Roofs that Leaks after a Hurricane

Risks Associated With Leaks

Recent hurricanes have shown that even houses with extremely high structural integrity can still be catastrophically damaged by the wind driven rains of hurricanes. These rains travel almost perfectly horizontally. Wind driven water intrusion can cause catastrophic damage to the walls, ceilings, interiors, and possessions of homes that leads to major disruption of households. When wind speeds get above 60 mph, rain water is driven against the exterior of your house with great penetrating force. Whenever water builds up on the exterior wall surface it is practically driven into any cracks or openings because as it spreads across a wall it is being pushed into the wall. And when there is lower pressure on the inside of your house, the water penetrates in large quantities (quarts and gallons) through cracks, holes and gaps in the siding and around windows and doors. When this happens for hours at a time towels and buckets simply are not up to the task of water management. After hurricanes usually there is no electricity available to dry out homes using air conditioning or dehumidifiers so mold invades the house that can be as devastating as direct wind damage. As far back as Hurricane Hugo in 1989, researchers observed that a number of homes looked completely intact from the outside but a closer look revealed that the interior wall surfaces were literally melting away, ceilings were collapsing and wallboard was coming off the walls. This meant people lost many possessions and had to move out of their houses, find another place to live, settle with insurance adjusters, arrange repairs, and await repairs. This was not a pleasant experience.

In an ideal world, your house would keep water out even in the extreme circumstances of hurricanes. However, because houses cannot affordably be built to submarine standards they can’t keep all water out. But you don’t have to sit back and take what comes. If you minimize the quantity of water that enters through attic ventilation system components, you will improve the chances that your home can be dried out without having mold develop to dangerous levels. Most houses have several roof and attic ventilation related vulnerabilities that allow water to enter that can be easily fixed, some in just an hour or so.

Entry Points for Leaks:
The main sources of water intrusion into houses (aside from floods) arise from windows and doors, attic vents (including the ones on the roof, vents on gable end walls, and soffits (eave and gable end), wall penetrations for utilities, cracks in wall siding. Each needs to be evaluated for risk to your home. The section on Walls includes a discussion of leaks through windows, doors, wall penetrations, and cracks and methods for retrofitting to reduce this water intrusion. Loss of roof coverings, to the point that roof decking is exposed, is usually catastrophic if it extends very much over living areas. Methods for reducing water intrusion due to roof cover loss is discussed in the What to do if you re-roof and What you can do if you don’t re-roof sections. The following primarily deals with water intrusion through the attic ventilation system components and retrofits that can be made to reduce this water intrusion.

How Far Can Wind Drive Water?
It is important to appreciate what a hurricane can do to drive water into your house. Armed with that, you can get a good feel for what needs to be done to minimize the risk of water intrusion. First, all houses leak air around windows and doors, through vents, cracks, holes, gaps and in a variety of other places. When winds blow on a house and flow around it, they create positive pressures on the windward wall and windward soffit and negative pressures on most other surfaces including the side walls, downwind wall, soffits above those walls and the roof. Consequently, the pressures inside the house and inside the attic are usually slightly negative (that is lower than the outside pressure). This tends to draw (or suck or pull) water on the surface of the house into the walls and ultimately into the house. When wind driven rain hits the windward wall it collects on the surface and this difference between the positive pressure on the windward wall and the negative pressure inside the house or the attic, acts as a driving force that pushes and pulls water through any cracks, holes, gaps etc. If a window or door fails, the situation gets even worse since water that has gained momentum from the wind gets carried into the house.

The pressures created by a 100 mph wind will drive water about 3-1/2 inches up through any crack or opening anywhere on the roof, gable wall or through the soffit.

The pressures created by a 130 mph wind will drive water about 6 inches up through any crack or opening anywhere on the roof, gable wall or through the soffit.

The pressures created by a 150 mph wind will drive water about 8 inches up through any crack or opening anywhere on the roof, gable wall or through the soffit. +

More information to follow on this issue. Call Amherst Roofing today for more information at 239-594-5480 or visit us at: