A roof overhang is a structure that protrudes beyond the walls of a building. Some call this structural element a box. The main purpose of the roof overhang is to protect the walls from all kinds of precipitation. For a higher efficiency of such protection, the rafters of the roof base are taken out of the walls for a segment of 50-60 cm. This indicator can be slightly increased.
In some cases, the truss system does not provide for protrusions beyond the walls of the building. At the same time, forced elongation of the rafters is used by means of special elements - filly.
It should be noted that the frontal part of the walls of the building also needs protection, which is also provided by overhangs.Typically, the width of the front overhangs is made at least 500 mm long. At the same time, a cornice-type board is mounted on the edge of the roof.
The lower part of the roof overhangs is to be sheathed. As a lining material for roof eaves filing, as a rule, use a tongue-and-groove board.
It should be noted that the designs of the pitched and frontal overhangs are somewhat different from each other.
Classification of roof overhangs
Throughout the history of construction, many different types of overhangs have been invented and successfully put into practice.
Let's consider the main ones:
- Unlined overhangs - great for hip roofs, single-pitched and gable type structures.
- Hemmed overhangs - also look good on hip roofs, are widely applicable on gable roofs.
- Box overhangs - applicable on single, gable and hip roofs.
- Shortened roof overhangs - used on almost every major type of structure.
Types of overhangs
Advice! The overhang should always be a continuation of the roof. The type of overhang, as well as the overall structure of the roof, is selected according to the climate of the region in which construction is being carried out.
Let us dwell in more detail on the design features of roof overhangs:
- A flush cornice overhang is formed when the rafters do not extend beyond the frontal boundary of the walls.This requires fastening along the edge of the rafters, the so-called drain board in a horizontal position in order to protect the ends from the penetration of moisture and at the same time to ensure fastening of the gutter system. In addition, such a constructive move will provide the roof with some individuality. The disadvantage of such cornice overhangs is the exposure of the upper parts of the walls from moisture. Flush overhang in wooden houses is usually performed in a length of at least 55 cm. As for brick and panel structures, a protrusion of an overhang of a shorter length is allowed here. If puffs are released beyond the front line of the walls, into which the rafter legs are embedded, in such a design it is recommended to install cornices, which will prevent the formation of drafts in the attic space of the structure and prevent snow from blowing into the cracks of the structure. In the absence of protrusions of the rafter legs beyond the line of the walls, they are lengthened with "fillies", which are used as trimmings of timber, screwed or nailed to the rafter ends. Directly to them and attach the cornice board.
- Eaves roof overhangs of an open type are formed when the main rafters of the roof structure protrude beyond the walls. In this case, the drainage system is fastened either to the side parts of the rafters or to the upper edges. This system is very often used in the construction of private houses.
- The cornice overhang of a closed (protective) type is formed when the cornice closes the ends of the rafters protruding beyond the gable part, which have a special groove on the inside. The skin elements are subsequently inserted into this groove.
Advice! If the attic is an isolated room, the closed eaves should be equipped with ventilation holes.
- The gable overhang can be arranged both flush and with a ledge beyond the walls. The method depends on the designer's idea, since in any case the choice will be correct. However, if the overhang protrudes beyond the walls, be sure to sheathe the area of the roof that is unprotected.
Materials for sheathing overhangs and its device
The most common material used for sheathing overhangs is a board. Coniferous woods are the most preferred here (spruce, larch, pine).
Particular attention must be paid to the moisture content of the selected material. If the humidity is too high, the material may deform over time, which will lead to damage to the appearance of the overhang.
In addition, the thickness of the wood paneling is also important. According to the norms, the thickness should be at least 17 mm, while being no thicker than 22 mm. The width and length of the boards are selected individually.
Fastening of plank sheathing is carried out on both sides, which does not apply to boards longer than 6 m - here the fasteners are performed in increments of a meter of sheathing material length.
Each board used is invariably treated with a waterproof mortar immediately before installation.
In this case, special paint or varnish for wood can be used. Wooden filing of roof overhangs requires processing every few years, then the overhang can please the eye for a long time.
An important factor is the overhang ventilation system. It is satisfied regardless of the type of construction. The inlets should be 1/600-1/400 in diameter of the area to be ventilated.
With proper calculation and implementation, air will enter these holes and exit through the hole in the roof ridge. The inlet openings are covered with a net so that bats, birds and insects do not penetrate into the attic.
In addition to boards, sheathing of overhangs is also made from the following building materials:
- Galvanized steel sheets. Sheathing of roof overhangs is made of steel with a thickness of not more than 0.6-0.8 mm. In addition to ordinary sheet steel, perforated metal sheets can be used. The height of the wave in this case should be no more than 20 mm. To cut such material to the required size, special equipment is used. After fitting the sheets to size, the cut edges are coated with a layer of paint to prevent corrosion.
- Aluminum sheets coated with a protective layer. The thickness of the sheets is chosen within 6mm, the width is 10-30cm. The length of the sheets should be no more than 6m. Fasten the aluminum cladding with special latches.
In addition to these materials, manufacturers offer a wide range of other materials and elements that improve both the functional and aesthetic properties of overhangs.
Strengthening and protection of overhangs
Incorrect installation and roof eaves lining can lead to their deformation, sagging and failure under the influence of wind and snow load. To avoid such troubles, it is necessary that both the overhang and its sheathing are connected to the roof truss system.
For more effective protection of overhangs, the “boxes” and connecting elements of the rafters should be carefully fastened.
In addition, to prevent clogging of drainage systems, heating elements are installed on the roof section located in front of the overhang and in the drainage system itself. This allows you to organize the kindling of adhering snow and its descent into the drain, thereby reducing the load on the roof overhang.
Organization of ventilation holes under roof overhangs
The ventilation device of the under-roof space allows you to avoid such unpleasant consequences as damage to the supporting truss frame and simply a poor internal microclimate of the attic.
Ventilation openings located on the eaves of the roof are of two main types:
- The simplest of this kind of holes is a small gap between the soffit (cornice sewing) and the bearing wall of the building.
- Special plastic ventilation grilles of various sizes can also be used, which are mounted in a soffit.
If a roof covering made of natural tiles is used, special tile slabs with ventilation holes are used. These tiles are mounted in the 5th row, if you start counting from the cornice overhang.
In the case of additional insulation of the cornice overhang, one should also not forget about the arrangement of ventilation holes, the length of which is chosen depending on the type of ventilation being installed.
When laying roof insulation these holes are left open, otherwise the quality of air ventilation in the space under the roof will leave much to be desired.
The lining should also have holes for ventilation in appropriate places.In other words, the path to fresh air must remain free.
Among other things, to achieve better ventilation of the attic, which has a sufficiently large size, auxiliary ventilation equipment can be used.
The result of all of the above is the fact that a well-mounted roof overhang will not only achieve a visually attractive effect of a private building, but also significantly increase the durability of both the roof itself and its base, and the structure of the entire structure as a whole.
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