Roof slopes perform not only protective-bearing functions, but also have a significant impact on the formation of the architectural and design image of the house. To a large extent, the visual adjustment of the proportions of the roof will depend on the characteristics of the overhang. This is a cornice unit, the width and position of which emphasize the boundaries of the roof slopes. Also, the design of this element can perform practical tasks.
Eaves structure
All elements of this roof structure can be divided into two groups:
- Directly continuing the truss system.
- Performing helper functions.
To begin with, it must be emphasized that the cornice begins at the point where the wall frame of the house ends. As a rule, the ramp is fixed in this area on the Mauerlat platform - a load-bearing beam installed on top of the outer wall. The system of the cornice unit of the roof truss is continued by the "roofing pie" withcrate and load-bearing slats. This is a power structural part that brings the slope line beyond the perimeter of the building frame.
As for the auxiliary elements, their presence just distinguishes the slopes on the slings from the cornice overhang. Firstly, this is a group of fasteners with a support board, spotlights and a supporting apron. Secondly, it is a number of functional components such as insulating layers, gutter, ventilation system, drip and other additions that are included in the design as needed.
Materials for the construction of the cornice
And again, the base will be carried out mainly according to the same rules as the truss system with a roof. Wood elements, metal sheets, plastic typesetting components, etc. are more often used. For example, a board will be good in terms of ease of processing - a pliable wood structure will allow you to form the most complex structural options for a cornice. Metal elements are usually galvanized steel sheets with a thickness of 0.8-1 mm. Sometimes aluminum with a thickness of 6 mm is also used, but in terms of strength characteristics, this is not the best option. And vice versa, the most reliable will be a brick cornice assembly formed by protruding masonry. In private housing construction, a small architectural form is usually used - the so-called sandrik. This is a small brick cornice that can perform the task of drainage, visual division of the facade horizontally, etc. The execution of the sandrik in shape also has different options. So,the construction of rectangular, triangular and even curvilinear structures is practiced.
Normative design parameters
There is a recommended format for organizing an overhang according to GOST, which determines the dimensions of a cornice made of different materials. In particular, the width of the overhang based on corrugated asbestos-cement sheets is 250 mm, and from galvanized steel - at least 120 mm. In systems with a flexible roof, small protrusions of the order of 70 mm should be made. One of the most common schemes involves pairing the eaves assembly with a metal tile - the width of this design should be 50-70 mm, depending on the characteristics of the internal lines in the under-roof space. The remaining parameters also do not have strict regulation and in each case they are approved by the designer of the truss system.
Optimal overhang proportions
When determining the configuration of the cornice, it will be useful to follow several rules. First of all, the height of the overhang relative to the ground should correspond to the level of the attic wall. If this part of the frame of the house is missing, then the eaves can even rely on the attic floor. The location of the cornice relative to openings and entrance groups is also important. In this part, the degree of shading for windows, camouflage properties and the organic design of the structure in a single composition with other roof elements should be taken into account. For example, an overly narrow eaves assembly looks unnatural, while an oversized one can cover other functional devices such as lamps, drainage systems, andetc.
Of course, as for a slope, a correctly calculated angle of inclination is important for an overhang. These two angles may not coincide with each other, since the cornice line is often refracted. And yet, a 45-degree slope is considered the standard, at which it is possible to evenly distribute loads over the overhang, while maintaining the functional content of the structure.
Design options
Basically, the formats for the implementation of the cornice overhang can be divided into the following types:
- Non-hemmed structures - used when installing a hip (four-pitched) rafter roof, as well as for some gable systems. In essence, these are continuations of slopes with a minimum slope, but without lower covering panels.
- Hemmed - also often used in the construction of hip and gable roofs, but with certain nuances. The fact is that the cornice unit of the rafter roof with filing forms a technical space that expands the functionality of the structure. Most often, sealed niches of overhangs are used as a hiding cavity for electrical engineering - lamps, lanterns and lighting devices are built into it.
- Box overhangs - a type of cornice with filing, which best reveals its advantages in single-pitched and broken truss systems.
- Short overhangs are a low-cost and simple design that provides a minimum set of functionality, but less load on the roof frame.
Features of the cornice unit in a flat roof
The main differences between this eaves and overhangs for pitched systems are the absence of a slope and a more reliable sealing device on the upper surface of the structure. The ledge can be completely horizontal - also continue the line of a flat roof, or it can have a slight slope of up to 5 degrees. The presence of even a minimal slope will facilitate the process of removing precipitation. By the way, it is the need for protection from rainwater and melting snow that explains the increased requirements for insulation of the flat roof eaves assembly and its joints. Several layers of hydro- and heat insulators are used, which are carefully soldered, treated with silicone and bituminous mixtures. In this case, the eaves can be based on both separate elements of the roofing deck, and part of the main frame in the form of a reinforced concrete floor.
Ventilation system in the eaves
Technologically, a branch pipe can be integrated into the design of the overhang to remove combustion products or provide air circulation. In addition, if the components of the system as such do not have ventilation channels, they should be created additionally, otherwise condensation will form in the under-roof space. The simplest ventilation system involves the creation of outlet holes in the same binder. Usually they are formed in a group way with a diameter exposure of the order of 5-10 mm. Again, it is worth noting that there are additional elements of the eaves assembly, in which there are already ready-made perforations and holes forair circulation. As for the outlet of the branch pipes, special holes of large diameter are made for them, which can exit through the rafter system, bypassing the ceiling.
Structure mounting tool
Roofing involves the use of several groups of tools and consumables. So, in preparatory activities, a complex of measuring and marking devices can be used, such as a range finder, goniometer, ruler, level, marker, etc. Directly mounting operations are performed by the following tools:
- Screwdriver.
- Hammer.
- Kyanka.
- Chisel.
- Tool for processing materials. For metal and wood, different devices are used, such as a hacksaw, jigsaw, circular saw, etc.
Depending on the requirements of the project, consumables for the cornice overhang are also selected. The node, in addition to the main prefabricated elements, will be formed by mounting fittings. These can be corners, clamps, brackets, profile parts and docking devices.
Installation of the base of the eaves
In the typical model, the structure is arranged on the basis of a cornice crate at the bottom of the slope, which, in turn, either abuts against the rafter, or bypasses it, falling even lower. The task of the roofer is to connect these elements with wooden, metal or plastic planks. The brick base mentioned above is usually arranged at the stage of erection of the wall structure.
So, the fastening of the cornice unit from the slats is carried out using bars or profiled metal elements, which are fixed to the underside of the slope. Further, according to the installed blanks, a crate is formed, on which the skin will be fixed in the future. The outer edge of the junction of the crate and the slope must also be closed with a plank so that it does not leave a gap on the upper side. It turns out a closed inclined overhang without a niche in the cornice space. To create it, you will additionally need to install the crate to the wall, after which another group of load-bearing planks is mounted to its lower beam from the outer edge.
Which fastener should I use?
In the installation of wooden bars, profile components and the frame of the crate as a whole, you can limit yourself to nails of the 0.8 mm format, correctly observing the indents. In the case of metal, self-tapping screws and bolts are used by default, but massive, responsible structures should be seated on more reliable hardware. For example, attachment points to a reinforced concrete eaves slab are made with anchor connections, and in the presence of reinforcement protruding outwards, welding can also be used. Heavy metal sheets to wooden planks are fixed through the counter-lattice using galvanized self-tapping screws with a seal.
Sheathing done
It is advantageous to use the lining from the bottom side not only because of the formation of a closed box in the under-cornice space. The very finishing of this kind allows you to decorate the design of the overhang, often eliminating itdefects. Actually, there can be several solutions to this problem - to the created carrier base from the crate, nail a number of boards, veneer the entire area with plywood, or use siding panels that are convenient to build into structures with different shapes and sizes. Also, do not forget about the gables, that is, the sides of the cornice assembly. From the rafter leg to the lowest point of the overhang, the finishing is done with the same material as the main horizontal filing. It is only important to take into account the different nature of external influences on this side. If the bottom filing practically does not come into contact with the rays of the sun, then the pediment will take on both ultraviolet and various mechanical loads.
Conclusion
A well-thought-out pitched system in conjunction with the facade and truss structure will help organize comprehensive protection of the under-roof space and achieve the aesthetic value of overhangs. Even at the design stage, it is important to consider what else the functional load on specific nodes of the cornice overhang can be. The roof allows the removal of melt water to water collectors remote from the foundation, but this will require an appropriate overhang with elements for sending wastewater. The same applies to the ventilation system, which can be based on aeration components of various configurations. At the same time, each function of the cornice should be calculated both in terms of the possibilities of technical implementation and decorative properties.
