Window Design Pressures for New and Replacement Windows

!±8± Window Design Pressures for New and Replacement Windows

New Building Codes change the industry:

The ever increasing demands of new building codes has significantly changed window and door design pressure ratings required for replacement windows, doors and sliding glass doors. This is especially true in wind-prone areas such as Florida. Not only are design pressures an important lifesaving issue for the everyday homeowner but they are critical for every high rise condo in over 4 stories. What's the issue? As the elevations of a building increase, the design pressures go up dramatically.

In addition to the elevation, the location of the window (corner versus middle of the building) may quadruple the pressures effects. For safety reasons, all impact windows and doors for these applications must meet newly updated and enhanced air, water and structural design performance requirements. Many Home Owner Associations (HOA), Property Management companies and even replacement window companies are not familiar with the older codes let alone the new ones. As many people do when anything changes, some may consider these new Replacement Window Design Pressures to be over-kill, however. In reality one hit from flying debris or winds from even a modest tropical storm may destroy your windows and compromise the integrity of your home.

Design Pressures:

The easiest way to explain Window Design Pressure is to take a walk through downtown Chicago. Picture yourself walking down a street on a typical Chicago winters day. On just about any street you will encounter some amount of wind but once you turn that corner, the gusts of wind can literally knock you off your feet. Tropical storms and hurricanes are no different in their wind gusts dramatically exaggerating the winds pressure and its effects on the designs of a building.

Likewise when it comes to high-rise condos the wind speeds and wind pressures are even more pronounced due to the surrounding trees, buildings and higher floor elevations. Similar in effect to the wind passing over an airplane wing (Bernoulli's Principle), these natural and man-made structures can generate negative air pressures that can lift or in this case suck windows and doors right out of the wall. Can you imagine what could happen if you were behind a window that gets sucked out at 150 mph? In some cases the winds can reach up to a staggering 300 mph or higher.

Choosing the right window and door for the application:

For high-rise condos, Single Hung Windows, Double Hung Windows, Casement Windows, Picture Windows and Sliding Glass Doors are available that are designed to meet and in most cases exceed regional and county design pressure codes. It is important to note that all windows and doors are NOT created equal. Finding a window dealer and installer who is experienced in dealing with design pressures is paramount. A reputable company can explain and help the homeowner to choose the right window and door product for their particular application.

High-Rise Condominiums:

Compliant window manufacturers have announced two major design pressure rating changes on Double Hung windows. Approved Double Hung window sizes now exceed a structural design pressure 40 rating, with most of them above a design pressure 45, and many reaching a design pressure 50 rating. These performance enhancements were made possible by modifications to the tilt latch, which now pulls the sash even more tightly towards the jamb. End result for you the homeowner, a greater energy efficient, quieter and more secure window.

Impact Windows:

The design pressure ratings on approved window lines - including single hung, double hung, transoms and picture window units - are also increasing. However approximately only 10% of the window and door products currently manufactured have been upgraded to meet the increased design pressure ratings. In order to meet these higher design pressure ratings, tested windows and doors were required to meet three (3) specific sets of criteria related to air, water and structural performance.

Air: The glass was required to show no evidence of air leakage around the weather strip or corner joints when installed in a 25 mph wind tunnel.

Water: Unit must withstand eight inches of rain per hour, driven by wind speeds of 55 mph.

Structural: Unit must remain structurally sound under 142 mph of wind pressure.

Finding the Right Company:

Here is where your real work will start as you will need to get yourself a little education. Finding a factory trained and certified window Installation Company that has not only been specifically trained on design pressure requirements but knows how to install those windows and doors is key. Many companies say they can do the job but few companies know how to do it right. Design pressure requirements can only be calculated with a "Structural Engineering" program. You can't just wing it. If the company you are working with doesn't have one, do yourself a favor, show them the door and move on.