Roofing in Malta

Malta's traditional roof is flat. For centuries Maltese builders spanned rooms with slabs of the islands' soft limestone and sealed them with layers of lime-based mortar, finished with deffun, a waterproof mix of lime and crushed pottery. The roof also served as a rain catchment for the cistern beneath every house. Research at the University of Malta has recently re-examined these roofs as naturally "cool" roofs.

Climate and hazards

Malta has a hot, dry Mediterranean climate. In 2021 the highest temperature recorded was 41.5 °C (106.7 °F) in June, and national electricity demand peaked in August. Rain falls mostly in the cooler months, so roofs had to collect it efficiently. Traditional deffun roofs need yearly maintenance after the hot summer, before the first September rains.

Roofing history

Corbelled stone huts called giren (singular girna) have been compared with the island's prehistoric megalithic temples, Sardinian nuraghi and the trulli of Puglia, but the resemblance may be superficial and most existing giren are thought to be relatively recent. A 1536 account by Jean Quintin may refer to them as "African huts".

The documented flat-roof tradition is strongly associated with the period of the Knights of St John (1530-1798), and University of Malta researchers describe traditional roofs as having been the norm for hundreds of years. Limestone slabs were first carried on stone arches and later on timber or iron beams. In more recent interventions, concrete slabs, screeds and bituminous membranes have replaced or covered the deffun on some old buildings, producing "hybrid" roofs, while new buildings use modern concrete roofs.

Traditional and vernacular roofs

The deffun roof is built up, from the bottom, of:

1. limestone slabs resting on stone arches, or later on timber or iron beams;
2. a fill of limestone chippings mixed with stone dust and lime;
3. a surface of deffun, hydrated lime mixed with crushed pottery, sprinkled with water, beaten and compacted (by hand in the past), then covered with straw to slow drying and help it cure.

The roof has a slight fall so that water drains quickly to the cistern. Because the mortar is porous, it absorbs moisture, including heavy summer dew, and evaporation from the surface cools it during the day.

The girna is a round, or sometimes square or oval, hut of undressed dry stone, usually coralline limestone, with walls about 90 cm (3 ft) thick formed of two faces with a rubble core (mazkan). Its roof is corbelled: each course projects slightly inward until flat slabs can close the top, giving a dome-shaped ceiling. The roof was usually covered with gravel and torba, or sometimes a pebbly material called ċagħqija. Giren are most common in northern Malta, around Mellieħa, Manikata and Selmun, with over 30 in Majjistral Park; on Gozo they cluster in Upper Coralline Limestone areas such as Xagħra, Nadur and Qala.

Roofing today

Modern Maltese roofs are typically flat concrete construction, such as concrete planks finished with a waterproofing membrane. The University of Malta's EO4HBCS project (2020-2022), funded by the Malta Council for Science and Technology, compared traditional, hybrid and modern roofs using satellite imagery, drones and sensors, and found that the traditional roof gave the best balance between dispersing heat and insulating. The team is exploring guidelines to protect traditional roofs and a modern version for new buildings.

Codes, standards and regulation

As an EU member, Malta applies the Eurocodes for structural design.

Notable roofs

• Traditional and hybrid roofs of Fort St Angelo, Birgu
• Giren of Majjistral Park

Local roofing terms

• deffun - lime and crushed-pottery waterproof surface
• torba - covering layer used on girna roofs
• ċagħqija - pebble-like roofing material
• girna / giren - corbelled stone hut(s)
• mazkan - rubble core of a double-faced wall

Sources and gaps

Specific Maltese roofing regulations and information on Maltese roofing manufacturers: published information is limited.