Lauze

A lauze is a flat slab of stone used to cover roofs and, in some places, to pave floors. Lauze roofs are characteristic of the Cévennes and Causses and neighbouring parts of the Massif Central such as the Cantal and Aveyron, and survive in other areas such as northern Isère, where they give villages their grey, heavy-looking roofscapes. They belong to the wider European family of stone roofs, alongside English stone slates and the piode of the southern Alps.

Rock types

In the département of Lozère, which has one of the best-documented lauze traditions, two families of stone are used:

• Schist lauzes (lauzes de schiste), quarried in the Cévennes, Mont Lozère, Margeride, the Lot valley and parts of Aubrac and the Tarn valley. Their thickness follows the natural bands of the rock, and quarries such as Lachamp near Marvejols, Le Tournel in the upper Lot valley and Galta in the Cévennes each produced stone with its own hardness and colour.
• Limestone lauzes (lauzes calcaires), used on the limestone plateaux of the Causses (Sauveterre, Méjean, Noir) and in the Tarn and Jonte gorges. These are split to their final thickness.

Laying

Schist lauzes usually sit on a timber roof structure with boarding (douelle or volige). Traditionally each stone was fixed with a wooden peg driven into the boarding; today they are usually nailed. Courses overlap by about two-thirds, leaving a third exposed (the pureau), increased to three-quarters on the lowest pitches, and stones are graded from the largest at the eaves to the smallest at the ridge. The biggest slabs, over 60 cm (24 in), are kept for gutters and ridges.

On the Causses, where wood was scarce, limestone lauzes were often laid dry on a bed of stone chips directly over a masonry vault, giving a "vault on vault" roof. Such roofs typically have a slope of 40-60% (about 22-31 degrees), set by the curve of the vault, and use mortar only at gutters and ridge. In northern Isère, where the technique has also been revived, slabs of schist or limestone held in place by their own weight on a strong oak or poplar frame are reported to last about a century.

Decline and revival

Lauzes were often quarried close to the house as a sideline to farming, with commercial quarries organised only in the 20th century. The craft declined because of low output, high laying costs, heavy reuse of salvaged stone and the spread of industrial substitutes; imported limestone lauzes that proved frost-prone caused failures around 1996-1999. Repopulation of rural areas from the 1980s and financial aid helped revive the trade, and heritage services have worked on it for more than 30 years. The Causses and Cévennes were inscribed on the UNESCO World Heritage List on 28 June 2011 as an evolving cultural landscape.

Local terms

• Lauzier: a craftsman who lays lauzes.
• Lauze qui chante: "a singing lauze", a stone that rings when struck, a sign of sound quality.
• Gouttier: large slab at the eaves.
• Lignolet: a ridge made of crossed lauzes.
• Coyau: a small piece that kicks out the roof slope at the eaves.
• Cailloutis: the stone-chip bed on a vault.

Sources and gaps

Weights per square metre for lauze roofs vary with the stone used; typical figures are not well documented in published sources.