Cedar shingle and shake roofs are coveted for their natural beauty and superior resistance to high winds. They are also expensive, so it makes sense to do all you can to extend the life of a beautiful cedar roof. At minimum that means performing routine maintenance and taking eventual restoration and preservation steps.
Whether you currently live under a cedar roof or have considered switching to one, you’ll want to know some of the ups and downs of its care. We consulted the Cedar Shake & Shingle Bureau (CSSB) for tips on cleaning and protecting cedar roofs — and evaluating whether a middle-age roof can and should be saved.
Basic care
New cedar has natural fungicidal properties that prevent decay and contains oils and resins that repel water. But over time, cedar roofing becomes less water-repellent and can curl, crack and grow things such as fungi, algae, lichens and moss.
To prevent rot, leaks and surface growth, shingles need to dry between rains. Sufficient ventilation begins with proper installation (built-in airspace under the shingles and a well-vented attic). To maintain desirable conditions, check that attic insulation does not
obstruct soffit vents, and always keep the rooftop free of debris.
Eliminate branches (or entire trees) that overhang or shade the roof. This keeps organic matter away and allows sunlight and air to reach the roof. Use a garden hose (spraying in a downward direction) to remove loose debris from the surface and the keyways (spaces between the shingles). Keep gutters clean, and never direct a downspout onto the shingles of a lower roof. To avoid damaging the roof, perform all these chores without walking on it.
Beyond the basics
With rising costs of reroofing and the improvements in roof finishes, additional maintenance (once considered a waste of money) may now be prudent, especially if a roof shows signs of premature failure. To determine whether restoration — a process of deep cleaning followed by an application of a protectant — is worthwhile, you must first evaluate the condition of the roof. Most professionals agree that it is not usually cost-effective to restore an untreated 15- to 20-yearold shingle roof or 20- to 25-year-old shake roof. In fact, traversing such a roof to repair, clean or apply treatments may do more harm than good.
The decision to restore a roof in its middle years becomes more difficult. Besides its age, you need to consider its other components (nails, sheathing, ventilation system, etc.), the quality of its construction and its maintenance history. Nails are an important component, according to Skip Schiappa, a roofing consultant and CSSB-certified installer from Wareham, Massachusetts. He recommends only stainless steel nails and claims that galvanized nails used in cedar will last only about 15 years. In other words, middle-age shingles — even if untreated — may outlast some nails.
A hands-on examination of your roof will help determine whether restoration is a good idea. Tug on the shingles to see how well they are secured. Loose, cracked or badly cupped shingles may require repair or replacement. Rub your thumb across the butt ends of shingles to further evaluate their condition. If you can remove more than 1/4 in. of decaying wood, the shingles are usually beyond restoration.
Clean thoroughly
The cleaning process starts with a chemical application to kill surface mildews or algae and to remove oxidized wood fibers. Use a 2:1 solution of water and household bleach (5.5 percent sodium hypochlorite), or mix 2 to 4 ounces of swimming-pool chlorine (calcium hypochlorite) with each gallon of water. Wood restoration chemicals, such as X-180 Weathered Wood Restorer or Shingle Shield Cleaner, are also options. If you plan to apply a finish, be sure to read its preparation instructions before selecting a cleaning product. Never add detergent, as some may leave a film on the surface or become toxic if mixed with chlorine.
Apply the solution with a pump-tank sprayer and allow it to soak for 30 minutes (or with commercial products, as directed). Rinse using only enough pressure to blast off loose debris. You may use a garden hose nozzle at its most powerful setting, a hose-end high-pressure wand or a pressure washer. (Use a pressure washer only if you plan to apply a
finish to the wood.) In any case, be gentle; high-strength solutions, excessive abrasion with brushes or aggressive pressure washing can turn the face of the wood to pulp.
Some forms of algae and moss will not go away with bleaching and rinsing, making pressure washing a requirement. Most professionals use a pressure washer that operates at low pressure (about 500-600 psi) and high volume (4-6 gpm). DIYers can do an acceptable job with a more readily available model, such as the 2,200-psi, 2-gpm Campbell Hausfeld unit we used for this project.
The CSSB says pressure washing roofs is a job for professionals only. In my opinion, DIYers can tackle this chore if they are aware of the risks and follow the proper procedures:
• Avoid pressure washing a very dry roof on a hot summer day. The sudden moisture changes can stress the wood.
• Set the pump to its lowest setting, and use a wide fan angle.
• Begin with the nozzle away from the roof and move in slowly, just close enough to loosen debris; hold the wand perpendicular to the roof.
• Keep the wand moving, but avoid swinging the wand in an arc.
• Never aim the wand at an upward angle to the surface — it can damage shingles and force water under them.
• Wear eye protection and rain gear.
Restore lost protection
Before applying a finish, allow the roof to dry completely (at least 48 hours after pressure washing). The CSSB recommends using products that are water-repellent, contain a UV inhibitor and/or an EPA-registered wood preservative and are labeled as appropriate for cedar roofs. Never apply a waterproofer, sealant or plasticizer to a cedar roof; they trap moisture that may enter the wood and encourage growth of microorganisms.
Studies by the U.S. Department of Agriculture’s Forest Products Laboratories (FPL) show that the most effective products are semitransparent penetrating oil-base stains with high concentrations of pigments, such as X-100 Natural Seal and TWP-200.
Apply the finish until no more can be absorbed, but don’t allow it to pool on the surface. Using a stain brush alone or immediately after spraying ensures thorough coverage. Alternately, a wet-on-wet two-coat application with an airless sprayer works well — and it’s much faster. You can rent a professional-quality airless sprayer fitted with an 18-in. extension and a No. 517 tip (10degree fan angle and .017-mm orifice) or a No. 211 tip (4-degree fan angle and .011-mm orifice) for more control in confined areas. When spraying, wear protective clothing, goggles and a paint respirator.
Professionals who use special safety gear to walk on the roof will work across it in full-width horizontal sections. But when using a roof ladder, you should apply stain from the ridge to the eaves on each side of the ladder, repeat the process and back-brush before repositioning. If you don’t have gutters, protect surfaces below from drips until the finish is dry.
Inhibit future growth
The best preventative against moss growth is zinc or galvanized flashing, according to FPL. As the metals corrode, they help control moss and fungi for 15 ft. below the flashing strips. Install them (with at least 1 in. exposed to the weather) at the ridge and below any skylights, chimneys or other obstacles that would block the treated water from passing over the shingles below. You’ll need another course 15 ft. down slope (or less), especially on steep roofs or in areas where the problem is severe. The extra measures will be worthwhile if you want to delay your next rooftop experience.