Dependence Of The Type Of The Slope

Dependence of the type of roofing on the steepness of the slope

When planning the construction of his own house, the landlord is probably already conducting an “estimate” both with his head and with family members – how their future housing will look like. The roof in this matter, of course, is of paramount importance. And here it is necessary to take into account the fact that not every roofing material can be used on roof slopes of different steepness. To avoid misunderstandings later, it is necessary to provide for this relationship in advance.


Roofs in terms of the slope angle can be conditionally divided into the flat (slope up to 5 °), with a small slope (from 6 to 30 °) and steep slopes, respectively, with a slope angle of more than 30 °.


Every roof has its advantages and disadvantages. For example, flat roofs have a minimal footprint but will require special waterproofing measures. Snow masses do not linger on steep roofs, but they are more susceptible to wind load due to their “windage”. So is the roofing material – due to its own technological or operational features, it has certain restrictions on applications with different slopes of slopes.


Black circles with arched arrows and blue numbers indicate the areas of application of various roofing coatings (the arrowhead indicates the minimum allowable slope value):


  • is shingles, chips, and natural shingles. In the same area lies the use of reed roofs still used in the southern edges.
  • natural piece tiles, bitumen-polymer tiles, slate tiles.
  • roll materials on a bitumen basis, at least four layers, with external gravel dressing, recessed into a layer of molten mastic.
  • similar to point 3, but for the reliability of the roof, three layers of roll material are enough.
  • roll roofing materials glued on hot mastic in at least two layers. Metal tile, corrugated board.
  • corrugated asbestos-cement sheets (slate) of a unified profile.
  • tiled clay coating
  • reinforced asbestos-cement sheets.
  • roofing sheet steel with flared connections.
  • slate covering of the usual profile.


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Thus, if there is a desire to cover the roof with a certain type of roofing material, the slope angle of the slope should be planned within the specified framework.

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Dependence of the height of the ridge on the angle of inclination of the roof

For those readers who have a good memory of the high school trigonometry course, this section may seem uninteresting. They can skip it right away and move on. But those who have forgotten this need to refresh their knowledge of the interdependence of angles and sides in a right-angled triangle.


What is it for? In this case, the construction of the roof is always in the calculations repelled from a right-angled triangle. Its two legs are the length of the projection of the slope onto the horizontal plane (length of the span, half span, etc. – depending on the type of roof) and the height of the slope at the highest point (on the ridge or when moving to the upper rafters – when calculating the lower rafters of the attic roof). It is clear that there is only one constant here – this is the span length.


The table shows two main dependencies, expressed through the tangent and sine of the slope angle. There are other dependencies (through cosine or cotangent), but in this case, these two trigonometric functions are enough for us.

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Graphic Scheme

Н – ridge height

S – it is the length of the roof slope

L – half the length of the span (with asymmetrical gable roof) or the length of the span (with a pitched roof)

α – roof slope angle

Calculator for calculating the length of the roof slope based on the known value of the ridge height

Skillful use of trigonometric formulas allows, with normal spatial imagination and the ability to perform simple drawings, to carry out calculations and more complex roof structures. Try the slope intercept calculator for slope calculations.


For example, even a hip or mansard roof that seems to be so “fancy” can be broken into a set of triangles, and then sequentially calculate all the necessary dimensions.

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Dependence of the size of the attic room on the angle of inclination of the roof slopes

If the owners of the future house plan to use the attic as a functional room, in other words, to make an attic, then determining the angle of the roof slope acquires quite practical significance.


Dependence of the magnitude of external loads on the angle of inclination of the roof

Another important application of the calculated value of the angle of inclination of the roof is to determine the degree of its influence on the level of external loads falling on the roof structure.


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There is an interesting relationship here. You can calculate in advance all the parameters – angles and linear dimensions, but they always end up with detailing. That is, it is necessary to determine from what material the parts and units of the rafter system will be made, what should be their cross-sectional area, the spacing, the maximum length between adjacent support points, ways of fastening the elements to each other, and to the load-bearing walls of the building, and much more.


This is where the loads that the roof structure experiences come to the fore. In addition to its own weight, external influences are of great importance. If we do not take into account the seismic loads unusual for our regions, then we should mainly focus on snow and wind.

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Snow load

Based on the results of many years of observations and calculations, a map of the country’s territory has been compiled, which indicates eight different zones by the level of snow load.


The eighth and last zone includes some sparsely populated areas of the Far East, and it can be ignored.


Wind load

With wind load, things are much more complicated. The fact is that it can be multidirectional – the wind is able to exert pressure on the roof, pressing it to the base, but at the same time aerodynamic “lifting” forces arise, striving to tear the roof off the walls.


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In addition, the wind load affects different parts of the roof unevenly, so it is not enough to know only the average level of wind load. The calculation takes into account the prevailing wind directions in a given area (“wind rose”), the degree of saturation of the area with obstacles to wind propagation, the height of the building and surrounding structures, and other criteria.