Roof pitch: definitions and formulas

The roof pitch calculator estimates building roof inclination in 3 units:

• Percentage (%) = (rise / run) × 100
• Degrees (°) trigonometric angle = arctan(rise/run)
• Rise:run ratio American style (e.g., 6:12 = 6 cm rise per 12 cm horizontal). Conversion formula: degrees = arctan(percentage / 100) and vice versa percentage = tan(degrees) × 100. Italian typical examples: 30% pitch = 16.7° = 3:10 ratio (standard residential roof); 40% = 21.8° = 4:10 (traditional double-pitched roof); 50% = 26.6° = 5:10 (sport pitched marked); 60% = 31° = 6:10 (Alpine snow shedding); 100% = 45° (square-pitch like many Trentino-Alto Adige Alpine roofs); 200% = 63.4° (steep mansards French Mansart 1650 style)

Italian recommended roof pitches by climate zone (D.P.R. 412/1993 zones A-F + UNI EN ISO 13788:2013 + NTC 2018 D.M. 17/01/2018 ch. 6 snow loads): Zone A-B Southern Italy (Sicily, Calabria, Apulia, Lampedusa <600 DD): minimum pitch 15-25% sufficient, low snow load (50-100 kg/m²); Zone C Center-South (Roma, Naples, Bari): 25-35%; Zone D Center (Tuscany, Umbria, Marche): 30-40% traditional double-pitched roof with Tuscan terracotta coppi; Zone E North plain (Milan, Turin, Venice): 30-45%; Zone F Alps (Trento, Cuneo, Belluno, Aosta >3,000 DD): 50-100% steep roof for rapid snow shedding (snow load up to 250-400 kg/m² Alpine zone, NTC 2018 snow loads calculated Eurocode 1 EN 1991-1-3). Minimum pitches by covering type: terracotta tile 25-30% min; Sicilian coppi 30-40% min; corrugated metal sheet 5-15% min (industrial warehouse); bituminous membrane 1-3% min (industrial flat roof); extensive green roof 1-15% (green garden); slate 35-50% min (no Alpine zones ice fragility).

Italian pitches and roof materials

(Source: Italian NTC 2018 ch. 3.4 snow loads + UNI 8089:2010 roofing design + Eurocode 1 EN 1991-1-3:2019).

Italian pitch calculation examples

• Tuscan 2-pitch Chianti coppi roof house 12 m × 8 m: traditional 35% pitch = 19.3° = 3.5:10. Center rise = (8/2) × 0.35 = 1.4 m at ridge (vs gutter 0). Material: traditional terracotta coppi Imprunetana or Marsigliese (Industrie Cotto Imprunetana 1968 Florence, Italy 30% market leader). Cost 30-50 €/m² coppi + installation
• Trento Alpine villa 80% steep: 8:10 ratio = 38.7° angle. 10 m × 6 m roof: center rise = (6/2) × 0.80 = 2.4 m ridge. Snow load NTC 2018: 250 kg/m² × 60 m² = 15 tons max snow load (zone F 1,000 m altitude). Material: slate + larch wood "cosul" Val di Fassa Trentino-Alto Adige tradition
• Padova industrial warehouse corrugated metal 10% pitch: 50 m × 30 m = 1,500 m². Center rise = (30/2) × 0.10 = 1.5 m. Trapezoidal galvanized/pre-painted sheet 40 mm high greca; snow load NTC 2018 zone E 130 kg/m² × 1,500 = 195 tons (Eurocode 1 structural calculations HEA-IPE steel frames Bolzano-Trento Tegolcanadese pre-insulated "Coibentate Sandwich")
• Roma Lazio green belt 30% pitch house: 12 m × 9 m hip roof 4 sides terracotta Portuguese red tile. 30% pitch = 16.7° = 3:10. Roman Portuguese tile cost 25-40 €/m² (Industrie Cotto Imprunetana, Tondach Austria, Wienerberger Tegole)
• Bormio Lombardia Alpine mansard 100% steep: 6 m × 8 m square 45° steep. Center rise = 3 m (equal to run). Mansard living space H 2.4 m at ridge, Velux GGL CK04 skylights (Velux Hørsholm Denmark + Italy distribution)
• San Donato Milanese Eni warehouse extensive green roof: 5% pitch = 1:20 ratio, 5° angle. ZinCo stratigraphy: 10 cm Sedum vegetation + Floradrain FD 25 drainage + root barrier + waterproofing protection (D.M. 28/4/2017 + 36% green bonus L. 205/2017)

Italian NTC 2018 snow loads zones

Italian NTC 2018 snow loads (D.M. 17/01/2018 + Circular 21/1/2019 n. 7 ch. 3.4 + Eurocode 1 EN 1991-1-3:2019): Zone I Mediterranean (Sicily, Sardinia, Calabria coast, Lampedusa): qsk = 0.60 kPa (60 kg/m² ground); Zone II Center-South (Lazio, Campania, Apulia, Abruzzo coast): qsk = 1.00 kPa (100 kg/m²); Zone III Center-North (Tuscany, Marche, Umbria, Emilia, Lombardia plain): qsk = 1.50 kPa (150 kg/m²); Zone IV North (Veneto, Friuli, Piemonte plain): qsk = 2.50 kPa (250 kg/m²); Zone V Alpine (Trento, Aosta, Sondrio, Cuneo Alps >1,000 m): qsk = 4.00 kPa (400 kg/m²); up to 10 kPa (1,000 kg/m²) Cervinia 2,000 m + Sestriere. Effective roof load qs = μi × Ce × Ct × qsk where μi shape coefficient (0.8 double-pitch 30°, 0.4 flat roof), Ce exposure coefficient (0.8-1.2 for wind exposure), Ct thermal coefficient (0.9-1 for thermal dispersion snow melting). Example Cuneo villa (zone V 1,500 m altitude) 30° roof: qs = 0.8 × 1.0 × 1.0 × 4.5 = 3.6 kPa = 360 kg/m². 80 m² roof → 28.8 t maximum snow load. Load-bearing structures: glued GL24 laminated wood beams + IPE S275 steel + Bortolotti 24 cm hollow brick panels + 14 cm rock wool insulation.

Italian roof safety standards

Italian roof safety standards:

• D.Lgs. 81/2008 "Workplace Safety Code" (TUSL): art. 115 mandatory fall protection devices >2 m height; art. 122 mandatory scaffolds/parapets for roofing work. Italian lifeline mandatory every 30-40 m² roof for new buildings (Italian Lombardia Region DGR IX/4007 2007 pioneer, Veneto DGR 2774/2009, Piemonte DGR 39-1814/2010). 1,500-3,000 € installation cost + 200 €/year annual inspection
• Italian UNI 11578:2015 "Roof anchoring systems" + UNI EN 795 fall arrest devices classes A-E
• D.M. 26/06/2015 "Minimum requirements" + APE Italian Energy Performance Certificate mandatory: insulated roof U_max 0.24 W/m²K zone F (Alps) → 0.38 zone A (South); typical thickness 14-18 cm rock wool/EPS/polyurethane
• Italian NTC 2018 D.M. 17/01/2018 ch. 6 seismic: seismic zones 1-4 + PGA Peak Ground Acceleration; Italian traditional wood + brick roof 200-300 kg/m² weight (vs 100-150 kg/m² lightweight metals)
• Traditional PDO-PGI Italian roofs: Imprunetana Tuscan coppi (Cotto Imprunetina 1968), Sicilian coppi traditional Caltagirone, Larch roofs Val di Fassa Trentino UNESCO heritage
• Italian roof tax bonuses: 50% Bonus Casa renovation (L. 197/2022 art. 1 c. 65); Sismabonus 65-85% seismic zones; 36% Green Bonus green roof garden (L. 205/2017); Superbonus 65% 2025 reduced cladding + insulated roof (DL 34/2020 + L. 67/2024). ENEA online documentation within 90 days project completion

How the calculator applies the NTC 2018

The tool converts the pitch between degrees, percentage and rise:run ratio, then computes the real slope area by multiplying the footprint by the factor 1/cos(angle) and adapting it to the roof type — gable, hip, shed, gambrel or flat. It checks the compatibility between pitch and material, flagging when the inclination is too low to ensure water runoff. The snow load follows the Italian Technical Construction Standards 2018 and Eurocode EN 1991-1-3: the climate zone's ground value is multiplied by the shape coefficient μ, which decreases on steep roofs where snow slides off. The common and hip rafter lengths complete the sizing. The values are preliminary estimates: the structural design of the roof is the task of a qualified professional.

Updated July 2026