Roof truss coverings come with varying pitches to ensure the appropriate drainage of precipitation from the roof and the protection of the structures beneath. The coverings themselves can be implemented using a variety of materials and element sizes.
I. Traditional Coverings
1. Bundle Coverings (Thatch)
Ancient traditional coverings include bundle coverings made of reeds or straw, as well as the pressed straw covering. A thatched roof is constructed by tying the straw into bundles, and making a continuous braid from smaller, rolled-up bundles of the sheaves' own fibers around the battening supporting the given course. This can be made with a smooth surface or in a stepped solution; in both cases, battening placed every 30-40 centimeters is necessary. Coverings tied according to the stepped solution can be made smooth by driving up (compacting) the ends of the courses; this is called the driven thatched roof.
When making a reed roof, the reed bundles are tied to the battening placed every 50-80 centimeters, and these are driven up row by row, moving from bottom to top.
2. Wooden Coverings
The small-element solution for wooden coverings is the shingle roofing. The 40-80 centimeter long shingle elements are made by splitting, typically from pine blocks. The elements are formed with a grooved joint; one long side is sharp (a feathered edge), and the other has a groove (a rebated edge). The shingles fit next to each other, creating a single-layer, scale-like covering.
For board roofing, one-meter, 10-15 cm wide elements made of hardwood are fixed by nailing or hanging. Elements made of softwood are wider, between 20-25 cm.
3. Slate and Tile Coverings
Slate can be used to make a roof covering by splitting and carving the square slate tiles to form a scale covering. It is fixed to the battening by nailing. However, the most successful traditional solution is the fired clay tile covering. It is a suitable small-element solution which meets modern requirements. Clay tiles are made in varied shapes, sizes, surface appearances, and colours. Two well-known solutions are:
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The monk-and-nun covering (widespread in the Mediterranean areas of Europe). Truncated cone-shell-shaped monk tiles and flanged flat nun tiles create vertical channels within the roof surface. The advantage of this type of covering is that it provides adequate water sealing even at a lower pitch angle.
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The beaver-tail tile covering is another widely-used form, allowing varied roof surfaces to be created due to the covering pattern. For adequate water sealing, a double lap covering or crown covering is necessary from the 35-40 centimeter long, 18-20 centimeter wide, lugged elements. In a double lap covering, a minimum of two layers of tiles cover each other over the entire surface at any point of the roof. This requires dense batten spacing (usually around 15 centimeters), providing an overlap of 22-25 centimeters between the layers of the scale covering.
II. Types of Modern Coverings
1. Small-Element Coverings
In modern practice, countless improved versions of ceramic tile coverings have been developed in recent decades. Among these, interlocking tiles are worth mentioning, which make the lateral connection of the elements more watertight. Pressed clay tiles represent a further step towards less material usage and more secure water sealing. In this case, interlocking connections can be formed all around. All these tile forms, including the traditional shapes, are also increasingly gaining ground in concrete form and are available in various colors. A special type of concrete tiles is the corrugated interlocking tile, which in appearance, evokes the monk-and-nun covering. Through the interlocking connections, modern tile coverings function as a single covering. Moreover, the necessary degree of overlap is reduced to a minimum.
Fibre-reinforced cement coverings are another small-element covering that has 4-5 mm thick elements which form a single or double covering depending on the element shapes.
Likewise, small-element bituminous shingle covering has a multi-layered structure with a coloured slate or basalt grit surface on glass, or plastic fabric-reinforced modified bitumen sheets.
Its construction requires full-surface sheathing or boarding.
The covering’s underlayment is a type of bitumen sheet.
2. Large-Element Coverings
Large-element coverings include tile-effect sheets, corrugated fibre cement sheets, or profiled metal sheet coverings.
Galvanized steel tile-effect sheets, 0.5 mm thick, imitate clay tiles by varying in dimensions from single or double-course panels to large format sheets covering 6-8 square meters. A major advantage is the low dead weight; its laying is done with the help of boarding (sheathing).
Corrugated fibre cement sheet covering is made of fibre-reinforced cement (asbestos-free slate). The 1.5-2 square meter corrugated fibre cement sheets are installed, element by element, to 2-3 wooden or steel purlins, in a grid arrangement, with 15-20 cm overlap in both directions. The sheets are generally fixed at the wave crests using fastening screws.
The characteristic material of the profiled metal sheet coverings can be aluminium, galvanized steel, or copper, which can be formed with wave, trapezoidal, or rare-rib profiling, with variable dimensions. Sheet size can range from 1.5 square meters up to 12 square meters, with a typical width of 1 meter. The coated, coloured, or material-patterned sheets are arranged in a grid, and these are screwed on steel or wooden purlins.
3. Flat-Sheet Coverings
Flat sheets from various metals can form a cohesive covering system with other flashings and gutters. Materials can be galvanized iron, galvanized steel sheets, aluminium, or copper sheets, similar to the roof's other flashings. Flat-sheet coverings require boarding in all circumstances, laid closed (tightly butted) or with gaps (spaced sheathing). Particular attention must be paid to ventilation; thus it must be designed as a two-layer (cold) roof in all cases. For non-absorbent, closed substrates, it is necessary to lay a ventilated underlay mat. The sheets or strips are connected watertight to each other using standing seam systems, either double-lock or single lock seams, or batten roll joints.
