1. 1 Constructing for High-Wind Events The Risk of Severe Wind in Virginia Characteristics of Destructive Winds How Homes Fail Building Wind-Resistant Homes

2. Jon AyscueJune 17, 2004 2 I. The Risk of Severe Wind in Virginia

3. Jon AyscueJune 17, 2004 3 Assessing Risks

4. Jon AyscueJune 17, 2004 Tornado Activity in the US

5. 5  The combining of these two factors allows the homeowner to determine the risk to their home Assessing Risks FEDERAL EMERGENCY MANAGEMENT AGENCY MITIGATION DIRECTORATE

6. Jon AyscueJune 17, 2004 6 Historical Hurricane Tracks 1851 - 1999

7. Jon AyscueJune 17, 2004 7 ASCE Wind Map

8. Jon AyscueJune 17, 2004 8 Wind Speeds for Virginia Localities 110 MPH100 MPH90 MPH Special Wind Region Counties of Accomack and Northampton. City of Virginia Beach Counties of Gloucester, Isle of Wight, Lancaster, Mathews, Middlesex, Northumberland, Southampton, Surry, York. Cities of Chesapeake, Franklin, Hampton, Newport News, Norfolk, Poquoson, Portsmouth, Suffolk. All other Localities Counties of Bland, Grayson, Scott, Smyth, Tazewell, Washington, Wythe

9. Jon AyscueJune 17, 2004 9 Fastest Mile vs. 3 Second Gust Why 3 Second Gust?  Standardization  More Realistic Measurement “Fastest Mile” = Hurricane “Maximum Sustained Winds” Fastest Mile (mph)3 Second Gust (mph) 7085 7590 80100 85105 90110 100120 105125 110130 120140 125145 130150 140160 150170

10. Jon AyscueJune 17, 2004 3-Second Peak Gust Maximum gusts to 94mph (42m/s) Maximum mean speed ~73mph (33m/s)

11. II. Characteristics of Destructive Winds

12. 12 Fujita Tornado ScaleSaffir-Simpson Hurricane Scale Damage and Storm Category TAKING SHELTER FROM THE STORM: BUILDING A SAFE ROOM INSIDE YOUR HOUSE

13. Jon AyscueJune 17, 2004 13 Hurricane-Force Winds  …are more turbulent than most other wind storms (tens of thousands of gusts)  …are sustained for longer periods of time (hours)  …change slowly in direction, seeking out the most critical angle of attack  …carry large amounts of debris

14. Tornadic Winds  …are relatively brief, minutes rather that hours  …are damaging outside the main funnel area due to inflow  …can occur with little if any warning, unlike hurricanes  …like hurricanes, can carry large amounts of debris which can be as or more damaging than the wind itself

15. 15 BUILDING PERFORMANCE ASSESSMENT TEAM

16. Jon AyscueJune 17, 2004 16 Tornado Inflow

17. 17  The Good News - most tornadoes are no stronger than minor hurricanes  The Bad News - a tornado doesn't have to strike your home to destroy it because of inflow  More Bad News - nothing can protect your home from a direct hit by a F4-F5 tornado Tornadoes: Good News and Bad

18. 18  Weak (F0-F1) 40-112 mph  Strong (F2-F3) 113-206 mph  Violent (F4-F5) 207-318 mph Historical Tornado Strength (United States, 1950-1994)

19. Jon AyscueJune 17, 2004 19 Historical Hurricane Strength (1900- 1996 Direct Landfalls) Category Wind Speed (mph) Damage 174-95Minimal 295-110Moderate 3111-130Extensive 4131-155Extreme 5>155Catastrophic

20. 20 Homes can be built to withstand all but the strongest hurricane winds  Mitigation during Construction  Post-construction Retrofitting Homes cannot withstand strong tornadoes  Saferooms provide protection > 250 m.p.h. Hurricanes and Tornadoes

21. III. How Homes Fail

22. Jon AyscueJune 17, 2004 22 Windborne Debris  Debris causes a large fraction of damage  Size increases with wind speed  Windows and doors are especially vulnerable Courtesy of Texas Tech University

23. Jon AyscueJune 17, 2004 23 Protecting from Windborne Debris  Eliminate Sources of Debris  Secure out-buildings  Remove unsecured items from around the house  Remove trees within ‘falldown” distance  Protect Openings  Especially garage and patio doors

24. Jon AyscueJune 17, 2004 24 Anatomy of a Destroyed Home The roof fails or gable-ends collapse Lost windows and doors contribute to failure With the roof lost, walls collapse

25. Jon AyscueJune 17, 2004 25 Courtesy North Carolina Blue Sky Foundation and Applied Research Associates Gust Wind Speed = 125pm Due to increased internal pressure resulting from a large missile hit, this unmitigated building losses one window and one sliding glass door Gust Wind Speed = 100mph Unmitigated building starts to lose some shingles

26. Jon AyscueJune 17, 2004 26 Courtesy North Carolina Blue Sky Foundation and Applied Research Associates Gust Wind Speed = >125pm More sheathing lost. Entire wood frame is exposed. Gust Wind Speed = >125mph Pieces of plywood sheathing start to be pulled away from the frame

27. Jon AyscueJune 17, 2004 27 Courtesy North Carolina Blue Sky Foundation and Applied Research Associates Mitigated Building Note the Secondary Water Resistance on top of plywood sheathing Windows secured Gust Wind Speed = >125mph Whole roof failure of the unmitigated building

28. Jon AyscueJune 17, 2004 28 The Vulnerable Roof  The roof is the most vulnerable element of the structure

29. Jon AyscueJune 17, 2004 29 The Vulnerable Roof

30. Jon AyscueJune 17, 2004 30 The Vulnerable Roof

31. Jon AyscueJune 17, 2004 31 Finding the Weak Point Failure is Progressive The weak point fails first Further failure becomes more likely

32. Jon AyscueJune 17, 2004 32 Every House has a Weak Point  Design Goal - 156 mph Wind Survival  As Built - 137 mph Survival  What’s the Weak Point? State Farm Good Neighbor House

33. Jon AyscueJune 17, 2004 33 IV. Building Wind Resistant Homes

34. Jon AyscueJune 17, 2004 34 Protecting Your Home from Wind Damage  Strengthen the Roof  Reinforce Gable-Ends  Ensure Proper Connections  Protect Openings  Eliminate Debris Sources

35. Jon AyscueJune 17, 2004 35 The Continuous Load Path  Holds the envelope Together  Transmits wind forces  to earth  Roof connections are  the most important

36. Jon AyscueJune 17, 2004 36 Construction Guides  Blue Sky guide is excellent.  Developed in conjunction with Clemson University  Construction techniques for up to 140-mph 3-second gust wind resistance  Available at:  www.bluesky-foundation.net

37. Jon AyscueJune 17, 2004 37 Building Codes  Building Codes are minimum acceptable standards for building design and construction  Can be “Performance” or “Prescriptive”  Building codes must be enforced in order to be effective  Since 1994, International Building Code (IBC) predominant  Virginia Uniform Statewide Building Code (USBC) based on the IBC  2000 International Residential Code for one and two- family dwellings  Does not apply to manufactured homes

38. Jon AyscueJune 17, 2004 38 Keeping the Roof On  Proper Sheathing Attachment  Gable-end Reinforcement  Continuous Load Path to Ground

39. Jon AyscueJune 17, 2004 39 Gable-End Bracing  failure can lead to roof failure  Gable-ends can be easily reinforced  Gable-end collapse was the most common failure during Hurricane Andrew

40. Jon AyscueJune 17, 2004 40 Protecting Openings  The Most Vulnerable Openings  Double-Wide Garage Doors  Patio Doors  Windows  Double Entry Doors

41. Jon AyscueJune 17, 2004 41 What’s the Weak Point? The Garage Doors Only rated to 137 mph State Farm Good Neighbor House