Have you ever considered opening your windows during a hurricane? It sounds crazy right!?! Well obviously not too crazy because this was the exact question that was put to test on The Discovery Channel’s “Mythbusters” with the help of m2e employee Cory Salzano. Follow me, I will explain.
According to the myth, a house would incur less damage during a hurricane if all of its windows were left open. The theory behind the myth is based on wind pressure. The intense winds of a hurricane create a very distinct (and complicated) flow field around a house. The basics….the upwind face of the house experiences a positive pressure load (i.e. acting to push the wall in), the downwind face experiences a negative pressure load (i.e. acting to pull the wall off), and the roof experiences a negative pressure (i.e. acting to pull the roof off). It is these loads that must be resisted by the structural framing of the house. The thought behind the myth is that if all of the windows are open, the surface area of the wall is reduced and thus the pressure forces on these walls will be reduced. In simple terms, the wind will just blow right through. You get it? Good. Let’s debunk with some engineering know how.
While creating open space in the wall will change the pressures on a house, the amount of open space that would be required to reduce the pressure acting on the house could not be reasonably achieved by merely opening the windows. Engineers design houses for wind based on the loads required by ASCE 7-05, Minimum Design Loads for Building and Other Structures. From a design standpoint, in order to significantly reduce the pressures on a house, the open space created by the windows would have to be significant enough to classify the house as an “Open Building” in the design. Based on the provisions of ASCE 7-05, an “Open Building” is a building having each wall at least 80 percent open. Therefore, assuming that you could consider a window as an opening in the design, windows would have to consist of 80 percent of the walls area. Still think it might be a good idea to keep your windows open? Wait, it gets worse.
By opening the windows of your house, you may actually make a bad situation worse (depending on the situation). Remember that flow field we talked about, well with an insufficient amount of windows open the wind will actually begin to create an elevated positive pressure inside the house. This may be thought of as blowing up a balloon. What happens when the pressure inside a balloon gets to high? POP! The elevated pressure inside the house combined with the negative pressure experienced by the roof will have a similar effect. The roof will pop of the house (granted it won’t be as dramatic). But wait, there’s more.
It rains during a hurricane. It rains a lot during a hurricane. Call your home owners insurance company and ask them if they think it would be a good idea to keep your windows open during a hurricane. They just may hang up on you. By opening your windows during a hurricane you are introducing yourself to a whole new world of problems that we engineers like to call water intrusion. Although, technically I guess it is not water intrusion IF YOU INVITE IT IN!! This water intrusion can lead to deteriorated finishes within the home, rotting wood and potential mold contamination.
So, in conclusion, if you didn’t catch the last episode of “Mythbusters” filmed at the University of Florida Hurricane Research Center, let me spoil the ending…please keep your windows closed.
Cory T. Salzano, E.I.