Lightning Risk Assessment Guide

Lightning loss risk assessment for your home or other buildings involves the evaluation of various criteria to determine the risk of loss due to a lightning strike. This guide will assist you in determining if your building is at risk for a lightning strike. It's not possible to cover each special design element in this guide that may render a structure more or less susceptible to lightning damage. In those special cases it is recommended that you seek advice from a lighting assessment expert. Personal and economic factors are often very important and should be considered in addition to the assessment obtained by use of the following guide.


The following variables should be considered to determine the need for protection against lightning for a given building or structure:

Please record the number value that is associated to the closest match in each section of the chart above. Select only one per section. Add sections 1 thru 5. Then divide by the number selected in section 6. Compare the result at the end of the page.

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Type of Structure - INDEX A

Index Structure	Index Value
Single family residence less than 5,000 sq. ft.	1
Single family residence over 5,000 sq. ft.	2
Residential, office, or factory building less than 50 ft. in height Covering less than 25,000 sq. ft. of ground area	3
Covering over 25,000 sq. ft. of ground area	5
Residential, office, or factory building from 50 ft. to 75 ft high.	4
Residential, office, or factory building from 75 ft. to 150 ft high	5
Residential, office, or factory building from 150 ft or higher	8
Municipal services buildings, fire, police, water, sewer, etc. Hangars	7
Power generating stations, central telephone exchanges	7
Water towers and cooling towers	8
Libraries, museums, historical structures	8
Farm Buildings	9
Golf shelters and other recreational shelters	9
Places of public assembly such as schools, churches, theaters, stadiums	9
Slender structures such as smokestacks, church steeples, spires, control towers, lighthouses, etc.	10
Hospitals, nursing homes, housing for the elderly or handicapped	10
Buildings housing the manufacture, handling or storage of hazardous materials	10

Type of Construction - INDEX B

Relative Location - INDEX C

Topography - INDEX D

Occupancy and Contents - INDEX E

Lightning Frequency Isoceraunic Level - INDEX F

Few areas in the United States are free from thunderstorms and their attendant hazards, but some areas have more storms than others. The map shows the incidence of thunderstorm days - days on which thunderstorms are observed - for the United States. Select one.