Contents
The roof of the house must be reliable and beautiful, and perhaps this is with the correct determination of its angle of inclination for this type of roofing material. How to calculate the angle of the roof – in the article.
The purpose of the under-roof space
Before calculating the angle of inclination of the roof, it is necessary to decide how the attic space will be used. If you plan to make it residential, the angle of inclination will have to be made large – so that the room is more spacious and the ceilings are higher. The second way out is to make a broken, mansard roof. Most often, such a roof is made of a gable roof, but it can also have four slopes. It’s just that in the second option, the truss system turns out to be very complicated and you simply can’t do without an experienced designer, and most people prefer to do everything on their own, with their own hands.
When increasing the angle of the roof slope, it is worth remembering a few things:
- The cost of roofing materials increases significantly – the area of uXNUMXbuXNUMXbthe slopes increases.
- Large slopes are more affected by the wind load. If we compare the load on the same house with an angle of 11 ° and 45 °, in the second case it will be almost 5 times greater. In order for the roof to withstand such loads, the truss system is made reinforced – they put beams and rafters of a larger section with a smaller pitch. And this is an increase in its value.
- If the slope angle is greater than 60°, snow loads are not taken into account – precipitation rolls down and does not linger. But when constructing a broken mansard roof, snow loads are taken into account when calculating its upper part – there the planes have a slope of less than 60 °.
- Not all roofing materials can be used on steep slopes, so look carefully at the maximum angle that these roofs can be used with.
The slope angle is displayed through the ratio of the height of the ridge and half the width of the building
This does not mean that low-slope roofs are better. They are cheaper in terms of materials – the roof area is smaller, but they have their own nuances:
- Require snow retention measures to prevent snow avalanches.
- Instead of snow retainers, you can make heating of the roof and drainage system – for the gradual melting of snow and timely drainage of water.
- With a small slope, it is likely that moisture will flow into the joints. This entails enhanced waterproofing measures.
So roofs with a small slope are also not a gift. Conclusion: it is necessary to calculate the angle of inclination of the roof in such a way as to find a compromise between the aesthetic component (the house should look harmonious), practical (with a residential under-roof space) and material (costs must be optimized).
The angle of inclination depending on the roofing material
The roof on the house can have almost any kind – it can have low slopes, maybe it is almost sheer. At the same time, it is important to correctly calculate its parameters – the cross section of the rafter legs and the step of their installation. If you want to lay a certain type of roofing material on the roof, you need to take into account such an indicator as the maximum and minimum angle of inclination for this material.
| Name of roofing material | Minimum tilt angle (in degrees) |
|---|---|
| Asbestos-cement slate and ondulin | 6° |
| Cement-sand and ceramic tiles | 10° |
| Flexible shingles | 12° |
| Metal | 6° |
| Asbestos-cement or slate boards | 27° |
| Galvanized steel, copper, zinc-titanium sheets | 17° |
| Profiled sheeting | 6° |
The minimum angles are specified in GOST (see the table above), but manufacturers often give their recommendations, so it is advisable to decide on a specific brand at the design stage.
More often, the angle of the roof slope is often determined based on how they are made by their neighbors. From a practical point of view, this is correct – the conditions for nearby houses are similar, and if the neighboring roofs are good, they do not leak, their parameters can be taken as a basis. If there are no roofs in the neighborhood with the roofing material that you plan to use, you can start the calculations with average values. They are shown in the following table.
| Type of roofing material | Recommended tilt angle min/max | What slope of the ramp is done most often |
|---|---|---|
| Roofing with roofing | 3 ° / 30 ° | 4 10 ° ° |
| Two-layer tole | 4 ° / 50 ° | 6 12 ° ° |
| Zinc double standing seam | 3 ° / 90 ° | 5 30 ° ° |
| Groove tile with 4 grooves | 18 ° / 50 ° | 22 45 ° ° |
| dutch tile | 40 ° / 60 ° | 45° |
| Ordinary ceramic tiles | 20 ° / 33 ° | 22° |
| Decking and metal tiles | 18 ° / 35 ° | 25° |
| Asbestos-cement slate | 5 ° / 90 ° | 30° |
| artificial slate | 20 ° / 90 ° | 25 45 ° ° |
| Straw or reed | 45 ° / 80 ° | 60 70 ° ° |
As you can see, in the “how they do” column, in most cases there is a solid range. So it is possible to vary the appearance of the building even with the same roof. Indeed, in addition to the practical role, the roof is also an ornament. And when choosing the angle of its inclination, an important role is played by the aesthetic component. It is easier to do this in programs that make it possible to display an object in a three-dimensional image. If you use this technique, then calculate the angle of the roof in this case – choose it from a certain range.
Influence of climatic factors
The angle of inclination of the roof is affected by the amount of snow that falls during the winter in a particular region. Also, when designing, wind loads are taken into account.
Everything is more or less simple. According to long-term observations, the entire territory of the Russian Federation is divided into zones with the same snow and wind load. These zones are marked on maps, painted over in different colors, so it is easy to navigate. Using the map, determine the location of the house, find the zone, use it to determine the value of the wind and snow load.
Snow load calculation
There are two numbers on the snow load map. The first is used when calculating the strength of the structure (our case), the second – when determining the allowable deflection of beams. Once again: when calculating the angle of inclination of the roof, we use the first digit.
The main task of calculating snow loads is to take into account the planned slope of the roof. The steeper the slope, the less snow can be held on it, respectively, a smaller section of the rafters or a larger step of their installation will be required. To account for this parameter, correction factors are introduced:
- the angle of inclination is less than 25° – coefficient 1;
- from 25° to 60° — 0,7;
- on roofs with a slope of more than 60 °, snow loads are not taken into account – snow is not retained on them in sufficient quantities.
As you can see from the list of coefficients, the value changes only on roofs with a slope of 25° – 60°. For the rest, this action does not make sense. So, in order to determine the actual snow load on the planned roof, we take the value found on the map, multiply by the coefficient.
For example, we calculate the snow load for a house in Nizhny Novgorod, the roof slope is 45°. According to the map, this is the 4th zone, with an average snow load of 240 kg / m2. A roof with such a slope requires adjustment – we multiply the found value by 0,7. We get 240 kg / m2 * 0,7 = 167 kg/m2. This is only part of the calculation of the angle of the roof.
Calculation of wind loads
It is easy to calculate the effect of snow – the more snow in the region, the greater the possible loads. Wind behavior is much more difficult to predict. You can only focus on the prevailing winds, the location of the house and its height. These data, when calculating the angle of inclination of the roof, are taken into account using coefficients.
The position of the house relative to the wind rose is of great importance. If the house is located between taller buildings, the wind loads will be less than when it is located in an open area. All houses are divided into three groups according to the type of location:
- Zone “A”. Houses located in open areas – in the steppe, desert, tundra, on the banks of rivers, lakes, seas, etc.
- Zone “B”. The houses are located in a wooded area, in small towns and villages, with a wind obstacle no more than 10 m high.
- Zone “B”. Buildings located in densely built-up areas with a height of at least 25 m.
A house is considered to belong to this zone if the specified environment is located at a distance of at least 30 times the height of the house. For example, the height of the house is 3,3 meters. If at a distance of 99 meters (3,3 m * 30 = 99 m) there are only small one-story houses or trees, it is considered to belong to the “B” zone (even if it is geographically located in a large city).
Depending on the zone, coefficients are introduced that take into account the height of the building (given in the table). Then they are used in calculating the wind load on the roof of the house.
| Building height | Zone “A” | Zone “B” | Zone “B” |
|---|---|---|---|
| less than 5 meters | 0,75 | 0,5 | 0,4 |
| from 5 m to 10 m | 1,0 | 0,65 | 0,4 |
| from 10 m to 20 m | 1,25 | 0,85 | 0,55 |
For example, let’s calculate the wind load for Nizhny Novgorod, a one-story house is located in the private sector – it belongs to group “B”. On the map we find the zone of wind loads – 1, the wind load for it is 32 kg / m2. In the table we find the coefficient (for buildings below 5 meters), it is 0,5. Multiply: 32 kg/m2 * 0,5 = 16 kg/m2.
But that is not all. It is also necessary to take into account the aerodynamic components of the wind (under certain conditions, it tends to tear off the roof). Depending on the direction of the wind and its impact, the roof is divided into zones. Each of them has different loads. In principle, in each zone you can put rafters of different sizes, but they don’t do this – this is unjustified. To simplify the calculations, it is recommended to take indicators from the most loaded zones G and H (see tables).
The found coefficients are applied to the wind load calculated above. If there are two coefficients – with a negative and a positive component, both values uXNUMXbuXNUMXbare considered, and then they are summed up.
The found values of wind and snow loads are the basis for calculating the cross section of the rafter legs and their installation step, but not only. The total load (weight of the roof structure + snow + wind) should not exceed 300 kg/m2. If, after all the calculations, the amount you have turned out to be more, you must either choose lighter roofing materials, or reduce the angle of the roof.
So, conclusions. To calculate the angle of inclination of the roof is, rather, to choose one of the possible options. It is only important that this choice is correct.