- Choosing a tree
- We put a ridge bar
- Elongated timber
- The device and installation of rafters
- Installation of bows
The rafter system is the foundation of your future roof, so its construction must be taken very seriously. Before you start work, you need to sketch for yourself a rough plan of the system in order to understand what the type of general structure will be and what functions its individual elements perform.
In order to calculate the parameters and technical characteristics of the rafter system for large objects, it is best to resort to the services of professionals. If your roof is intended for a private building of a relatively small size (house area up to 100 m2), then you can carry out the installation, guided by the materials below.
The first step is to determine the angle of inclination of the slopes. Usually, average calculations are based on the amount of materials, which has a very good effect on the material component of the issue, it is generally accepted that the smaller the angle of inclination, the more profitable and cheaper the building will cost. In fact, it is necessary to choose the angle of inclination from two main indicators – wind loads and the weight of precipitation (in particular in winter), as you can see, the question of prices in the technical parameters is not taken into account. The universal angle of inclination for our climate is 45-50 degrees, with such parameters, the strength indicators are maximally balanced before loads, both wind and those that can be caused by precipitation pressure. Sometimes it happens that about 180 kg of snow falls on one square meter of the roof. In addition, the financial component will also be at an average level, which is much better than saving money by reducing the angle of inclination, but subsequently overpaying two prices for eliminating defects that will be caused by the above factors.
Choosing a tree
For the rafter, two parameters are important – strength and lightness of the structure, so ordinary pine is suitable for installation. It is often used for such structures, since it has these two qualities, plus it has a favorable price compared to noble wood species. It is necessary to use a board of the first grade, measuring 150-200x50x6000 mm, we also need a bar with a section of 200×200 mm.
An important technical point is the moisture content of the wood. A freshly sawn tree has a 50% moisture coefficient, it is impossible to mount such a tree, because if it dries out in a state of tension, it can be driven, it will bend and crack in places where knots are located. It is necessary to purchase material with 15-20 percent moisture content.
When buying, check that all boards are even and free of rot, the strength and durability of the structure depends on this.
When the tree is delivered to your construction site, it must be treated with antiseptic drugs and laid in the most ventilated area. Laying the tree must be done in a certain way: first we lay three or four transverse slats, on them, along, we lay boards so that there is a distance of 0.5-1 cm between each board, then again a row of transverse slats and a row of boards.
Thanks to this, we will create an air space between each unit of lumber, they will be ventilated in the right conditions, which will allow us to avoid rotting and moisture accumulation..
We put a ridge bar
The ridge bar is the center top bar that is designed to evenly transfer the total weight of the roof to the gables, distributing the pressure area around the entire side perimeter. Installation of a bar is a very complicated process. First of all, let’s decide on its length. As a rule, according to the plan, there are small canopies (from 0.5 to 1.5 m) from the sides of the roof, the ridge beam should lie exactly along this length with all the protrusions outside the gables. On concrete bases, in places of contact with the timber, we lay pieces of roofing material so that the tree does not touch the pediment directly – only through the waterproofing. We bend the roofing material around the timber, and drill on the sides and insert two segments of the 12th reinforcement, 0.4 m each. We do not drill the timber itself to avoid cracks.
Very rarely, a standard 6 meters is enough for a “ridge”. In most cases, this length has to be increased. The build-up takes place at the place of installation, otherwise the spliced timber will be very difficult to lift up and install. The joining point of the timber must be chosen in such a way that it is as close as possible to some partition or other point on which a temporary vertical support can be placed. For vertical support, we measure and cut off the board, on the sides of which we nail two small boards, so we get something like a wooden fork, between the teeth of which there will be a joint of the ridge bar. On the upper side of the ridge, we pull a thread, which will serve as a level for us before we fix the beam to each other. It is necessary to fasten them with two one and a half meter segments of the board, the joining segments are located exclusively on the sides, in which case the load will be applied to the tree in the right direction, reducing the risk of fracture at the junction. The boards are fastened with nails, since if you try to organize bolted joints, the timber can give a number of cracks when drilling.
This element is used for joining the rafters with the longitudinal bases of the bearing wall, for a point distribution of the load of the entire structure. It must be laid using roofing material (as is the case with the ridge). Choose the flattest boards, they should adhere to the wall surface as much as possible. The Mauerlat is fixed with 0.2 m long anchor bolts. The points where the anchor will be placed must be calculated in advance, their location should be in the intervals between the future rafter boards, so that the anchor heads do not interfere with us when further fastening the following elements.
If the standard length of the board is not enough, feel free to pick up the boards and fasten them in the same way as the joint between the Mauerlat boards will be organized – it does not matter, the main thing is that they fit snugly to the concrete.
Do not forget to put the Mauerlat on short sections behind the gables, where you have planned the roof peaks.
The device and installation of rafters
The first step is to determine the number of rafters, for this we take the total length of the roof and divide it by approximately 1.2-1.4 m, after we get an integer, we divide the length of the roof by it. An integer is the number of rafters on one side, dividing the length by this number will give us a more accurate step between them, for example, if the roof is 9 meters long:
- 9 m / 1.3 m = 6.92 (round up) = 7 – the number of rafters;
- 9 m / 7 = 1.28 m – step between rafters.
We multiply the number of rafters by two and again by two, thanks to these calculations we will get the total number of boards that will need to be used to make the structure.
The next step is to cut the boards at the angle of the roof. To do this, on one side of the board, the perpendicular between the cut and the longitudinal part must be shifted downward by the required number of degrees. With the help of a protractor and a pencil, everyone can perform this procedure. Next, we cut the board along the outlined line, we will get a template according to which we will trim all the other boards.
First, we mount the extreme rafters that are inside the zone between the gables. Installation of rafters is carried out on two levels, the first at the ridge, the second near the Mauerlat. The marking of the step between the rafters should be done both above and below. This line is the middle of the rafters, the structure of one rafter consists of two boards, the distance between them is 50 mm.
We cut off 9 boards 30 cm long and fasten them on the ridge beam clearly according to the step markings. Fastening is carried out using self-tapping screws and corners, the board should lie on top and perpendicular to the ridge. These segments will serve as a connecting link for attaching two opposite rafters..
In the same way, we attach 9 segments on each side to the Mauerlat, only the length of the board should be 20 cm, and it should be located vertically, this node will be used to fasten the lower sides of the rafters.
Now you can start with the basic procedures. On each upper segment (30 centimeters), it is necessary to draw an average vertical line, it will play the role of a guide, where the joining of two boards cut at an angle takes place. The installation of the rafters begins with the fact that the first board is aligned in the center from the top and tacked onto a nail to a 30-centimeter segment. Then the second board is nailed on the other side. It is necessary to ensure that the boards are at the same horizontal level, for this it is necessary to undermine the board, which is planted below, and raise it to the level of the second board, fixing it on a nail to the connecting jumper. It is highly discouraged to make cuts in the ridge bar. Below, to level the level between the boards, the opposite procedure is performed, the board, which turns out to be slightly higher, is heated into the Mauerlat, for this you need to hollow out a small groove using a chisel.
After the boards are adjusted to the level, it is necessary to pull off the lower part of the rafter with two nails and make two bolted connections, one at the top, the other at the bottom, in the places where the boards are baited on the nails. The bolted connection must be through three planks.
After that, we get an almost finished rafter, which must be strengthened in order to give it rigidity. Let’s conditionally divide the length of the rafter into four parts, you can sketch out the markings with a pencil. At the junction of the first and second quarters, we fasten a 60-centimeter segment between the boards to tighten the rafter. We use nails as fastening materials. We perform a similar procedure at the junction of the third and fourth quarters..
Further, according to the above technology, we mount the rafter from the opposite side.
After the four rafters are mounted, we have two extreme triangles, at the bases and at the top it is necessary to pull the threads along the entire roof, which we will use as guides to adjust the level of all diagonally located elements.
After the side rafters, the central part is mounted, now you can knock out the support, which is located at the junction of the ridge beam, we no longer need it, at this stage the structure already has a sufficient margin of safety. Next, all the other rafters are placed, one section on each side in a checkerboard pattern, for even distribution of loads. Upstairs, at the joints of opposite rafters, it is necessary to additionally strengthen the connections, we use connecting plates and self-tapping screws for this.
When all the rafter sections are in place, it is necessary to cut off with a hand hacksaw all the corners that go beyond the level of the rafters, in particular, these are the corners of the connecting boards on the timber and on the Mauerlat.
Installation of bows
The bow is a connecting board that is located approximately at the level of the centerline of the rafter triangle. It serves to reduce the load on the sides of the roof, thanks to the bows, the likelihood of roof deflection under the weight of precipitation and the likelihood of oscillations under wind loads is greatly reduced.
In our case, the lifting height of the ridge bar is a little more than 4 meters, which means that the arrangement of the bows can be done strictly in the center, thus, all the loads are distributed evenly, plus the ceiling height of the attic will be relatively normal and there will be no obstacles for movement of a person with average height in it.
As in the case of the rafters, the first bows are attached to the sides, after which two threads are pulled, they will help us maintain the level. After that, the central bow and all the others are attached. On the extreme rafter triangles, bows are not needed, this will spoil the appearance of the roof, besides there are very weak loads, so from a technical point of view this step is not required.
One side of the bow is wound in the middle of the rafters and sits on the nail, the second side, after observing the horizontal level, also cites on the nail, then we make two bolted connections. It is very important to adhere to the level at this stage, since the bow is not only a spacer, but also the basis of the ceiling of the attic or attic room.
In fact, this technology is very simple, no matter how complicated it may seem at first glance. Armed with a sheet of paper and a pencil, draw the roof in stages, as indicated in the article, then the whole puzzle will fold into one accessible and elementary picture.
With a standard set of building tools, two people can build a similar roof in 5-6 working days.