Mastering Roof Inspections: Slate Roofs, Part 9

In addition to competency, having the specialized equipment necessary to adequately inspect the roof may be a problem for many inspectors.

Don’t walk slate roofs. They can be fragile, slippery and dangerous, as well as expensive to repair. It’s often difficult to tell the condition of the slate.  Old slate can be soft and crumbly, and easily damaged. You can go through the roof, and you can go over the edge. Don’t walk slate roofs.

Contractor Qualifications

Slate roofs require maintenance just like all other kinds of roof-covering materials do. Damaged or missing slates should be replaced by a qualified contractor, and “qualified” is the key word here. As slate roofs become increasingly rare, so do the contractors qualified to work on them. Any time you make a recommendation that a roof (or any other part of the home) be evaluated or repaired by a contractor, insert the word “qualified” in front of the word ”contractor."  That way, if your client takes a low bid on work and the contractor makes a mess of it, it will be difficult for the client to include you in a lawsuit because he didn’t follow your recommendation and hire a qualified contractor.

Broken Slate 

Look for broken slates, including missing corners. As a general rule of thumb, a slate corner is considered to be missing if the broken area exceeds 1x1-inch on the sides of a triangle. Even on a new roof, corners broken less than this are accepted as slates that will not leak or reduce the overall performance of the roof. Broken corners are very noticeable, and you should note them in your report, along with a comment on the degree of threat, if any, that they represent to the roof's integrity.

It’s not unusual for corners to be broken during fabrication. It’s the responsibility of the nail-hole puncher to ensure that nails are punched in a location that will result in broken corners being hidden by the slate in the course above, as well as in a location where they won’t be likely to cause leakage.

Here are some other inspection concerns and common reasons for broken slates:

• If you see an unusually high number of slates broken along the eaves, check to see if a cant strip was installed.
• Poorly supported slates can be broken by snow and ice sliding off an overhanging roof.
• Anyone walking the roof can damage it. This includes contractors and those performing repair work and maintenance on roof components, such as chimney sweeps.
• Falling trees and tree limbs can damage slates.
• Thrown objects, such as rocks and balls, can damage slates.
• Ladders leaned against an eave can cause damage.
  
  

Snow sliding off the roof can be dangerous.  Poorly installed avalanche preventers -- also called snow-retention devices and snow guards -- can cause damage.

Look for these typical problems:

• Guards are attached to slates instead of sheathing. This will eventually result in loose or lost slates.
• Fasteners can eventually loosen, allowing the L-shaped guard to pull loose and possibly lift the slate above.
• Guards are sometimes placed too far apart in an effort to save money. Guards can bend, break or pull out if they’re over-spaced.

You may see pipes installed as snow guards.

When this is the case, pay attention to how they’re attached to the roof. The preferred method is a bracket that replaces an entire slate.

A wide variety of snow guards is available, as you can see here. Important in evaluating snow guards is being able to determine if they are spaced properly. This will exceed the scope of your inspection.

Gutters

You may find gutters built into the roof. Because slate is fragile, these gutters are often walked in, or used to support a ladder, or hold tools. Also, because they’re hidden, maintenance is often neglected. Do your best to get a look at these gutters.

During the early 1900s, downspouts for these built-in gutters were sometimes routed to home plumbing. If you find leaks in older homes whose roofs appear to be in good condition, check to see if the gutters are still connected to the home's plumbing waste pipes.

Cleaning Slate

Whether slate can be cleaned depends on the source of the stain. Here are some common sources and their remedies:

• Tree sap can be removed using a diluted, non-acid-based masonry cleaner and a rag.
• Moss can be scraped off and the stain removed using the same methods used for cleaning tree sap. Moss usually indicates a moisture problem, and slate may be damaged beneath the moss. During your inspection, scrape off some moss and check the condition of the underlying slate. Look for efflorescence and delamination.
• Concrete, paint and oil do not remove well and efforts to clean them may make the staining worse.
• Some dark slates installed on roofs in cities may develop a greenish tint.
  
  

Slate Roof Design

Design problems affecting slate roofs are generally the same as those for other roof-covering materials. Steeply pitched roofs extend the lifespan of the slate by shedding runoff more quickly. Runoff should have a clear path to the roof’s edge.