Retrofitting Homes to Withstand Major Hurricane Strength Winds

From Email to President Joseph Pluta (and other individuals) from County of Maui Maui Emergency Management Agency (MEMA)


"...below you will find some information about retrofitting homes to withstand major hurricane strength winds.
 
In 2010, FEMA developed guidance on retroftting your home to withstand a major hurricane to encourage mitigation of existing buildings in hurricane-prone areas. According to the ASCE (American Society of Civil Engineers) 7-05, the entire state of Hawaii is in hurricane-prone area. There are three (3) levels of mitigation measures when selecting a retrofit project for your home. They are: Basic, Intermediate, and Advanced.
 
Basic (or Intermediate) Retrofit: This measure focuses mainly on the building envelope such as enhancing the roof system, attic ventilation, wall structure, integrity, openings (windows, skylights, doors...etc.) and other attached structures.
 
Some examples of Basic and Intermediate retrofits are:

• enhancing the roof sheathing using thicker wood board decking
• larger diameter nails
• stainless steel fasteners
• secondary water barriers (SWBs; e.g. Bitumen polymer tape, bitumen polymer sheet, self-adhering underlayment); see: https://www.doi.sc.gov/DocumentCenter/View/2399/Section-C-Secondary-Water-Barrier
• Gable end bracing (see: https://doi.sc.gov/DocumentCenter/View/2547/Section-E-Gable-End-Bracing)
• strengthening vents and soffits
• Replacing windows with ASTM E1996, 1886 compliance coverings certified to resist a Type D Missile (As defined in ASTM E1996)

Advanced Retrofit: A continuous load path from the roof to the foundation would be needed and evaluated. A continuous load path ensures that the load distribution of the house does not shift causing a structural failure. The total load of the home is transferred directly through the structure of the building down into the foundation. Essentially, this will help the house stabilize during high wind events largely lowering the likelihood of a single point of failure.
 
Some examples of the Advanced retrofits are:

• Creating a continuous load path
• Anchoring chimneys
• Enhancing interior and exterior wall coverings

Based on a Cost Effective Determination study performed by FEMA
​(see: http://www.fema.gov/media-library-data/1424368115734-86cfbaeb456f7c1d57a05d3e8e08a4bd/FINAL_WindRetrofit_BCA_JobAid_13FEB15_508complete.pdf) they estimate a cost of an intermediate retrofit to be ~$24,000 (roof retrofit included). MEMA would strongly encourage the adoption of these FEMA guidelines into the future Lahaina building code. We also hope the county as a whole will adopt these guidelines in conjunction with a modern building code.
 
Download links to documentation.
 
Please see FEMA P-804 (attached) Chapter 3 + 4 for an in-depth review of homeowner retrofits.
 
https://www.fema.gov/media-library-data/20130726-1753-25045-2304/508versioncombined_804.pdf
 
Executive summary of P-804
 
https://www.fema.gov/media-library-data/1464805957280-eecf7b63734a9208ed471158c8f69094/P804WindRetrofitFactSheet06011658.pdf