Condensation and mould on windows in Malta

Malta's winter is humid, not cold

The damp patch on your window in January is not a Maltese quirk. It is what happens when humid indoor air meets a cold surface.

Work by C. Galdies at the University of Malta, using Malta Airport MetOffice station data (WMO 16597, Luqa) on a 1961–1990 baseline, puts mean relative humidity at 61% in July rising to 87% in January. Extreme monthly means in that record were 89% in December 1993 and 54% in June 2006, and January is one of the two months with the highest variability. The same work makes the point that humidity drives winter discomfort, while summer heat stress tracks temperature instead.

Temperatures do the rest. Modelled 1991–2020 figures for Luqa give mean lows of 9–11°C from December to March with highs of 16–17°C. Those are NASA POWER estimates rather than station readings, so treat them as context rather than measurement, but the shape is familiar to anyone who has spent a January in an unheated Maltese flat: not freezing, never warm, and the glass and frames sit near outdoor temperature all night.

That is the whole mechanism. Air holds a certain amount of water vapour; cool it enough and the vapour condenses out. The surface in your home most likely to be cold enough is a window.

Where the cold actually is

Two parts of a window run coldest: the frame and the edge of the glass.

Frames. Australian default window data gives single-glazed plain aluminium a U-value of 6.7 W/m²K, thermally broken double glazing 3.6, and timber or uPVC double glazing 3.0 W/m²K. These are foreign default figures, not Maltese ones, and not any kind of legal requirement here. What they illustrate is the direction of travel: a lower U-value means a warmer inner surface, and a warmer inner surface is less likely to drop below the dew point. A plain aluminium frame with no thermal break is the coldest thing in the room on a January night, and it is usually where the water appears first.

The glass edge. Inside a double-glazed unit, a spacer bar holds the two panes apart around the perimeter. Technoform, a manufacturer in this field, explains that aluminium spacers let heat escape at the edge, so the room-side glass edge ends up colder than the room; below the dew point, condensation forms in that band around the edge of the pane. Warm-edge spacers — non-metal or hybrid — keep the edge warmer. Technoform puts the effect on the whole-assembly U-factor at roughly 0.02–0.03 BTU/°F·hr·ft², with stainless steel box spacers at about 0.01. It is an industry source and the units are American, but the mechanism is the point: if you are specifying a double-glazed unit, the spacer is a real variable, not a detail.

The health side — and who actually says so

We found no Maltese official guidance on damp and mould in homes. What follows is foreign, and we flag it as such.

The World Health Organization's 2009 indoor air quality guidelines on dampness and mould identify the most important effects as increased respiratory symptoms, allergies and asthma, and disruption of the immune system. Their central recommendation is simple: prevent or minimise persistent dampness and microbial growth on interior surfaces and in the building structure.

UK government guidance (DHSC, UKHSA and DLUHC, updated 1 April 2026) goes further on the detail. It describes moisture from showers, cooking and indoor laundry condensing on cold surfaces such as window frames and room corners, and it is explicit that the root causes are building faults, ventilation, heating and insulation — not ordinary daily life. The health effects it lists include cough, wheeze and breathlessness, aspergillosis, worsened asthma, rhinitis and COPD, along with eczema and mental-health impacts. A 2019 England estimate attributed around 5,000 asthma cases and 8,500 lower respiratory infections to damp and mould. Groups it identifies as most at risk: children, older people, people who are pregnant, the immunocompromised, and anyone with a lung or heart condition.

Those figures are English. No equivalent Maltese estimate exists in anything we hold.

What the guidance says to do

The UK guidance's practical list is short and translates straight to a Maltese flat:

• Use extractor fans — humidistat-controlled or with an over-run timer — in the bathroom and kitchen.
• Keep trickle vents open where the windows have them.
• Ventilate while cooking and bathing, not an hour later.
• Improve glazing and insulation so the cold surfaces are less cold.
• Remove mould with a product made for mould, not bleach, and re-check the same spot at about six weeks.

Drying washing indoors with the windows shut is the commonest way to push a room over the edge in January. So is heating one room and leaving the rest at 11°C: the moisture migrates to the cold rooms and settles there.

Malta-specific complications

Shell form. Most Maltese property is sold as a shell and finished by the buyer, so the apertures, their frames and the reveals around them were specified by whoever finished the place — not by a single building standard applied throughout. If the previous owner fitted non-thermally-broken aluminium to save money, that choice is now your condensation pattern.

Apartments. Changing apartment apertures is bound by the condominium's rules as well as by planning. Under Legal Notice 552.08, Schedule I, Class 1(ii), replacing apertures is permitted development unless it materially alters the character of the building; in scheduled buildings or those of conservation value, restorable original timber apertures must be retained and restored rather than replaced. A ventilation problem does not override that.

Gozo. Every delivery to Gozo crosses on the ferry, which affects scheduling rather than specification.

If you are thinking about replacement

There is a live grant. The REWS 2023 RIDG retrofitting scheme pays 50% of eligible cost including VAT, capped at €1,000 for double glazing, extended to 31 December 2026 by GN 2031/2025. It is first come, first served. Part A must be submitted before you purchase. The product and the retailer must be REWS-registered, the final U-value must be 3.7 W/m²K or better, the property must be your own primary residence (owner, or lessee of more than five years), the work must be fitted within six months, and a five-year warranty applies. Whether funds remain in the scheme is not something we can verify, and Budget 2027 on 26 October 2026 may change the picture. Nobody should assume they qualify — read the scheme conditions.

The Birżebbuġa 2024 scheme, BCA Irrinova Darek 2026 and PA Irrestawra Darek 2026 are all closed.

On cost: published Maltese figures exist for ready-made standard PVC windows at €169–319 supply only and PVC doors at €509–579 supply only, and for aluminium at €200–450/m² non-thermal and €350–700/m² thermal break. There is no published fitted PVC price and no published price for a double-glazed unit in Malta — those are quoted after the measure-up, which is when the actual reveal, the actual frame depth and the actual access get measured.

Replacing windows will not, by itself, remove water from the air. It makes the surfaces warmer so the water has fewer places to land. Ventilation and heating still have to do their part.