The Insurance Institute for Business & Home Safety (IBHS), in conjunction with the American Modern Insurance Group, has conducted a series of tests to evaluate the effect of high winds, such as those experienced during hurricanes, low level tornadoes and severe thunderstorms, on attached structures to manufactured homes.
- Attachments to site-built or manufactured houses, such as carports, awnings, and porches, are typically designed to lower building standards than those of the houses themselves. In fact, most building codes allow these kinds of attachments to be built to withstand lower wind speeds. Consequently, attached structures frequently fail at much lower wind speeds than the buildings to which they are attached.
- An IBHS analysis of closed insurance claim files from 2004’s Hurricane Charley indicated that attached structure failures occurred about 80 percent of the time (IBHS 2005). Unfortunately, failure of these structures often leads to damage to the host building, and potentially, to other buildings nearby.
- This problem is especially important for manufactured homes built to the U.S. Department of Housing and Urban Development’s (HUD) Manufactured Home Construction and Safety Standards, commonly called the HUD Code.
- A study of Hurricane Charley damage to manufactured housing conducted by The Institute for Building Technology and Safety (IBTS) for HUD found that about 80 percent of structures attached to manufactured housing suffered partial or total destruction (IBTS 2005). This result is very similar to that found in the IBHS Hurricane Charley study of damage to site-built homes.
- Despite manufacturers’ recommendations to the contrary, attached structures, such as carports and porches, with solid roofs are usually attached to manufactured homes.
- Since June 1976, every newly constructed manufactured home has been required to comply with codes adopted by HUD. In July 1994, wind load requirements for the HUD Code were revised to address common types of damage observed during Hurricane Andrew.
- The improved wind provisions of the HUD Code stipulate that manufactured homes shall be designed and constructed to conform to one of three wind load zones. The appropriate wind zone to use depends on the location for the home’s installation (see the HUD Wind Zone map).
- Homes designed and constructed to HUD Wind Zone I cannot be installed in a higher wind zone, but homes designed and constructed to HUD Wind Zone II can be installed in HUD Wind Zone I and II areas, and those designed to HUD Wind Zone III can be installed in Zones I, II, and III.
- HUD Wind Zone I = 70 mph basic fastest-mile1 wind speed (compares to 90 mph 3-second gust2)
- HUD Wind Zone II = 100 mph basic fastest-mile1 wind speed (compares to120 mph 3-second gust2)
- HUD Wind Zone III = 110 mph basic fastest-mile1 wind speed (compares to 130 mph 3-second gust2)
- The primary objective of this testing was to develop and demonstrate effective mitigation measures for strengthening carports and associated connections.
- A secondary objective was to demonstrate the superior performance of manufactured homes built to HUD Code Zone III standards.
- While this research focused on wind performance of carports attached to manufactured homes, the test results also are applicable to other attached structures, such as porches, awnings, canopies, etc.
- The test results also are applicable to attached structures on site-built homes.
Using a well-anchored HUD Code Zone III home, IBHS researchers:
- Attached a standard carport to the side of a manufactured home built to HUD Code Zone III standards following conventional installation procedures
- Instrumented the structure to monitor wind loads and tested it at various wind directions under both uniform flow and simulated turbulent boundary layer winds
- Subjected the home and attached structure to steadily increasing winds and windstorm simulations (once the basic load data was measured) until local or global failure occurred
- Installed a sequence of similar size new carports and carport components with incremental enhancements to connections and repeated testing to determine relative benefits of various mitigation measures
- Attached a new carport with optimized mitigation measures, tested it and the home to the full wind capacities of the IBHS Research Center’s huge array of 105 fans each with 350 HP motors
- Opened a window and door on the home’s windward side to evaluate performance of a Zone III manufactured home during a high-wind event
Using a well-anchored HUD Code Zone I home, IBHS researchers:
- Attached both a typical older design carport and a carport with optimized mitigation measures to a home built to HUD Code Zone I standards to evaluate relative performance during high-wind conditions
- Tested the carport with optimized mitigation measures, and the home to which it was attached, to the full wind capacities of the IBHS Research Center’s huge array of 105 fans each with 350 HP motors
- Opened a window and door on the home’s windward side to evaluate performance of a Zone I manufactured home during a high-wind event, as well as to identify any additional vulnerabilities when an attached structure is connected to a weaker building