Rafter system

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From this article you will learn what a rafter system and rafters are, what types of roofing are there. We will consider the device of the roof rafter system, types of roofs, the advantages and disadvantages of the most popular types. Also, the article will talk about an alternative to the wooden rafter system.

Rafter system

A rafter system is a structure that supports the roof, protects the house from wind and precipitation, and in some cases creates additional space (attic, attic). We will consider in more detail what elements it consists of, what types of devices of this design are..

Types of roof systems

There are many varieties of roofing systems. They can be conditionally subdivided into traditional and individual ones. For ease of understanding, we will cover a few basic terms..

Rafters or rafter leg– an inclined element, one of the edges of the roof slope. Located from the ridge to the support wall, or to the edge (overhang) of the roof.

Rafter system

Roof slope– the plane of the roof, located at an angle to the horizon (as a rule, from the ridge to the walls).

Rafter system

Roof ridge– a straight line along which the roof slopes (planes) are joined. Its projection, as a rule, passes between two load-bearing walls of the house..

Rafter system

Mauerlat– the base of the rafter system. Strapping of thick timber or boards along load-bearing walls.

Rafter system

Filly– an element that extends the rafters for the roof overhang.

Rafter system

Attic floor or attic– living space in the attic of the house, less than the lower floors. The roof has a broken shape.

Rafter system

Traditional truss systems

The simplest and most proven designs, for the creation of which a minimum level of knowledge and skills is sufficient. The design of traditional systems has evolved historically for many centuries, so they can be called the optimal solution for most cases. When creating a traditional system, for a building no larger than average (up to 80 square meters), only the necessary minimum of parts are used, assembled in an intuitive way.

Shed roof

The roof rafter system, consisting of one slope, is used only on temporary and ancillary buildings – a garage, a shed or an extension, a terrace, a shed, a canopy. To create such a system, a row of rafters is raised from one side (along the supporting wall) to a height of 1/10 (10% slope) to 1/3 (33% slope) of the length of the rafter projection (distance between the supporting walls).

Rafter system

The properties of such a rafter system rarely allow it to be used for residential buildings due to the limited area of ​​the ramp, and therefore the entire building. Despite the lowest consumption of roofing material, the lean-to layout is the least effective in organizing the under-roof space. In order to ensure sufficient bearing capacity, powerful beams are used.

Gable roof

The simplest roof type for a residential building. The gable roof rafter system consists of two planes created by rafters that converge at the ridge. In most cases, the slopes are made equal in size..

Rafter system

Advantages:

  1. No need to dock additional planes.
  2. Less waste of roofing material (no corner trimming).
  3. Lowest material consumption.
  4. The smallest total weight of all elements.
  5. Mauerlat is optional.
  6. A wide variety of options – from an attic roof with a height of 400 mm to a full attic floor.
  7. The spread of the length of the slopes – from 1 to 6 m.

Disadvantages:

  1. Load distribution on two load-bearing walls.
  2. The vertical pediment takes up significant wind load.
  3. Consumption of wall material for the pediment (as a rule, it is more expensive than roofing).
  4. Normal appearance.
  5. A gable roof deforms faster than a four-pitched roof due to less spatial expansion.
  6. With a heavy snow load, additional supports and a decrease in the ridge angle (to make it sharper) are required *.

* – reducing the angle of the ridge is possible only by increasing the height of the attic space, since the bearing walls are motionless.

The slopes are most often of equal size, but unequal roofs are also found. The optimal ridge angle is 90 °. The gable rafter system is suitable for any buildings with lightweight roofing material (all modern materials – metal, profile, slate, etc.).

Four-pitched roof

“Derived” from a gable roof. The rafter system of the hipped roof has developed historically. Due to the use of clay tiles as a roofing material, which has a large weight, it became necessary to distribute the load over all walls and corners of the building. When supporting the ends of the rafters on the Mauerlat, fillets are built up to them to increase the roof overhang and drainage.

Rafter system

In this variation, the gable rafter system receives two additional ramps. In other words, the pediment is replaced with a roof slope, which has a triangular shape and is called “hip”. That is why hipped roofs are most often hip.

Advantages (in comparison with gable):

  1. Significantly high bearing capacity.
  2. Spatial rigidity of the rafter system.
  3. The load is distributed over four load-bearing walls.
  4. Replacing wall material with roofing – less load on the foundation.
  5. Damping the wind load on the pediment with an inclined slope (hip).
  6. Ability to withstand roofing material and snow load of significant weight.

Disadvantages:

  1. Advanced carpenter skill required.
  2. Mandatory device Mauerlat.
  3. Higher material consumption of the rafter system.
  4. Higher consumption of roofing material (corner trim).
  5. Greater total weight of all materials.
  6. Part of the attic is inaccessible due to the hip.

Rafter systems that have more than 4 slopes are called multi-slope. They basically repeat the hipped roof system, but are designed individually, based on the characteristics of the building..

Individual roof systems

In the case when the building has a complex shape in plan or a complex layout of the attic space, the rafter system turns into a complex structural element with combined functions. The construction of such systems requires a high skill of the carpenter and an understanding of load distribution during operation. We will consider the most common cases of combined roofing.

Mansard rafter system

The simplest of the individual ones. It is mainly used in the reconstruction of a building – the superstructure of an additional floor. In this case, beams are thrown between the bearing walls, which serve as the basis for the overlap and tightening at the same time. A number of vertical posts with a height of 1.5 to 2.5 m are installed along the beams. Roof slopes and a ridge are arranged along the top of the beams.

Rafter system

The advantage of such an attic organization:

  • combination of room functions;
  • reduction of the roof area carrying the snow load;
  • expansion of the living area of ​​the house.

Hip rafter system

As it was said, the hip is a triangular slope instead of the gable roof gable. Therefore, it is called hip according to the principle of the device. For example, in the case when such a slope is arranged only on one side, such a roof is called a hip tilt. The principle of its structure is described in the section on the four-pitched roof..

A special case of a hip is a half-hip. The pediment and hip intersect above the overlap level. There is no practical sense in such a solution (except for a slight decrease in wind load), but the building takes on an interesting appearance. The combination of hips, canopies and roof windows creates a striking appearance.

Rafter system

Another special case of a hip roof is a hipped roof. The roof has four hip ramps that converge at one point. Such a roof does not have a ridge and is only suitable for square-shaped houses in the plan..

Dome and vaulted roofs

They are used for historical decoration, in buildings of artistic value. The rafter system in the form of a dome or hangar, a tower cap or wave-like is a work of art in itself. This requires not just an understanding of the load, but also painstaking calculations taking into account climatic conditions, especially wind and snow loads..

Rafter system

Roof material

It is quite simple to decide on the roofing material – based on the appearance. But the choice of material for the rafter system should be approached more carefully. Traditionally, it is customary to create it from wood. This is quite understandable, given the properties of this material – light weight, ease of processing, relatively low cost. However, the tree has significant drawbacks that negatively affect the entire structure:

  1. Shrinkage. Over time, any wooden material dries up, while the size of the hardware seats increases. As a result, the fastenings are weakened. That is why, when erecting a rafter system, it is recommended to use not nails, but screws (self-tapping screws).
  2. Susceptibility to decay and insect damage. Alas, this is the fate of all natural materials. In addition, homeowners rarely remember about preventive wood treatment..
  3. Relatively low bearing capacity. A coniferous tree does not hold significant loads on cut, crushing and fracture.

Rafter system

In many cases, the use of wood becomes unprofitable and inconvenient – too large a section of the element is required to ensure sufficient bearing capacity. Then the rafter system is made of metal. Here are the most common applications for a steel truss system:

  1. With significant spans. Metal trusses can be up to 12 meters long.
  2. Under heavy load. Steel frame to withstand even concrete roofs.
  3. During the construction of monumental structures (temples, train stations, museums). When fencing large spaces, for example, domed ones, is required, steel trusses are used, designed individually. In addition to the bearing capacity, a long service life is required here – from 100 years.
  4. If high humidity is expected. When exposed to moisture, wood loses its properties many times faster than metal.

Correctly calculated and assembled rafter system is the key to the reliability and comfort of the whole house.

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