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33 of Your Toughest Roofing Questions Answered

Covering Your Roof Issues

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Putting a safe roof over your head isn’t necessarily a one-time deal. Shingles stain, condensation collects, and high winds carry roofs wherever they please. That’s where the TOH crew’s knowledge and your sweat equity enter the picture. Here, we cover roof-related scenarios to help prevent future mishaps, like a missing roof.

Spot a Failing Roof

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Q: How do you know when an asphalt shingle roof needs replacement? Are there clues to look for before telltale water stains appear on our plaster ceilings?

—Pat, Plymouth, Minn.

A: Tom Silva replies: There are several clues, and the biggest one is age. If your roof is more than 20 years old, there’s a good chance it’s due for replacement. But younger roofs can fail too, so it’s a good idea to inspect a roof at least once a year. Don’t use a ladder, though. Binoculars are easier and a lot safer, and you can spot most problems from the ground.

Here’s what to look for: numerous shingles that are lifting up, cracked or missing, with curled edges, or with smooth dark areas, which indicate that the protective granules have worn off. Also, go into the attic on a sunny day and, with the lights off, check the underside of the chimney and the stack vent. If you see little pinhole spots of light, the flashing is shot—another indication that the roofing might not be in good shape.

While you’re in the attic, scan the underside of the roof sheathing for any new signs of water staining since the last inspection, as well as any soft or moist spots, which tend to show up after a heavy rain. If these problems are widespread, it’s a sure sign that you need to call a roofer.

The Importance of Roof Pitch

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Q: Everything being equal (ventilation, shingle type, climate, etc.), which roof will last longer: one with a steep pitch or one with a shallow pitch? Seems to me a steep hillside erodes more quickly than a low slope, so I’d think that roof shingles would wear out more quickly on a steeply sloped roof.

—George, Oglesby, Ill.

A: Tom Silva replies: It’s difficult to say. On one hand, a steep roof is less likely to collect leaves and other debris that hold moisture against the shingles and invite the growth of moss and algae. On the other hand, that same roof in an unshaded area facing due south will take the full brunt of the sun, which is hard on any roof.

Actually, factors other than pitch have a greater effect on shingle durability. The side facing your worst weather typically fares worse than the leeward side. Likewise, a roof system that isn’t vented properly and allows heat to build up beneath the roofing has a shorter life than one that is vented.

Up Under the Roof

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Q: We have a major leakage problem and are getting a new roof. What is the best underlayment to protect the valleys in my roof from leaking: ice and shield guard, metal flashing, or double rolled shingles?

—Jerry, Collinsville, Ill.

A: Tom Silva replies: First, your roofers should lay down an ice and water shield over the entire roof. Made of polyethylene and rubberized asphalt, this membrane prevents water that has slipped under shingles from penetrating to ceilings below. The valleys should then be covered with metal flashing or weaving. I would also recommend two layers of the ice and water shield on the lower section of the roof (along the eaves), around chimneys and beside the dormers.

Roof Plan, or Roof Scam?

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Q: My friend has a new 9,000-square-foot home and has had problems with the roof leaking. The roofing man and two painting guys have told her that the caulk on her roof was the source of the problem. They told her that she should have it checked every six months for cracking and possible replacement because the caulk doesn’t last long. I have never heard of this before and was wondering if they are pulling her leg or if this is a real problem?

—Shari, Park Hills, Mo.

A: Tom Silva replies: I’ve got to tell you, it sounds like they’re pulling your leg. You shouldn’t need any caulking on a roof with proper flashing. You need a second opinion.

Roof Flashing Damage

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Q: A friend recently mentioned in passing he thought some of the “flashing” on my roof looked as if it were in rough shape. Can you explain exactly what roof flashing is?

—Britney, Fort Worth, Texas

A: Tom Silva replies: Flashing is just material—usually aluminum or galvanized steel—that’s used over joints in roof and wall construction to prevent water seeping in and causing damage. Depending on the style of your house’s roof, you probably have it in the valleys, around the chimney and pipes, and around any dormer windows or skylights. Most damage shows up either in flashing that’s deteriorating due to weathering and oxidizing, or in flashing that has come loose.

I can’t say for sure without seeing your roof, but most flashing problems can be patched or repaired fairly easily. Professional roofers typically cut and shape their own flashing from sheet metal, but the most common flashing pieces also come pre-formed and can be applied without much difficulty using caulking or roof cement.

A word of warning: Because of the danger involved, I never recommend people do work on roofs unless they are professionals or they’re used to being on roofs and are familiar with the one they’re working on. So if your flashing needs any significant repairs, consider hiring a contractor to do it for you.

Lightweight Roof Protection

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Q: Why is felt paper used in roofing?

—Bill, Pleasant Hill, Miss.

A: Tom Silva replies: Felt paper is typically used in most roofing as a release between the two materials, wood and asphalt. Years ago, it was used on roofs because when sap would come out of the wood, it would break down the “backside” of the asphalt shingles and cause them to deteriorate, which isn’t a problem anymore. But I also think of it as a lightweight protection against any damage on a stormy day. Let’s say a shingle or a tile should break in a storm. If the roof has a layer of felt paper over it, it has got some protection that will resist the driving rain at least for a little while. But you need a different weight of felt depending on the type of roofing product you’re using.

Windows on the Roof

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Q: What is the difference between skylights, sky windows, and roof windows?

—Edith, Ashland, Ore.

A: Tom Silva replies: Not a whole lot. Any glazed assembly that admits natural light through a roof can be called a skylight. Some manufacturers use the term “roof window” to describe a relatively large skylight placed low enough that you can see out to the landscape. So I guess if you can see only sky, it’s a skylight, but if you can see sky and land, you call it a roof window. Also, roof windows are generally big enough to qualify as means of egress in case of a fire. That’s seldom if ever the case with a skylight. The term “sky window” is not as common as the others. At least one manufacturer uses it to describe huge glazed areas in a flat roof. Most skylights are meant for roofs with a slope of at least 15 degrees.

Shingle Stain Removal

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Q: My roof is streaked with black stains. Is there anything I can do to get rid of them? The shingle manufacturer says that staining isn’t covered by the warranty because it doesn’t affect the performance of the shingles.

—W. Howard, Warwick, R.I.

A: Tom Silva replies: The dark streaks are a type of algae that lives off the minerals in some types of roof shingles. Algae thrives in moisture, so it’s seen most often on shaded or north-­facing roof slopes that don’t get a lot of direct sun.

While it’s true that algae doesn’t damage roofing, it sure looks bad. To get rid of it, use a pump sprayer to wet down the roof with a mix of one part bleach to two parts water. Bleach will damage foundation plantings, so rinse them well with fresh water before you start and after you’re done.Then scrub the surface gently with a soft window—washing brush mounted on a telescoping extension pole. Don’t use a pressure washer, which could damage the shingles. Also, do this work from the safety of a ladder or from the ground, not by climbing on the roof.

To stop the algae from returning, mount zinc or copper strips near the roof ridge. Then, every time it rains, the water that washes over the strips’ exposed edges will pick up ions from the metal and inhibit the algae from regaining a foothold. And when it’s time for a new roof, look for shingles with algae—resistant granules and the best warranty you can find.

Amateur Roofing

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Q: Is installing a metal roof something an amateur can do?

—Maryann, Charleton, Mass.

A: Tom Silva replies: It depends on just how amateur the amateur is. The safety risks of working on a roof should be pretty obvious. I don’t personally recommend that anybody work on a roof who isn’t either a professional, or familiar with the roof from being on it on a regular basis.

The task of installing a metal roof seems pretty simple in the field, at least until you come to working at the ends and around chimneys and skylights, valleys and hips. When an amateur is putting in a metal roof there are a number of things that can go wrong and cause the roof to fail. Nail the aluminum incorrectly, for instance, and your roof will definitely leak. So if the building you’re talking about is a tool shed, that’s one thing; just be careful. If it’s your home, you’ll probably be better off letting a professional do the job.

Installing Emergency Roofing

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Q: Any hints for temporarily protecting a storm-damaged roof? We sure could have used this information during the hurricanes we had last year.

—Nora, Pensacola, Fla.

A: Tom Silva replies: Anybody who lives where hurricanes or tornados are a regular threat needs to know a little about emergency repairs. But that same know-how can be helpful in other parts of the country, too. It doesn’t take much for a heavy tree limb to snap and take out part of a roof, for instance.

Basically, what you want to do is cover the damage with a woven plastic tarp that is held in place with 1×3 wood strips. Here’s how I do it. First I roll one end at least twice around a long 1×3, then screw it to the undamaged side of the roof. The 1×3 “roll” should be against the roof so it won’t collect water and debris. The rest of the tarp goes over the ridge and down the other side of the roof several feet beyond the damage. Then I roll the opposite end of the tarp around another 1×3 and screw it to the roof sheathing, roll side down. Now it’s just a matter of using more 1x3s and screws to hold down the tarp’s sides. They don’t have to be rolled in the tarp. A “blue roof” isn’t pretty, I’ll admit, but it will keep the weather out until someone can repair the damage.

Having said that, this type of emergency repair is best left to someone who has the equipment and skill to do it safely. Roofs are treacherous, particularly when wet, and tarps are slippery even when dry. You don’t want to be wrestling with one in high winds, either. Better to submit a claim for property insurance than to have your family submit a claim for life insurance.

Overhanging Shingles

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Q: The roof shingles on one side of my house hang over the gutters so much that birds have built nests under the overhang. I tried to cut the shingles back using tin snips but haven’t had much luck. What should I do?

—Keith, Merrick, N.Y.

A: Tom Silva replies: It sounds like someone set the shingles way too far over the edge the last time your roof was done. Shingles should extend past the drip edge of the roof only by about ½ to ¾ inch. Once you determine how much overhang you need to cut off, mark your cutline with chalk and a straightedge. On some roofs, you might be able to use the exposed butt edges of the roofing course as a guide to keep your cuts straight.

How you cut them depends on what kind of shingles they are. With asphalt or fiberglass shingles, a sharp utility knife will do the trick. Just support the edge of the shingle on a block of wood as you make each cut, and change blades frequently. For wood shingles, use a ­circular saw or reciprocating saw fitted with a short metal-cutting blade—its small teeth will make a smoother cut than a wood-cutting blade. Be sure to hold the recip saw at a low angle—almost horizontal—so that the blade doesn’t jab your gutters or cut the brackets.

Holding Down the Roof in High Winds

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Q: My daughter lives in hurricane country in a 15-year-old stucco house. Can she install hurricane clips to prevent her roof from blowing off?

—Don, McKeesport, Pa.

A: Tom Silva replies: Those galvanized metal straps and clips that strengthen the connection between walls and rafters really do help to hold a house together in high winds. But it will be next to impossible to reach those spots from the attic. The only way to retrofit hurricane clips in most houses is by cutting out a section of the siding and the wall sheathing at every spot where a rafter rests on a wall or taking off the roof sheathing at the eaves.

Here’s an easier option: Go up into the attic and run a bead of construction adhesive alongside each rafter where it meets the plywood roof deck. That simple measure will roughly triple a roof’s resistance to being torn off by wind.

Eggs on an Asphalt Roof

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Q: Not long after we moved into our home, some wise guy threw eggs at our asphalt shingle roof. I went up there and scrubbed with every cleanser I could think of, but all I got was a bad manicure. What should I do about this unsightly mess?

—Carrie, Grand Junction, Colo.

A: Tom Silva replies: Egg residue should come off just fine if you flood the area with water while the egg is still wet. But if it gets a chance to dry, or worse, if it gets baked on by the sun, the job isn’t as easy. I’d try soaking the area with water, then spraying it with a nontoxic, biodegradable cleaner such as Simple Green, which was originally formulated to remove protein stains. Let the cleaner soak in for a while as you keep the area moist, then gently scrub the area with a soft-bristle brush. Working with cleaners and water on a roof will make surfaces slippery, however, so be very careful.

When you’re done, the color of the roofing may be noticeably different, but there’s nothing you can do except wait it out. Maybe it will blend in over time.

Two Roofs are Not Better Than One

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Q: I have an old tract house with composition roof shingles. I need to re-roof but the roof has two layers of shingles on it already. Do I have to have them taken off? Also, which rate or weight of composition shingles is best to use?

—Irene, Riverside, Calif.

A: Tom Silva replies: Yes, you need to strip the shingles. I don’t like to shingle over any old shingles, but one layer is acceptable. Two is not. A single layer looks better, lasts longer, and won’t put any unnecessary extra weight on the roof.

As to which shingles to use, the longer the warranty, the heavier the shingle and the greater the cost. You want to look for the best warranty you can afford.

Old Concrete Roof Tile Replacements

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Q: My house is a 97-year-old Victorian with a concrete-tile roof. It was installed in 1929 to replace the original cedar shakes and has weathered hurricanes like a champ. How can I find matching replacements for some of the missing and damaged tiles?

—Patricia, Beaumont, Texas

A: Kevin O’ Connor replies: A roof more than 75 years old? No wonder you want to keep it. To find an answer for you, I called Rick Olson, technical director at the Tile Roofing Institute. He says that you should look on the back of one of your tiles to see if there’s a manufacturer’s name cast into it. If so, then you can check the list of U.S. roof-tile manufacturers on the Institute’s website, tileroofing.org. If there’s no name on the tile, or the company isn’t listed, perhaps you’ll find similar tile patterns by going to each company’s website. If not, you may be able to find a company that will custom-make the ones you need. You can also check with companies like thetileman.com, which sell salvaged roofing tiles, or search the Web for overseas suppliers; many tile profiles in this country were inspired by European designs. Importing tiles might seem expensive, but it probably will cost less than having new tiles custom made or installing a new roof.

Snow Guard for the Roof

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Q: Our house sits only 11 feet from our property line, and our neighbors’ house is so close to the line that their gutters are almost right over it. Last year, they added another story to their house and installed a metal roof. Now, when the ice on their roof begins to melt, it slides past their gutters and sails into the side of our house where our bedroom is. Can you please help us?

—Lisa, Austin, Texas

A: Tom Silva replies: I’ve never encountered that problem, but there is a straightforward solution. Ask your neighbors to install a snow guard on their roof near the eaves. These guards effectively halt roof avalanches and hold the ice in place until it melts. The type of guard that best suits your situation has two or three pipes mounted parallel to the eaves and a screen on the pipes to catch flying ice.

Insulating a Roof

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Q: For the last four years, my wife and I have been building a house. She decided on open beam ceilings in the living room, so we put up insulation. But, before we could put up the Sheetrock, winter came. From the heat and the cold mixing, we have condensation between the insulation and the roof. If I put the Sheetrock up, will that stop the dripping, or do I need roof vents?

—Sean, Corbett, Ore.

A: Tom Silva replies: When insulating any roof, you need an air space of at least two inches between the underside of the roof sheathing and the top of insulation. Proper vents can be stapled to the roof sheathing to create an uninterrupted airflow. The soffit and ridge should also have venting. Install a good vapor barrier under the insulation—on the warm side—making sure there are no holes. Any seams, if needed, should be overlapped by at least 16 inches. Foil taping or polyurethane caulking the seams won’t hurt. The insulation should be R-30. (R-value refers to a material’s ability to resist the transfer of heat. The higher the R-value, the more insulating power the material has. ) Make sure you don’t compress the insulation, which makes it less effective, if it doesn’t fit correctly in the space. Cut a new piece instead.

Ridge Vents on Low-Slope Roofs

Q: I plan to reroof my early-’60s ranch house and am concerned about ventilation. The house now has three gable vents, with soffit vents in every rafter bay front and back. When I reroof, I want to add a ridge vent, but my roof only has a 4:12 slope. Will that be a problem?

—John, Toledo, Ohio

A: Tom Silva replies: Ridge vents are great, but I’d avoid them in this case. Your roof has a fairly low pitch, and snow (or rain) could blow into the attic through the vent. So unless you’ve noticed signs of ventilation problems, such as ice damming in the winter or roof shingles bubbling and curling from overheating in the summer, I think you should stay with your existing arrangement.

By the way, 4:12 is about the minimum slope suitable for asphalt or fiberglass shingles. To improve the weather protection, I’d reduce the maximum exposure of the shingles from 5 to 4½ inches, and I’d use six nails per shingle instead of the standard four.

Frosty Roof Nails

Q: The last couple of times that I’ve been in my attic when the temperature is really cold, I’ve noticed ice on the nail tips sticking through the roof sheathing. Do you know why? Is there anything I should do about it?

—Stasia, Wood-Ridge, N.J.

A: Tom Silva replies: What’s happening is that warm, moist air from inside your house is seeping into the attic and the moisture is condensing and freezing on the cold steel. And yes, you should do something to stop the seepage because it can reduce the effectiveness of your insulation and encourage mold growth.

There are three steps to solving this problem. First, seal off any openings for air to leak into the attic. Maybe a bathroom fan isn’t venting outside or the pull-down attic stairway needs weatherstripping or the light-fixture boxes aren’t sealed. A home-energy specialist with a thermographic imaging device can pinpoint many small leaks you can’t see.

Second, try reducing moisture levels in the house by turning on exhaust fans when bathing and vent fans when cooking.

Third, make sure the attic is well ventilated so that any moist air that gets past your defenses has a way to escape. Soffit and ridge vents are more effective ventilators than fans, and they don’t use any energy. If you already have these vents, make sure they aren’t being blocked by insulation.

Leaky Porch Roof

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Q: We purchased an 84-year-old two-story house that has a 40- to 50-year-old back porch on the ground floor. The porch roof leaks where it meets the side of the house. Are there any easy solutions, other than reroofing the entire porch?

—Lou, Newport News, Va.

A: Tom Silva replies: It’s always tricky to pinpoint the exact location of a leak. It may appear to originate in one area, but water is sneaky and moves in unexpected paths. So before you jump into this job, try to determine where the leak is coming from. If the porch has a finished ceiling, for example, remove a few boards and check the underside of the roof sheathing for water stains—they may help pinpoint the leak’s location. In the case of a low-pitched roof, you may have no alternative but to remove all the roofing just to track down the problem.

Chances are, the leakage is probably due to the flashing, not the roofing material itself. Damaged, corroded, or improperly installed flashing is a common problem at this location (and a lot of other locations, too). If the roofing material is in good condition, you may have to remove an area of siding as well as some of the roofing to replace any damaged flashing. (Generally, the only reason to remove all of the roofing would be if it’s nearing the end of its useful life anyway.) A capable roofing contractor should be able to make this repair for you.

Resist the temptation to turn the problem over to a handyman with a bucket of tar. You might save some money in the short run, but slathering roofing tar on the flashing doesn’t really fix the problem, and can actually accelerate corrosion by trapping moisture between the tar and the metal.

If it does turn out that the roofing is shot and has to be removed, you should have the flashing replaced at the same time. There’s no point trying to protect a new roof with old flashing.

Fire-Retardant Cedar Roof

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Q: I’m reroofing with red cedar shakes treated with a fire retardant. They have a class C fire rating, the minimum required by state law. We’d like to keep them looking light and new as long as possible. But mostly we just want to preserve them and maintain their fire resistance. Any suggestions?

—Raymond, San Jose, Calif.

A: Tom Silva replies: Just one: Forget about keeping your roof looking like new; wood is going to turn gray no matter what you do. As for fire resistance, do not apply any coating that claims to be a fire retardant. Shingles that are certified as fire-retardant will be permanently protected from fire. As for preserving them, the main thing is to keep the roof clean. An annual sweeping (or blowing) removes pine needles, leaves, and other debris that can accumulate on the roof and trap water against the wood. Pruning overhanging tree branches will help reduce the debris and discourage the growth of moss, another surefire killer of wood roofs. There are any number of products that claim to prolong the life of a cedar roof, and little agreement about their effectiveness. Even the Cedar Shingle & Shake Bureau doesn’t come right out and recommend anything. It simply suggests that if you’re going to put them on, you should at least enlist the services of a reputable contractor with a solid record locally. According to the bureau, the most suitable products will be formulated specifically for wood roofs, and contain a UV inhibitor, a water repellent, and/or an EPA-registered wood preservative. Before you apply anything, check with the company that made your shakes to be sure it’s compatible with the fire retardant.

Roof with Ridges

Q: The roof on my five-year-old cottage is plagued with little ridges. The house is a timber-frame structure covered with 6-inch-thick structural panels filled with urethane insulation. It was built in wet-weather conditions and the timbers were green when assembled. Do you think that caused the problem?

—Scott, Portsmouth, N.H.

A: Tom Silva replies: What’s happening is that moisture vapor inside the house is getting between the ends of the roof panels because they weren’t sealed properly with foam. When the vapor hits the roofing felt, the felt expands, which in turn pushes up the shingles. Problem is, the felt doesn’t flatten out even when it dries, so the ridges don’t go away. Heavier shingles may help to keep felt from pushing up — but then again, maybe they won’t. And even if they do, the moisture may eventually cause the panels’ OSB sheathing beneath the felt to rot.

The solution is to strip off the shingles and felt and inject spray foam into the joints through small holes drilled every 8 inches. But first hire a company with thermographic imaging equipment (your local utility can probably recommend one) and have them take pictures of your roof so you know the location of all the heat leaks; moisture vapor follows the same paths. Then, after the gaps are filled, have them take pictures again, to make sure nothing was missed.

One more thing: Before you reroof, add some ventilation. Nail lengths of 1×3 strapping facedown to your bare roof. Run them from peak to eaves with their centers spaced 16 inches apart, cover with ½-inch sheathing and builder’s felt, then shingle. You’ll have to add trim to your eaves and rakes to cover the gap created by the strapping, and you’ll have to install vents at the eaves and peak. When you’re done, this roof-on-a-roof will keep the underside of the shingles cooler and the top side of the panels dry.

I know this isn’t the news you wanted to hear, but I’m afraid there isn’t a cheap fix. If you haven’t already, get in touch with the builder and the panel manufacturer. Perhaps the manufacturer has a warranty you can take advantage of. Or maybe the builder will want to maintain a good reputation (or avoid a lawsuit) and will cover or defray the cost of putting things right. Just be glad you caught the problem early. I once saw a house where all of the panels had to be removed due to a lack of joint sealant; the sheathing was just rotting away.

Ridge Vent

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Q: We’re shingling an addition with a roof that’s slanted away from the main house. The roof meets the aluminum siding on the main house. We want to vent it but can’t use a ridge vent. Is there something we can use to fill between the siding and the roof and allow ventilation without letting in water?

—Elaine, South Easton, Mass.

A: Tom Silva replies: There is a vent system that is made for that type of application, where you have a roof that meets a side wall. You cut a slot in the roof, and one row of shingles will come out and under to become flashing. Then your siding comes down and hides that piece. So it’s basically a ridge vent cut in half.

Heating Cables for Gutters

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Q: Last winter, we had a serious problem with ice clogging our gutters. And every time it melted a bit during the day, the overflow would spill onto the walkway and driveway and refreeze at night into a sheet of ice. How can we stop this from happening?

A: Tom Silva replies: One way is to run electric heating cables inside the gutters and downspouts. Turn the cable on during snowy, freezing weather so the water drains away and stays off your walk and drive. Be sure to use cables with thermostatic controls so they don’t overheat or run up your electric bill.

But these cables only treat the symptom of a bigger problem: inadequate roof ventilation. In other words, the heat escaping from the house is getting trapped under the roof and melting the snow, even when the weather is below freezing. That meltwater ends up refreezing in your gutters.

A roofing contractor can install the ridge and soffit vents that a properly ventilated roof should have. But if you can’t get this work done before winter, try placing a small box fan in the attic to cool the underside of the roof. Face it towards the area of the roof that gets warm, and run it whenever there is any snow on the roof. That’s a lot less expensive than installing and operating heating cables.

Fake-Slate Shingles Update

Q: In the October 1999 issue of This Old House, there was an article about the new products used on Dick Silvas TV project house in Billerica, Massachusetts. At the time, Dick said he really liked the recycled-rubber shingles on his roof—the ones that look like slate. I’m thinking about installing them on my house and wonder how his are holding up.

—George, Rainier, Wash.

A: Tom Silva replies: Dickie still likes his “rubber” shingles and says he’d use them again. (They were actually made of a recycled synthetic rubber called EPDM, and plastics.) “Next time, though,” he says, “I’ll install snow guards.” Like slate, the surface of his shingles is relatively smooth, so snow slides off suddenly in great clumps, clobbering gutters, porch roofs, and unsuspecting passersby. Pad-type or rail-type guards will hold the snow in place, away from the eaves, so it can slowly melt. You can add them to almost any kind of roof, including asphalt shingles, but they’re much easier to install during the roofing process. Just so you know, the manufacturer now makes these shingles out of recycled TPO (thermoplastic olefin), a material that is more durable and stable and has more UV inhibitors than the old formulation. These new shingles are also available in five colors.

Sod Roof Basics

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Q: I would like information on putting on a sod roof. Do you have information or good sources that I can look up?

—Gloria, Cook, Minn.

Tom Silva replies: I’ve never done a sod roof, but your biggest worry will be moisture. Make sure you install waterproofing (like an ice and water shield) that prevents condensation inside the house, and insulate underneath the roof with the foam insulation. Taking these steps will create a thermal break and keep heat and cold from being transmitted rapidly, which can cause condensation, or even leaking or ice dams.

Roofing Nails That Missed Their Target

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Q: In replacing my wood-shingle roof with cement-tile roof, I noticed that the nailer sometimes missed the trusses when attaching the sheathing. I’ve heard that if I leave them they may work their way through the underlayment and cause leaks. Should I worry about these nails?

—Susan, Weston, Fla.

A: Tom Silva replies: By all means yes! Whenever a nail misses its target, it should be removed.

The installer of the roof shouldn’t have left them there. So if possible you may want to contact the contractor who installed your old roof. If that’s not an option you’re going to have to have your new contractor get those nails out.

Sources for Old Roofing Products

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Q: I’m building an addition to an early 1930s one-story home with a hip roof. The existing house has a metal-tile roof with a stamped pattern. I’d like to match the new roof to the old one, but I can’t find a source anywhere. What does This Old House do in a situation like this?

—Neal, Charleston, W. Va.

A: This Old House replies: Locating a source of materials to match what’s already on an old house is a real detective job; it’s time consuming and sometimes frustrating. But it’s been our experience at This Old House that, more often than not, we find what we’re looking for. Your search will be tricky because basic building materials, particularly those on the exterior of a house, are often regional specialties, and they’re not likely to end up in architectural salvage lots. So, like any good gumshoe, first make sure you have a sample or a good closeup photo of what you’re looking for. Then show it to every every old roofer, every hardware store, and every building-material supplier you can find. Check with local or regional preservation agencies. Post a photo on an Internet discussion board devoted to house restoration. Look under one of the roofing tiles for identifying names or markings—and launch a Web search. Get in touch with an industry group like the Metal Roofing Alliance or the National Roofing Contractors Association; they may be able to put you in touch with an expert who will know exactly who made the tiles on your roof and whether they are still being made. When we can’t find a matching material no matter how hard we look, we sometimes find a craftsman or manufacturer who can make new pieces to match the old. Custom runs are expensive, but they can be a cost-effective alternative to complete replacement of the old material. Good luck, and enjoy your search. You’re bound to meet a lot of interesting people along the way.

Dealing with a Mossy Roof

Photo by Kristine Larsen

Q:

What, if anything, should I do about all the moss that’s growing on my roof?
—Dorothy Plummer, Dingmans Ferry, PA.

A:

Tom Silva replies: Moss holds moisture against shingles, shortening their life. It also catches debris—twigs, leaves, dirt—that makes the moisture problem worse. But before removing the moss, grab a pair of binoculars and take a good look at your roof. If you see shingles with surface cracks, small blisters, curled-up edges, or areas where the surface granules have worn off, you probably need new roofing. But if the shingles are in good shape, here’s how to get rid of the moss.

First, take these precautions: Spray water on all the plants under the section of the roof you will be working on or cover them with plastic tarps. The 50-50 mix of water and bleach that’s used to kill moss can also kill or damage any foundation plantings it drips on. Also, because the roof will become very slippery when you spray the moss with the bleach mixture, stay off the roof and on a ladder during the entire process. An extension ladder with a roof standoff provides a secure platform.

Apply the bleach solution with a pump sprayer until the moss is saturated, then wait 15 minutes or so to rinse the roof thoroughly. If your foundation plants aren’t covered, rinse them, too. Now wait a week or two for the moss to dry up. If you can, get on the roof to brush it off. If not, the dead moss will eventually wash away.

To prevent the moss from returning, install zinc or copper strips near the roof ridge, above the areas that tend to get mossy. Rain washing over the strips will leach out metal ions and send them down the roof, preventing new moss from taking hold. You can find these strips online at zincshield.com. Also, trim any overhanging tree branches as much as you can. Moss thrives in the shade that trees provide and the debris they drop.

Wha to Do with Old Roof Sheathing

Photo by Kolin Smith

Q:

We plan to replace the roofing on our 100-year-old house with architectural asphalt shingles that can stand up to the occasional hurricane we get around here. While we’re at it, should we also take off the roof’s original board sheathing, which is still sound, and replace it with plywood?
Ed and Peggy Simmer, Suffolk, VA

A:

Tom Silva replies: There’s no need to remove the board sheathing. It actually adds strength to the roof and makes it easier for roofers to do their job. Just have them nail any loose boards tight to the rafters. Then they can cover the entire roof with ½-inch plywood sheathing.

Make sure the new plywood sheets are placed so that their short edges land over a rafter and there’s about a 1/8-inch gap around each sheet to allow them to expand. In hurricane country, plywood should be nailed every 6 inches into each underlying rafter using galvanized, ring-shank, 8d common nails, such as the HurriQuake nail made by Bostitch. Anything less and your roof could blow off in a storm. The underlayment and shingles have to be applied with similar care, following the requirements laid out in the local building code.

Stripping Roof Paint

Photo by © Randy Duchaine/Alamy

Q: Is removing latex paint from a copper roof something I might be able to do myself?

—David, New Harmony, Indiana

A: This is a big job requiring a lot of material and a lot of hard work. Although if the copper roof is in good shape and you want to expose it, it could well be worth it. However, it’s just not something that is necessarily worth trying to tackle yourself. An alternate option: get a price from a professional paint stripper on doing the job professionally. It’s important to be sure you’re dealing just with latex paint and that there is no lead paint to remove. Also, as always, use extreme caution when doing any work on your roof, especially if your experience is limited.

For more on exterior paint see: All About Exterior Paint

Getting Algae and Moss Off the Roof

Q:

What causes the mold on my roof? How can I get rid of it? How can I keep it from coming back?

— Trudy, Muskegon, Michigan

A:

This Old House replies: The black mold-like stains and streaks that appear on roofs, particularly light-colored asphalt shingles, is actually a blue-green algae (Gloeocapsa magma). Commonly found in climates with warm, humid summers, it does no damage to the roofing, but it certainly does looks bad.

You could replace all the roofing with new shingles dark enough to disguise the staining, or with shingles laced with copper granules, which are lethal to algae. But that would only make sense if the shingles were worn out.

The less expensive solution is to spray wash the roof with a 50 percent mix of water and bleach to get rid of the algae. (No pressure washers, please. They’re likely to damage the shingles.) Just be sure to wet your foundation plantings first, and rinse everything in clean water when you’re done. Plants don’t like bleach, and wetting them with plain water first protects them.

To keep the algae from coming back, insert 6-inch-wide strips of zinc or copper under the row of shingling closest to the roof peak, leaving an inch or two of the lower edge exposed to the weather. That way whenever it rains, some of the metal molecules will wash down the roof and kill any algae trying to regain a foothold on your shingles.

You can probably see this same principle working on roofs in your neighborhood. Look for chimneys with copper flashing; the areas directly below the flashing will be free of any algae stains.

The strips also work on roofs suffering from moss buildup. Just scrub it off first with a brush, then bleach as above.

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