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, 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.
The structure of the eaves overhang
All elements of this roof structure can be divided into two groups:
- Directly continuing the rafter system.
- Performing auxiliary 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, a ramp is fixed in this area on a Mauerlat platform - a supporting beam installed on top of an external wall. The system of the eaves node of the rafter roof is continued by the “roofing cake” with a crate and load-bearing trims. This is a power structural part, which displays the slope line beyond the perimeter of the structure frame.
As for the auxiliary elements, their presence just distinguishes the slopes on the slings from the eaves overhang. Firstly, this is a group of fasteners with a support board, soffits and a bearing apron. Secondly, it is a series of functional components such as insulating layers, gutter, ventilation system, drip and other additions, which are included in the design as necessary.
Materials for the construction of the cornice
And again, the foundation will be carried out mainly according to the same rules as the rafter system with a roof. More often used are wood elements, metal sheets, plastic typesetting components, etc. 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 versions of the 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. Conversely, the most reliable will be a brick cornice unit formed by a protruding masonry. In private housing construction, they usually use a small architectural form - the so-called sandrick. This is a small brick cornice, which can perform the task of drainage, visual division of the facade horizontally, etc. Sandric execution in shape also has different options. So, the construction of rectangular, triangular and even curved structures is practiced.
Design Guidelines
There is a recommended format for the organization of the overhang in accordance with GOST, which determines the size of the cornice made of different materials. In particular, the width of the overhang based on corrugated asbestos cement sheets is 250 mm, and of galvanized steel - not less than 120 mm. In systems with a flexible roof , small projections of about 70 mm should be made. One of the most common schemes involves pairing a cornice unit with a metal tile - the width of this structure should be 50-70 mm, depending on the characteristics of the internal slings 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 rafter system.
Optimal overhang proportions
Defining the configuration of the cornice, it will be useful to follow several rules. First of all, the height of the overhang relative to the surface of the earth should correspond to the level of the attic wall. If this part of the frame of the house is missing, then the cornice can even rely on the attic floor. It also matters the location of the cornice relative to the openings and entrance groups. 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 excessively narrow cornice assembly looks unnatural, and too large can block other functional devices like lamps, drainage systems, etc.
Of course, as for a ramp, a properly calculated slope angle is important for the overhang. These two angles may not coincide, since the eaves line is often refracted. Nevertheless, the 45-degree slope is considered the standard, at which it is possible to evenly distribute the loads over the overhang, while maintaining the functional content of the structure.
Design Options
Fundamentally, the formats for the implementation of the eaves can be divided into the following types:
- Unfinished constructions - are used in the construction of a hip (four-gable) rafter roof, as well as for some gable systems. In essence, these are extensions of the slopes with a minimal slope, but without the 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 of the rafter with a hem forms a technical space that extends the functionality of the structure. Most often, sealed overhangs of overhangs are used as a hiding cavity for electrical engineering - lamps, lanterns and backlight are built into it.
- Box overhangs - a kind of cornice with a binder, which best reveals its advantages in single and sloping rafter systems.
- Shortened overhangs are a low-cost and simple design that gives a minimal set of functionality, but less loads on the roof frame.
Features of the eaves node in a flat roof
The main differences of this eaves from overhangs for pitched systems are the lack of tilt and the device more reliable sealing on the upper surface of the structure. The protrusion can be completely horizontal - also continue the line of the flat roof, and may have a slight slope of up to 5 degrees. The presence of even a minimal slope will facilitate the process of precipitation. By the way, it is the need for protection against rainwater and thawed snow that explains the increased requirements for insulation of the cornice of a flat roof and its joints. Several layers of hydro and heat insulators are used, which are carefully soldered, processed with silicone and bitumen mixtures. In this case, the cornice can be based on both individual elements of the roofing and part of the capital frame in the form of reinforced concrete floors.
Cornice ventilation system
Technologically, a branch pipe can be integrated into the overhang design for the output of combustion products or for ensuring air circulation. In addition, if the system components 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 provides for the creation of outlets in the same binder. Usually they are formed in a group manner with a shutter speed of about 5-10 mm in diameter. Again, it is worth noting that there are additional elements of the cornice assembly, in which there are already ready perforations and holes for the circulation of air flows. As for the outlet of the pipes, special holes of large diameter are made for them, which can exit through the rafter system, bypassing the overlap.
Construction mounting tool
Roofing involves the use of several groups of tools and supplies. So, in preparatory measures, a complex of measuring and marking devices like a range finder, an angle meter, a ruler, a level, a marker, etc. can be used. Directly mounting operations are performed with the following tools:
- Screwdriver.
- Hammer.
- Mallet.
- Chisel.
- Tool for processing materials. For metal and wood, different devices are used like hacksaws, jigsaws, circular saws, etc.
Depending on the requirements of the project, consumables for eaves overhang are also selected. The node in addition to the main prefabricated elements will be formed by mounting hardware. It can be corners, clamps, brackets, profile parts and docking devices.
Mounting the base of the cornice
In the standard model, the design is arranged on the basis of a cornice crate in the lower part of the ramp, which, in turn, either rests against the rafter ceiling, or passes it, sinking even lower. The roofer's task is to connect these elements by means of wooden, metal or plastic trims. The brick foundation mentioned above, as a rule, is arranged at the stage of erecting a wall structure.
So, the fastening of the cornice assembly of the slats is carried out using bars or shaped metal elements that are fixed to the underside of the ramp. Further, on the installed blanks, a crate is formed, on which the lining will be fixed in the future. The outer edge of the junction of the crate and the slope must also be covered with a bar 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. To create it, you will additionally need to install the crate to the wall, after which another group of load-bearing strips is mounted to its lower beam from the outer edge.
What hardware 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 format 0.8 mm, correctly observing the indentation. In the case of metal, screws and bolts are used by default, but massive critical structures should be seated on more reliable hardware. For example, the attachment points to the cornice made of reinforced concrete are performed by anchor joints, and in the presence of outwardly extending reinforcement, welding can also be used. Heavy metal sheets to wooden planks are fixed through the counter-lattice using galvanized self-tapping screws with a sealant.
Sheathing
It is advantageous to use the casing on the underside not only because of the formation of a closed duct in the cornice space. Finishing itself of this kind allows you to decorate the design of the overhang, often eliminating its own defects. Actually, there can be several solutions to this problem - to nail a number of boards to the created support base from the crate, veneer the entire area, or use siding panels that are conveniently built into structures with different shapes and sizes. Also, do not forget about the gables, that is, the sides of the cornice unit. From the rafter leg to the lowest point of the overhang, the same material is trimmed as the main horizontal hem. It is only important to take into account the different nature of external influences on this side. If the lower binder is practically not in contact with the rays of the sun, then the pediment will take on both ultraviolet and various mechanical loads.
Conclusion
A well-designed pitched system in conjunction with the facade and the rafter structure will help to organize comprehensive protection of the roof space and achieve the aesthetic value of the overhangs. Even at the design stage, it is important to consider what other functional load on specific nodes of the eaves can be . The roof allows drainage of melt water to the water basins remote from the foundation, but for this a corresponding overhang with overhanging elements will be required. 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 according to the possibilities of technical implementation and decorative properties.