There is a lot of debate about how or if Lightening Rod systems really will prevent or lessen a strike. The proponents Mfgs. of systems will fight to the end that it works. Government agencies will never suggest that they may not work because they don't want to stick out their neck. The NFPA has a bulletin NFPA-780 that has the guidelines but many people in and out of the agency don't know or think it will work.
Read this to understand the reason for doubt.
http://www.straightdope.com/columns/...ds-really-work
The problem is if you don't have rods and you get struck it is assumed that the rods would have prevented the strike or bled off the strike. It just doesn't seem possible for a few relatively light gauge cables will work. That is what is the bone of contention. If you have ever been really close (100 feet) when a strike goes to ground it is unbelievable the shock wave and how much electricity dances around in the air.
You will never be criticised for adding a lightening system just be aware it may or may not work. A Faraday Cage is the only thing that would prevent a strike on a house and that's not practical.