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Gallery 3

Raise the Roof

A model house with a flip lid roof demonstrating how wind flows around a house.
A model house with a flip lid roof demonstrating how wind flows around a house.

Strong winds create differences in air pressure, causing house roofs and walls to fly off.

How it works

Press the 'wind' button to blow air onto the model house and rotate the house to see what happens when the wind comes from a different direction.

Things to try or ask around the exhibit

  • Check the tiny styrofoam balls in the Venturi meters. These represent differences in air pressure. When the ball is high in the tube, it indicates low air pressure around the tube.
  • What pressure conditions cause the roof to lift?

Background

During cyclones, severe thunderstorms or tornadoes, house roofs can be damaged or blown off completely if they are not built to withstand strong, forceful winds.

As wind hits a building, the flow of air is changed. Wind that blows over the top of the roof causes the air to swirl and form vortices. These produce a suction pressure above the roof, so the roof tends to be lifted upwards. If the wind blows in the door of a building, or if flying debris smashes a window, wind rushes into the house and produces a high pressure which pushes on the inside of the house. The push from inside the house and the suction from above will lift the roof (or parts of it such as tiles) and may blow it away if it is not held down well. The effects of wind uplift on a roof depend on roof height, slope, style and house location.

Finding the science in your world

During a cyclone, the walls of a building also tend to be sucked outwards. In tall buildings this suction can be enough to rip cladding from the building, and windows from their frames. After Cyclone Tracy devastated Darwin on Christmas Day in 1974, building codes were revised for cyclone-prone areas, including well attached cladding on buildings and having roofs tied to the foundations.