Roof geometry elements
Roofs consist of a load-bearing structure usually made of wood, but can also be made of reinforced concrete, steel or as a mixed structure. The remaining layers are insulation, both thermal and vapour-tight, underlay and top cover.
In order to be able to talk about roofs at all, you should first familiarise yourself with a certain name for its elements.
1 The roof slope is a surface at a certain angle, limited by the edges.
2 The eaves are the lower, lowest edge of the slope. It protrudes slightly beyond the face of the building, and it is to it that the gutters are attached.
The ridge is on the other side of the roof slope. It consists of two slats intersecting at the highest point, parallel to the eaves.
The corners are formed by two adjacent slopes, which intersect to form a convex angle, which is also a diagonal edge.
The basket is defined similarly to eaves with the difference that in this case, the intersection of a slope creates a concave angle. The basket is responsible for draining water from the roof slope.
The shape of the roof
As we know from observation, roofs can have a variety of structures and shapes. But what determines their choice?
Most often these are structural, climatic or functional conditions, but there are also situations where regional conditions are involved.
In places where there is frequent and heavy rainfall and snow on the roof can stay for long weeks, we will instead use roof solutions with higher slope inclination. However, where these conditions are much less frequent, we can afford flatter roofs. However, it should be remembered that the flatter the roof, the tighter materials are needed to cover it. Thus, roofing felt, and other bituminous materials are more often used for flat roofs, tiles are used for a structure with a higher slope.
Here are some basic shapes of roofs, without unnecessary descriptions:
Structures of wooden roofs
Wooden roofs, most often used in single-family houses, are mainly made of pine or spruce wood. This is determined by both the properties of these species and the economic aspect.
Roof trusses, because so-called roof structures are made by carpenters. They differ both in quality and the way they are made. In order to be able to talk about roof truss constructions, you should first get acquainted with its basic elements:
– The rafter is a sloping beam that takes over the loads acting on the roofing;
– The purlin is a horizontal beam which supports the rafter and is mounted along the roof slope. Due to its location, we distinguish between an alloy purlin, an intermediate purlin and a ridge purlin;
– The purlin is an alloy purlin. The masonry-based purlin transfers the loads transmitted by the rafters directly to the building wall;
– The column is used to directly transfer the load from the purlins to the floor of the top floor, sometimes the values of these reactions are so high that a foundation is required;
– The foundation is a beam laid under the columns to distribute the forces transmitted by them over a larger area;
– A wind girder is an element nailed diagonally to the rafters to stiffen the structure and prevent deformation caused by the wind. Most often the wind girder is simply a longboard;
– The wind girder is a horizontal element which is intermediate support for the rafter;
– The sword is a sloping element which has the task of stiffening the purlin/pillar connection;
– The tongs are horizontal beams designed to hold the rafters on both sides and thus provide horizontal stiffening to the structure;
– The tick is an additional diagonal element that connects the foundation to the column.
The simplest two-bay roofs in terms of construction. Used for a span of 6.0m. Rafters supported in two places, directly above the wall and in the ridge. The whole structure is stiffened with windchests.
The structure is similar to the rafter one with an additional stiffening mole introduced. This procedure allows to lengthen the rafters, and thus increase the slope, and thus also the height of the attic. It is dedicated to the span of 6.0-11.0m.
Purlin and tick roofs
They are used in wider buildings with internal load-bearing walls. An additional point of support for the rafters is intermediate purlins supported on columns. The structure consists of two types of trusses: intermediate – consisting of rafters and solid – i.e. trusses with columns. Horizontal bracing of the structure is provided by ticks.
As the name suggests, it is a combination of ceiling and roof, so this hybrid should meet the requirements of both. Of course, we can distinguish between several types of roofs, but regardless of which one we take into account, some of their elements will be common.
The floor slab consists, of course, of a load-bearing structure, thermal insulation, vapour barrier, as well as a layer giving it a slope and, naturally, a covering which will be bituminous in most cases.
Types of floor slabs
- solid roofs – best suited for rooms not heated or heated to low temperatures, due to the problem of water vapour transmission.
- ventilated roofs – made in buildings intended for permanent human habitation, where the temperature exceeds 18°C. The structure consists of a ceiling and a roof between which there is a certain unused space or in some cases a passageway.
The individual structural layers are shown in the figure below:
The inverted roofs are characterised by the fact that the waterproofing is laid on the structural layer first, only on it the thermal insulation with low absorption. Reverse roofs allow using the roof slope as a terrace or car park. A specific type of inverted roof is green roofs, so-called roof gardens.
As you can see, choosing a roof structure is an extremely complicated matter. The number of factors to be taken into account is very large, and the decision related to some choices is not easy. Everything we have said here is only about general knowledge and construction. We have not yet mentioned the roofing. Yes, the topic of roofs is extremely extensive.