Painting and damp in Coimbra: Mondego fog, the Alta hill and 45% of buildings needing repairs

At the IPMA station Coimbra / Bencanta (26.6 m above sea level, near the Mondego), the 1991-2020 normal gives 866.0 mm of rain a year, peaking in November (121.5 mm), October (114.5 mm) and January (113.5 mm), with only 8.9 mm in July. There are 94.0 days a year with 1 mm or more and 29.6 with 10 mm or more. The mean temperature is 16.2 °C and there are 6.0 frost days a year (minimum below 0 °C).

That 1991-2020 file has no humidity or fog table. The only figures we found are from the earlier 1971-2000 normal for the same station: mean relative humidity of 81% at 9 a.m. UTC (86% in January, 85% in November and December, 76% in May and June) and 31.6 days of fog a year, most in September (5.0 days) and October (3.4). That period also had 18.7 frost days, three times today’s figure. The data is 30 years older: treat it as an order of magnitude.

What this means for walls: from October to January it rains a lot and the morning air sits near 85% humidity, which slows the drying of stone walls and favours mould on cold bedroom walls with little ventilation. Interior paint dries badly in those months; leave the work for spring or summer, when rain drops below 30 mm a month in June, July and August.

Exempt works. Painting a facade without changing anything else is, as a rule, conservation work exempt from a licence and prior notice under the RJUE (Decree-Law 555/99, article 6(1)(a)). Decree-Law 108/2026 amended the RJUE on 1 October 2026 and we could not reopen the consolidated text for this page: confirm the article with the council. Coimbra’s building and fees regulation (RMUE, Regulamento 381/2017) defines “facade structure” in article 4 as the sizing, composition and materials of the facade planes, openings, eaves and parapets: changing those is no longer just painting.

Scaffolding. The RMUE says, in article 66, that occupying public space for works exempt from prior control needs an administrative licence, requested up to 15 days before the start (para. 1). Starting depends on paying the fee and holding accident and civil liability insurance (para. 5), and the period cannot exceed the works (para. 6). Article 75 prefers aerial scaffolding, covered vertically with fine mesh or sheeting, and article 76 provides for pedestrian corridors. Loading and unloading of up to 24 hours pays no fee (article 73). This is the 2017 text: we did not confirm whether it has been amended since.

Alta and Sofia. The municipality approved a building and rehabilitation regulation for the area of the University’s World Heritage bid and its protection zone. The only text we read is the draft published on 4 November 2011: it asks for traditional colours backed by a technical-historical study (article 6(4)©), bans textured, sanded, sponged or glossy paints on renders (d)) and favours lime-based renders (i)). We did not read the final version (Aviso 2129/2012) or later amendments: before painting in the Alta, Rua da Sofia or the historic centre, ask the council.