, more rarely, on a dome.

Drainage Adapted slope (%) The slope varies from 25% to 70%; the common slope ranges between 25% and 40%. Wind exposure is lessened when the slope is weak; with a weak slope, a slower flow can cause water infiltration.

Water collecting and drainage Rainwater is more and more often collected by gutters, particularly in urban environment. They are generally drawn away from façades by overhanging eaves (projecting roof).

Construction principle: materials and type of laying – sections, modules and laying details

This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.

2/6

D6 Med i t e r r a n e a n S p a c e – S l o p e d S l a t e ( s c h i s t ) r o o f i n g

C O N S T R U C T I O N P R I N C I P L E (C O N T I N U E D ) Illustrations

Drainage (next) Processing of specific points (bargeboards, runoff, neck gutters, ridge sheathing...) Various works are the subject to particular processing: Ridge sheathing When the roof slope is weak, the ridge sheathing is sometimes made up of large schist or slate slabs sealed with lime mortar, slightly turned in the direction of dominant winds, and covering each slope (15 cm minimum) ; sometimes, crossed schist or slate slabs overlap one another, held by notches. Sometimes, a row of stones helps maintain schist or slate slabs exposed to wind. Hip rafters The schist or slate slabs, wedged with a lime mortar weather strip, sometimes overlap by 5cm to 15cm the part most exposed to dominant winds and rain ; they are often cut like schist or slate bargeboard slabs. Side bargeboards Schist or slate bargeboard slabs, selected for their great width (up to 140cm), are often round on the pinion side and round on the roof side, according to the alignment of the bargeboard; they are sealed with a mortar of lime on the wall top, or doubly fixed to the battens when sufficiently close, or when the frame is jutting out. To avoid tearing off from wind, and protect the pinion wall, the jutting out of the bargeboard is between 15cm and 20cm. If greater jutting out is necessary, one or two rows of rectangular schist or slate slabs anchored on the top of the wall can be sealed with lime mortar. Neck gutters Schist or slate slabs selected for their lengthwise hollow shape, and cut to be broader on the higher edge; wedged in the angle or fixed on battens according to the slope; on both sides of the neck gutter, schist or slate slabs are carefully inclined, to take on a curved shape. Sewers A - superimposed schist or slate slabs jutting out horizontally : large schist or slate slabs (width 50cm to 110cm) rectangular shape, aligned with a string and sealed flat on a lime mortar on one to three overhanging rows spaced 12cm to 20cm (according to the height of the façade to be protected). B – Jutting out of roof made with rafters (end sometimes cut in a corbel piece) under wooden battens. C - Jutting out held by horizontal wooden corbel piece , resting on the wall. D – Cornice full carried out in cut stone (ashlar) or from a shape of rendered masonry, or made up of semicircular rectangular tiles or bricks (mainly in Corsica and Roussillon), allowing for an infinite variety of mouldings. E – Hollow cornice shaped by a formwork of wooden in the Alpes-Maritimes and in Corsica).

Construction principle: materials and type of laying – general views

lathing with plaster rendering (mainly

"Rafter" (Rafters) Schist or slate slabs jutting out, covered with a row of sewer slabs, jutting out 15cm to 20cm, aligned with a string and slightly tilted (slope from 15% to 30%); the joints between sew er slabs are sometimes covered with narrow schist or slate slabs . A second weak sloped row of average size slabs is sealed with lime mortar. From the third row onwards, slabs are nailed with battens or wooden shingles on a stronger slope, making up a rafter between the second and the third row, which makes it possible to slow down water towards the sewer, and blocks slabs of the higher part of the roof. Chimneys Stocks; simple shape or lanterns produced in schist masonry (for schist roofs), covered with a hat of one or more schist or slate slabs, on skittles, crowned with a decorative block to avoid tearing from wind.

This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.

3/6

D6 Med i t e r r a n e a n S p a c e – S l o p e d S l a t e ( s c h i s t ) r o o f i n g

C O N S T R U C T I O N P R I N C IP L E (C O N T I N U E D ) Tools

Illustrations

The tools generally used are a small pickaxe to recut schist or slate slabs (flat side) and, in the case of nailed schist or slate slabs, drilling (pointed side).

Trades Trade, Number of people necessary According to cases, a roofing with schist or slate slabs is implemented by a specialized roofer or a mason. Two to four people at least are necessary to carry out this work.

Performances Waterproofing, Protection against bad weather Weather resistance of schist or slate roofings is not always good. Although schist and limestone are materials relatively resistant to the weight of snow, certain schist or slate slabs, in particular limestone, are frost breaking and not very tight, because of porosity. Moreover, schist or slate slabs provide little transverse pressure resistance. Sometimes, stones are laid on the roofside, to avoid tearing of the schist or slate slabs by wind.

Thermal insulation The thermal performance of a roofing with schist or slate slabs, generally average, depends mainly on the nature of the support. The thickness of the frame due to the weight of the slabs contributes to the thermal insulation of the roofs.

Ageing pathology Linked to materials and climatic conditions : Porous schist or slate slabs rot with time, when becoming soft and friable, they do not ensure waterproofing any more. The rough texture of schist or slate favors moss and lichen, which can harm good water run-off ; to limit development, it is appropriate to turn ov er the faces of schist or slate slabs, at the time of roofing maintenance. The weight of schist or slate slabs, plus the weight of snow, can cause sag, sometimes-even frame breaking, a deformation of the roof and water infiltration.

Linked to the technique : Wear of the nails (or wooden pins), as well as the infiltration of water in the laying mortar, can cause the schist or slate slabs to slide.

Construction principle : treatment of particular points, drai nage – eaves, cornices, bargeboards, ridge sheathing, chimneys

This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.

4/6

D6 Mediterranean Space – S l o p e d S l a t e ( s c h i s t ) r o o f i n g

REALIZATION DESCRIPTION Conditions of realization : The realization of the work must be done in dry weather, to avoid rainwater infiltrations ; no particular protection is necessary. Preliminary works : Nailed schist or slate slabs In the case of a roof with regular shape slabs (rectangular, scale laid or pointed), the roofer (or the carrier) cuts and shapes them using a small pickaxe, according to a vein defined by their texture, to facilitate downwards water run-off. Cutting is done in the reversed direction of laying, so that the protruding chippings are on top. Cutting like fish scales makes it possible to optimize the use slabs (less falling off), spread starting from the end of XIXth century: this shape allows a better lateral runoff of water, reduces the crushing of slabs and the accumulation of dust between jointed schist or slate slabs. Dimensions of slabs are defined by the shape of the schist plate. The faces with a convex profile are positioned on top, reinforcements are directed downwards so as not not to thicken covering too much. Fixing is done through nailing (formerly with wooden pins) requiring drilling with the point of a pickaxe on one to three points, at a distance of 2cm to 5cm of the top side, which makes it possible to thin down the slab on the under-face. When a slab is too hard, a side notching sometimes replaces drilling. Cut schist or slate slabs are classified according to height, the slabs sized or adapted to bargeboard sewer and ridge sheathing are classified separately. Schist or slate slabs laid with mortar or stacked in tas-de-charge. Schist or slate slabs are squared beforehand. In the case of a built frame roofing, a mortar of earth or a thin lime is prepared. Realization : Nailed schist or slate slabs Common laying is done by successive horizontal rows, shifted laterally to cover the joints, according to decreasing length of slabs and gauges. To balance the laying on gable roofs, the rows are assembled simultaneously on each slope. In the case of trapezoidal faces , it is necessary to add incomplete intermediate rows of schist or slate slabs, to correct the difference of rows between sewer and ridge sheathing; a progressive correction on several rows offers a more elegant solution. Schist or slate slabs laid with mortar or stacked in tas-de-charge. The schist or slate slabs, wedged on battens, wooden shingles or arch masonry using a thin mortar of lime, earth or stones, are laid or stacked in tas-de-charge, covering from two thirds to three quarters of the lower row. The laying is made by successive rows shifted laterally to cover the joints, the dimension of schist or slate slabs decreases from the sewer to the ridge sheathing. Significant details : Throughout the laying phase, the roofer must be attentive to balancing reinforcements to obtain overall flatness: using his pickaxe he must thin the heads when necessary, to remove bumps, or to reduce the width of the slabs. The roofer must constantly keep schist or slate slabs high enough for the row he is laying, and wide enough for a good covering of the joints. Means of verification : One can check roofing waterproofing by sprinkling water to detect possible infiltration.

This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.

5/6

D6 Mediterranean Space – S l o p e d S l a t e ( s c h i s t ) r o o f i n g

USE, EVOLUTION AND TRANSFORMATION Use Types of buildings Roofing with schist or slate slabs is found on all types of buildings through the MEDA area.

Period when the technique first appeared / Period of use of the technique - contemporary or disappeared. Roofings with schist or slate slabs appeared in the Middle Ages ; this technique, still in use , has disappearing in France and Morocco.

Reasons of the disappearing or the modification of the technique No object. This technique is still in use today.

Evolution / Transformation The materials Slabs of schist or limestone, doors, expensive and long to lay, are often replaced by industrial slates, tiles or plates of coated sheet or enamelled steel, requiring less maintenance.

The technical aspects The techniques of laying evolved to save time. Various systems (microporous felts, sheets of zinc or lead) appeared to improve the waterproofing.

Evaluation of materials and replacement techniques The replacement of schist or slate slabs by industrial slates, mechanical flat tiles, or plates of coated sheet or enameled steel, is not satisfactory for the restoration of old construction. On the other hand, waterproofing sheets in zinc or lead are satisfactory, provided their visual impact is limited.

This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States.

6/6