The roof performs a number of important functions in creating decent living conditions, coupled with providing visual appeal. It is quite reasonable that it is considered a significant structural component of the building. The rafter frame is responsible for the formation of the roof structure. It must withstand the load, determine the configuration and be combined with the exterior of the house.
Only a well-chosen roof base can cope with the tasks at hand. Do right choice it is much easier if the owner country estate everyone is known possible types and diagrams of rafter systems, the specifics of their construction and scope of application are clear.
The list of roof responsibilities goes beyond weather protection. Although confronting weather phenomena in a specific area, without a doubt, tops an impressive list of tasks.
The roof, as the final architectural touch, complements the appearance of the building, gives it a stylistic direction or completely deprives it. The rafter system as the basis of the roof structure must meet the entire range of technical and aesthetic requirements placed directly on the roof.
Factors in choosing the “backbone” of the roof
The rafter system is an indisputable accessory pitched roofs, which:
- sets the configuration and steepness;
- holds topcoat and components roofing pie;
- creates conditions for the flawless operation of roofing system elements.
Choosing a roof ultimately comes down to determining ideal option rafter system, which, in addition to the personal preferences of the home owner, is also influenced by such compelling factors as:
- The amount of winter and summer precipitation characteristic of the area in which construction is planned.
- The strength and direction with the speed of the winds prevailing in the region.
- The owner’s desire to use the space under the roof to organize utility or residential premises.
- Finish type roofing.
- Financial capabilities of the owner.
Climatic data greatly influences the choice of roof and the design of the rafter system. In regions with abundant snowfall, it is not advisable to erect structures with a slight steepness, which contributes to the formation of snow deposits. In areas with gusty winds, on the contrary, streamlined and low-sloping shapes are preferred, which will be difficult to be torn off and carried away by a powerful weather phenomenon.
It is clear that the flat design is not adapted to the device in it useful premises. For those wishing to equip the space under the roof, there are rafter 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 building a rafter system of any type.
In order not to suffer from guessing about the most rational shape and angle of inclination of a pitched roof, it is enough to take a closer look at the surrounding low-rise buildings.
The proven configuration can be safely taken as a basic option 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 rafter systems.
Basic options for rafter systems
A pitched roof can be simplistically represented as a set of slopes - planes along which atmospheric water “rolls”. The slopes are formed by the ribs of the rafter legs - the main elements of the rafter system. The classification of pitched roofs and their corresponding rafter systems is made depending on the number and configuration of the slopes. According to the indicated characteristics, their ranks include:
- Single-pitch. Roofs with one slope are installed mainly over utility buildings, extensions, and verandas. rest on two walls or two rows of racks. One of the walls or one row of supports must be higher than the other so that water can flow along the plane formed by the rafters without obstacles.
- Gable. Roofs with two rectangular slopes are most often found in domestic spaces. Rafter legs gable systems rest on two walls of a rectangular box of the house. In the classic version, the area of both slopes is equal, as is the height supporting walls. True, they have often become design solutions with slopes of different areas and supporting walls of different heights.
- Hip. Otherwise called hipped, based on the number of pitched planes. The rafter legs of the hip system form a pair of trapezoidal and a pair of triangular slopes. The rafters of the trapezoidal components rest on the long walls of the box, and the triangular ones rest on the short end walls. In plan, the hip roof looks like a postal envelope. Looks impressive and can be used everywhere. The hipped category includes roofs with shortened triangular slopes, which are strongly recommended for construction in areas with high wind loads.
- Tent . A roof that consists of triangular slopes converging at one vertex. The minimum number of slopes is 4, the upper limit is unlimited. The rafters of the tent system rest on walls or supports of equal height. They prefer to erect tent structures over verandas and gazebos. Variations in the steepness of hipped roofs allow them to be installed in regions with any wind load.
- Broken. They are also called attic, because it is the broken technology that allows you to create the most spacious rooms under the roof. Rafter legs of broken structures are installed by analogy with gable systems, but are constructed in two tiers. The lower rafters rest on the walls of the box being equipped, the upper ones on the supports of the lower tier of the rafter frame.
The listed types of roofs and rafter structures have numerous variations on the pitched theme. For example, a gable roof can have a regular gable gable on one end and a hip on the opposite side, or it can be complemented by a shed structure over a porch in the middle of the main slope.
When two gable systems are combined crosswise, a composite roof with four wooden gables or stone gables is formed. In the arrangement of boxes with a T-shaped or L-shaped configuration, several types of rafter systems are often involved simultaneously. The upper tier of a sloping roof can be built using hip technology.
A rafter structure of any complexity can be represented as a set of simple forms. To make it easier to understand the intricacies of construction, it is better to conditionally divide the object into separate blocks. They will tell you how to build each of the parts and connect the basic types of rafter frames listed above to each other.
Overview of pitched rafter structures
In order to understand the abundant variety of structures and the possibilities of their layout, we will consider the main types of rafter systems and the corresponding diagrams.
Type #1 – lean-to rafter frame
Most shed roofs are classified as non-attic, because regardless of the steepness, the space they create under the roof is not large in volume. However, if you want to build a strictly horizontal ceiling, a ceiling separating the attic from the main rooms is still built.
The scheme depends on the size of the span to be covered with a single slope:
- If the distance between the upper and lower supports of the rafter leg is less than or equal to 4.5 m, additional struts and racks are not used.
- If the span is in the range from 4.5 m to 6 m, a bench is laid near the high wall. The strut rests against it - under rafter leg, ensuring the rigidity of the rafters closer to the top of the span.
- If a span of 6m to 9m is to be covered, the beams are laid on both sides and the rafter legs rest against both beams.
If it is necessary to cover a larger span, it is divided into sectors with the distances indicated above. At the border of adjacent sectors, racks for purlins are installed, and within the sector, beds and struts are installed according to the described rules. For construction in regions with high wind activity, single-pitch rafter structures are supplemented with diagonal wind braces from the inside.
In plan, the diagram of a single-pitch rafter frame resembles a series of parallel beams. A roof with one slope is not very beautiful, but it is very economical. The optimal angle of inclination is from 4º to 12º, and a greater inclination is not prohibited.
It is advisable to equip structures with low slopes with continuous sheathing and waterproofing, which is not necessary for steep roofs. As finishing coating It is better to use corrugated sheets or roofing metal for low structures for arranging steeper structures.
Type #2 – rafter systems for gable roofs
Gable rafter frames 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, rafter legs used in the installation of gable roofs are divided into:
- Layered. These are rafters that have a strong support under the upper and lower heel. They are manufactured and installed like the rafters of pitched roofs. Layered rafter systems are constructed over boxes that have an internal load-bearing wall. It is needed as a supporting structure for the ridge girder. The role of a wall can be played by a number of supporting posts or columns. In the simplest layered scheme with a span of up to 5 m, the tops of the rafters rest on a purlin, which, through support posts leans on the bench. Rigidity is provided by struts. Schemes for more substantial spans are equipped with contractions, headstocks and additional runs.
- Hanging. Hanging type rafters have only a lower support; their tops rest against each other. The elements of the hanging rafter frame are immediately made in the shape of a triangle, so you can dispense with the Mauerlat. In such cases, the function of the Mauerlat is trusted to the base of the triangle - a tightening used to compensate for the thrust 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 cover long-span structures, the hanging system is equipped with headstocks, struts, ties, etc.
Depending on the technical characteristics of the roof, the sheathing is arranged continuous 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 passages.
Type #3 – hip and half-hip system
Hip, or “envelope” roofs, differ from gable structures in that the place of vertical gable gables in their structures is occupied by inclined triangular slopes - hips. The central part of the roof is occupied by a standard gable rafter system, to which the same hips adjoin at an angle.
Diversity in the family of hip structures is achieved through variations with proportions. By 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 rafter frames the following are used:
- Layered or hanging rafter trusses with corresponding structural elements: beams, ridge purlins, tie rods, etc.
- Diagonal rafters connecting the tops of the outer trusses to the corners of the frame.
- Sloping shortened rafters that form inclined slopes of the hips and parts of the main slopes adjacent to the hips.
Hip structures can be attic or non-attic. I must admit, they are not very suitable for organizing rooms under the roof. Four inclined slopes seriously limit the space. However, for fans attic houses There is a Danish variety with a shortened hip. Adherents of non-standard architecture will certainly like the Dutch type, which belongs to the category called “” along with the Danish version.
Rafter systems for hip and roof types are erected with an angle of inclination from 10-12º to 60º. The absolute priority is the classic proportions with a slope of 25-30º.
In addition to penetrations, ridges and eaves overhangs, all convex and concave corners need enhanced waterproofing hip design. The complex configuration of the slopes dictates the use of piece materials in finishing. When cutting metal tiles and corrugated sheets, there will be too much waste.
View #4 – hip roof
A simple hipped hipped structure is a hip roof without a ridge. Its plan layout resembles a square with diagonals running from corner to corner. Triangular slopes are connected at one vertex, which makes the roof similar to a tent. Build over boxes of a clear rectangular or polygonal shape.
In the construction of hip rafter systems, standard layered and hanging principles are used:
- A rafter structure of the layered variety is erected above the box with a central support or load-bearing wall.
- A frame is erected over an object without an internal wall or support using the hanging principle.
The steepness and number of slopes depend on the personal preferences of the future owner. The ideal roofing covering for finishing triangular slopes would be piece material, solely because when cutting large sheets, an impressive amount of waste remains. Regardless of the steepness, they prefer to equip tent structures with continuous lathing and a waterproofing carpet.
View #5 – broken rafter system
Rafter frames for broken lines, i.e. specifically focused on increasing attic space for the purpose of creating domestic or residential premises in it.
Broken technology is mainly used in construction attic roofs, which can be cold in country houses and insulated in permanent residences.
Each slope of a classic sloping roof can be divided into two rectangular parts, creating between them external corner. Required form obtained by changing the sizes of parts of the slopes, the angles between them and the angle in the ridge zone.
An attic-type rafter system is one of the most complex types of rafter systems: diagrams and drawings of a broken frame introduce the complex structure of the structure. It consists of two tiers perched on top of each other:
- The lower tier of the rafter legs rests through the Mauerlat on the beams of a wooden floor, reinforced concrete slabs or the ceiling beam of a wooden house. To support the top of the rafters, purlins are installed, which also serve as support for the bottom of the rafters of the upper tier. The rafters of the lower part of the sloping roof are only allowed to be layered.
- The upper tier of rafters rests with their lower heels on the purlins of the tier located underneath. The purlins serve as the basis for laying ceiling beams attics. In the construction of the upper part, both layered and hanging methods can be used. The task of the top is only to form the ridge part, because the responsibilities for distributing the roofing pie are assigned to the lower part of the attic roof.
The owner chooses the angle of inclination of the lower and upper parts of the slopes according to his own preferences. The ideal shape is considered if the five corners are intersected by an imaginary circle. Solid or sparse sheathing is installed depending on the type of roofing, and there are no restrictions on its choice at all.
It is better to install continuous sheathing and waterproofing on the flatter upper part. On the steep lower part of the slopes, precipitation does not linger, but it is threatened by heavy winds.
To prevent the sloping roof from falling off in areas with frequent strong winds, each rafter is attached with a wire bundle to the wall, and not through one, as is customary when fixing conventional pitched roofs.
Video review of types and shapes of roofs
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Presented schemes different types rafter systems are suitable for arranging a wooden house, brick and foam concrete frame. The only difference is in the fastening of the Mauerlat on wooden and stone walls. Information about the basic types of rafters will help you correctly determine the type and configuration of the roof for a country property.
They say that the roof of a house is the fifth facade. Any owner country cottage knows well that the overall perception of the building depends on how well the roofing covering is chosen.
We have already told users of our site about the features of choosing a roofing covering.
But the roof is only the visible part of a complex system called the roof. The basis of any roof is a reliable and properly designed rafter system.
In this material, FORUMHOUSE experts will talk about the main nuances of constructing a rafter system for a wooden and stone house.
From this article you will learn:
- Where does the construction of a rafter system begin?
- What nuances need to be taken into account when installing the rafter system of stone and wooden structure;
- Which structural elements rafter system compensates for the shrinkage of a wooden house;
- What features does the rafter system have? log house;
- What is a Mauerlat and why is it needed in a stone structure?
- What are the requirements for the materials of a wooden rafter system?
- What is a rafter system built using LSTK technology.
General principles for choosing a rafter system for a stone and wooden cottage
Often, novice developers believe that the choice of rafter system design can be left “for later,” when the walls have already been erected. Practice shows that this is fundamentally wrong. The roof even country house- This a complex system, consisting of many elements. The design of rafters must begin at the design stage of the house.
Company manager "DDM-Stroy" Vera Vavilova, Moscow:
– The rafter system is the basis (skeleton) of the roof of the house. The quality and durability of the roof directly depends on how well it is done. The manufacture of this structure, especially complex ones, must begin with its design. This is the only way that will allow you to take into account all the nuances and install it efficiently.
The service life of the roof largely depends on how well this structure is chosen and installed. It is also necessary to maintain a balance between functionality and design delights.
Director of company " Smart-Stroy" Pavel Orlov:
– Designing a rafter system begins with choosing the type of roof - mansard or cold attic. For mansard roofs The angle of inclination of the rafters is 35 degrees and above. For a cold attic, the base angle of the rafters is 25 degrees.
The simpler the roof shape, the simpler design, the faster it is to manufacture, and the less likely builders are to make a mistake. Therefore, it is cheaper to build and easier to operate a roof that has a simple shape. Big square roofs, the presence of bay windows, and the complex polygonal shape of the building significantly complicate and increase the cost of the design of the rafter system - it requires competent design and calculation.
The most cost-effective rafter system is the simple one gable roof with an inclination angle of at least 25 - 30 degrees.
The main factors that influence the complexity of manufacturing and the final price of the design:
- Type of finishing roof covering. The choice of one or another coating determines the composition of the roofing pie, the type of sheathing and the load on the rafter system. The most popular roofs are metal tiles, soft roof, CHR ( cement-sand tiles), ceramic or seam roofing;
- Roof inclination angle. It determines the loads, which is a major factor in structural design;
- Will the structural elements (decorative element) be visible or will it be completely hidden behind the ceiling cladding;
- Large overhangs on the roof significantly increase the cost of the rafter system.
If in design last floor The houses are designed with large unsupported spans, this entails an increase in cost and complexity of the design. In this case, depending on the distances, the rafter system is performed using trusses.
- The presence of large fireplace chimneys, skylights and other passage elements in the project significantly affects both the complexity of manufacturing the structure and its price.
The design of a rafter system (especially a complex one) should be carried out by a person with relevant experience. This design is always calculated for a specific building. The common approach – “I’ll make a rafter like my neighbor’s” – leads to disastrous construction results. The rafter cannot withstand the loads, which ultimately leads to expensive alterations.
Design begins with collecting the expected roof loads.
1. Constant values, including the total weight of the roof covering, thermal insulation material and fastening elements;
2. Temporary quantities. These are the loads that climatic conditions, especially snow and wind, have on the roof.
Designers set the design pitch of the rafters in accordance with the expected load. Let's see how true this is.
Pavel Orlov:
– In my opinion, it is better to choose the pitch of the rafters for attic, well-insulated roofs based on the size of the insulation - so that the distance between the rafters is 1 cm less than the width of the insulation. This will make it easier to install.
The main load for which the rafter system is calculated is snow. Usually, all such structures are designed with a margin, but if in doubt (it is planned to install a heavy roofing covering - natural tiles, etc.), you can slightly reduce the pitch of the rafters.
Although the snow load is variable, the rafter must be calculated taking into account the totality of all loads acting on it. The calculation must be carried out not “back to back”, but with some reserve in case of heavy precipitation (prolonged snowfall) or increased wind load.
The “work” of the rafter system is significantly influenced by the choice of material for the walls of the house.
Features of the rafter system in a wooden and stone house
The main difference between the rafters of a stone house and a wooden one is that stone walls have a structure that is not subject to shrinkage and deformation.
Pavel Orlov:
– The rafters of a stone house do not need deformation elements, since stone house practically does not shrink. main feature rafter system of a stone house is the need for reliable fastening of the Mauerlat. In wooden houses, the role of the mauerlat is played by the wall.
Mauerlat is a roofing element (paired boards 50x150, timber sized 100x150 or 150x150), which is laid along the entire perimeter of the upper wall of the house. The lower part of the rafters rests on the mauerlat. Thus, the Mauerlat redistributes the point load transmitted from the rafters to the entire area of the upper part of the wall.
Also, when designing the truss system of a stone house, it is necessary to take into account the thickness of the walls.
Pavel Orlov:
– The design requires calculation of the permissible lateral load of the rafters on the wall with a fixed Mauerlat.
A thin and high wall can withstand less lateral load. This requires the use of rafters for the load-bearing structure additional elements– supporting posts and purlins.
Wooden houses also have their own nuances that must be taken into account when manufacturing the rafter system.
Vera Vavilova:
– The main feature is that the walls, which are the basis for the rafters, shrink and change their geometry as the weather, temperature and humidity change outside and inside the house.
The main element that compensates for the shrinkage of the walls relative to the rafters is a sliding support (also called a sliding support). Sliding support necessary to compensate for distortions truss structure, resulting from shrinkage of wood due to natural moisture.
A sliding support is a composite fastener that includes a bent plate and an angle with a guide.
When the house shrinks, the rafter slides along the guide, thus compensating for all distortions in the overall structure of the house's rafter system. The sliding part of the support is attached to the rafter beam so that there is a gap between it and the rafter. And the corner with the guide is screwed to the beam.
The slide must be installed strictly perpendicular to the rafters, with a notch in the timber for installation of its base. In order to ensure that during shrinkage wooden structures to ensure maximum travel of the slide; when installing it, it is installed in the most extreme position.
The degree of shrinkage of a wooden house (and therefore the amount of movement acting on the rafters) depends on the material used in the construction of the walls. Timber with natural moisture shrinks more, dry profiled timber shrinks less, and laminated veneer lumber gives minimal shrinkage, etc.
The walls of a house made of dry timber can shrink by 6% of their total height. If we are talking about the walls of a house made of timber with natural moisture, then the shrinkage can be even greater. Our article explains in detail what are the pros and cons .
Construction of a roof on a log house
In addition to timber, wooden houses are built from so-called hand-cut logs. Practice shows that the rafter system of such a house has its own characteristics.
Dmitry Filippov, company specialist "Traditional carpentry technologies":
- IN log houses Based on the log house, a male-slat roofing system is used plus a “sliding” rafter part.
Roofing in a house made of logs, installation.
Roof for log house has its own design features. Sledges - horizontal logs cut into a log gable (the top of them is the ridge) - are seated together with the log house. Afterwards, a board lining (aka ceiling) is laid on the logs (lay down). Next, the rafters are mounted (in gable roofs they are attached to each other at the ridge with sliding fasteners). Then a roofing pie is formed - vapor barrier, insulation, waterproofing, counter batten, sheathing, roofing material is laid on top.
Dmitry Filippov:
– Thus, the rafter part with the roofing pie is not tied to the log house, but, as it were, “lies” on it, which allows the roof to retain its shape and integrity when the log house shrinks.
From our article you will learn about the types of structure and roof shapes of log houses.
Materials going to the rafters
In addition to taking into account the characteristics of wooden and stone houses, when designing a rafter system, it is necessary to understand the requirements for lumber.
Vera Vavilova:
- Pine and spruce will do. These are inexpensive wood types that meet the basic strength characteristics of rafters.
It is important to ensure that the lumber meets grade 0-2 according to GOST 8486. The rafter elements should not contain large falling knots, rot, wane and cracks. These defects weaken the load-bearing capacity of the rafter system.
Pavel Orlov:
– Edged coniferous wood with a moisture content of up to 20% is used for the rafter system. All lumber used must be treated with certified fire-retardant impregnations.
If you place freshly sawn, raw wood on the rafters, then during the drying process the already installed rafters will move. This will cause deformation of the roof and roof covering.
To avoid this, it is better to make rafters from chamber-dried calibrated lumber.
Another option for materials used to make rafters can be trusses and glued beams.
The use of these materials is determined by the project, based on the size of the spans and the expected load on the structure.
Vera Vavilova:
In this case, the elements of the rafter system are manufactured at the factory and delivered to the site in the form of parts ready for assembly.
This eliminates the so-called “human factor”. It also saves time, because such a structure is assembled faster than one made on site with inevitable sawing and fitting of parts on site.
Factory rafter systems are manufactured strictly according to the design and technical specifications. Thanks to this, it is achieved high quality the foundations of the future roof, because the wood has already been treated with antiseptic agents, and the entire rafter system is assembled according to the principle of a designer.
Another material used in the construction of rafter systems for a stone or wooden house can be light steel thin-walled structures (LSTS). This type of rafter does not need to be treated with antiseptic agents, it is lightweight, long term service and high fire resistance. Let's consider the main features of the rafter system built using this technology.
Deputy Commercial Director of the company "Polymetal-M" Andrey Usachev:
– The roof truss system, made using LSTK technology, includes galvanized rack and guide profiles. If it is necessary to install a warm roof, a thermal profile is used (a profile with perforations along the entire length), which will remove the cold bridge and avoid heat loss.
The thickness and cross-section of the profile used in the design depends on the load expected on the rafter system.
Each element of the system has strictly specified dimensions according to the project.
This significantly reduces assembly time and also avoids waste on the construction site.
Each profile is marked in accordance with the drawings and assembly instructions.
Andrey Usachev:
– Markings make assembly easier. Each profile is marked with a punch (extrusion). Because the metal frame is fastened together with self-tapping screws, then thanks to the extrusion it is clear where the connection should be. The dowel increases the rigidity of the assembled assembly, reducing the shear force on the self-tapping screw.
In the FORUMHOUSE topic you can find out what begins. Also here you will find all the information about. Read on to learn how to build it yourself.
Watch our video about roofing in Russian wooden architecture.
Rafters serve as the basis for the entire roofing structure, and their installation is one of the most important tasks when building a house. The frame of the future roof can be made and installed independently, observing the technological features of roofs of different configurations. We will present the basic rules for the development, calculation and selection of a rafter system, and also describe the step-by-step process of installing the “skeleton” of the roof.
Rafter system: rules for calculation and development
The rafter system is a supporting structure capable of resisting gusts of wind, taking on all external loads and evenly distributing them to the internal supports of the house.
When calculating the truss structure, the following factors are taken into account:
- Roof angle:
- 2.5-10% - flat roof;
- more than 10% - pitched roof.
- Roof loads:
- constant - the total weight of all elements of the “roofing pie”;
- temporary - wind pressure, the weight of snow, the weight of people carrying out repair work on the roof;
- force majeure, for example, seismic.
The amount of snow loads is calculated based on the climate characteristics of the region using the formula: S=Sg*m, Where Sg- weight of snow per 1 m2, m-calculation coefficient (depending on the slope of the roof). The determination of wind load is based on the following indicators: type of terrain, regional wind load standards, building height.
Coefficients, required standards and calculation formulas contained in engineering and construction reference books
When developing a rafter system, it is necessary to calculate the parameters of all components of the structure.
Elements of the truss structure
The rafter system includes many components that perform a specific function:
Materials for making rafters
Rafters are most often made from coniferous trees (spruce, larch or pine). For roofing, well-dried wood with a humidity level of up to 25% is used.
The wooden structure has one significant drawback - over time, the rafters can become deformed, so metal elements are added to the supporting system.
On the one hand, metal adds rigidity to the rafter structure, but on the other hand, it reduces the service life of wooden parts. Condensation settles on metal platforms and supports, which leads to rotting and damage to the wood.
Advice. When installing a rafter system made of metal and wood, care must be taken to ensure that the materials do not come into contact with each other. You can use moisture-proofing agents or use film insulation
In industrial construction, metal rafters made of rolled steel (I-beams, T-beams, angles, channels, etc.) are used. This design is more compact than wood, but retains heat less well and therefore requires additional thermal insulation.
Choosing a rafter system: hanging and suspended structures
There are two types of rafter structures: hanging (spacer) and layered. The choice of system is determined by the type of roof, floor material and natural conditions of the region.
Hanging rafters rest solely on the external walls of the house, intermediate supports are not used. Hanging type rafter legs perform compression and bending work. The design creates a horizontal bursting force that is transmitted to the walls. Using wooden and metal ties you can reduce this load. The ties are mounted at the base of the rafters.
A hanging rafter system is often used to create an attic or in situations where roof spans are 8-12 m and additional supports are not provided.
Layered rafters are installed in houses with an intermediate columnar support or an additional load-bearing wall. The lower edges of the rafters are fixed to external walls, and their middle parts are on the inner pier or supporting pillar.
Installation of a single roofing system over several spans must include spacer and layered roof trusses. In places with intermediate supports, layered rafters are installed, and where there are none, hanging rafters are installed.
Features of arranging rafters on different roofs
Gable roof
Gable roof, according to building regulations, has an inclination angle of up to 90°. The choice of slope is largely determined by the weather conditions of the area. In areas where heavy rainfall prevails, it is better to install steep slopes, and in areas where strong winds prevail, flat roofs are installed in order to minimize the pressure on the structure.
Common option gable roof- design with an inclination angle of 35-45°. Experts call such parameters the “golden mean” of consumption. building materials and load distribution along the perimeter of the building. However, in this case attic space It will be cold and it will not be possible to arrange a living room here.
For a gable roof, a layered and hanging rafter system is used.
Hip roof
All roof slopes have the same area and the same angle of inclination. There is no ridge girder here, and the rafters are connected at one point, so the installation of such a structure is quite complicated.
It is advisable to install a hip roof if two conditions are met:
- the base of the building is square in shape;
- in the center of the structure there is a load-bearing support or wall on which it will be possible to fix a rack that supports the junction of the rafter legs.
Create hip roof It is possible without a rack, but the structure must be strengthened with additional modules - racks and puffs.
Hip roof
Traditional design hip roof assumes the presence of slanted rafters (diagonal) directed towards the corners of the building. The slope angle of such a roof does not exceed 40°. Diagonal runs are usually made with reinforcement, since they account for a significant part of the load. Such elements are made from double boards and durable timber.
The joining points of the elements must be supported by a stand, which increases the reliability of the structure. The support is located at a distance of ¼ of the length of the large rafters from the ridge. Shortened rafters are installed in place of the gable roof gables.
The rafter structure of a hipped roof can include very long diagonal elements (more than 7 m). In this case, a vertical post must be mounted under the rafters, which will rest on the floor beam. You can use a truss as a support - the beam is located in the corner of the roof and fixed to adjacent walls. The truss truss is reinforced with struts.
broken roof
Broken roofs are usually created for arrangement larger attic. The installation of rafters with this roofing option can be divided into three stages:
- Installation of a U-shaped structure - supports for purlins that hold the rafter legs. The base of the structure is floor beams.
- At least 3 purlins are installed: two elements run through the corners of the U-shaped frame, and one (ridge purlin) is mounted in the center of the attic floor.
- Installation of rafter legs.
Gable roof: do-it-yourself rafter installation
Calculation of inclination angle and loads
Of course, you can calculate a gable roof yourself, but it’s still better to entrust it to professionals in order to eliminate errors and be confident in the reliability of the structure.
When choosing the angle of inclination, it is necessary to take into account that:
- an angle of 5-15° is not suitable for all roofing materials, so first choose the type of coating, and then calculate the rafter system;
- at an angle of inclination over 45°, material costs for the purchase of components of the “roofing cake” increase.
Load limits from snow exposure range from 80 to 320 kg/m2. The design coefficient for roofs with a slope angle of less than 25° is 1, for roofs with a slope from 25° to 60° - 0.7. This means that if there are 140 kg of snow cover per 1 m2, then the load on a roof with a slope at an angle of 40° will be: 140 * 0.7 = 98 kg/m2.
To calculate the wind load, the aerodynamic influence coefficient and wind pressure fluctuations are taken. The value of the constant load is determined by summing the weight of all components of the “roofing cake” per m2 (on average 40-50 kg/m2).
Based on the results obtained, we find out the total load on the roof and determine the number of rafter legs, their size and cross-section.
Installation of Mauerlat and rafters
Do-it-yourself installation of rafters begins with the installation of a mauerlat, which is fixed with anchor bolts to the longitudinal walls.
Further construction of the structure is carried out in the following sequence:
Installation of rafters: video
Methods for connecting rafter structure elements: video
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It's hard to imagine a house without a roof. Without it, the house cannot be called complete. The roof, as you know, protects the house from precipitation, inclement weather, etc. In addition, it is used to complete the architectural image of the constructed object. In this case, it is necessary to correctly calculate and install roofing system, only then will the roof last long years, and it will not need to be repaired every year.
The structure of the rafters can be very different. We propose to consider their most common types and types, methods of their fastening.
As you know, the roof can be flat or pitched. As for suburban construction, in this case the installation of a gable roof rafter system is especially popular. If the house is very large, then the roof will be of the appropriate size, for example, hipped (more details: ""). Thus, the developer must imagine the design of the rafter system hipped roof. The simplest option is to install a rafter system pitched roof, since it is very labor-intensive and requires sufficient knowledge.
Still, it is worth noting that the installation of a gable roof rafter system is considered the most common option today. The design consists of two planes that are on the same level. They are also the load-bearing part that rests on the walls of the house. Usually there is an attic under the roof slopes. If it is heated, then it can be used as attic floor, where you can arrange a functional room.
It is worth noting that the angle of inclination of the future roof will depend on the roofing material. It is usually measured in degrees.
Determining the reliability of the rafter system
When installing a roof, developers Special attention given to the rafter system. It must be made reliable, because the service life of the roofing structure depends only on this system.
The reliability of the rafter system is usually affected by the following points:
Construction of a rafter roof: structural components
We can conclude that if the rafter system is calculated incorrectly and unprofessionally, it may simply not withstand the load in the future. In this case, terrible consequences cannot be avoided.
When calculating the design of the rafter system, the following points must be taken into account:
- roof shape;
- location of internal supports;
- floor span size;
- expected operating loads.
In the design of the rafter system, the triangle is the main figure. Rafter legs are also important in such a design; maximum attention must be paid to their design. They are usually laid along the roof slope. The sheathing is supported precisely by the rafter legs.
What types of rafters are there?
Today rafters can be:
- hanging;
- layered.
The optimal sections themselves will be the following options:
- for boards – 16-18x4-5 cm;
- for bars – 16-18x12-14 cm;
- for round timber – 12-16 cm.
The axis distance between the bars and logs should be 150-200 centimeters. The distance of the rafters between the beams of the boards is usually 100-150 centimeters.
At the end of each rafter leg, so-called fillies must be nailed. A regular board is suitable for their implementation. Along the entire cornice along the slope of the filly, you need to nail the formwork, which will serve as the base for the boardwalk. It is on this decking that the roof material is attached.
The installation of a rafter system for a gable roof or any other may encounter such a difficulty as expansion (read: ""). To avoid expansion of the rafter system, the rafters must be attached to the ridge very firmly.
If the device is used incorrectly, displacement of the ramp may also occur. If you cut the rafter legs into the wood floor, this will not happen. The strength of the joint can also be achieved with an overlay, or with reliable fastenings, which are made using bolts and dowels.
In this case, it is necessary to take especially seriously the calculation of the maximum roof load, and we must not forget about the snow cap. Price roofing works in this case, it will increase significantly, since more lumber will be required, and the tiles themselves are not cheap.
Due to such high costs, many people choose soft roofing. In this case, you need to remember about the sheathing, which is made entirely of boards or plywood. This type of roof also requires underlay carpets. Consequently, the developer will also have to pay a considerable amount when purchasing building materials.
21.02.2017 1 CommentThe rafter system of a gable roof is a simple design that can be installed with your own hands even by a novice developer. You just need to make preliminary calculations, familiarize yourself with the details and stages of roof construction, and calculate the materials needed for installation. When making calculations, it should be taken into account that the load-bearing capacity of a gable roof depends on the influence of loads from wind, snow, and the weight of materials on it.
To make the process of building a gable roof rafter system as easy as possible for you, below is detailed step-by-step instructions for installing a rafter system with your own hands.
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Requirements for building materials
For the installation of a rafter system the best option There will be the use of lumber from coniferous wood - pine, spruce or larch, grades I - III.
The material for the rafters is taken at least grade II, the mauerlat is made from boards or timber of grade II, material of grade II is taken for racks and purlins, the sheathing is made from lumber of grades II-III, it depends on the roof. Crossbars and tie-downs are made of Grade I material. Can be used on linings and linings material III varieties.
Note! The lumber must be dry with a moisture content of no more than 20%. It should be treated before installation fire retardant compounds and antiseptics against fungal diseases.
Lumber should be stored under a canopy, providing protection from the sun and moisture. Level the storage area and cover the lumber with pads for ventilation.
For installation you will need fastening elements: ties, plates, studs, bolts with washers and nuts, self-tapping screws with EPDM gaskets, 2.8 mm thick, mounting tape, galvanized brackets.
Brackets are used when attaching the Mauerlat; they are secured with nails or self-tapping screws.
KR corners serve to attach the rafters to the mauerlat and prevent the rafters from moving.
All fastening material must be made of high quality material and be protected against corrosion.
Tools for constructing a rafter system
To install a gable roof rafter system, you will need the following set of tools:
- tape measures of different lengths 5, 10, 20 meters;
- markers, pencils;
- cord for tensioning;
- hammers, for various purposes, nail puller;
- scissors, for cutting;
- roofing knife;
- putty knife;
- scotch;
- hacksaws, electric saw, electric drill with various drills and attachments;
- screwdriver with attachments;
- markings, horizontal and vertical levels;
- slats, rulers;
- polyurethane foam;
- safety belt and rope - for safe work.
Keep all tools on the roof in a tool bag for safety reasons.
Types of rafter systems for a gable roof
Sent rafters
They rest on the mauerlat and racks installed on the internal wall, with a pitch equal to the rafters. To provide rigidity for spans of 6 m, additional struts are installed.
Scheme of layered rafters of a gable roof
Hanging rafters
If the building is small in width, you can arrange a rafter system where the rafters rest on the mauerlat or walls, without intermediate supports. The maximum span is 9 meters. Such roofs can sometimes be installed without a Mauerlat. The rafters are installed on the wall using spacers; in this embodiment, a bending moment acts on the rafters.
To unload, wooden or metal plates are installed. They securely strengthen the corner. For hanging rafters For a larger span, a headstock and struts are installed. For hanging systems, the rafters are made with a larger cross-section, and lumber is chosen at least grade I II.
Scheme of hanging rafters of a gable roof
Calculation of the rafter system
You can determine the cross-section of a gable roof beam required in a rafter system by collecting all the loads acting on it: the weight of the covering, sheathing, snow, wind pressure, precipitation.
Constant loads can be determined by the weight of 1 m 2 of roofing and sheathing. It is important that the weight per 1 m 2 of roofing be in the range of 40-45 kg.
Variable loads from snow and wind are calculated using tabular values of SNiP normative documents, depending on the height of the building and temperature zone. The load from snow is equal to its weight multiplied by a coefficient depending on the slope of the slope. All these calculations are performed during the project.
What if there is no project and the roof is being erected on a small building? You need to look at the construction of a house in the neighborhood, which is being carried out according to a design whose roof area is the same as your building. The gable roof rafter system will serve as a model.
Dimensions of timber for rafters
At the top point a ridge is laid that connects the rafters. The height of the ridge depends on the slope of the roof. The slope is affected by the choice of coating material. Minimum dimensions are:
- For tiled roofs, slate 22 gr.;
- for metal tiles - 14 g;
- ondulin - 6 g;
- corrugated sheeting - 12 gr.
The optimal angle is 35-45 degrees. tilt, ensures rapid discharge of water and snow. In regions with strong winds, the roofs are made flat and then the angle of inclination is within 20-45 degrees.
The height can be determined using the formula: H=1/2Lpr*tgA. Where A is the angle of inclination, L is the width of the building.
The task is simplified when using a ready-made table. The coefficient depends on the width of the building and the angle of inclination. Multiply the coefficient by 1⁄2 the width of the building.
The rafters are made from pine or spruce bars, with a section of 50x100 mm, 50x150 mm.
The size of the rafters depends on the pitch. Rafter spacing is smaller, installable large quantity, the cross section will decrease. The distance between the rafters on a gable roof ranges from 600 mm to 1800 mm, it all depends on the design of the roof and the materials used for its construction.
|
Length rafters, mm |
Distance between rafters, mm | Rafter beam cross-section size, mm |
| up to 3000 | 1200 | 80×100 |
| up to 3000 | 1800 | 90×100 |
| up to 4000 | 1000 | 80×160 |
| up to 4000 | 1400 | 80×180 |
| up to 4000 | 1800 | 90×180 |
| up to 6000 | 1000 | 80×200 |
| up to 6000 | 1400 | 100×200 |
The roof does not end at the level of the walls; it is extended outward by 500 mm. The rafter leg can protrude, or a board or block can be built up. In this case, moisture does not get on the wall and the foundation is not poured.
Step-by-step installation of a gable roof truss system
The rafter system of a gable roof consists of the following elements:
- Mauerlat.
- Lay down.
- Racks.
- Rafters.
- Struts.
- Puffs.
- Lathing.
Mauerlat installation
Fastening the Mauerlat to a monolithic reinforced concrete belt
Mauerlat evenly distributes the load on the walls of the building; its installation can be done in several ways:
- attached to the wall through a reinforced concrete belt with studs;
- studs are inserted into the masonry;
- simple and common way to simple roofs, fastening with wire rod.
For it, take timber with a cross section of 100×100 mm, 150×150 mm or 200×200 mm. Which section to choose depends on the size of the roof and its covering. The Mauerlat is joined along its length; to do this, make 100 mm cuts, 500 mm long, fold the bars and fasten them with pins.
In the corners, the mauerlat is tied with notches into the floor of the timber, fastened with staples or bolts. U wooden buildings, Mauerlat is the last crown. On brick walls, make a monolithic reinforced concrete belt with a cross-section of 400×300 mm. Along the belt, place threaded pins 12 mm in diameter, every 120 mm, for fastening.
Drill holes with a diameter of 12 mm in the Mauerlat, lay them so that the pins go into the holes. Tighten the top with nuts. First, we lay two layers of roofing felt or roofing felt under the block. On the outside of the wall, lay the mauerlat with bricks. Lay the Mauerlat on a horizontally and vertically level base. You need to check with a level that the surface is horizontal. Check diagonals. If necessary, level with pads.
Installation instructions for beds, racks, rafters, struts and tie rods
The installation of a gable roof rafter system with your own hands is carried out in the following order:
- Install the beam with the rafters in place.
- Mark the installation step of the rafter legs.
- Prepare according to the size of the rack.
- Install them if there is a need to secure them with spacers.
- Lay the purlin. Check geometry. Install fasteners.
- Try on the first rafter leg and mark the cutting areas.
- Mark the points and install the rafters at the beginning and end of the roof, stretch the cord between them in order to align the remaining elements along it.
- Having installed the rafter leg, we first attach it to the mauerlat, then to the ridge purlin, to each other.
- Screw each second leg to the mauerlat with wire.
The rafters are fastened to the mauerlat using notches, stop corners and a hemmed support bar. Secure with nails or staples.
Methods for attaching rafters to the Mauerlat
Install the support posts on the beds or pads and overlays. A log is a beam 50×100 mm or 50×150 mm, laid on the middle wall along a layer of roofing felt. Place brick pillars under the linings, 2 bricks high.
The rafter legs are connected to each other at the ridge. Let's consider the common connection nodes of the rafter system:
- They make cuts at one leg and cut down at the other. Insert one leg into the cut of the other and fasten with a bolt.
- Install overlays, wooden or metal.
- Using notches in the purlin, they are secured with nails or bolts.
Methods for connecting rafters on a ridge
To ensure the roof's resistance to wind loads, tie-rods, struts and purlins are installed. The tightening is a 100×150 mm block, purlins and struts are made from a 50×150 mm or 100×150 mm block.
With the installation of contractions, the reliability of the rafter structure increases. The sections of the timber are the same as the rafters. They are attached to the legs with bolts or nails. The device of struts adds rigidity to the structure. They are installed tightly to the surface of the rafters
The lumber has a standard length of 6 m. The rafters can be longer. Then you need to dock them. There are several connection methods:
- Fasten by placing bars on both sides at the junction, connecting them with nails in a checkerboard pattern.
- Connect with an overlap, one part of the rafters to another, at a distance of 1 meter, fasten with nails in an alternating order.
- Make a cut obliquely, cut out part of the rafter legs, connect them, strengthening them with bolts.
Sheathing device
Lathing is installed along the roof rafters. It serves to distribute the load from roofing material and snow onto the rafters. Plays the role of an air gap between the roof and the rafter system.
The design of the sheathing depends on the roofing material used:
- under the soft tiles, make the sheathing continuous, lay an anti-condensation film on the rafters, press it on top with a counter batten, nail the sheathing onto it, then OSB boards and underlayment carpet, lay the tiles on top.
- Under the roof made of corrugated sheets, the sheathing should be sparse. The pitch of the sheathing depends on the brand of corrugated sheeting, its thickness and the angle of inclination of the roof.
- The lathing for standard slate should be made in increments of 500 mm from a bar of 75×75 mm or 50×50, as well as boards from 30×100 mm. The design features of the roof should be taken into account when making the final choice of the appropriate option.
The lumber from which the sheathing is made is first or second grade pine. It is advisable to take the width no more than 14 cm. With a wider width, the boards may warp and damage the roofing. The length of the nails should be three times the thickness of the sheathing. Lay the boards along the ridge. Install the first board of greater thickness to the height of the roofing.
Install continuous sheathing along the roof slope.
The first layer is to place a board along the ridge from it at a distance of 500-1000 mm to the next one and so on. Lay the second layer of sheathing along the rafters. Place the joint between the boards only on the rafters at intervals. Sink the nail, head and all, into the flesh of the wood.
Cornice overhangs
Arranged to protect against atmospheric precipitation, play an aesthetic role. Eaves overhangs are arranged tightly without gaps. The final stage on roofing.
Diagram of the eaves overhang of a gable roof
Gable
The gable roof has two gables. They have the shape of a triangle, with the apex at the ridge and the sides coincide with the slopes of the roof. The gables support the rafters and enclose the attic space. They protect from wind and precipitation and provide stability to the roof.
In wooden buildings, the pediment is framed. IN brick buildings, frame or brick. Gables made of brick or gas block are erected before the roofing is installed. They require very precise execution.
Frame pediments fit into the finished opening when the rafter system is already assembled.
The frame is made of bars or boards. The frame elements are connected on tenons or in the wood floor, all fastened with nails. They are sheathed by nailing boards, lining or siding, maintaining the color scheme in the decoration of the building facade. To construct a window opening, an additional frame is made under it according to the size of the window. If the attic is insulated, then the gable also needs to be insulated. The insulation is placed in the middle of the frame. Mineral wool insulation with reduced flammability is used. On the outside, the frame is covered with a hydro-windproof film or windproof membrane, with inside under finishing material nail a vapor-proof film or vapor-proof membrane.
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