Roof system mansard roof - installation of rafters and

As they say experienced builders, the attic can be equipped in the house, would be the roof. The type of roof affects how much this measure will increase the usable area, whether it is comfortable to use this room and what complexity of work will be required. Common types of roofs for arranging residential sub-roofing premises are considered to be gable straight and broken slopes.

The truss system of the mansard roof is designed in such a way as to free up space in the center, where the ceiling height reaches an acceptable height, placing the bulk of the supporting elements along the edges. This article will tell you what the roof frame is made of, how to choose the best design option and correctly perform the installation.

Types of roof systems

Starting to design the roof system for the roof, pay attention to the layout of the house. Based on the types of supports, choose the appropriate version of the device:

1. Outrageous This type of truss frame is suitable for houses in which a partition wall runs in the middle. Then the weight of the roof structure is distributed between it and the external walls of the structure. This is a non-burdensome and rational way of organizing the framework, but it is suitable if the distance between the outer walls and the inner support does not exceed 7 m.
2. Hanging. This type is used then, the code inside has no bearing partitions or columns that are used to transfer the weight of the roof onto them. Hanging rafters are based on the mauerlat and ridge girder. For roofs up to 50 square meters. m, with a small weight of the roof apply the simplest configuration, consisting of rafter legs and horizontal puffs. To block the construction of a large size, this structure is strengthened with stanchions, fights, struts. These elements increase the stability of the roof, but "eat up" the useful space of the attic. The permissible distance between the walls of the structure for hanging trusses is 14 m.
3. Combined. A mixed type of truss system is used when supporting columns are installed in the house instead of a bearing partition in the middle. It turns out that part of the rafters can be laid on the columns, and the rest can be mounted as hanging. This method is often used for the construction of mansard roofs, as it allows the use of less auxiliary elements, reducing the load on the foundation and not cluttering the roofing room.

Please note that the attic device must be planned at the stage of project creation, because the type, weight and design of the truss system are necessary to calculate the foundation. If the decision to build a mansard roof arose at the final stage of construction, it is necessary to recalculate the mass of the house, taking into account the new data, in order to check if the foundation withstood the additional load, especially if the section had complex soil and a small distance between the surface and the groundwater.

Calculation of the elements of the truss system

By building standards, a room is called residential if the height from the floor to the ridge is at least 2.5 m and there are sources of natural light, that is, windows. Therefore, the main parameter of the mansard roof, which must be calculated is the angle of its slopes. The catch is that if you lay a small slope, then the height of the attic ceilings will be lower than permitted by the rules. And if you make covered ramps, the roof will be very heavy, expensive and unstable. Therefore, a broken type of roof is used, the slopes of which change the slope, its upper rafters have an acute angle of 30 degrees, and the lower ones - 60 degrees.

An important stage in the design of the mansard roof is the calculation of the cross section of the elements of the truss system. The easiest way to find out is the recommended size in the reference table with calculated values ​​that take into account the length, the distance between adjacent elements, the type and quality of the material. However, if the roof is of a non-standard size, it is necessary to perform a calculation based on the calculation of the total load of the weight of the roof, which falls on the roof system. The calculation scheme also takes into account temporary loads in the form of snow mass, which is reflected in the climatic coefficient characterizing the nature of the weather at the construction site.

To create a truss roof system, wood is used, but this is not advisable in all cases, since the rafters can cope with the load, it is necessary to increase the cross-section of the sawn timber used, which further increases the weight of the structure. To break out of this closed loop, you must abandon the tree in favor of rafters of greater strength of metal.

Construction truss system

The components of the truss frame of the mansard roof are no different from the design of other types of pitched roofs. It includes:

• Mauerlat The base of the roof, a kind of foundation that takes the weight of the roof and distributes around the perimeter of the supporting walls. It is made of timber with a size of 150x150 mm or thicker. The installation of the mauerlat is carried out using anchor bolts or studs mounted in the reinforced concrete belt. Between the surface of the wall and the bar lay a waterproofing layer or process it with bitumen mastic. A very important moment of fasteners is to calculate the location of the studs, the distance between them is chosen so as not to fall under the rafter legs.
• Rafters. These are the elements of the truss system that form the slope of the roof. The top of the rafter leg is fixed on the ridge bar, and the bottom - on the mauerlat or stand, if we are talking about the upper rafters of a broken roof. The legs are made of boards 50x150 mm or 100x150mm. The distance between them is called pitch, it varies from 50 to 120 cm depending on the weight of the roofing material. The interposition and cross-section of truss legs describes the scheme of the truss system, facilitating installation.
• Rack. Racks support the ridge or, which is more common in the construction of mansard roofs, the middle part of the rafter legs. Racks are made of timber, the cross section of which coincides with the size of the power plate. They are placed on the floor beams, so the distance between the racks corresponds to their step.
• Strut It is accepted to call struts the element supporting rafter legs, having an angular arrangement. The main task of the strut is to reduce the deflection of the rafters under the weight of its own weight.
• Tightening. Tightening is made of durable sectional planks corresponding to the size of the rafters. It is attached horizontally, tightening a pair of truss legs at the top or bottom. The smaller the distance between the puff and the ridge, the thicker this element should be, since the load on it is greater. Installing the puff removes the bursting load that acts on the rafter.

In most cases, the elements of the truss system are made of high quality wood. To avoid deformation during operation, it must be dried to a moisture content of 15-18%, treated with antiseptic impregnation of deep penetration and a fire retardant if you plan to remove the chimney to the roof.

Assembly sequence

Assembling the truss system is best done with the help of an experienced master, since even lifting heavy, long bars is problematic. It is not recommended to engage in installation in rain and snow, since the moisture content of wood during the work will increase. Usually the build process is as follows:

1. The first step is to install the power beam on the top trim of the walls. By the way, the functions of this element in log and log buildings are performed by upper crowns, reinforced with brackets.
2. The next stage of installation is the installation of floor beams. They are attached to the power plate or protrusions in the wall. There are two methods of laying floor beams - with or without removal. If the overlappings are mounted by the first method, then they are taken out beyond the perimeter of the house to form an overhang so that the distance between the end of the beam and the wall is 50-100 cm.
3. Establish a vertical rack, defining the middle of the ceiling beam and departing from it equal intervals. The distance between the racks corresponds to the width of the attic.
4. On the rack with metal corners fix the tightening. It turns out that each pair of racks forms a structure in the form of the letter p.
5. Install the lower truss elements, fixing on the rack with nails or screws. To the mauerlat, the rafters are mounted by means of a slider, a movable mount that compensates for the change in the size of the bars during shrinkage.
6. Fix the upper rafters, connecting the upper parts of each pair with a metal lining or a bar.
7. A waterproofing membrane is laid on the rafters and fixed with a stapler. Pin on top of the crate. The sheathing scheme is selected for the used roofing material, for the soft types they use a solid one, and for the profiled ones - a lattice one.

The reliability of the truss system of an attic roof depends, first of all, on the correctness of calculations, therefore, if you are not confident in your engineering skills, it is better to use a typical project created by a professional architect.

Video instruction