The roof is a complex, multi-component construction, the design, assembly and installation of which is a serious obstacle for an inexperienced master. The most important step in the construction of the roof is considered the device of the truss frame, which sets the shape, slope and carrying capacity of the slope. The rafters bear the load of the weight of the roofing material and snow, so they must be strong and durable. But what to do if the length of the slope far exceeds the standard size of lumber? In this article we will describe how the splicing of the rafters between them is performed correctly to increase the length of this element.
Appearance and function
Rafter legs or rafters are the main elements of the truss frame of the roof, which are arranged in pairs along the ridge joint, forming inclined planes of the slopes. Usually they are made of healthy, durable wood or metal profile. In the design of the roof rafters perform the following functions:
- Form the shape and angle of the slopes. It is the angle between the truss feet and the base of the roof that define the recognizable geometry of the roof, facilitating the descent from the surface of the thawed and rainwater and snow.
- Evenly distribute the weight of roofing. Taking into account the snow load, the roofing pie can weigh up to 300 kg / m2, therefore the rafters must withstand considerable weight along the entire length, and also distribute it between the supporting walls.
- Serve as a basis for fixing the roofing material. The finish coating is fixed on the crate, nailed across the frame rafter legs.
Note! There are three parameters of rafters, which are determined when calculating and creating a roof project: the length of the rafter foot, the distance between them and the size of the cross section of these elements. They mainly depend on the slope of the slopes, climatic conditions and the weight of the finish coating.
Rafter legs that distribute the weight of the waterproofing coating and thermal insulation of the roof between the supporting walls, on which the slopes are supported, must have a high bearing capacity and excellent strength properties. In addition, they should be light, so that with its considerable length not to bend under its own weight. Optimal materials for the manufacture of rafters consider:
- Tree. Wood is a lightweight, durable building material that is easy to handle with the most primitive tool manually. Rafter legs from this bar with a section of 100х100 mm or 150х150 mm withstand up to 500 kg / m2. Due to the fact that the standard size of sawn timber does not exceed 6 m, wood is used for the manufacture of private rafters, because with a slope length exceeding 6 meters, it is necessary to build boards. The disadvantage of wooden rafters is considered weak resistance to decay, so they are treated with antiseptic compounds.
- Metal. Metal rafters are used mainly in industrial construction, as economic, commercial and industrial buildings, as a rule, have a large size. The high bearing capacity of the metal profile allows the use of elements of a smaller section. In addition, the metal has a high corrosion resistance.
Experienced craftsmen note that even if the length of the slope exceeds 6 meters, the rafters for the roof frame can be made of wood. And it is absolutely not necessary to purchase expensive lumber of non-standard length. When the roof is large, splicing the rafters is carried out or they are put in place by fillers.
The length of the truss leg consists of the length of the slope and the length of the overhang of the roof, so it can exceed the standard size of lumber, which is 6 meters. To lengthen the boards from which the rafters are made, you need to connect two or three boards together. In order for the composing truss foot not to lose its strength properties, it is necessary to correctly calculate the place of the splice and fix it securely using one of the following methods:
- Butt joint To increase these rafters by the method, the ends of the timber are sawed off at an angle of 90 degrees, connected to each other, and then on both sides they impose wooden lining, fixing them in several places with long bolts in a checkerboard pattern. This method is suitable for splicing rafters made of boards with a section of 50x150 mm.
- Connection "oblique prirub". If the rafters are made of square bar, then it is easiest to build them with the method of "oblique hem". This technology lies in the fact that the ends of the connected elements are cut at an oblique angle, and then connected through a through vertical hole with a pin. The main thing is that the diameter of the hole corresponds to or was 1 mm smaller than the fastener, otherwise there will be a backlash in the structure causing a bending stress.
- Connection overlap. To build rafters from wooden boards along the length, it is possible to join individual elements with an overlap. This is an easy way to get a fairly rigid and durable mount. The overlap between the boards should be not less than 1 m, and the fastening with nails is carried out in a checkerboard pattern.
Important! Another reliable method to increase the length of the truss naga is to make composite or twin rafters. It should be noted that the composite elements are cheaper than doubled ones, however, they are significantly inferior in their strength.