Old Gilan houses had roofs either of “gali” thatch or of marsh plants such as reed and rice straw. Wikipedia says these pitched plant roofs were that rainy climate’s answer. Later came clay tile, then metal sheet, and now “ardoise”. When we design a pitched-roof villa in the north today, the question is: which covering?
The short answer isn’t “this one beats them all”. Each covering has a lifespan, a weight and a weak point, and the north is harder on some of them.
Source: Rural architecture of Gilan — Persian Wikipedia
First: what exactly is “ardoise”?
The name comes from the French word ardoise, meaning slate; a stone that splits into sheets and which, according to French Wikipedia, is mostly used as roofing.
But in the Iranian market the name is used for other things too. Just search “ardoise” in Persian and you’ll also see “metal ardoise”, “plastic ardoise” and “cement ardoise”. So when someone says “let’s use ardoise”, first ask what it’s made of: real slate, asphalt shingle, or patterned metal sheet. Their lifespans and weights differ a lot.
Source: Ardoise — French Wikipedia
Three main families
Tile. Wikipedia says high-quality clay and slate tiles have a proven lifespan of over 100 years, while concrete and synthetic tiles usually last 30 to 50 years. Because cement is porous, cement tiles are made thick and heavy and, according to the same source, are among the heaviest roofing materials on the market. So “tile” isn’t one thing either; ask whether it’s clay or concrete.
Asphalt shingle. What many people call ardoise. It’s light and simple to lay. But according to Wikipedia a typical shingle roof lasts about 25 years; basic three-tab shingles are usually replaced after 15 to 18 years and dimensional ones after about 24 to 30. Their edges carry a self-sealing strip that bonds to the row below in the sun so wind can’t lift them.
Metal sheet. From corrugated galvanised sheet to standing seam. Wikipedia says standing seam lasts at least 50 years and needs less maintenance than corrugated sheet, because its fasteners aren’t exposed. Every exposed screw is a potential hole; we covered that in roof leaks.
Sources: Roof tiles — Wikipedia; Asphalt shingle — Wikipedia; Metal roof — Wikipedia
What the north adds to the sums
Pitch. Every covering has its own minimum pitch; shingle and tile need more than standing-seam metal. We gave the table in pitched or flat roof. If the design has a low pitch, that alone narrows your choice of covering.
Moss and algae. In always-humid air, roofs turn green. Wikipedia says of asphalt shingles that algae doesn’t damage them but spoils their look, and that moss feeds on that algae and debris on the roof. Zinc or copper strips along the ridge prevent growth, and some manufacturers sell algae-resistant shingles.
Weight. A heavy covering means a heavier structure. Concrete tile and slate should be in the structural calculation from the start, not placed later on a light structure. In an earthquake-prone region this matters more; we explained why in the earthquake-resistant villa.
Salt. Near the sea, any metal is at greater risk of corrosion. If you choose metal sheet, ask the supplier what coating it has for a coastal environment and what the warranty covers.
Source: Asphalt shingle — Wikipedia
Side by side
| Covering | Lifespan per sources | Northern note |
|---|---|---|
| High-quality clay tile | Over 100 years | Heavier; the structure must allow for it |
| Concrete or synthetic tile | 30 to 50 years | Concrete tile is among the heaviest coverings |
| Slate (real ardoise) | About 60 to 125 years, if properly fixed | Costly and specialist; proper fixing is essential |
| Asphalt shingle | About 25 years | Light; plan for algae and moss |
| Standing-seam metal | At least 50 years | Light; anti-corrosion coating matters near the sea |
Sources: Roof tiles; Slate; Asphalt shingle; Metal roof — Wikipedia
A few questions before you order
- What exactly is it made of? Especially if it’s called “ardoise”.
- Does our roof pitch meet this covering’s minimum pitch?
- Has the structure been designed for its weight?
- Who will do the details around the chimney, vents and gutters? A good covering with a poor joint still leaks.
- What exactly does the warranty cover, and for how many years?
The cheapest covering over thirty years isn’t always the cheapest over ten. If you’re designing a villa in Babol, Babolsar, Sarkhorud, Amol or Sari, let’s look at the roof’s pitch, covering and structure together.
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