In adding on to a structure with a pre-existing lightning protection system, is there an added risk to the new addition?
A lightning protection system is designed to protect a structure when lightning is going to attach to it by taking the direct strike and routing it into the ground. It doesn’t have any great attractive capability. To give you an over-simplified idea, if a lightning rod was mounted on a 30 ft. tall pole, it would protect about a 30 ft. radius area around the pole at ground level. An air terminal or system of lightning rods on a roof is designed to protect that roof only. If you put on an addition of equal height, or even at somewhat lesser height that extends out some distance from the protected area, it is probably not protected by the existing system and can accept a strike. For a full explanation of “zone of protection” you should refer to the NFPA 780 or LPI 175 documents. Both may be purchased from our store by clicking here.You may also refer to Annex L of the current addition of NFPA 780 titled “Risk Assessment” to assist in determining the need for lightning protection. Although
