Question 1

What is roof pitch and how is it expressed?

Accepted Answer

Roof pitch describes the angle of the roof surface relative to the horizontal. It is expressed in degrees, percent or as a ratio. 45 degrees equals 100% slope (ratio 1:1). In Germany, pitches between 20 and 45 degrees are common.

Question 2

How do you calculate rafter length?

Accepted Answer

Rafter length is calculated from half the building width (for gable roofs) and the pitch angle: rafter length = half width / cos(angle). With overhang: rafter length = (half width + overhang) / cos(angle). For a 10 m wide building at 35 degrees with 50 cm overhang: (5 + 0.5) / cos(35) = 6.71 m.

Question 3

What formula is used for roof area?

Accepted Answer

For a gable roof: roof area = 2 x rafter length x (building length + 2 x overhang). The rafter length includes the eave overhang. Roof area is always larger than floor area since the sloped surface is longer than the horizontal projection.

Question 4

Which snow load zone is my location in?

Accepted Answer

Germany is divided into 5 snow load zones (Zone 1 to 3). Northern German lowlands are typically in Zone 1, central mountain ranges in Zone 2, Alpine foothills in Zone 2a or 3. The exact assignment follows DIN EN 1991-1-3 Annex NA. Your local building authority can provide guidance.

Question 5

What minimum pitch do roof tiles need?

Accepted Answer

Clay and concrete roof tiles require a minimum pitch of 22 degrees. Slate needs 25 degrees, asphalt shingles 15 degrees, standing seam metal just 7 degrees and trapezoidal metal 5 degrees. EPDM membranes can be used from 2 degrees. Below the prescribed minimum, leaks may occur.

Question 6

What is the difference between a gable and hip roof?

Accepted Answer

In a gable roof, the roof surfaces end vertically at the gable sides, creating triangular gable walls. In a hip roof, the gable sides are also sloped (hipped), so no vertical gable walls exist. A hip roof therefore has more roof area but less wall area and is more wind-resistant.

Question 7

What purpose does a roof overhang serve?

Accepted Answer

Roof overhang protects the facade and base area from driving rain and direct sunlight. Typical overhangs are 30 to 80 cm. A larger overhang provides more protection but requires longer rafters. On the gable side, the overhang is called the rake.

Question 8

At what pitch is a roof considered flat?

Accepted Answer

A roof is considered flat at a pitch below 5 degrees (approx. 8.7%). Most flat roofs have a pitch of 2 to 3 degrees for drainage. Between 5 and 20 degrees, it is called a low-slope roof.

Question 9

How do I measure the pitch of an existing roof?

Accepted Answer

Easiest with a digital spirit level on a rafter or roof tile. Alternatively, measure the horizontal run and the rise in the attic and calculate the angle: arctan(rise / run). Smartphone apps with inclinometers also work.

Question 10

How much does a new roof covering cost per m2?

Accepted Answer

Costs vary greatly by material: concrete tiles 20-35 EUR/sqm, clay tiles 25-50 EUR/sqm, asphalt shingles 15-30 EUR/sqm, standing seam metal 50-90 EUR/sqm, slate 80-140 EUR/sqm. These prices include material and installation but not battens and underlay.

Guide: Roof Calculator

Calculate Roof Pitch: Rafter Length, Roof Area & Snow Load

Gable Roof Pitch: What Angle Is Ideal?

Snow Load Zones Germany: Map & Calculation

Lean-To Roof: Pitch, Area & Drainage

Roof Tiles or Metal? Costs & Minimum Pitch

Calculate Rafter Length: Formula with Overhang