Roof pitch

Graphic representation of the roof pitch

The roof pitch describes the slope or steepness of a roof surface . It is usually given as an angle in degrees to the horizontal, occasionally also in percent , only rarely as a numerical ratio.

Depending on the roof pitch, roofs are called flat roofs , flat roofs or pitched roofs . In addition to stipulations for the prescribed roof shape, zoning plans often also contain specifications for the roof pitch.

calculation

The roof pitch results from the roof height h (= vertical distance from the roof ridge to the eaves ) and the basic dimension g to the roof ridge (= horizontal distance from the roof ridge to the eaves). The angle of inclination can be calculated trigonometrically: ${\displaystyle \alpha }$

${\displaystyle \alpha =\arctan {\frac {h}{g}}}$

The following formulas help when converting the angle of inclination into slope and vice versa: ${\displaystyle \alpha }$ ${\displaystyle x}$

${\displaystyle \tan \alpha =x}$

${\displaystyle \alpha =\arctan \left(x\right)}$

A roof pitch of 45 ° corresponds to a slope of 100%.

Structural aspects

The roof pitch has an impact on the type of roof covering , as certain systems are only suitable for a defined pitch range.

The lower the roof pitch, the greater the risk that drifting rain or drifting snow will get under the roof and damage the roof structure . For this reason, the roof pitch of buildings in cold countries with snowfall is greater than in warm countries. But the choice of roofing also has an impact on rain resistance. Roof tiles, for example, protect the roof from rain damage, as the precipitation is directed from the higher, covering roof tiles to the roof tiles below in such a way that the water cannot penetrate the substructure. Likewise, the self-cleaning effect of the roof covering is at risk with low inclinations and the risk of moss formation is increased. Even with flat roofs (≤ 5 °), the roof pitch should be at least 3 ° so that rainwater can drain off safely and no puddles form on the roof.

Standard roof pitch

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The standard roof pitch is the pitch up to which a roof covering has generally proven to be rainproof. This means that water flowing towards the eaves normally does not penetrate. Examples:

• FZ roof panels , German cover 25 °
• Slate , old German cover 25 °, old German double cover 22 °,
• Concrete roof tiles , high longitudinal fold 22 °
• Double groove interlocking tile 30 °
• Flat roof tile 22 °
• Plastic plates 15 °
• Trapezoidal profile, steel and aluminum 4–7 °
• Industrial standing seam 0.5 °
• Bitumen shingles 15 ° to 85 °, depending on the rafter length and shingle shape

The standard roof pitch is also often referred to as the minimum roof pitch . This is not entirely correct, because the term minimum roof pitch would mean that this roof pitch must never be undercut. However, a roof can be covered with a roof pitch that is less than the standard roof pitch. Since then the rainproofness cannot be guaranteed, additional measures are necessary, for example a waterproof sub-roof .