Roofs in Bragança: frost, regional tile and the historic zone

The IPMA station in Bragança (1991-2020 normals; altitude 690.7 m; latitude 41.80 N, longitude 6.74 W) is in the municipality. Rainfall is 783.9 mm a year, mostly in December (112.3 mm), October (106.9 mm) and January (100.6 mm); July has only 15.1 mm. There are 86.3 days with 1 mm or more, 26.4 with 10 mm or more and 3.6 with 30 mm or more. The heaviest daily fall was 77.9 mm, on 7 December 2000. The mean annual temperature is 12.9 °C. IPMA classes the series as hybrid.

Cold matters more than rain: 53.4 days a year with a minimum below 0 °C, 51.6 of them between November and March (13.1 in December, 15.5 in January, 12.0 in February). The lowest minimum was -10.2 °C on 2 March 2005, and there were days when even the maximum did not pass -1.5 °C (19 January 1992 and 18 February 2003). Summer is tough too: 45.5 days with a maximum of 30 °C or more, 7.3 with 35 °C or more, and 39.7 °C on 3 August 2018. The sheet does not count snow days, and we did not confirm the snow load the standard asks for in Bragança.

SCE climate zone. For the Alto Trás-os-Montes region, the SCE Manual starts from a reference altitude of 680 m, with 2,015 heating degree-days and a June-September mean of 21.5 °C. Result: winter zone I3 and summer zone V2. In winter the zone follows the building’s altitude: I1 up to 169 m, I2 from 170 to 526 m and I3 above 526 m, and the IPMA station, at 690.7 m, is above that limit. Under Portaria 138-I/2021, horizontal exterior elements of the opaque envelope, in new works or a renovated element, must have a thermal transmittance of at most 0.30 W/(m²·°C) in zone I3 (0.35 in I2); conservation works are excluded. The Portaria does not make clear whether a pitched roof counts as a horizontal element: ask the SCE assessor. See the roof insulation aid guide.

In the area of the Detail Plan for the Historic Zone of Bragança I (Council of Ministers Resolution 99/2007), article 26 says the tile is regional, in clay of natural colour (no. 6), that fibre-cement, corrugated sheet and tile of an unusual colour or glazed are not to be used (no. 7), that the slope may not exceed 36° (no. 3), that replacing the roof keeps the form, pitch, volume and look of the original (no. 4) and that the timber of a traditional structure is repaired or replaced by one of identical form and material (no. 5). Article 29, no. 3, does not admit solar panels on roofs, except in new buildings or remodelling that integrate them perfectly. The council’s page shows the plan as in force; we did not look for later amendments.

The Municipal Urbanisation and Building Regulation (Regulamento 2/2016, of 4 January 2016) exempts conservation works from prior control (article 7) and also swapping the timber of a pitched roof for prefabricated joists, if it does not change the roof’s form, the structure or the building height (article 8, no. 1, letter g). The exemption does not apply to listed buildings or buildings being listed, nor to those in their protection zone or in a listed group (article 8, no. 4). Article 23 bans letting water fall from eaves straight onto the public road and requires connection to the public rainwater network where one exists.

We did not read Bragança’s PDM. Before ordering the roof, ask the council’s planning office whether the building is inside the detail-plan area or a protection zone.