Slate Roof Coverings The Good And The Bad
Although the majority of roofing material used in New Jersey is asphalt based there are some homes that have slate roof coverings. A requirement of New Jersey Home Inspectors is to identify the roofing material and inspect the visible areas of the roof.
Slate roofs have been around for hundreds of years and are composed of slate tiles, wood decking and special nails. The slates are overlapped to form a water tight covering. Slates are installed with a three inch head lap and secured with two nails that are covered by the slate rows above. The most important aspect of installation is the head lap which makes for the water tight seal.
Not all slate is equal in terms of quality and longevity as a roof covering. There are varying qualities and slate softness. As a general rule the softer the slate the shorter its life expectancy. However even soft slates can have a useful life of over fifty years. The harder slates can last in excess of eighty years. The actual type of slate used is usually not going to be confirmed during New Jersey home inspections.
One of the major failure mechanisms of slate roofing is flashing failures. Flashings can wear out much before the actual slate roof covering. Flashings can be found in roof valleys, dormer areas, and around roof penetrations. Typical materials used as flashings in slate roof construction are copper, sheet metal, lead coated steel, and lead. When flashings fail they should be replaced. Often the flashings can be replaced by removing sections of the slates, installing new flashings and then re-roofing with the same slates in exactly the same location from where they were removed.
When performing your new Jersey Home Inspection I will be inspecting the slate roof from the grade level. Slate roofs can not be walked because damage will occur to the slates. Slate roofing contractors use platforms to do their work in order to avoid causing damage to the roof. If damage or broken slates are found you should have the slate roof fully evaluated by a slate specialist.
Many slate roofing problems stem from poor installation and repair practices. Slate roofs are specialized and your slate roof should only be repaired by a qualified slate roofing expert. Often roofing tar and patching on the surface of the roof can be viewed. Roofing tar or other compounds should never be applied to the surface of a slate roof. Another repair issue is that contractors face nail the slates to the roof. So now there are exposed nail heads which will ultimately leak.
Slates have naturally occurring hairline cracks and imperfections. The imperfections can cause slate failures over time in the form of broken or cracked slates. It only takes one broken or missing slate to cause a roof leak. Damaged or missing slates should be replaced by a qualified contractor. There are two accepted methods to replace slate roofing tiles. One method is called the slate hook method. A small stainless hook is used to hold the replacement slate in place. The other method uses a copper flashing called a bib flashing that covers the new nail that is installed to attach the new slate to the roof.
Slate roofs should be inspected each year by a slate roof specialist. Regular inspections will help to identify broken and missing slates and give you an opportunity to make repairs on a regular basis rather then wait until you have a failure and roof leakage. Slate roofs are a beautiful and functional roofing material but they are expensive to both repair and replace.