While performing home inspections in New Jersey I do come across my fair share of slate roof coverings. Slate roofing is a highly specialized roofing system that dates back hundreds of years. A slate roof is rather simple in design. It consists of thin layers of slates overlapped so they create a water tight covering. The question that I always get while performing home inspections in New Jersey is how long does a slate roof last. Typically the slate roof will late around 80 years. It really depends on the type of slate used and the manner in which it is cared for. Slates are secured using two nails per slate. Each slate overlaps two courses of slates under it creating a water tight covering. I was recently inspecting a home in Bergen County New Jersey and it had a slate roof that was really in bad shape. Typically the flashing fail, and the fasteners fail before the slates themselves will fail. That is why it is imperative to give the slate roof regular maintenance. The experienced slate roofing contractor will look for areas of loose and damaged slates and repair them. You should have a Slate roofing contractor come in once per year an inspect the roof for damage and areas that need attention. You should never walk on a slate roof. While performing home inspections I will view the slate roof covering with binoculars. Slate roofing is also very expensive both to maintain and to replace. Many of the slate roofs that I view on NJ home inspections are at or past their statistical life expectancy. If you are purchasing a home with a slate roof you should be aware that the roof is most likely very old, is close to its statistical life expectancy and is expensive to repair and maintain. The condition of the slate roofing material is only one small aspect that we cover on the New Jesey home inspection. http://www.looksmarthomeinspections.com/FAQ.html