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We design and build the best custom mahogany windows when nothing less will do.~Lewis Stewart, Founder

Design Pressure Testing

Design pressure tests were designed to measure how resistant windows and doors would be when subjected to several different severity’s of storms. The test also measures the products resistance to Wind Loads. DP testing was first established in the 1940’s by a group of window manufacturers and engineers that had concerned about hurricanes and other types of severe weather systems. The intent was to measure how a variety of building products performed in these types of extreme conditions. The design pressure tests were designed to measure Wind Loads and how resistant windows would be to different severities of storms.

National building codes (IBC, IRC and HUD) now require testing and certification of windows and doors. Windows and sliding glass doors must meet the requirements of industry standards that include air, water and structural testing along with some other ancillary tests. Conventional entry doors (with hinges running along the left or right side) only require structural testing. This part of the code is enforced primarily in the Atlantic and Gulf coast states while other states are not yet enforcing this part of the code. Even though testing is not mandatory in our current market area, Stewart Brannen Millwork proceeded, voluntarily, to insure that our SBmpact units perform beyond current requirements.

Structural testing of door systems measures the wind load resistance that a door can withstand before it exhibits signs of failing. Design pressure, or DP, ratings are established at various levels. For example, a DP-20 test replicates a 90 MPH wind while a DP-50 rating utilizes 140 MPH winds.

Water resistance is an optional test for doors. The tests are administered in two ways – with air pressure or without air pressure. Without pressure testing is a pass/fail test and is referred to as DP-0. In a chamber, water falls on the exterior of the door from top to bottom without any wind force. If no water penetrates the interior part of the unit then the test is passed. Wind pressure water tests vary based on the wind speed. DP-20 tests simulate 8” of rain per hour in 34 MPH winds. DP-50 simulates 8” of rain per hour in 54 MPH winds. When winds reach 39 MPH, the National Weather Service considers these tropical storms and gives them a name. Additionally, these tests simulate water volumes of 8” of rain per hour.

Three major code agencies are utilized in the United States:

• IRC – International Residential Code. This is the primary code used for one and two family residential dwellings.
• IBC – International Building Code. This is commonly regarded as a light commercial code but is also used for residential dwellings in certain geographies.
• HUD – Housing and Urban Development. The governing code for the manufactured and modular home segment. Fortunately, for all of us, all three utilize the same code section from HUD:

Testing is expensive and time consuming. But we know that all doors are not created equal. We do not believe in taking chances with your possessions. The link below will take you to our test reports.


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