With the height of hurricane season fast approaching, now’s a perfect time to learn more about key terms and potential hazards of the season! While everyone knows that wind is a hazard during hurricanes, many are less familiar with nuances like windward vs leeward wind pressures and how they each impact the home differently.
What is windward and leeward in the context of a home exposed to hurricane conditions? What effects do these pressures have on homes? How thoroughly does a home need to be prepared for both?
Let’s go over these hurricane basics:
Windward vs Leeward: What Does Windward Mean?
During a hurricane, the windward side of a home is the side that is directly taking the oncoming wind. The winds push into the windward side of the home, exerting positive pressure (also referred to as inward-acting pressure).
Windward vs Leeward: What Does Leeward Mean?
The ‘leeward’ side of the home is the side of the home that is opposite the direction that wind is coming from during a hurricane. Many people tend to assume that this means the leeward side of the home is safe from wind damage, but that isn’t the case.
A building’s leeward side is exposed to suction force (a.k.a.: outward-acting pressure) as the air pushed by the hurricane moves around the home, creating a negative pressure pocket that pulls on the side of the home opposite the incoming wind.
How Windward and Leeward Changes Throughout a Storm
Aside from the effects of negative pressure, there’s another reason why homeowners can’t simply assume that the ‘leeward’ side of their home is safe from wind pressure is and flying storm debris is that, as the hurricane moves through the area, the sides of the home that are directly facing the incoming wind and the suction pressure will change.
For example, say that your home is in Dunedin, in or near the Golden Acres area. If a hurricane rolls in from the Gulf, it will be coming from the west. Due to the Coriolis Effect, a counterclockwise spin is applied to hurricanes in the northern hemisphere.
So, a hurricane coming from the west will have winds moving to the north along its eastern edge, meaning that the southern side of your home would be the ‘windward’ side in this situation.
However, as the storm continues to roll eastward, the direction of the wind in relation to your home would change. If the eye of the storm is more to the south than your home, as the outside edge of the storm moves to the east, the eastern side of your home would then become the windward side from the north edge of the storm. If the storm was more northerly, then the west side of your home would be the next side to face the wind directly.
If the storm moves completely past your home before dissipating, the northern side of your house may become the windward side.
In other words, it’s entirely possible for every side of your house to be the windward or leeward side throughout a storm. And, the closer your home is to the coastline, the more likely it is that you’ll face stronger winds throughout the life of the hurricane.
This is why it’s important to ensure that every window and door opening in your home has adequate protection from high wind pressure and flying storm debris.
How Can You Tell if a Window Is Designed to Withstand Windward and Leeward Conditions in Your Area?
As noted earlier, the windward side of the home is subjected to positive, inward-acting pressure while the leeward side will experience negative pressure comparable to the positive pressure acting on the other side.
Inward pressure (and accompanying debris impacts) push the window into the home and may crack the glass if the force exceeds the window’s design pressure (DP) tolerances. Meanwhile, outward-acting pressure pulls on the window, potentially causing cracks or even pulling the whole window out of the frame if it isn’t properly installed or its negative pressure DP rating is too low.
You can identify a window’s design pressure ratings by checking its National Fenestration Rating Council (NFRC) label. The NFRC label will have both a positive and a negative number that indicates how much pressure per square foot the window (or door) can handle.
For example, a label that reads +60 and -55 would mean that the window was tested to be able to withstand 60 psf of inward-acting pressure, and 55 psf of outward-acting pressure.
To be approved for installation in a wind borne debris zone, a window needs to have a DP rating sufficient to withstand 130 mph or stronger winds.
Much of Hillsborough County is in a 140 mph wind borne debris region. At 140 mph and a standard sea level air density of 0.0765 lbs/ft3, that would mean a window would need to have a DP rating of 50.12 lb/ft2 to withstand that wind force (Source: Wind Load Calculator). For safety’s sake, let’s round up to a DP of +/-55 to consider a window good enough to meet the minimum requirements for use in Hillsborough County.
140 mph is solidly within the range of a Category 4 hurricane on the Saffir-Simpson hurricane wind scale. And that’s the baseline for any impact window being installed in Hillsborough or Pinellas.
Why Installation Matters for Windward and Leeward Pressure Resistance
When it comes to getting new impact windows to weather the changing positive and negative pressure conditions brought by a major hurricane, it isn’t enough to simply get a strong window. Even the best windows on the market can’t protect your home effectively if they aren’t installed correctly.
When installers cut corners, doing things like:
- Not placing securements between the window frame and the edge of the opening correctly
- Using cheap screws that easily rust or bend
- Using wood shims instead of water-repellent composite shims
- Not properly aligning the window to the opening
- Skimping on insulation and flashing around the window opening
- Not measuring your window openings correctly before ordering new windows
- Sealing with cheap caulk
The consequences can be dire. In extreme cases, impact windows have been pulled cleanly out of the homes they were supposed to protect. They rested intact on the ground as the home they were installed in suffered extreme damage from sudden pressurization and water infiltration.
Prepare Your Home for Hurricane Season with Karoly Windows!
When you need strong windows that can withstand both windward and leeward conditions in the middle of a hurricane, Karoly Windows & Doors is your go-to choice!
For decades, Karoly has installed windows and doors throughout Hillsborough, Pasco, and Pinellas. And, unlike many other so-called ‘installation’ companies, we never outsource our installation work to a third party subcontractor.
Every Karoly installation is performed by a Karoly technician. A specialist in window and door installation who is on the Karoly payroll and held to our company’s high standards. That’s how we can guarantee that you won’t have to worry about the corner-cutting that so many other installers resort to.
We’re so confident in our installation quality that we back it up with a lifetime labor warranty. If there’s an issue with your installation, we’ll fix it for free for up to 25 years after the installation date.
Reach out to Karoly Windows & Doors today to get your home the best impact windows with the best installation in Tampa Bay!
Get a free in-home estimate
Tell us about your windows or doors and we'll give you a free, no-obligation quote.
