Imitation Slate Roofing
I read your articles about slate roofs. Ours needs replacement but the price of replacing it with real slate is probably way out of our budget. Do you know anything (good or bad) about imitation slates?
My first concern is the experience and qualifications of the person that has condemned the roof. Too often I find someone with experience only with newer roofing systems lacks the knowledge to determine that, with proper repairs and regular maintenance, there may be some life left in an old slate roof. On other occasions, it can be obvious the person pronouncing a roof dead makes their living, and the most profit, selling quick-to-install roofing systems.
Another concern is if changing the roof system may alter the historic character of the building. The Secretary of the Interior's Standards for Rehabilitation advises "deteriorated historic features shall be repaired rather than replaced" but goes on to state "where the severity of deterioration requires replacement of a distinctive feature, the new feature shall match the old in design, color, texture, and other visual qualities and, where possible, materials."
If it's not economically feasible to preserve the old slate roof or replace it with natural slate, I think it's best to find a material that comes closest to matching what is being replaced. For example, if your home has gray Pennsylvania slate and other homes in your area have the same, installing an imitation of New York red or Vermont green wouldn't be appropriate. In addition to color, the texture, dimension, and thickness should also be considered when comparing alternative materials.
Up until the last couple decades, standard asphalt shingles have had a pretty boring two-dimensional appearance. Now "dimensional" shingles create textures that are more representative of natural roofing products. Also, some styles have darker color granules applied in strategic locations to appear as shadows, furthering the appearance of random thickness. Although it is probably the least costly of the slate alternatives, this product relies on illusions.
Tiles: Concrete or Clay
Clay tiles have been used in roofing for hundreds of years. Concrete tiles, although not common, have a fairly long and successful history. These can be very thick and heavy, sometimes heavier than the original slate. Reinforcement of some framing may be necessary for their installation. The available colors are somewhat limited and textures aren't quite as good as some other products that imitate slate.
These are made with thermoplastic resin, sometimes ground slate or fiberglass, and/or recycled rubber. The latter ingredient enables the manufacturers to jump on the "green" marketing progression. These are available in many colors but haven't been around long enough for me to see how the colors (and the overall product) hold up to weather and UV. The shingles are made by injecting the composite into molds, so the textures and edges can closely replicate natural slate. I'm sure some of the molds are cast from the real thing. These are becoming a very popular slate alternative. So far, the only issue I've found is some cupping and curling up of corners. This might be due to improper storage or installation of the material.
The earliest imitation of slate roofs were with cement asbestos tiles that proved to be quite durable, but the colors didn't last. The thickness, texture, and dimensions didn't exactly replicate natural slate either. About 20 years ago, there were many new fiber cement roofing products introduced but there were some major failures. Severe cracking, crazing, and discoloration showed up on several products, resulting in many warranty claims and class action lawsuits. Many of the manufacturers moved away from the fiber cement roofing and others have made changes to their product. The more recent fiber cement roofing materials haven't been around long enough for me to determine if the earlier problems have been completely eliminated.
Some folks looking into slate alternatives are quite shocked to find that some of the imitations are actually quite expensive. Not as expensive as natural slate but enough for them to seriously consider a cheaper roofing system.
Life expectancy is another issue to consider. These newer, manufactured products often tout a lengthy warranty. Read these "limited" warranties and you may likely find that advertising a fifty year warranty certainly doesn't guarantee the roof will last 50 years. If the roof fails, at say 30 years, read what the manufacturer will actually do for the claim.
Most types of natural slate have a known life expectancy well beyond that of the average person. Some of the products available for imitating a slate roof might have a life expectancy beyond that of the average person's pet.
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.