Roofs are the topmost elements of building systems. The building material used in these elements is generally wood. In this article, we will try to examine the reasons, advantages and disadvantages of wood material in roof.
What is a roof?
They are the elements created to protect the building from atmospheric effects. In these types of building elements, wooden material is generally chosen while creating the carrier system and coating elements.
The use of wood material on roofs dates back to prehistoric times. The main reasons for choosing the material are:
- It is resistant to corrosion
- High strength
- Being an economical material
- Easy to shape
Today roofs; It is divided into two as roofs with (cold) and not (hot) spaces.
Cold roofs are roof systems used before the Industrial Revolution and produced with a slope. These roofs do not allow the use of the attic as the insulation material is applied to the ceiling part of the building rather than the sloping part.
Warm roofs do not cause a problem in the use of the attic, as the thermal insulation material is made on the roof system.
As we can guess from these definitions, hot roofs are generally used in roof systems.
Comparison of Wood Material with Other Materials
Different materials can be used in the production of the roof system. Let’s examine the various comparisons of wood materials with other building materials in the research entitled “Alternative Roofing Materials in Housing Construction” published in 1994, from the table below.
Performance Criteria Required for Roofs
Atmospheric effects such as snow, rain, wind, water vapor, sunlight shorten the life of wood.
- The roof must be strong enough to carry the moving loads coming to it and must be able to transmit these loads to the carrier system.
- Since water causes deterioration and decay in wood, structural and chemical measures can be taken against this situation. As a structural measure, the roof slope can be increased in order to drain the water early. As a chemical measure, wood material can be impregnated and its resistance against degradation can be increased.
- Temperature and sun rays can cause expansion and contraction of the elements. Such situations may cause different deformations on the roof. As a precaution, insulation materials can be preferred between the rafters or on the floor.
Layers on Roofs
- There is also the possibility of the roofs being blown due to the wind. For this reason, the dimensioning of the roof should be done safely according to static and dynamic loads.
- In addition to the weight of the building itself, the weight of the roof also comes as an extra load on the structure. For this reason, there is a need for a member that will reduce the weight of the roof but with high strength, and this appears as wood.
Wooden Roof Elements
Coating: It is the element that ensures the smooth creation of the roof surface. Covering board is used underneath to set the coating.
Rafter: It is a roof element on which the under-coating board rests and sits on purlins with an axis interval of approximately 50 cm.
Aşık: They are the elements on which the rafters sit. The purlins try to bend the loads of the rafters and are transferred to the pillars in the fixed roofs.
Pillar: Elements that transmit the loads received from the purlins to the structure. Pillars on suspended roofs are called “bos”. Post sizes are usually chosen as 10/10 or 12/12.
Tree Types Used for Roofs
Before the Industrial Revolution, solid materials were generally used as materials, but later composite materials were used.
Solid Material: These are materials that are dried or used directly without drying.
Composite Material: Materials formed by the combination of at least two different materials.
While materials such as oak, chestnut and poplar were used as massive materials, today trees such as pine, spruce and fir are used more.
OSB (Oriented Strand Board) is generally used as covering material. This material is divided into classes according to moisture and humidity.
Solid materials are generally preferred for elements such as purlins, rafters and roof trusses.
The choice of material to be used in roofs, which are the carrier elements of building systems, depends on many factors. The mechanical properties of the material, its resistance to environmental factors, its economy and sustainability should be the main issues to be considered in this selection.