Installing roof rafters on the floor joists: how to properly support the rafter system
If you now come close to the question of choosing the design of the rafter system, the first thing you need to decide how exactly you will transfer the load from the roof. to the house. For example, in a classic scheme of the rafter system, the rafters are evenly supported by the ends on the walls or mauerlat, around the perimeter or on both sides, depending on what shape the slopes. But often today the rafters are attached directly to the attic floor joists, not the mauerlat, and this technology has its own valuable advantages.
And how to properly install the rafters of the roof on the beams of the floor, what are the technical solutions and how to perform such mounting nodes. we now tell.
To better navigate in this topic, you need to know what are the rafters, what they are, what are they attached to, in which cases choose a particular type of rafter system.
Roof rafters are load-bearing structures of pitched roofs, which take the entire load of the roof and snow cover on it, transferring it to the walls of the building. In private housing they are most often made of timber or boards with a large cross-section, put on the rib. Much less often used metal structures in the form of prefabricated elements or prefabricated trusses. Of what and how to make the rafters, it is decided on the basis of the calculated load on them and the preferences of the customer.
Structurally the rafters are divided into hanging and strung:
- Hanging rafters are installed on small houses, garages and other outbuildings that have a span between the walls is not more than 5-6 meters. The upper ends they are connected to each other without additional support, and the lower ones, resting on the walls, tighten with horizontal elements. straps. Bracing reduces rafter loads on the walls by taking them up.
Additional overlap increases the span to 8 m and the push-pull props increase the span to 10 m Source obustroeno.com
- Strung rafters are installed on buildings with large spans of more than 10-12 m with an average load-bearing wall or supporting columns. Their upper ends rest on the ridge purlin, which in turn is supported by posts resting on the purlin. a horizontal beam resting on columns or an interior wall. If you are faced with the problem, how to install the rafters on a single-pitch roof, then you also choose a lean-to design, since it performs the role of ridge beam higher wall.
Moving on to measurements
(I’ll show you how to calculate everything manually, without a calculator. approx. translator).
Here are the rafter system measurements we need: rafter angle (Pitch), Rise, Run, and Diagonal. If you know the dimensions of any two of these four dimensions, you can easily find all the others.
(for those who understand English. approx. translator)
Look at our model of the roof (picture above), initially we need to know the dimensions of its two elements: the width of the building and the thickness of the ridge board.
The width of the building, for example, would be 8.8 meters. (8.75 meters and an inch of trim on each side of the house of 0.05m):
Each rafter stands on its side of the building and connects to each other on the ridge board. Therefore subtract the thickness of the ridge board from the total width of the building, otherwise you will make a mistake when calculating the rafter length. Let’s take its thickness of 50 mm.
Calculate the total width of the building without the ridge board: 8.8 m. 0.05 m (50 mm) = 8.75 m.
Now we need to divide the result by 2 to get the “run” (Run) of each rafter. Calculate the “mileage” of each rafter: 8.75m/2 = 4.375m.
Now we need one more element, which we know in advance, the angle of slope of the roof. In our case let it be 6 to 12 (26.5 degrees. approx. translator).
Since our roof has a slope of 6/12, which means we have a rise that is half the run (t.к. 6 is half of 12). Calculate the lift: 4.375/2 = 2.187m. (half a millimeter rounded)
Now we can calculate the diagonal, t.е. The length of the rafter from the ridge beam to the wall trim (not the whole rafter, t.к. not yet taken into account the overhang). The diagonal is the hypotenuse, and we all remember how it is counted.
Let’s calculate the diagonal: Run(“2)Rise(“2)=Diagonal(“2) (“2). I have designated “squared”. 19.1406 4.7851 = Diagonal (“2) Diagonal = square root of 23.9257 Diagonal = 4.891 = 4 meters 89 cm 1mm
The next step after the calculations is to make a template for the rafters. To do this, you need to bolt the bosses to your angle piece (it’s more convenient, but you can do it without it) at 6 and 12 inches (or 15 and 30 cm in the metric system).
Now I put a square to the side of the board along its width and begin to mark the place of the cut on the top of the rafters (at the junction with the ridge board. approx. interpreter). Keep in mind that most cuts in frame construction are made this way: the length of the board is cut on the thin side, and the width of the board is cut horizontally.
I make this saw on top of the rafter with the circular saw (in the video) before marking the notch in the bottom of the rafter (the so-called “bird’s beak” or incoming angle or cut. interpreter). This is convenient because I can hook the end of the tape measure to the saw on the top and one mark the distance to the “bird’s beak” on the rafter (see. below in the picture)
Now from the top of this line we measure “diagonal” 4 meters 89 cm 1mm.
Then, using an ordinary joiner’s angle (some carpenters prefer Swanson’s measuring angle-transporter), I draw a parallel line for the trimmer to the first saw across the rafter. This line for the trimmer is a line for the plumb line trimmer (t.е. parallel to the wall and perpendicular to the ceiling of the frame house) on the rafters at the edge of the building.
Supports for diagonal elements
The design of the hip rafter system, regardless of size implies the mandatory presence of supports, reinforcing diagonal rafters legs. If the length of the mower is more than 9 meters, then you need to install at least two poles. shorter spans may be supported on a single support positioned at the top.
Supports for diagonal rafters can be:
- Vertical props placed directly on the slab. If the ceiling is reinforced concrete, it is obligatory to put a piece of waterproofing material under the pillar.
- Struts, which the lower part rest against the beam and are located at an angle of 45 degrees, and the magnitude of the slope angle does not play a special role.
- Sprangles, which are made in the shape of the letter “T” upside down. This element is used in cases where the diagonal needs two or more supports (about “Elements of the rafter system. what the structure consists of, the rules of the device”). When installing it is important to ensure that the base of the sprengel is perpendicular to the head. In most cases, such supports are placed closer to the corner of the roof, that is, at the bottom of the rafters.
Additional supports are best made of paired boards and installed in places where the greatest load is expected.
Fixing the rafters for the single-pitch roof of the garage
Very often garages are built of foam concrete blocks, so you should know how to arrange the rafter system in this case. If the upper part of the walls are not cast reinforced concrete belt, it is mandatory to lay a mauerlat. Single pitch roofing system involves the use of timber laid on the front and rear walls of the garage, which have different heights.
Solving the problem of how to properly install the rafters on a single-pitch roof, you need to adhere to the following order:
- A 1015 cm timber is placed flush with the inner surface of the walls. The result is a mauerlat roof with a single slope. To protect the wooden elements from the effects of foam concrete, you should lay them on the waterproofing material. To fix the mauerlat recommended to use roofing corners of size 99 cm, setting the fastener at a distance of 0.8 meters. Additionally, they can be strengthened by a cast lintel. Angle is attached to the wall with dowels 14 mm in diameter.
- Make a template of rafters, using a board 520 cm. The length of the rafters of a single pitched roof is determined as follows: the workpiece is installed on the mauerlat, leaving a margin at the top and bottom up to half a meter. This reserve should slightly exceed the standard width of the eaves, 0.4-0.5 meter. After all the rafters are installed, the extra sections are trimmed.
- Mark the tie-in positions on the rafters, remembering that the tie-in must not be very deep. Most often it is a third of the width of the board.
- Perform a marking of the walls, making sure that the distance between the rafters and the wall was not less than 5 cm.
- Using the template make the rafters for the whole roof, install and secure them with brackets or angle brackets.
- Determine the width of the overhangs and make a template of mares. You can use scraps of boards for this. Ready template used for the manufacture of all eaves elements. When installing them always put a waterproofing material that eliminates the contact of wood with the concrete wall.
- Align the size of the rafters for a single-pitch roof and all around the perimeter are nailed wind board, using a material size of 2.510 cm.
- Rafter system for a single-pitch roof over the garage of foam concrete blocks is considered ready. Then on the rafters nailed purlins, determining the step depending on the roofing material.
In this case the eaves were formed by means of overhangs. You can use another option, which involves taking the mauerlat beyond the perimeter of the building. The overhang is determined by the width of the eaves. The length of rafters in this case also increases by the width of the overhang. Overhangs must be made between the two outermost rafters. All other steps are performed according to the standard plan.
Basic rules of attaching rafters to the roof trusses
For a reliable connection you need to carefully fasten the connecting elements, select them with the required dimensions. It is necessary to precisely align the cuts, make them not more than a third of the size of the base. Use a high-quality timber for the base of the correct section.
Important! Do not use only nails and screws for mounting, such fixation can not be considered reliable, you should use metal fasteners of various types.
How to Measure and Cut Rafters
The roof will be strong and durable, if properly performed calculations, correctly selected material and correctly installed nodes connection.
Pluses and minuses of hip roofs
Despite the complexity of the construction of such structures are very common in Europe and Russia. They have advantages over other types of roofs:
- high strength and rigidity;
- resistance to wind loads due to the streamlined shape;
- The weight of the roof is transferred evenly to all walls
- no need to build gables, their function is performed by palms;
- Compatibility with a variety of roofing materials;
- The possibility of using in different architectural styles.
- technically complex construction;
- high consumption of roofing materials;
- squatting, which gives beveled slopes;
- small volume of attic space compared to a gable roof of the same size.
Walled structures can be combined with gable, hipped or conical. A variety of bay windows, turrets, protruding dormer windows and other architectural elements look this interesting, while eliminating the squatness of the structure.
Mounting the top ends of rafters
Choosing how to install the rafters, it is important to assess the complexity of the work and the weight of the rafters. If the truss has a relatively low weight in assembled form, or there is an opportunity to use lifting equipment, it is easier to assemble the structures on the ground, and then lift and mount them on the roof. If the elements of the system have a large weight and they have to be lifted manually, the assembly of trusses is performed on the roof. About the technology of installing trusses explained in the video instructions.
Connecting the upper ends of the rafters can be performed in different ways. First of all it is a butt joint fastening. The counter rafters are notched at the right angle. Then the rafters are joined by the resulting ends and fastened to two nails. Connection is further strengthened by a wooden or metal overlay.
Overlapping rafters are fastened using bolts or studs with wide washers and nuts. In this case the rafters touch the planes.
If the rafter system is mounted on a wooden house with gables made of timber or logs, put the rafters on the walls is required to use sliding fasteners to avoid deformation of the roof during shrinkage of the structure. Accordingly, the ridge rafters must be connected in a special way: the rafters should be placed with a gap, and they are fastened using a special movable connecting element made of metal.
If there is a ridge beam, the installation of rafters on the ground is not required. the rafters are installed one by one, and attached to the ridge purlin.
The ridge purlin must be positioned strictly horizontally so that the rafter system distributes the load that the roof experiences evenly.
What is the secret of the quality of the rafter system: the three main rules of the master
When the rafter system is ready, it is time to install battens, insulation and roofing material. But this is another interesting topic, which we will definitely tell in the next article. For now, we wish you quality materials, easy work and good assistants!
How to measure and cut the crowns for the house
Although a lot of stores for improvement or companies can give you ready-made crowns for your home or building, the creation of their own crowns is the ideal project for yourself. Not to mention the fact that building your own crocs is often less expensive than buying already made kits. You should have an idea about the basic design of the roof before you measure and cut any crock. As soon as it will be determined you can create strong building blocks for your construction project.
Building materials are an important part of the construction of the house.