In fact, as anyone involved in the construction industry can testify, Bermuda's hallmark peaked roofs of limestone slate are very heavy. Few things appear less capable of flight.

During hurricanes, however, strange things can happen to roofs. They can lift up and shatter on impact, or detach completely from the house, rise serenely into the air and crash to earth -- or water -- some distance from the building.

Roofs are designed to keep out unwanted air and water, which makes them particularly useful accessories during hurricanes. Bermudians are well aware of this.

The old maxim goes something like this: to prevent your roof from being blown off during a storm, it's a good idea to leave a window open on the lee side of the house.

The lee is the sheltered side of a building.

During high winds the flow of air around a building creates a pocket of negative pressure in the lee side -- a partial vacuum.

Conversely, air pushed against your house by hurricane winds tends to pile up inside -- positive pressure. Opening the window on the lee side allows this pent-up air to escape from your house.

Without this, the positive pressure can flip off the roof: the difference between the inside and the outside of a building can get as high as 400 kg per square metre.

Peaked roofs, during high winds, become a crude aerofoil: the movement of air leaves negative pressure on the lee side. A 747, at first glance, doesn't look that capable of flight either, but relies on some of the same principles to get off the ground.

When windows on the windward side shatter, the surge in air pressure inside the house can blow the roof off.

"Bermudian roofs have some very clever designs,'' structural engineer Neil Allan of the Department of Works & Engineering noted. "Their angle of 30 degrees is close to optimum for withstanding winds.'' Surprisingly, he added, the head of Hurricane Watch in Miami recently renounced the time-honoured tradition of opening the lee window in favour of closing the house up.

"A lot of locals, including myself, would consider that nonsense,'' Mr. Allan said. "I think it's a matter of design differences.

"In American houses, perhaps because of wood as a building material, the Stone walls give great protection are apparantly more vulnerable than the roof during hurricanes. By this logic, you wouldn't want to open the lee window. You'd want to keep that extra pressure inside the house, because it would help strengthen the walls.'' Bermudian houses have stone walls capable of withstanding high winds, he said.

"Our roofs, rather than walls, are our houses' weak spots. By opening the lee window, we allow air to escape from the house, and that helps hold the roof on.

"Conversely, whenever there's a breach in the windward side, the positive pressure inside rises very quickly. In many cases, the roof has popped off almost immediately after this happens.'' Anything puncturing the "skin'' of the house, such as a shattered window, a breached wall or a door staved in by flying debris, can cause a surge in the house's inside pressure if it takes place on the windward side.

Even for a house of stone, the pressure of more than 400 kg per square metre and the resonance vibrations (shaking) can be sufficient to break this "skin'' -- and a 70 knot wind can smash large windows, and topple shallow-rooted trees such as that notorious hurricane casualty, the casaurina.

"I think the old Bermudian practice of keeping that lee window open is a sound one,'' Mr. Allan said. "Both strategies are probably right. It's just a matter of different constructions.'' One very, very important consideration: "You've got to remember that hurricanes are revolving beasts,'' Mr. Allan said. "If a hurricane passes over the island, the winds will return from the opposite direction after the eye passes over.

"If you've left a lee window open, remember to switch them around.'' Positions are reversed: close the lee windows and open the windows at the other side of the building. When the winds return) the eye takes from a few minutes to an hour to pass overhead), they are at their strongest: gusts can easily exceed 100 knots.

Winds from a severe hurricane are strong enough to pull the roof off a building HURRICANES SUPPLEMENT HUR