Construction of rafter roof is quite difficult and responsible, but long-awaited operation of completion of the main works at construction of residential building or auxiliary facility. There is roof over the head — it is possible to do all the rest, without being afraid of bad weather.
The rafter system is load-bearing framework for the subsequent laying of roof. The framework consists of various elements and for simplicity is called rafter roof or rafters. The system has to be executed in due form, neglect which can negatively affect operation of the building.
Types of rafter systems
There are five types of rafter systems which are most often used at construction of owner-occupied dwellings.
Lean-to
The Bescherdachny roof with one slope is arranged most often over auxiliary buildings: sheds, garages, verandahs, baths, etc. The slope of roof turns out installation of rafters on walls with different height.
Twin
The most widespread and economic type of roof. It is carried out from two rectangular planes in the form of isosceles triangle. The pediment in faces of roof is sheathed by the material other than roof covering. The type of slanted roof when corners of slopes are various is less widespread. The garret space is very convenient for storage of wood product, lengthy objects, it is possible to arrange premises also.
Mansard
Kind of duo-pitch system for the maximum increase in garret space. The difference consists in separate performance of rafter racks — rafters are executed from two boards under different corners in relation to floor beams. The mansard roof is used for arrangement of the inhabited or auxiliary room.
Valmovye
The roof has 4 slopes and is executed, most often, in the form of pyramid. Tilt angles of rafters are defined with the maximum snow and wind load characteristic of this area. The pediment is absent. Such type of roof gives to the building unusual look and is especially emphasized with material and color of covering. Due to the lack of pediment is slightly more economic, but it is more difficult performed by. It is possible to use garret space only from within, via the ceiling hatch.
Tent
Resemble covering over serf towers superficially, settle over gazebos, bay windows, etc. The roof can be round shape or consist of several planes (more than 4). Have rather decorative character emphasizing identity of the building and certain taste of owners. Are rather difficult performed by at joint of various volumes of roof.
There is huge number of combinations of various types of roofs, but for simplicity will consider option of performance of gable roof — technological stages of its device are characteristic of all other types of rafter systems.
Material for rafter system
Practically all rafter systems are carried out from pine wood. It is the best of all to create products from pine which is quite often called "timber". The tree easily gives in to processing, strong, with small percent of suchkovatost. High content of pitches in fibers of board increases resistance to atmospheric humidity. The pine is easily drilled also fixing material — nails, ruffs, self-tapping screws — without problems connects boards in design.
Rules of the choice of wood for rafter system:
- The humidity of tree has to be no more than 2.5% — material has to be dry.
- It is the best of all to buy the wood for roof in the summer or in the fall, prior to the beginning of rains, having allowed boards to have a complete rest in the winter under canopy. Leads drips of water and formation of sleets to defeat of boards fungus which cannot be removed subsequently. Between ranks of boards it is obligatory to lay logs for airing, at a slow pace meter, in order to avoid deflections.
- To store boards in the open sun, allegedly for drying, it is strictly forbidden. The tree very easily begins to be deformed, conducts it and the board takes propeller form. It is impossible to straighten such board.
- Boards should not have longitudinal chips and cracks — small in the beginning, in use they can cause serious problems.
All these simple rules need to be known to buy quality material. The conscientious seller of wood will create necessary conditions for high-quality storage of products. If the firm does not follow these rules, it is better to look for goods in other place.
For storage and work with wood it is the best of all to have the certain platform with canopy and hard surface, near the building under construction. On this site, besides storage and drying of tree, are made cutting of boards on products, processing by their antiseptics or painting.
Elements of rafter roof
Let's consider basic elements for the device of rafters. Standard length of all boards is equal to six meters. From this size it is necessary to proceed at design and the device of roof. In construction all sizes on workshop drawings are given in millimeters.
- Foot of a rafter — device supporter for roof slope. It is carried out from board, length of the equal plane of roof. Section of board depends on height of roof, rated snow and wind loadings, roof covering type. The section of 150х50 mm is most widespread.
- Inferior purlin — the bar fixed on walls of the house and intended for installation of bottom of rafters. The inferior purlin also redistributes constant and temporary loads from roof of building walls. It is usually carried out from bar of 150х150 mm, at smaller loading the board of 150х100 mm laid flatwise for increase in area bearing is allowed.
- Ridge piece — the horizontal supporting beam intended for support of massive feet of a rafter in the most upper part of roof. The most loaded framework element. It is carried out from bar with a section of 150х100 mm or 200х150 mm. The run on the racks (with the section equal to run width) leaning on main walls is established.
- Inhaling — the horizontal bar connecting two feet of a rafter in the absence of basic run in the top third of height of framework. Section of inhaling is 150х50 mm, 100х50 mm.
- Drag strut (knee brace) — the auxiliary beam exposed at an angle to foot of a rafter from the center of framework. Are established with big height of roof, for removal of stress in the most loaded part of foot of a rafter. Usually drag struts are established at an angle 45o from the central axis of the building. All auxiliary elements of framework usually are carried out from the boards equal by section to foot of a rafter.
- Furring — the board or bar fixed on top of feet of a rafter on all plane of roof. Furring is intended for association of rafters in space framework. Can be continuous — for the device of soft roof with small corners of slopes — or with the certain step depending on covering material. Furring under slate or tile is carried out from bar of 50х50 mm, under professional flooring or ondulin the board of 100х25 mm approaches.
Creation of duo-pitch rafter system
The basis of framework of roof is formed by the triangular farm consisting of two feet of a rafter connected by horizontal inhaling and auxiliary struts. Triangular farms rafters are established on inferior purlin, step of 60-90 cm on all length of the building.
If the building small by the sizes — no more than 4х6 m — easy rafters gather on the earth and are established without supporting beam on the center. Connection of rafters in space framework is carried out by furring elements.
The building bigger by the sizes, with high mansard roof demands other way of the device of rafters. It is the best of all to carry out all elements of such roof on the earth and to unite in framework already above. It is supposed that beams of covering and draft floors are already executed. For convenience of works it is possible to lay sheets SMALLPOX on all surface of the attic on floors and to fix temporarily.
Sequence of actions
Process of production of rafter system can be separated into the following stages:
- Installation of racks and ridge piece. The most responsible and dangerous stage of work. Elements have to be carefully verified across and verticals. Before laying of run of rack fasten temporary struts. The run with racks on corners self-tapping screws is the best of all to fix.
- Installation of inferior purlin. In walls on depth of 40 cm threaded studs with a diameter of 10 mm are drilled. In bar openings of large diameter are drilled, it is strict on step of pins. The inferior purlin nuts drags on, the washer has to be special, the increased area. Also do not forget to lay waterproofing under beam.
- Installation of feet of a rafter. Collect at height false roof frame from all elements of framework, with support on run and inferior purlin. On template to designate all grooves, dredging, exact geometry of parts. It is possible to execute from it from board 25 mm thick. Template to zamarkirovat, sort, lower and cut basic elements on the earth.
In the beginning extreme rafters are established. Single parts of the first foot of a rafter to lift and mount on the place. Installation of all auxiliary elements of rafters is conducted: drag struts, inhalings, props, swell dowels if the big overhang of roof is provided. Further the subsequent ranks of rafters gather. In process of readiness of rafter it is necessary to fix temporarily by horizontal and inclined rails as all of them are unstable.
The team contract is possible: one person cuts out parts below, two work above as it is necessary to establish and fasten at the same time elements among themselves. In such sequence it is possible to collect the main framework of rafter roof in one day.
Completion of works
After final check and adjustment of all system the laying of furring is carried out. The lower and top number of furring for initial communication of all rafters is arranged. The step marking on extreme rafters is carried out. Further there is mounting of each row from below up for convenience of movement. At the same time temporary fastenings are removed. Final fastening of rafter system can be carried out corners on self-tapping screws, drive brackets or wood-grouses self-tapping screws with hexagon head. Boards of furring it is possible to fix nails, killing them not perpendicular to board, and with inclination, for durability.
In general, the device of rafter roof is considered one of the most difficult and dangerous types of construction jobs. Alone to the inexperienced person it will be very difficult to master this work — will take too much time. It is better to work three together under the leadership of the master more expert in this case.