Repair, Replace, Revive
A roof restoration can be as simple as replacing a single damaged slate or as difficult as removing, repairing and reinstalling the whole roof, depending on the material and how it’s been maintained.
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By Marieke Cassia Gartner
Hand-split cedar shakes and sidewall shingles were used on this residence. Replacing individual cedar shingles is not a problem since all cedar will weather to the same gray. Photo: Celia Pearson, courtesy of Cedar Shake & Shingle Bureau
Roofing comes in a variety of materials, each with its own set of potential problems for a restoration or renovation project.
In general, an evaluation of any type of roof depends on whether the project is a restoration or renovation, and “whether it has any historical significance and what the cost is versus the benefit of repair versus replacement,” says John F. Toates, AIA, principal with Peter Zimmerman Architects of Berwyn, PA. Visual assessment can be the first step, but a professional roofer experienced in the type of material the roof is made of should be hired for a more thorough evaluation.
The three basic product types for wood roofs are hand-split and resawn shakes, shingles and taper-sawn shakes. Wood roofs can last from 20 to 100 years, depending on the quality of the wood. “Old-growth cypress and red cedar have life expectancies of up to 100 years,” says John G. Waite, partner with Albany, NY-based John G. Waite Associates, Architects PLLC, “while new-growth cypress will last 20 years at most.” As a result, thicker shingles are used to counter the lesser quality of the new wood. Toates says, “We have moved over the past decade to 15 years from working with wood roofs with ¼ - to 3/8-in. shingles to 5/8- to 7/8-in. shingles that have the same lifespan as the old ¼-in. ones.” Dales Frens, AIA, of Frens & Frens, LLC, in West Chester, PA, also uses thicker shingles in his work. “Blue Royals, at ¼ in. thick, got less than 20 years of wear 20 years ago. Now we use 5/8- or ¾-in.-thick shingles that will last 30 or 35 years.”
Craftsmen from The
Durable Slate Company work to install new flashing and replace
slate on a ridge and valley of the
former Fleischmann estate in Ohio.
The building is to be established as an arts center by the Greenacres Foundation. Photo: Ed De Long
Before the lifespan is spent, however, many problems can arise, including aging and weathering, as well as those resulting from the lesser quality of a product and the quality of the installation.
Wood quality is usually transparent. “You can tell the quality of product by looking at it,” says Lynn Christensen, director of operations at the Cedar Shake & Shingle Bureau, “if you know your grading rules.
Lower-grade products will have features such as excessive flat grain, knots or pieces that are too short or too thin.” Shingles should be split with the grain perpendicular to the surface, so that moisture won’t enter the grain and cause rotting. Poor installation can also be seen easily, for example with exposed fasteners such as nail heads or incorrect spacing between each shake or shingle.
Like other roofs, wood can be partially repaired if the damage is localized. Cedar roofs, for example, are easy to partially repair. “You can take a shingle out, put in a new one, nail it properly and be done,” says Christensen. “And you don’t have to worry about matching color. Cedar will always weather to the same gray.” Waite adds, “If the roof is fairly new, then just one individual shingle can be replaced. If you have localized problems with an old-growth wood roof, you can repair it, such as the flashings or a few cracked shingles. If the problems are widespread, the inclination would be toward total replacement.” Generally, he says, when the wood shingles start to fail, total replacement will be necessary. For example, for a restoration done on Mount Vernon by Waite’s firm, the architects used sunken logs that were hundreds of years old to replace the wooden roof. “Because the logs were loaded with natural enzymes they will last 100 years or more,” he says.
As for maintenance, if the roof has a lot of debris, such as leaves from overhanging branches, a professional contractor should sweep it twice a year. “You don’t want debris building up,” says Christensen. Gutters and downspouts should not be clogged, and ventilation should not be blocked, which would cause heat and moisture to build up in the attic. Ridge caps, which usually take the brunt of a storm, should be checked after inclement weather to make sure that there are no loose pieces that can fall.
In addition to performing routine maintenance on this graduated roof of Vermont purple, unfading green and weathering green slates, The Durable Slate Company installed a matching roof on the addition to the rear of the house. The unusual thickness of these slates means that they will last for an exceptionally long time. Photo courtesy of The Durable Slate Company
“Some companies offer a topical treatment for maintaining cedar roofs,” says Christensen. “These should be approached with caution, as some are reputable but others are overly aggressive in their claims. The Cedar Shake & Shingle Bureau only recognizes pressure-impregnated fire-retardant-treated cedar shakes and shingles for Class A, B and C roofing systems. Pressure-impregnated preservative-treated products are also available. Each type of pressure-impregnation treatment is locked into the cells of the wood at the factory and will not leach out after rainstorms. A topical maintenance product likely will need to be re-applied every three to five years, not every 10 as some claim.”
Mistakes are widespread in specifying wood roofing. For example, “If an architect is trying to reduce the exposure of the product to create a pattern for design purposes, for example reducing the exposure of a 24-in. shake to 7½ ins., more product must be purchased,” says Christensen. In addition, “We get many questions from architects about coatings and finishes,” she says.
Slate and Tile
In terms of durability, slate and tile are good choices. “Clay tile usually lasts well over a century,” says Carey Warner, marketing manager with New Lexington, OH-based Ludowici Roof Tile. However, both can suffer damage – slate usually from weather and tile from impact, whether from tree branches or walking on it. Slate is susceptible to breakage from ice, and soft types can erode and suffer from chemicals such as acid rain. Tile is vulnerable to cracking during freeze-thaw cycles, although “normally it is the underlayment or decking that goes bad before the tile,” she says.
Visual assessment is possible and should include looking for missing slate or tile or accumulated pieces on the ground, says William H. Johnson, III, AIA, project architect with Peter Zimmerman Architects. “Is the slate flaking? Is the slate thick or thin? Thin slate won’t last as long as thick,” adds Toates. Clay tile will wear consistently, so damage tends to be of a mechanical sort. “The clay tile might be too flat or installed too tightly to account for expansion-contraction,” says Frens. “Sometimes, the cracks are invisible, so you have to touch or pull on the tile,” he warns. “We never repair tile. We only replace it,” adds Andy Moore, inside sales coordinator with Ludowici Roof Tile, “since there is no way to repair a tile properly. To determine the condition of the tile, we conduct ASTM 1167 standard testing to determine if the tile is still of Grade 1 quality. If so, you can lift and re-lay, that is, take the tile off, repair the underlayment, nails, screws, etc. and set the original tile back up on the roof.”
Top and bottom: This roof, on a house restored by Peter Zimmerman Architects
of Berwyn, PA, features handmade English clay tile. The original roof featured red clay tile, which couldn’t be replicated, even with glazing, so a new roof was installed and the old tile was sold as salvage. Photos: Erik Kvalsvik
“You have to take into account how old the slate already is,” adds Mike Chan, president and CEO of The Durable Slate Company in Columbus, OH, “and how long it was meant to last. In addition, a roof’s lifespan depends on which direction the roof faces because of sun damage and how steep the roof is [steeper roofs last longer because they shed water more quickly].” Pennsylvania Black slate, for example, will last 75 to 100 years, he says, while Vermont slate can last 150 years or more. But the biggest culprit, says Frens, “is painters walking around on the tile and cracking it.”
Problems usually occur around the metal flashings, adds Waite. Ferrous metals will rust (flashings as well as nails), and copper can be damaged by microscopic pieces of slate breakage. Slippage often occurs with slate and tile roofs, which can be the result of galvanized nails that have failed. If this is the condition of the entire roof, the entire roof may be removed and refastened with copper nails that won’t corrode or fail. “All the flashings must be redone in this case as well, so their longevity is equal to that of the roofing material,” Toates says. “You can take a tile roof off completely to replace the flashings and put in a new underlayment,” Waite adds, “but I don’t recommend that with slate since it can break so easily.”
Instead, a slate roof can be removed in stages. “We’ve worked on both clay tile and slate roofs where we have repaired the material and removed several courses to get access to built-in flashings,” says Frens, “especially at built-in gutters but also at valley flashings and dormers. In that case, the original roofing shingles were removed and reinstalled.” Still, there’s always a certain amount of breakage, “so we have to order a limited amount of custom tile with clay tile or a source for shingles similar to the original with slate. We have the roofer either scatter the new tile or slate so no pattern is formed or, if the replacement is on some inconspicuous part of the roof, we use the original slate or tile where they’re visible, and the new where they’re not.”
Both slate and tile are easy to partially replace. If the damage is isolated, spot repairs can be done, says Toates. “If the roof is in good condition and you can match the materials seamlessly, there’s no reason not to keep the original material,” he says. “First, identify exactly what the original material is and where it’s from – that way you can get replacement material of the same type, thickness and color range, indigenous to a certain area.” Waite adds, “It’s harder to get replacement tile than replacement slate. Most companies that were active at the turn of the 20th century are out of business now. You can have the tile custom made, but that can be fairly expensive and tedious. However, Ludowici still makes tile like they did 100 years ago.” Warner says, “We manufacture tile that matches the existing roof. We can instantly age the tile to give it the look of a 100-year-old roof. The new tile will last the life of the building.”
The roof on this residence (top) was restored with Ludowici’s Colonial Tile in Black Mist, which is distinguished by a highly textured surface and irregular, rough bottoms, closely resembling slabs of tree bark (bottom). Photo courtesy of Ludowici Roof Tile
Weather damage and the type of slate installed affect the repair as well. “If the slate is pockmarked from hail, for example, you know it’s very soft and needs to be replaced,” says Chan. “If 10 to 20 percent of the roof is damaged and the damage isn’t all in one place, then you might as well replace the entire roof because the possibility of cracking slate next to the slate you’re repairing is high.” Cracked slate is not only the result of the weather, however. “Slate is attached by nail here,” he explains. “In Europe, slate hooks are used. When slate is installed by nails, it doesn’t give very much, so if it doesn’t settle correctly, the slate can crack. Another condition for total replacement is if the slate is so soft that a nail can be pushed halfway through it. In that condition, it will absorb so much water that constant wetness will occur, which will cause severe problems.” For tile, “If a significant amount fails ASTM 1167 Grade 1 quality, the entire roof should be replaced,” says Moore.
There are special techniques for replacing slate or tile. When they’re installed, they are always nailed in a way that the slate course above them covers the nails. “If you’ve lost one or have to replace an individual slate, you have to use a tool that’s called a slate ripper, which is a flat bar that has two hooks at the end, with an offset handle,” says Frens. “You put it underneath the slate and you can use hooks to grab and pull out nails to which you have no direct access. Then you can remove the top half of the slate and put the new slate in. Instead of putting in pre-punched holes, a single hole is put in at a location that will be in the center of the slate, one-third down from the top, which will be an exposed place in the joint in the course above. After the slate is nailed in with an exposed nail, a strip of copper or lead-coated copper 3 ins. wide by 10 ins. long is pushed up in the joint to cover the nail. A good roofer can really conceal a replacement. Sometimes, roofers will use a bright shiny metal like stainless steel or white aluminum that you can see, which can ruin the look of the roof. For that reason, dark metal is better.”
Slate can last up to 150 years with the proper maintenance. “There’s a church that was built in the 1860s that still has its original slate roof,” says Waite. “Every year they replace the broken slate, which stops any larger problems from occurring.” An annual review each spring by a professional should include checking gutters and downspouts. “Water is the enemy,” says Toates. Damaged and cracked slate or tile should be replaced and the ridge sealed properly. “This may seem costly,” he adds, “but it’s nothing compared to major repair down the line. Cracks lead to more cracks, which lead to leaking, which leads to plaster damage, rotten wood and mold. All this could be avoided if one broken slate is fixed when the damage occurs.” In addition, slate should be checked before winter as well. “A chip here and there is not a big deal,” says Chan, “but look for big holes or weathering all in one place, like four pieces of slate lying in one place in the gutter. Most holes occur not in the crease of a valley but where water runs from the slate onto the valley, right on the edge of the slate.” The best thing you can do, he says, is stay off the roof.
Chan has seen his fair share of mistakes made in repairing slate. “I would not use caulks to patch slate together,” he says. “Sometimes, people just glue half-broken slate. Caulk doesn’t last long, and it gives enough so it can form a crack that comes apart enough to draw in water and hold it there.” Another problem he has come across is tar shoved up between slate and metal in a valley. “If a slight break occurs between the tar and the metal or the tar and the slate, it will draw in water, and when it fails, it fails miserably so that water will just pour into a house,” he adds. Other issues in replacement concern using the correct type, size and thickness of slate and putting it back together the way it was done originally. “When the repair is done, it should look like nothing much was done,” he says. “And, of course, old slate should be used on an old roof, because new slate won’t match the faded look of the old.”
Craftspeople from Pittsburgh, PA-based NIKO installed this new batten-seam and flat-lock copper roofing for a building in Bloomfield Hills, MI. Copper doesn’t need to be painted, as it will oxidize to a self-protecting finish. Photo courtesy of NIKO Contracting
A repaired roof will last as long as the original tile or slate was meant to last. But the flashings won’t necessarily last as long, although they can last from 50 to 75 years. “At 50 or 60 years old, start inspecting the flashings every five years to make sure they’re not wearing out,” says Chan. “Two things occur when they do: steel flashings will rust, and acid water and pollutants in the air will erode and wear a hole through copper.” If the flashings are steel, they can be painted every 10 years or so with high-quality, oil-based paint with rust inhibitors to counter the damage, he adds.
A great variety of metals are used for roofing, including lead, tin (or tin-plate iron), copper (flat and standing seam), sheet iron, terne plate and zinc. Each material has special conditions, but generally there are four reasons that metal roofs fail: corrosion, mechanical breakdown, weathering and connection failure (bolts, rivets, pins and welding). “Corrosion is the major cause of deterioration of architectural metals,” says Waite. Exposure to the atmosphere, heat, moisture and pressure can transform metals into oxidized versions of themselves, all allowing the roof to fail. Abrasion, expansion-contraction, fire, “creep” and overloading are all mechanical ways in which a metal roof can fail. With ferrous roofs, the problem is rust.
Inert metals will often corrode to a self-protecting finish, such as the desirable green patina often found on copper. Other metals need to be protected with paint or other coatings, such as galvanic or terne ones. “Generally, the success of the coating depends upon surface preparation, type of primer and finish coating, and the method of application,” says Waite. “Paints reduce corrosion by permitting only a sluggish movement of ions through the paint film lying between the metal and corrosive environment.” Frens adds, “What can become the biggest problem is the maintenance coatings that have been put on the roof. The worst thing is if someone used a tar or asphalt coating. Then it would be impossible to solder it, resulting in the removal of entire areas.”
One can see obvious defects such as chipped paint, rusting, patches done incorrectly or too much tar, but with the inert metals, one would have to look more carefully for damage since the corrosion won’t show through. “The first thing you look for is coatings and patches,” says Nicholas D. Lardas, owner of Pittsburgh, PA-based NIKO Contracting. “If it’s an old tin roof, it should have some sort of paint on it; whereas a copper roof shouldn’t be coated. If the roof is loaded with coatings or patches, that’s an indication that there’s been a lot of leakage and the roof is probably well past its useful life.”
However, what seems to be true is not always so, says Waite. “If you have a ferrous metal roof, iron plating or iron sheet plated with tin or terne, oftentimes it’s very resistant to corrosion, so if the damage is localized it can be cleaned off and replated,” he explains. “If the roof is steel sheet beneath terne, it’s much more susceptible to corrosion.”
This breezeway’s aged copper roof matches the one on the front entry porch of the house to its right, which was restored by Peter Zimmerman Architects. Photo: Lawrence Williams
To combat damage already there, a metal roof may be patched if the damage is localized. Copper roofs can have new material spliced into them relatively easily, says Frens. Or, if necessary, one can replace the metal roof in stages, he adds. “For instance, if the valleys and gutters are heavily worn they can be replaced without replacing the rest of the roof, because metal won’t weather differently on different parts of the roof [as long as it’s been kept painted].” Lardas adds, “If the roof is generally in good repair, taking into account its age, we’ll investigate problems like leakage and determine whether it’s a maintenance issue or something else. For instance, an old tin roof still might get cracking at the solder seams, and while you can’t do a long-term repair, you can clean it and use sealing tape to try to extend its life.” While some repairs can be done with metal, such as resoldering, painting or patching, Lardas says that it’s more common to do minor repairs or full replacement – not much in between. “There has to be a way to tie the new into the existing material,” he says.
“If the metal has deteriorated to a point where it has actually failed, duplication and replacement are the only courses of action,” Waite adds. “If you see rusting, you’re better off replacing.” Of course, it depends on how much rust there is and deciding whether or not to solder in new material, says Frens, which is usually possible. If replacement is necessary, there are guidelines offered by the Sheet Metal and Air Conditioning Contractors’ National Association (in its "Architectural Sheet Metal Manual") on how to separate similar metals so corrosion won’t occur. “If installed properly, those issues shouldn’t arise,” says Toates. In addition, corrosion can occur from the top or the bottom. “If there’s a lot of condensation under the roof, corrosion will occur, and there’s nothing that can be done for that long term,” says Lardas.
Another problem is design that does not allow for expansion and contraction. “That’s the biggest mistake I’ve seen,” says Lardas. The result will be broken seams, and the only long-term solution is replacement, since allowance for proper expansion has to be designed into the system. “It’s difficult to retrofit a roof for that,” he adds. “The new terne roofs have large pan sizes, and tin plate roofs have 10x14-ft. or 14x20-ft. pans, which are good because they leave lots of room for expansion and contraction. If a terne plate is 8 ft. long, expansion and contraction can become a problem,” says Waite.
Copper often fails because of improperly soldered joints. “In that case, you can take off the corroded product and resolder it,” he says. “Some historic roofs were laid with seams of lead paste, which can be duplicated with a high-performance sealant, which is better than solder because it allows for more movement.” Lead roofs are the most durable and can last for centuries. “In Europe, roofers take up the lead sheets that have been there for hundreds of years, cast them again and put them back on,” he adds.
In order to replace a metal roof, the roof is ripped apart in sections. “Water tightness is always the main issue,” says Lardas. “You assess the decking and if it needs repair, it needs to be done immediately. Temporary waterproofing of some sort is used while the work is being done, and the new metalwork is installed as you go.”
Restoration projects often involve unique roofs. “Jefferson used his own invention in hanging tin plate on Monticello and at the University of Virginia,” says Waite. “Tin plate isn’t made anymore, so in order to restore it, a new material that looks like it and has a similar longevity had to be found. Terne-coated stainless steel turned out to be metallurgically similar to the old tin plate and was used.”
In order to maintain a metal roof, the most important thing is to keep the paint coatings in good condition. “Repainting should be done every five to seven years,” says Frens, “depending on the coating and how well it was applied.” Inspection is also important, since a piece of slate from a slate roof, for example, could puncture the metal roof of a porch, a situation Frens has seen a lot. Lardas adds, “A brick from a chimney may fall on the roof and puncture it, but you won’t know right away because the underlayment will prevent the leak from coming in the house. Eventually, however, it will cause premature failure, which is why inspection semi-annually is important.”
“You also want to make sure the gutters and downspouts are clean and running, with no build-up of debris, snow or ice,” adds Johnson. “Those things can cause corrosion or damage. For instance, oak leaves sitting in water cause acid to leach out and eat through copper. Even if the roof is installed correctly, if conditions somehow change – if the house was insulated later and plugged the path of ventilation – or the soffit vent is plugged, dry rot will be the result.” In addition, sealants should be checked where there are flashings, seams and joints should be checked for premature failure and any minor problems should be taken care of immediately, says Lardas. Waite concludes, “If the seams aren’t soldered, a metal roof can last a century or more.”
Traditional roofing materials vary with regions, budgets and periods, but all can claim longevity as a great virtue. With care, a restored roof can have its life extended even further and retain its historic character.
Click here for a list of suppliers of roofing and roof specialties