Roofs with two slopes are the most suitable option for self-implementation. They consist of two rectangular planes that converge at a certain angle. Such structures are characterized by strength and practicality: a house covered in this way will be well protected from any vicissitudes of the weather. The reliability of the entire structure will depend on the correct installation of the gable roof truss system.
What is a gable roof made of?
The list of structural elements includes several items. All elements should be studied and well aware of their structure and purpose.
Mauerlat and rafter legs
Mauerlat is made of coniferous timber with a thickness of 100-150 mm. They lay all load-bearing walls, for fastening to which anchors or threaded rods are used. Thanks to the mauerlat, uniformity of load transfer from the rafter legs to the load-bearing walls is achieved.
The material for the manufacture of rafter legs is a bar 150x100 or 150x50 mm. The rafter legs serve as parts for assembling a triangular roof contour, which directly resists wind, rain, hail, snow and other natural phenomena. In order to achieve good strength of the entire system, the spacing of the rafter legs is selected within 60-120 cm. The location frequency directly depends on the total weight of the roof structure: the heavier it is, the more often the rafters are mounted. In addition, the dimensions of the step are also affected by the features of the roofing.
Lying, tightening, racks
The bed is made from the same square bar as the Mauerlat (100x100 or 150x150 mm). It is mounted in a horizontal position on top of the internal load-bearing walls, which makes it possible to achieve uniform transfer of loads from the roof racks.
Hanging truss systems are completed with a puff. Thanks to the puffs, the triangular contour of the rafters receives the proper structural strength.
Racks are made of square timber (100x100 or 150x150 mm). Through the vertical racks of the truss system, the load from the ridge is transferred to the internal load-bearing walls.
Struts, crate
Struts serve as an intermediate link from rafters to load-bearing elements. The puff and brace fastened together form a truss, which is distinguished by increased strength. Farms are able to withstand loads even from large spans.
The lathing serves as a frame for laying the roofing, transmitting the weight of the roof to the truss system. The material for the manufacture of the crate is usually bars or boards laid at an angle of 90 degrees to the rafter legs. In some cases (when a soft roof is used), solid-type frames are used, constructed from moisture-resistant plywood.
Skate, overhangs, filly
The ridge is the upper horizontal part of the roof, in which both slopes converge. It is formed by connected rafters.
Special ledges of roof slopes on the sides (approximate size of the ledge - 40 cm), which protect the walls from rain and water flowing down the roof, are called overhangs. They are taken into account in almost any design of the truss system.
Fillies are used only in case of a lack of rafter length, which is why there are no overhangs. To fix this, legs are extended with boards of smaller thickness: this additional element is called a filly.
What are gable roofs
Based on the design features, gable roofs are divided into ordinary symmetrical, asymmetric and broken ones.
symmetrical
The most convenient for self-implementation is considered to be a time-tested classic roof, consisting of two identical slopes. It is easy to calculate and build it with your own hands, since its ergonomic design is based on an isosceles triangle. The pediment is triangular. Due to the sharp angle of the intersection of the slopes, high-quality and reliable removal of precipitation is ensured, regardless of the roofing material used.
Depending on the angle at which the slopes intersect, symmetrical structures are:
- classic (angle 45 degrees). Most often, houses no wider than 8 m are designed in this way;
- flat (angle less than 45 degrees). Suitable for small buildings in regions with strong winds;
- pointed. Used on large houses, providing a quick descent of snow and rain.
In general, the calculation of the angle of inclination of symmetrical gable roofs (they are also called gable roofs) is carried out depending on the climatic features of the area (steep slopes are suitable for regions with heavy snowfalls, gentle slopes for windy regions).
asymmetrical
In the case of an asymmetric roof, the length of the slopes varies. This constructive move has a twofold purpose. On the one hand, this gives the roof a special originality and beauty, on the other hand, it becomes possible to additionally attach a gazebo, garage or greenhouse without the need to build a separate shed. This way you can save a lot of money.
Broken lines
This shape of the roof suggests that the slopes have two sections. The angle of inclination of the upper one is 30 degrees, and the lower one is 60. As a result, it is possible to make the under-roof space large enough to equip a living room (attic) there. The ceiling height is quite high, with the possibility of installing vertical windows.
Types of truss systems
The truss systems of gable roofs are hanging, layered and combined.
hanging
They are used in buildings where there are no internal capital partitions and additional supporting pillars inside the building, the distance between the walls of which does not exceed 10 m. This design specificity implies a significant load on the load-bearing walls, including the bursting effect. To reduce stress, it is practiced to use additional fastening elements to tighten the rafters (we are talking about crossbars and puffs).
Tightening reduces tension: as a result, the wall experiences only horizontal loads. The resulting rigid triangular structure (truss) is practically not subject to deformation. In the case when the construction of the attic is planned, the puffs are replaced by floor beams. The advantage of this solution is that you can refuse to use the Mauerlat. As for the stops under the rafters on top of the walls, it is not difficult to install them.
Layered
In houses with internal load-bearing walls (usually we are talking about buildings with a width of more than 10 m), it is more convenient to use layered rafter systems. They are much easier to arrange than hanging ones: this is due to the creation of a reliable support due to the internal walls. The basis for installing the lower edge of the rafter is the top of the Mauerlat or the ceiling crown of the log house. The top of the leg rests against a parallel rafter or a special run (a beam passing under the ridge in a horizontal direction). The first option is called spacer, the second - non-spacer. There are three subspecies of non-thrust layered systems.
How is the calculation of the truss system
In order to correctly determine the parameters of the elements that make up the gable roof truss structure, it is necessary to understand what loads will have to be resisted. Usually, there are three types of factors that require mandatory consideration - this is a constant, variable and special impact on the truss system.
Definition of permanent loads
We are talking about loads that have a constant effect on the roof frame - this is the weight of the roof, waterproofing material, lathing, insulation, vapor barrier and other elements of the system. All these factors are characterized by the constancy and continuity of the impact due to their fixed weight. Accurate determination of the length of the rafters involves calculating the mass of the roofing cake. To obtain the final result, it is necessary to calculate in turn how much 1 m2 of each layer weighs.
For example, we can take the determination of the mass of the roof, where ondulin is used as a topcoat. Each of the values can be taken approximately, since there are no requirements for jewelry accuracy in this case. The composition of the roofing pie includes ondulin, waterproofing (most often we are talking about polymer-bitumen compounds), insulation (in this case, basalt wool) and a crate made of boards 25 mm thick.
Tilt angle
The calculation of a suitable angle of inclination of a gable roof largely depends on which roofing material is used: each of them has its own performance characteristics. When using a soft coating, the slope of the slopes should be in the range of 5-20 degrees. It is desirable to lay a more rigid coating of slate, metal tiles or corrugated board at an angle of 20-45 degrees.
Another important factor in determining the degree of slope steepness is the climatic features of the region. For example, if in an area where a strong wind is constantly blowing to build a roof of great height, in the event of a hurricane it can simply be torn off. But if we are talking about heavy rains and snowfalls, then the steeper the slopes, the faster moisture will drain from them. The most convenient in all respects is the classic angle of 45 degrees.
Step and length of rafters
Rafter legs on gable roofs are usually placed at a distance of 60-100 cm from each other. This is influenced by the characteristics of the roofing material and the total mass of the roof structure. Further, to determine the number of rafters, the size of the slope is divided by the gap between the rafter pairs, adding a unit to the result. To calculate the length of the rafters for the roof, there are special online calculators. This can also be done manually by applying the Pythagorean theorem: the desired element in this case is the hypotenuse of a right triangle. Its length is determined by the ratio between the leg and the cosine of the opposite angle.
Rafter section
To be able to adequately calculate this parameter, the total load on the truss structure was determined. As it increases, the cross section of the rafters has to be taken more. The thickness of the timber to some extent depends on the pitch and length of the rafter leg. Especially for this, tables have been developed that make it possible to quickly calculate the cross section, focusing on the length and installation step. It is necessary to take into account the material of manufacture (different types of wood have different strengths) and the type of elements used (the level of load resistance for logs, timber and glued laminated timber varies).
Recommendations for self-installation of the truss system
Installation work can begin only after carefully carried out calculations and drawing up a detailed drawing. In the absence of proper experience for calculations, it is better to resort to special online programs. In general, working with your own hands requires a lot of responsibility.
Mauerlat mount
The place of installation of the beam is the entire length of the walls that serve as a support for the rafters. The Mauerlat function in log cabins is performed by the upper crown. In houses where porous material (aerated concrete, foam concrete) was used as a material for construction, all load-bearing walls must be decorated with Mauerlat (the same applies to brick buildings). Other cases allow its installation only in the gaps between the rafters.
Since the length of standard lumber is not enough for the entire length of laying, they are spliced. To do this, it is necessary to cut the beam at a right angle of 90 °, using bolts to fasten the two parts.
The place of laying the Mauerlat is usually the center of the wall. Some displacement of the beam to the side is also allowed, the main thing is that its cut is not closer than 50 mm from the edge. To protect the beam from moisture, it is recommended to lay a waterproofing layer of ordinary roofing material under it. Mauerlat should be fixed as securely as possible, since a serious wind load is exerted on the roof slopes.
The material of the walls affects the method of fastening:
- monolithic houses. The best option is fixing with anchor bolts;
- wooden or log cabins - fastening with wooden dowels or staples;
- aerated concrete, foam concrete. Usually studs or rebar are used;
- if the house shrinks, it is recommended to use sliding fasteners.
As an additional measure, the attachment point can be reinforced with annealed wire.
Truss assembly
There are two options for implementing this procedure. In the first option, the beam is mounted directly at the installation site. Suitable for small buildings, when working at height to perform measurements and trimming does not cause difficulties due to the dimensions of the rafter legs.
The second option is the assembly below. In this case, the layout and fastening of the constituent elements of the truss system occur on the ground, and then the finished structures rise to the top. As a result, work at height is reduced to a minimum and completed much faster. To file and expose rafter pairs, special mechanisms are usually required due to the significant weight of the structures.
For the convenience of assembling the same type of elements, the use of templates made from boards is practiced. This makes it possible to obtain absolutely identical farms at the output.
Mauerlat mount
Ready pairs must be raised to the roof surface and attached to the Mauerlat. To facilitate the procedure, the legs are still on the ground equipped with special cuts in the lower part. The end structures are mounted first: they are placed opposite each other from the side of the pediment. To correctly place the first two pairs, temporary ties are used. A string is stretched between the established trusses, which serves as a guide for intermediate pairs, indicating the level of the ridge along the way. At the end of this stage, a special ridge support is mounted. If necessary, the length of the rafter legs can be increased locally.
Installation of the skate
To create it, it is necessary to properly fasten all the rafter legs. There are several splicing methods - both with the use of a support beam and without it. A more modern solution is the use of special intermediate steel clamps with the possibility of adjustment.
Arrangement of the crate
The purpose of the batten is to facilitate movement on the roof and provide a secure base for the top coat. It is the characteristics of the roofing material that have a decisive influence on the parameters of the frame. A solid crate is used in the case of arranging a soft roof. The step of the frame under the metal tile is approximately 35 cm, and under the corrugated board or slate - 44 cm.
For the installation of a gable roof truss system, it is best to choose a fine autumn or spring day, after enlisting the support of 2-3 assistants.
The final success of the work largely depends on a correctly drawn up drawing.
In any pitched roof there is a system with inclined planes (slopes). The selection and calculation of the truss system must be done taking into account the supports necessary for it, as well as the type of roof, dimensions and shapes of the structures to be covered. Having calculated the truss system of a gable roof, you can choose the right size of the rafter leg, as well as ensure the high strength of the roof.
Types and arrangement of the gable roof truss system
This system should be chosen from the conditions and the number of supports, as well as the distance between them.
For example, layered types of rafters will be supported by the load-bearing walls of structures (from the outside), as well as on additional. supports inside, if suddenly there will be more than four and a half meters between the main ones. In the lower part, the rafter leg rests on beams that transfer weight between the roof and the wall of the structure. As for the upper end, it is connected to the ridge type of run, as well as to another rafter leg.
The hanging truss system of a gable roof has a puff located at the level where the lower support nodes are located, and maybe higher than they are. There are no intermediate supports. As for the distance between the carriers from the outside, it should be up to six and a half meters. This option refers to a triangular farm, and between them the distance according to the plan is from 1.3 to 1.8 meters.
Coatings
Eternite types of roofing - fibrous or flat asbestos-cement sheets. They are cheap and easy to install.
Slate refers to slate roof options, they are made from natural materials of layered slates. Slate also includes ondulin and euroslate.
Metal coatings are used to cover residential buildings. They will reliably protect from the effects of the atmosphere, are not heavy and are easy in terms of installation work. These include aluzinc, galvanized and corrugated board.
Roll type refers to a soft roof. It has the property of not letting in moisture, and is very resistant to negative environmental influences. They are also easy to install. This includes roofing material, bito-polymer material, membrane roofing.
Some use wood roofing. But very rarely, because they are difficult in terms of installation.
Roof options that transmit light are made of glass, polymer.
We crate
It is the crate - the foundation of the roofs. It is made from beams or wooden boards. If a wooden, metal, tiled roof is being equipped, a beam is selected, the cross section of which is:
5 by 5 cm, if the distance between the rafters in the range of one meter is 1.1m).
5 by 6 cm, if the rafter pitch is from 1.2 to 1.3 meters.
6 by 6 if the step is 1.4 or 1.5 meters.
In other cases, boards can be up to 2.5 cm thick.
From wood, log options are used, which are cut down literally on one edge. In order to make layered rafters, a section of a round log with a diameter of 12 to 20 cm is more suitable.
How to calculate the desktop rafter leg?
Between the legs there can be a distance from a meter to one and a half. Their cross section must be determined in accordance with the calculations. For this, the strength and rigidity of structures are recognized. Therefore, you need to find out what is the constant load on the rafters, which includes regular loads and snow, per linear meter.
To carry out calculations, you need to know such data as:
- The step with which the rafter legs are installed
- What is the angle of the roof
- What are the dimensions of the roof
What parameters will be chosen and, in general, many coefficients, depends on the chosen material for the roof and its detailed composition.
It should be borne in mind that there must be a reliable pairing between the runs and the rafter legs. Thanks to this, the walls of structures will not be destructively torn open. If you have wooden structures, they need to be inspected periodically.
Variants of gable roofs are quite common today. But having properly equipped the roof, you will have a strong, beautiful and very durable housing!
The erection of the roof is one of the most important stages of construction. The durability of the building itself and the level of comfort of living in it directly depend on the reliability of the "umbrella" from above, on its resistance to precipitation and any external influences.
Of all the variety of roof structures, gable can be attributed to the most popular, simply because of the relative simplicity of its construction. However, behind this "simplicity" lies a lot of different nuances, the need to carry out certain calculations and follow technological rules. However, this publication has the main task: to show that installing the rafters of a gable roof with your own hands is a completely doable task, even for a novice builder.
Let's walk through the process of installing rafters for such a roof together, from the basics of preliminary design to an example of practical implementation.
General arrangement of a gable roof
Basic concepts
Structural elements of the gable roof truss system
Let's make a reservation right away that this scheme, of course, cannot reflect the entire possible variety of designs, but the main parts and assemblies on it are shown quite clearly.
1 - Mauerlat. This is a board or beam that is rigidly attached to the upper end of the external load-bearing walls of the building. Its purpose is to evenly distribute the load from the entire roof system to the walls of the house, creating conditions for reliable fastening of the rafter legs at their lower fulcrum.
2 - rafter legs installed in pairs. They become the main load-bearing parts of the entire roof system - it is the rafters that set the steepness of the slopes, will be the basis for attaching the batten, roofing, and if the roof is planned to be insulated, then the entire thermal insulation "pie".
For the manufacture of rafter legs, high-quality boards or timber are used, and round timber can also be used. About the section of lumber, which will be sufficient to ensure that all possible loads can be guaranteed, will be discussed below.
The rafters may end on the Mauerlat, but more often they go beyond the perimeter of the walls of the house, forming a cornice overhang. However, lighter parts can also be used for this - the so-called "fillies", with which the rafter legs are increased to the required width of the overhang.
To form a cornice overhang, the rafters are extended with “fillies” 3 - skating run. It can be a beam, a board or even a composite structure. The run runs along the entire line of the ridge and serves to securely connect the upper points of the paired rafter legs, connect all rafter pairs in order to impart overall rigidity to the entire roof structure. In various roof options, this run can be rigidly supported by racks, or tied only to the connection node of the rafter legs.
4 - puffs (contractions, crossbars). Horizontal details of the reinforcement of the system, additionally connecting paired rafter legs to each other. Several puffs located at different heights can be used.
5 - floor beams, which will serve as the basis for mounting the floor in the attic and the ceiling from the side of the room.
6 - and this beam simultaneously performs the role of a bed. This is a beam that runs along the entire length of the roof, which is a support for installing additional reinforcement parts for the truss system. The bed can be installed as shown in the figure (like a floor beam), or it can be rigidly laid on a capital partition inside the building.
7 - racks (headstock) - additional vertical supports of the rafter legs, preventing their deflection under the influence of external loads. Racks at the top can rest against the rafters themselves, or against an additional run, longitudinally connecting the rafter legs at a certain height.
8 - braces. Often, with a large length of the rafter legs, their bearing capacity is not enough, and reinforcement only with racks does not provide the necessary strength. In these cases, diagonal reinforcing elements are used, resting on the bed from below, creating an additional point of support for the rafters. The number of struts and the place of their installation can vary in roofs of varying degrees of complexity.
Some differences between hanging and sloping gable roof systems
Gable roofs can be divided into two types of structures - with layered and hanging rafters. In addition, combined systems are widely used, in which both principles of construction are combined. What is the fundamental difference?
Laminated rafter system
This design of the truss system is characterized by the presence of support on the internal capital partition in the building. On the upper end of this partition, a bed is mounted, on which drains are supported, supporting the ridge run. Thus, the rafter legs are “leaned” on a vertical support, which makes the entire system as strong as possible.
This scheme is the most popular because of its reliability and relative ease of implementation. If it is possible to create an additional point of support in the center, then why not take advantage of this? True, if it is planned to place a living space in the attic, then vertical racks can sometimes become a hindrance. However, their presence is also sometimes “beaten up”, using, for example, an internal light partition for mounting.
Depending on the number and placement of internal partitions, the design of the layered truss system may vary. Some examples are shown in the illustration below:
Fragment “a” shows the simplest option, which, by the way, on short rafter lengths (up to 5 meters) may not even have struts shown - a row of central racks under the ridge run is enough
With an increase in the width of the building, the system naturally becomes more complicated, and additional reinforcing elements appear - puffs and struts (fragment "b").
Fragment "c" clearly demonstrates that the internal main wall does not have to be located exactly in the center, under the ridge. Such an option as shown in the illustration is also quite possible, but with the condition that the displacement of the lying relative to the ridge does not exceed one meter.
Finally, fragment "d" shows how the rafter system can be supported in a large building, but with two main partitions inside. The distance between such parallel beds can reach up to a third of the width of the building.
Hanging rafter system
Graphically, this roof scheme can be depicted something like this:
It immediately catches the eye that the rafters rest only on the lower part, and then are connected to each other on the ridge. There is no additional support in the center, that is, the rafter legs seem to “hang”, which predetermines the name of such a system. This feature imposes certain restrictions on the use of hanging rafters - usually such a scheme is practiced with a distance between the bearing walls on which the Mauerlat is fixed, no more than 7 meters. Installed puffs only partially relieve the load from the external walls.
The illustration below shows several options for a hanging system. However, some of them already, rather, can be classified as combined.
Fragment "d" - hanging rafters are interconnected by a screed at the level of the Mauerlat or fixed to a powerful floor beam, forming a triangle with it. There are no other reinforcing parts. A similar scheme is permissible with a distance between walls of up to 6 meters.
Option "g" - for the same size house (up to 6 meters). The puff (bolt) in this case is shifted upwards, and is often used for filing the ceiling of the attic.
Options "e" and "h" are designed for a span between walls up to 9 meters. Multiple puffs may be used (or top puff in combination with bottom floor beam). Another approach is to install racks under the ridge run, by analogy with a layered system. Only as a lower point of support, it is not a bed on the main partition that is used, but the racks are supported by a puff or a floor beam. To call such an option purely “hanging” is already difficult, since here is clearly a combination of parts from both designs.
To an even greater extent, such a combination of two schemes is expressed in the "and" variant, which is designed for large spans, from 9 to 14 meters. Here, in addition to the headstock, diagonal struts are also involved. Often, such trusses are generally assembled on the ground, and only then they are lifted and set in place, connected to each other, thereby forming the entire roof frame.
So, in preparation for the construction of a gable roof, it is necessary to study the principles of the device of a particular system, evaluate their advantages and disadvantages, choose the best one for your conditions and draw up a graphic working diagram. It will be needed both when purchasing the necessary material, and for the production of the installation work itself. However, drawing up a drawing should still be preceded by some calculations.
Calculation of the basic parameters of the gable roof truss system
Let's take another look at the concept of a gable roof device to highlight those parameters that need to be calculated.
So, in the process of calculation, we need to decide on the following values.
The initial data is the length of the side of the house along the gable part (highlighted in blue - F), and the length of the house along the ridge (purple - D). It is assumed that the owners have already decided on the type of roofing in advance - since there will be certain restrictions on the steepness of the roof slopes. (angle a).
- The height of the ridge above the plane of the Mauerlat (H - green), or, conversely, determine the angle of the slope, starting from the planned height of the ridge.
- The length of the rafter leg (blue color - L), and, if necessary, the extension of the rafter to form a cornice overhang of the required width (l).
- Calculate the total loads that fall on the truss system in order to determine the optimal cross-section of lumber for the manufacture of rafters, their installation step (red color - S) and the allowable span length between the support points. All these parameters are closely interconnected.
- When these calculated values \u200b\u200bare on hand, it is already easy to draw up a graphic diagram, determine the need and optimal arrangement of reinforcement elements, and calculate the amount of material for their manufacture.
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We calculate the steepness of the slope and the height of the ridge
The slope angle of the slopes can be determined by the owners according to various evaluation criteria:
- For purely aesthetic reasons - when the appearance of the building becomes "at the forefront". Many people like roofs with a high ridge, but at the same time, one must not forget that the wind load increases sharply on such a roof. Yes, and materials for the manufacture of a high roof will go immeasurably more. At the same time, on steep slopes, the snow load is reduced to almost zero - it is possible that for "snowy" regions this assessment parameter may become decisive.
- For reasons of useful use of the attic space. With a gable roof scheme, in order to achieve the maximum attic area, it is necessary to build slopes with a very steep slope, that is, with the same consequences as mentioned above.
- Finally, there may be a completely opposite approach - for reasons of economy, make a roof structure with a minimum height in the ridge. But in this case, you will have to focus on the minimum allowable slope angles for a particular type of roofing. To reduce the steepness below the indicators recommended by the manufacturer is to “plant a bomb” in your roof, both for reasons of its strength and durability, and from the standpoint of the waterproofing qualities of the coating.
It is not difficult to calculate the height of the ridge above the floor plane (Mauerlat). At the heart of the vast majority of nodes of any roofing system is a triangle, which, in turn, obeys strict geometric (more precisely, trigonometric) laws.
So, in our case, the width of the roof along the gable line is known. If the roof is symmetrical, then the ridge will be located exactly in the middle, and for calculations, you can simply divide the width F by two (the base of the triangle f=F/2). With asymmetrical slopes, you will have to project the top of the ridge onto line F, and measure the distances f1 and f2 from it to the edge of the triangle (to the Mauerlat) on each side. Naturally, in this case, the slope of the slopes will be different.
H =f × tga
In order not to force the reader to look for the values of tangents and carry out calculations manually, a calculator is placed below, in which the necessary tabular values \u200b\u200bare already entered.
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