At the heart of each roof is a large number of beams, rafters, racks and girders, which are collectively called the truss system. Over the centuries-old history of the types and methods of its organization, a lot has accumulated, and each has its own peculiarities in the construction of knots and pieces. In more detail about what can be the rafter system of a dual-sloped roof and how at the same time rafters and other elements of system have to fasten we will talk in more detail.
The design of the truss system gable roof
In the section, the dual roof is a triangle. It consists of two rectangular inclined planes. These two planes are connected at the highest point into a single system with a ridge bar (girder).
Gable roof layout
Now about the components of the system and their purpose:
- Mauerlat – a timber that binds the roof and walls of the building, serves as a support for the rafter legs and other elements of the system.
- Rafter legs – they form the inclined planes of the roof and are a support for the sheathing under the roofing material.
- Ridge (bead or ridge) – combines two planes of the roof.
- Tightening – transverse detail that connects the opposite rafter legs. It serves to increase the rigidity of the structure and compensate for strut loads.
- Lay – bars located along the mauerlat. Redistribute the load from the roof.
- Side girders – support truss feet.
- Racks – transfer the load from the runs to the sunbeds.
There may be fillies in the system. These are boards that lengthen trusses to form an overhang. The fact is that to protect the walls and the foundation of the house from precipitation, it is desirable that the roof ends as far as possible from the walls. To do this, you can take long truss legs. But the standard length of lumber of 6 meters for this is often not enough. Order non-standard – very expensive. Therefore, the rafters just grow, and the boards that do it are called “fillies”.
The designs of roof systems are quite a lot. First of all, they are divided into two groups – with slings and hanging rafters.
The difference in the design of nasled and hanging rafters
With hanging rafters
These are systems in which truss legs rely only on external walls without intermediate supports (load-bearing walls). For gable roofs, the maximum span is 9 meters. When installing the vertical support and the system of struts, it can be increased to 14 meters.
The hanging type of a truss system of a gable roof is good because in most cases there is no need to install a power plate, and this makes the installation of truss legs easier: you do not need to cut the cuts, it is enough to mow the boards. For the connection of walls and rafters used lining – wide board, which is attached to the studs, nails, bolts, bolts. With this structure, most of the opening loads are compensated, the impact on the walls is directed vertically downwards.
Types of truss systems with hanging rafters for different spans between load-bearing walls
Double roof rafter system for small houses
There is a cheap variant of the truss system when it is a triangle (photo below). Such a structure is possible if the distance between the outer walls is not more than 6 meters. For such a truss system, it is possible not to calculate the angle of inclination: the ridge must be raised above the puff to a height of at least 1/6 of the span length.
But with this construction, the rafters have significant bending loads. To compensate for them, either take the rafters of a larger section or cut the ridge part so as to partially neutralize them. To give greater rigidity in the upper part, wooden or metal lining is nailed on both sides, which securely fasten the top of the triangle (also look not at the picture).
The photo also shows how to grow trusses to create a roof overhang. A cut is made that should extend beyond the line drawn from the inner wall upwards. This is necessary to shift the incision site and reduce the likelihood of fracture of the rafter.
Ridge knot and fastening of rafter legs to a baseboard with a simple variant of the system
For mansard roofs
Option with the installation of the bolt – is used when organizing a roof under the roof of the dwelling – attic. In this case, it is the basis for filing the ceiling below the room. For reliable operation of this type of system, the bolt hinge must be non-hinged (rigid). The best option is a half-crocodile (see the picture below). Otherwise, the roof will become unstable to loads.
Raised dual roof system with a raised puff and bolt cutter assembly
Please note that in this scheme there is a mauerlat, and the rafter legs to increase the stability of the structure should go beyond the walls. For their fastening and docking with the mauerlat, a cutting is made in the form of a triangle. In this case, with uneven load on the slopes, the roof will be more stable.
With this scheme, almost all the load falls on the rafters, because they need to take a larger section. Sometimes raised tightening strengthen suspension. This is necessary to prevent its sagging if it serves as a support for the ceiling cladding materials. If the tightening is of short length, it can be secured in the center on both sides with boards nailed on nails. With a significant load and the length of such insurance can be several. In this case, there are also enough boards and nails.
For large houses
With a significant distance between the two outer walls of the grandmother is installed and the struts. This design has a high rigidity, as the load is compensated.
Rafter roof system for a large span and knots of the ridge and rafter
With such a long span (up to 14 meters), it is difficult and expensive to make a one-piece tightening, because it is made of two beams. It is connected by a straight or oblique prirub (figure below).
Straight and oblique edge for a puff connection
For reliable joining, the joint is reinforced with a steel plate mounted on the bolts. Its dimensions should be larger than the size of the cut-in – extreme bolts are screwed into solid wood at a distance of at least 5 cm from the edge of the cut.
In order for the scheme to work normally, it is necessary to make the struts correctly. They transfer and distribute part of the load from the rafter legs to tighten and provide rigidity to the structure. Metal lining is used to strengthen the joints.
Fastening of struts for truss system by hanging rafters
When assembling a double-slope roof with hanging rafters, the lumber cross-section is always larger than in systems with laminated rafters: the load transfer points are smaller, therefore, each element has a large load.
In gable roofs with suspended rafters, the ends they rest on the walls, and in the middle part they rest on the bearing walls or pillars. Some schemes burst the walls, some not. In any case, the presence of the power plate is required.
The simplest option for slant rafters
Non-contour schemes and knotting knots
Houses made of logs or timber react poorly to space loads. For them, they are critical: the wall can fall apart. For wooden houses, the truss roof system should be non-distant. On the types of such systems we will discuss in more detail.
The simplest flow-free diagram of the truss system is shown in the photo below. In it the rafter foot rests against the power plate. In this embodiment, it works on bending, not bursting the wall.
Simple girdle-free gable roof system with overlap rafters
Pay attention to the options for attaching truss legs to the mauerlat. In the first, the support area is usually mown, and its length is no more than a section of the beam. Cut depth – no more than 0.25 of its height.
The top of the rafter legs is laid on the ridge bar, not fastening it with the opposite rafter. Two single-shed roofs are obtained by the structure, which in the upper part are adjacent (but not connected) to one another.
Such a scheme without experience is not recommended: with the slightest inaccuracy of performance, expansion forces appear and the design becomes unstable.
It is much easier to assemble the version with trussed legs fastened together in the ridge part. They almost never give rise to a wall.
The option of mounting rafters without strut on the walls
For the operation of this scheme, the truss legs at the bottom are fixed by means of a movable joint. To secure the rafter leg to the mauerlat, one nail is hammered from above or a flexible steel plate is placed below. Options for attaching truss feet to ridge girder look at the photo.
If the roofing material is planned to be used heavy, it is necessary to increase the carrying capacity. This is achieved by increasing the cross section of the elements of the truss system and strengthening the ridge knot. It is shown in the photo below.
Strengthening the ridge knot under heavy roofing material or with significant snow loads
All of the above gable roof schemes are stable under uniform loads. But in practice this is almost never the case. There are two ways to prevent the roof from sliding towards a greater load: by installing a scramble at a height of about 2 meters or with struts.
Variants of truss systems with contractions
Installation of contractions increases the reliability of the design. In order for it to work normally, in places of its intersection with drains it is necessary to fasten nails to them. The cross section of the bar for the fray is used the same as for the rafter.
Schemes of roof systems gable roofs with contractions
By rafter legs are attached with bots or nails. Can be installed on one or two sides. See the figure below for the attachment of the scrum to the rafters and the ridge girder.
Attachment of the scrum to the rafter legs and ridge bar
In order for the system to be rigid and not “crawl” even with emergency loads, it is enough in this variant to provide a rigid mount for the ridge beam. In the absence of the possibility of its displacement in the horizontal, the roof will withstand even significant loads.
Slatted floor systems with struts
In these cases, for greater rigidity, add-underframes, which are also called braces, are added. They are set at an angle of 45 ° with respect to the horizon. Their installation allows you to increase the length of the span (up to 14 meters) or reduce the cross-section of the beams (rafters).
The strut is simply substituted at the required angle to the beams and nailed from the sides and bottom. An important requirement: the strut must be cut accurately and fit snugly to the racks and truss foot, excluding the possibility of its deflection.
Systems with rafter feet. Top spacer system, bottom-free Nodes for proper cutting for each located nearby. Below – possible schemes for mounting the brace
But not all houses have an average bearing wall located in the middle. In this case, it is possible to install struts with an inclination angle relative to the horizon of 45-53 °.
System rafters with vertical run offset from the center
Systems with struts are necessary if significant uneven shrinkage of the foundation or walls is possible. The walls can sit down differently on wooden houses, and the foundations on layered or abyssal soils. In all these cases, consider the device truss systems of this type.
System for houses with two internal bearing walls
If the house has two load-bearing walls, install two subrafter beams, which are located above each of the walls. The intermediate bearing walls are laid down. the load from the subrafter beams is transferred to the rails through the racks.
Systems with subrafter beams
In these systems, the ridge run is not set: it gives expansion forces. The rafters in the upper part are connected to one another (they are cut and joined without gaps), the joints are reinforced with steel or wooden plates, which are nailed.
In the upper slack-free system, the shearing force is neutralized by a puff. Please note that the tightening is put under the girder. Then it works effectively (the upper diagram in the figure). Stability can be provided by racks, or struts – beams, set obliquely. In the spacer system (in the picture below), the crossmember is a crossbar. It is installed above the girder.
There is a version of the system with racks, but without subrafter beams. Then a stand is nailed to each truss leg, which with the second end rests on the intermediate supporting wall.
Fastening the rack and tightening in the truss system without underlap girder
For fastening the racks nails for 150 mm and bolts 12 mm are used. Dimensions and distances in the figure are in millimeters.
Types of rafter systems: analysis of basic versions with analysis of technological features
The roof has a number of important functions to create decent living conditions, coupled with the provision of external attractiveness. Quite reasonably, it is considered an important constructive component of the building. For the formation of the roof structure meets the truss frame. He is obliged to bravely hold the load, determine the configuration and be combined with the exterior of the house. Only the competently selected base of the roof is capable of coping with the assigned tasks. Making the right choice is much easier if the owner of a country estate knows all the possible types and schemes of roof systems, the specificity of their construction and scope of application is clear.
The list of roof duties is not limited to weather protection. Although resisting weather phenomena in a particular locality, no doubt, tops an impressive list of tasks.
The roof as the final architectural touch complements the appearance of the building, gives it a stylistic focus or completely deprives it. The roof system as the basis of the roof structure must meet the whole range of technical and aesthetic requirements for the roof itself.
The rafter system is an indisputable accessory of pitched roofs which:
- sets the configuration and slope;
- keeps the topcoat and components of the roofing pie;
- creates conditions for the flawless operation of the elements of the roofing system.
The choice of the roof ultimately boils down to determining the ideal version of the truss system, which, in addition to the personal preferences of the house owner, is also influenced by such weighty factors as:
- The amount of winter and summer precipitation, characteristic of the area in which construction is planned.
- Strength and direction with the speed of the winds prevailing in the region.
- The desire of the owner to use the space under the roof for the organization of economic or residential premises.
- Type of roofing finish.
- Financial capabilities of the owner.
Climatic data to a large extent affect the choice of the roof and the device truss system. In regions with abundant snowfall, it is impractical to build structures with a slight steepness contributing to the formation of snow deposits. In areas with gusty winds, on the contrary, streamlined and low-pitched shapes are preferable, which will be difficult to be disrupted and carried away by the powerful weather phenomenon.
It is clear that the flat design is not adapted to the device in it useful premises. For those who want to equip the space under the roof there are roof systems designed for construction in regions with varying degrees of wind loads.
If there is no need to use an attic, a roof of a complex or simple configuration can be built without it. There are a lot of options, including various combinations of basic versions, familiarization with which will give an idea of the essence of the construction of a truss system of any type.
In order not to suffer in conjectures about the most rational form and the angle of inclination of the pitched roof, it is enough to look at the surrounding low-rise buildings.
The proven configuration can be safely taken as a base case in order to adjust and modify it in accordance with the requirements of the future owner and the technical characteristics of the roofing. If you don’t want to copy your neighbors, you should familiarize yourself with the design and operational specifics of various roof systems.
A sloping roof can be simplified as a set of slopes – planes along which atmospheric water “rolls”. The slopes are formed by the ribs of the truss legs – the main elements of the truss system. The classification of pitched roofs and their corresponding roof systems is made depending on the number and configuration of the slopes. According to the indicated signs in their ranks are listed:
- Monopitch Roofs with one slope suit mainly above economic objects, extensions, verandas. The rafter legs of the shed system are supported on two walls or two rows of struts. One of the walls or one row of supports must be higher than the other, so that water can flow without obstacles along the plane formed by the rafters.
- Gables. Roofs with two rectangular slopes are most often found on domestic expanses. The rafter legs of the gable systems rest on the two walls of the rectangular box of the house. In the classic design, the area of both slopes is equal, as is the height of the supporting walls. However, design solutions with slopes differing in size and supporting walls of different heights became frequent.
- Hip. Otherwise called chetyrehskatnymi, based on the number of pitched planes. The rafter legs of the hip system form a pair of trapezoid and a pair of triangular rays. Rafters trapezoidal components based on the long walls of the box, and triangular counterparts – on the short end. In terms of the hip roof looks like a postal envelope. Looks impressive, is used everywhere. Roofs with shorter triangular slopes are strongly recommended for construction in areas with high wind loads.
- Tent. The roof, which consists of converging triangles at one vertex. The minimum number of skates is 4, the upper limit is not limited. The rafters of the tent system are supported on equal walls or supports. Tent structures prefer to hoist over the verandas and gazebos. Variations with the steepness of the hip roof allow you to arrange them in regions with any wind load.
- Broken. They are also called mansard ones, because it is the broken technology that makes it possible to create the most spacious premises under the roof. Rafter legs of broken structures are established by analogy with gable systems, but are constructed in two tiers. The lower rafters rest on the walls of the set up box, the upper ones on the supports of the lower tier of the rafter frame.
The listed types of roofs and trusses have numerous variations on the sloping theme. For example, a gable roof can have a usual gable-gable from one end and a hip from the opposite side, or it can be supplemented by a shed construction above the porch in the middle of the main ramp.
With the cross-joining of two gable systems, a complex composite roof is formed with four wooden tongs or stone pediments. In the arrangement of boxes T-shaped or L-shaped configuration often involves several types of roof systems at the same time. The upper tier of a broken roof can be built on hip technology.
The rafter design of any complexity can be represented as a set of simple forms. To make it easier to understand the construction intricacies, the object is better conditionally divided into separate blocks. They also will prompt how to build each of parts and to connect the basic types of rafter frameworks listed above with each other.
In order to understand the abundant variety of designs and the possibilities of their layout, consider the main types of roof systems and the corresponding schemes.
Most of the shed roofs are classified as bescherdnyh, because regardless of the steepness, the space created by them under the roof is small in volume. However, if you wish to build a strictly horizontal ceiling, the ceiling separating the attic from the main premises is still constructed.
The scheme of a single-sided truss system depends on the size of the span to be covered by a single ramp:
- If the distance between the upper and lower support of the rafter leg is less than or equal to 4.5 m, additional supports and racks are not applied.
- If the span is in the range from 4.5 m to 6 m, the ground floor is laid near the high wall. It is supported by a strut – a subrafter leg, which provides rigidity for rafters closer to the upper part of the span.
- If the span of the span from 6m to 9m is to be overlapped, the legrests are laid on both sides and the subrafter legs rest against both of the legrests.
If necessary, block a larger span, it is divided into sectors with the distances indicated above. On the border of adjacent sectors, the racks are installed for the runs, and within the sector, the rails and struts are installed according to the described rules. For construction in regions with high wind activity, single-sided trusses from the inside complement diagonal wind ties.
In terms of plan, the single-sided truss frame resembles a series of parallel-laid beams. The roof with one slope is not too beautiful, but very economical. The optimum angle of inclination is from 4º to 12º, and a greater gradient is not prohibited.
It is desirable to equip designs with low slopes with a continuous crate and waterproofing, which is not necessary for steep roofs. As a finishing coating, it is better to use soft types of roofing for low structures, professional sheet metal or roofing metal for arranging structures in a steeper way.
Duo-pitch trusses are built on reinforced concrete floors and wooden beams, mainly with attics. The most common type of roof has a huge number of low and high, insulated and cold modifications.
Depending on the architectural and technical conditions of the object, the rafter legs used in the device of dual-slope roofs are divided into:
- Outcast. These are rafter, having a strong support under the upper and lower heel. They are made and installed like the rafters of lean-to roofs. They construct suspended truss systems above the boxes with an internal load-bearing wall. It is needed as a support structure for the ridge girder. The role of the wall can be played by a series of supporting posts or columns. In the simplest naslon scheme with a span of up to 5m, the rafters rest on the girder, which through the supporting posts rests on the ground level. Stiffness provide struts. Schemes for more solid spans are equipped with contractions, attendants and additional runs.
- Hanging. The rafters of the hanging type have only the bottom support, with the tops they rest against each other. The elements of the hanging truss frame are immediately made in the shape of a triangle, due to which you can refuse the power plate. The function of the power plate in such cases is entrusted to the base of the triangle — the puff used to compensate for the spread on the roof from the weight of the snow, the roof, and the system itself. Hanging technology is used in the arrangement of small boxes that do not have internal support for the ridge girder. If it is necessary to overlap the large-span structures, the hanging scheme is equipped with heads-suspensions, struts, braces, etc.
Structures with two slopes recommended slope from 10º to 60º. For finishing you can use all known types of piece, roll and krupnolistovyh coatings.
Depending on the technical characteristics of the roof, the crate is arranged solid or sparse. Low slopes up to 12º are completely covered with a waterproof carpet, high ones – only in places of possible leaks: along the eaves, ridge, valleys, around pipes and other roofing aisles.
Hip, they are the roof “envelope” from dvukhskatnyh structures are different in that the place of the vertical gables gables in their designs is occupied by inclined triangular slopes – hips. The central part of the roof is occupied by the standard dual-sloped truss system, to which those very hips are at an angle.
Diversity in the hip family is achieved by variations with proportions. Changing the ratio of the length of the ridge to the length of the base and the height of the slope, you can get a design that meets any taste and architectural needs.
In the construction of roof frames for hip roofs are used:
- Suspended or suspended trusses with appropriate structural elements: sunbeds, ridge girders, puffs, etc.
- Diagonal rafters connecting the tops of the extreme trusses with the corners of the box.
- Slanted truncated rafters, forming sloping hip slopes and parts of the main skates adjacent to the hips.
Hip constructions are attic and bescherdnymi. Admittedly, they are not very suitable for organizing rooms under the roof. Four sloping slopes severely limit the space. However, for lovers of mansard houses there is a Danish variety with a shortened hip. Adherents of non-standard architecture will surely like the Dutch type, belonging to the category called “half-gummed roofs” along with the Danish version.
Roof systems for roofs of the hip and half-hinged varieties are erected with an angle of inclination from 10-12º to 60º. In absolute priority, the classic proportions of the steepness of 25-30º.
In addition to penetrations, skates and eaves overhangs, all convex and concave corners of the hip construction need reinforced waterproofing. The uneasy configuration of skates dictates the use of piece materials in finishing. When cutting metal tiles and profiled sheet too much will be waste.
A simple hip hinge design is a hip roof, devoid of the ridge part. Its plan in the plan resembles a square with diagonals passing from corner to corner. Triangular slopes are connected in one vertex, which makes the roof similar to the tent. Tent roofs are built over boxes of a clear rectangular or polygonal shape.
In the construction of tent rafter systems, standard suspended and hanging principles are used:
- Above the box with a central support or bearing wall erected truss construction naslonnogo variety.
- Above the object without an internal wall or support erect the frame on the hanging principle.
The steepness and the number of skates depend on the personal preferences of the future owner. The ideal roofing coating for trimming triangular ramps will be piece material, solely because an impressive amount of waste remains when cutting large sheets. Regardless of the steepness, tent structures prefer to be equipped with a continuous crate and waterproofing carpet.
Rafter frameworks for broken, i.e. mansard roofs are specifically focused on increasing the attic space in order to create residential or residential premises in it.
The broken-line technology is mainly used in the construction of garret roofs, which can be cold in country houses and warmed in homes.
Each slope of the classic broken roof can be divided into two rectangular parts, creating an external angle between them. The required shape is obtained by changing the sizes of the parts of the slopes, the angles between them and the angle in the ridge zone.
The truss system of the mansard type is one of the most complex types of truss systems: diagrams and drawings of a broken frame introduce the complex structure of the structure. It consists of two tiers perched on each other:
- The lower tier of truss legs rests through the mauerlat on wooden beams, reinforced concrete slabs or the ceiling beam of a wooden house. To support the top of the rafters set the runs, which also serve as a support for the bottom of the rafters of the upper tier. The rafters of the lower part of the broken roof are only allowed to be nasal.
- The upper tier rafter bottom heels rests on the runs of the tier below it. Runs also serve as the basis for laying the attic ceiling beams. In the construction of the upper part can use both naslonnaya and hanging techniques. The task of the top is only in the formation of the ridge part, because the responsibilities for the distribution of the roofing pie are assigned to the lower part of the mansard roof.
The owner chooses the angle of inclination of the lower and upper parts of the ramps according to his own preferences. An ideal form is considered if the five corners of the roof roof are crossed by an imaginary circle. Solid or sparse crate arrange depending on the type of roofing, and restrictions on his choice does not exist.
It is better to mount a continuous crate and waterproofing on the flatter upper part. On the steep lower part of the slopes, precipitation does not linger, but it is threatened by squall winds.
To prevent a broken roof from breaking down in areas with frequent strong winds, each rafter is attached with a wire bundle to the wall, rather than through one, as is customary when fixing conventional pitched roofs.
The presented schemes of different types of roof systems are suitable for arranging a wooden house, brick and foam concrete boxes. The only difference is in fixing the mauerlat on wooden and stone walls. Information on the basic varieties of trusters will help you correctly determine the type and configuration of the roof for the suburban property.
It would seem, what could be easier than installing the roof? In his youth, he helped the uncle with the construction of the house. Uncle all his life he worked as a builder, and even sabashnichal parallel. So he put the roof on paper without any special calculations. Apparently, the experience of the work done gave such an opportunity. All the joints measured, trimmed to fit to the maximum. There are still no problems with the roof, neither in winter nor in autumn.
Here we are just building now. The house is only in the project, the site is small. Of course, I would like to “come off” at least in height, so that you can make a lot of shelves and, maybe, put a bunk bed. They thought it was a narrow and high house to build, with a high roof, so that half of the first and second floors would be in half – that is, equally. But after the picture about the wind, which is trying to turn over such a roof, I thought. We have a place on the mountain, the winds always walk “hoo how” and, probably, too high will not suit us?
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Sources: http://kryshadoma.com/stropilnaya-sistema/kharakteristiki-i-konstruktsiya-krysh-stropilnye-sistemy.html, http://stroychik.ru/krysha/stropilnaya-sistema-dvuxskatnoj-kryshi, http: // krovgid.com/proekt/vidy-i-sxemy-stropilnyx-sistem.html