Karmen Peternelj, Sanja Alaber, Miloš Bavec, Stefano Devoto, Stefano Furlani, Goran Glamuzina, Jernej Jež, Tvrtko Korbar, Maja Oven Stanič, Maria Luisa Perissinotto, Fabiana Pieri, Duška Rokavec, Ivan Stanič, Domen Zupančič
In order to calculate the amount of stone required for the roof, we use quantities per square metre (m2) and cubic metre (m3). When renovating an existing roof, it is necessary to replace part of the weathered and missing roofing tiles (up to as much as 80%). Overlap must be taken into account when calculating quantities; overlap can be either standard or increased . The increased type of overlap is frequent on roofs of residential buildings, while standard overlap is found on commercial buildings and less demanding single-cell buildings (shepherd's huts, chicken coops and pigsties). Buildings outside built-up areas (in forests, at the edges of pastures and fields) that are intended for occasional use and have no commercial significance employ the standard overlap roofing method.
elements can either be uniform in their general features or specific from one building to another
We should mention the special features that we encounter regularly when surveying heritage: elements can either be uniform in their general features or specific from one building to another. All of the abovementioned structures and elements were created based on the available sources of stone and using the available financial resources, as well as by employing the knowledge of masters who handled the building material. The mentioned plate thicknesses, the top view dimensions of plates and other specification are general and frequent; however, exceptions and special features must be considered as well. The specific weight of the hollowed out or heavily porous Karst limestone ranges from 2640 to 2692 kg/m3. When using roofing stone plates (tiles) on the roof and other architectural elements, we use the weight of stones without pores or hollows, which is 2720 to 2791 kg/m3. The data on the weight of the roofing material affects the roof’s load-bearing structure. The calculation of the weight and volume of the elements is a compulsory task when inventorying architectural heritage. When preparing the detailed design for the renovation, reconstruction or new construction, the project design engineer produces a detailed project design inventory of the works and quantities along with a cost estimate. Without such an expert's report, the planning is incomplete and the management of the buildings representing architectural heritage is unsuitable. When estimating the weight of the roof, the following must be added to the weight of the roofing tiles: the weight of mortar, of the sub-structures on which tiles are placed, of spacing rafters (in the case of a ventilated roof), of secondary roofing material (may be disregarded), of the sarking boards between rafters, of heat insulation (in the case of an insulated roof), of the load-bearing roof structure, of the lower insulation layer (the enclosing of insulation differs depending on the material) and of the final finishing layer of plaster or other finishing of the visible surface of the roof frame.
The list comprises the typical layers of the roof frame cross-section. Variants (structural thicknesses, selection of materials) differ from one project to the next. The planning of roofs and changes to the building's load-bearing structure without suitable project design documentation and the acquisition of a building permit is prohibited. Project designs are prepared by certified architects in accordance with the conditions and approvals of expert services and in cooperation with other experts and engineers involved in the building project design processes.
The calculation of the surface area of the required quantities of stone for the roof is performed in two steps. Necessary documentation is prepared first, which is followed by the data for the calculation.
In terms of the cross-section, the roofing material is laid in several layers, i.e. up to four layers in the vertical profile of the roof cross-section. A stone-built roof is heavy. The documentation comprises several types of content, but we focus on the measurements and plans at this point as they suffice for the calculation of quantities. Quality documentation allows the sound planning of all subsequent project phases. Economic use of resources is not of major concern at this point as the documentation serves as the basis for subsequent decisions on the comprehensive protection and management of the building's heritage (immovable and movable). At this point, we only list certain basic methods of production of a working schematic of the building's height:
We design the data table, enter the quantities in metres and use trigonometric functions or Pythagoras's theorem to calculate the surface areas or measure the lengths from the drawing. Data is determined either by calculation or graphically as both methods are possible.
The measurement of lengths from the plans is straightforward, but the documentation used must be of quality and authentic
The measurement of lengths from the plans is straightforward, but the documentation used must be of quality and authentic. The usefulness of plans is demonstrated in cases where the roofing is a combination of two types of roofing materials (the use of stone exclusively in the gable walls, the roof of the building, the eaves (soffits) or when covering parts of buildings that project beyond the basic body of the building). If no plans are available for the building, Pythagoras's theorem is used to calculate the lengths of the roof in cross-section. Using trigonometric functions, we calculate the pitch values for the roof. The calculation procedure is as follows:
Roofs are simplest on smaller, simple buildings. Buildings that are of modest, straightforward rectangular shapes. Rafters are placed on the outer load-bearing walls, onto which the stone roof is then placed. The roofing plates undergo minimum processing. Plates have larger visible upper surfaces (standard overlap type). Surface areas are between 12 and 15 cm. Shed-type roofs are also common in the construction of simple, architecturally less important annexes to main buildings (Fig. 5.6).
The most frequent roof type is the gable roof. Owing to the sheer weight of a stone roof, gable roofs are generally symmetrical. The symmetry of both sides of the roof allows equilibrium and equal loads on the roof support structure from all sides.
The weight of stone roofing plates can be as much as 500 kg/m2. The covering of a gable roof is performed simultaneously on both sides of the roof. When covering roofs, one can observe the arrangement of plate sizes depending on the position on the roof. The selection of roofing plates depends on the following:
The described method of construction is termed tectonics in architecture. The simultaneous symmetry of covering with stone plates indicates tectonics. The size of the plates towards the top decreases, and the plates are also thinner towards the top.
Roofing stone plates are semi-carved plates and are processed as little as possible, i.e. only as much as necessary to fit the roof and to reasonably drain precipitation. Stone plates can be used to cover various floor plan shapes including rectangular, square, multi-angled and round designs.
Multi-angled shapes are generally symmetrical and rest on gables or the side walls of the building. The most frequent floor plan shapes in the area of the Karst and the Adriatic are octagonal houses or derivations thereof with sections of the basic floor plans. These floor plan designs are frequent for sacral buildings (apses, front door canopies) as well as for annexes to residential buildings (e.g. spahnjenca black kitchens on the Karst, Bišćević houses in Mostar)(Fig. 5.7).
