Skip the roofing frustration
Whether you do it yourself or hire a contractor, roofing mistakes can turn what should be a project to boost curb appeal and protect your home into a disaster. In fact, common roofing mistakes, like using mismatched shingles, installing a new roof over an old one, and ventilation missteps, can lead to leaks, mold mildew, higher electrical bills, blown-off shingles, dry rot, ongoing insulation problems, and more. Here, we discuss 30 examples of what can go wrong during a roof replacement, so you can learn what to avoid and watch for.
While you may think you are getting a deal by reusing shingles or buying from second-hand sellers, you are actually setting your roofing project up for big problems. Asphalt roofing is manufactured in batches, so failing to use a consistent dealer (and batch) could leave you with mismatched shingles that create an odd-looking roof. You may also miss out on manufacturer warranties if you are not installing a coherent roofing system.
“If you are doing a simple repair, getting a matching shingle can be tricky,” says Ami Feller, owner of Roofer Chicks in New Braunfels, Texas. “If you are doing it yourself, you can take a sample of what you have to a local supply house. Even then, it probably will not be an exact match.”
It is also worth remembering that shingles can dry out and become brittle over time. So, a spare pack of shingles that has been hanging out in your garage for the past 10 years might not be the best choice, either.
Avoid installing new asphalt roofing over old. While there are some roofing systems that can be applied over an existing roof, this is not the default. It is actually illegal in some places to install a new asphalt roof without removing the old one first.
The problem with just laying new shingles over old ones is that you could be covering up a problem without realizing it. Another big issue with layering shingles is that they can add unnecessary weight that may compromise your roof structure and walls. Instead, it is wise to bring in a roofing inspector to spot weak points or fragile areas during that opportune time when the shingles are off and your roof deck is exposed.
Shingles that do not line up vertically or horizontally with the other shingles near them will be visibly misaligned from the ground. This is an aesthetic and functional problem. Not only does it look sloppy and haphazard, but misaligned shingles also leave gaps in coverage where water can get in. This can create problems with all parts of a roof, as well as cause leaks and roof deck damage, and it may allow shingles to blow off or break, creating even more issues.
Slate is a solid, long-lasting roofing material that can last a lifetime with little to no maintenance; however, since it is a natural material, getting matching roof slates for repairs can be a challenge. In the worst cases, this can make slate roofs look uneven, checkered, spotty, and mismatched. Some contractors combat this by intentionally mixing slate colors or carefully choosing installation order so that slight variations are uniformly scattered.
To prevent mismatches if a few damaged slate tiles must be replaced, consider purchasing non-fading slates when you install a new roof; for semi-weather and weathering tiles, buy extra and put them in an exposed area where they can weather or fade at the same rate as your roof slates.
Your roof decking (also referred to as roof sheathing) is the wood layer that fits over roof trusses and under your underlayment and top roofing layers. While you do not necessarily need to replace it every time you replace your roof, you do need to ensure any roof decking you keep is solid and in good condition. It is a critical structural element, and any weakness in the decking will lead to weakness of the outer layer of roofing itself, causing leaks or worse.
After removing the old roofing materials, you or your contractor need to look carefully at the existing roof deck, watching for holes, dry rot, sags, any signs of previous water damage, or other flaws. You should also verify that it is the correct thickness recommended for your new roofing. If it is not pristine or is too thin, it is better to replace it now to prevent future damage to your new roof.
If you are not a roofing expert, you might not realize that your roof shingles should hang over the edge of your roof, rather than stop right at its edge. This encourages rainwater to drain completely off the roof and not settle onto or into the fascia. Conversely, if your shingles hang over too far, they are more likely to blow off or crack or tear at the long end.
Starter strips, sometimes also referred to as starter shingles, are the first layer of shingles that is laid along the eaves and rake edge of a roofline. This line of specialty shingles seals along the eaveline, helping prevent rain and meltwater from seeping in and under the shingles from the exposed edge. Sometimes installers skip this step, either to make the job go faster or to save a few dollars; in the end, though, that can increase the chance of needed repairs and roof replacement costs.
It is obvious why choosing the wrong length of nails or incorrectly placing roofing nails is a major roofing mistake. Choose nails that are too short, and they will not penetrate the roof decking, allowing shingles to shift and come off. When nails are driven into the wrong place or left exposed instead of being tucked under shingles, they can allow wind to raise shingles or rainwater to use them as a pathway directly into your roof deck or attic, or they can corrode over time, leaving holes in your shingles. That is why it is imperative that nails be placed in the correct locations during roof installation.
Common roofing nail mistakes include the following:
Nails that are too short
Nails with heads that are too small
Nails without barbed shanks
Using too few nails
Using too many nails (four to six per shingle is average, depending on manufacturer instructions)
Driving nails above the self-sealing strip on shingles
Driving nails into knot holes or gaps in the roof decking
Improper nailing patterns
Driving nails in too far, not far enough, or at an angle
Check your attic when you install a new roof. Good attic ventilation is one of the keys to prolonging the life of your new roof. Poor ventilation causes shingles to wear out prematurely, and it can contribute to mold and wood rot in your roof decking, which will compromise your entire roof. One of the top shingle and metal roof installation mistakes is incorrect ventilation. Fortunately, it is easy to have a ventilation expert come in to run a test to let you know how your attic is performing.
Roof ventilation systems are classified as either passive (open vents that harness the power of natural airflow) or active (using electricity or solar energy to power fans that move air out of the attic), and while you need to choose one, you should never have both in the same home. That is because the two systems can compete, disrupting natural airflow patterns and preventing hot, moist air from escaping the attic effectively. This, like other ventilation errors, can lead to heat and moisture buildup, mold and mildew, roof damage, higher energy bills, and overtaxed HVAC systems.
Most cases of overventilation happen when homeowners DIY a roof job or inexperienced roofers try too hard to get ventilation right. Instead of doing their homework and installing the correct type and number of intake and exhaust vents, they get carried away and install too many and in the wrong places. This can mean too many holes in the roof that may eventually leak, cause competing ventilation systems and airflow, and waste money on the wrong type or number of vents.
When roofs are underventilated, they get hot and humid, and that can have dire results. As heat and moisture build up, mold and mildew form, along with dry rot, which can make for unhealthy indoor air quality and permanent damage to your roofing system. Heat and moisture are terrible for roofs, and they can damage all types of roofing materials, underlayments, and roof decking. Insulation can also become waterlogged or moldy, which degrades it and increases energy costs. In the worst cases, your roof decking and supports can rot away, causing structural issues for your roof and home.
Bathrooms can get hot and damp; the answer to this is bathroom fans and exhaust vents that draw moist, warm air up and out of the bathroom. But when these fans are vented into attic spaces, they can encourage heat and moisture to collect there, causing serious damage to roofing and roof supports. The same can be true for clothes dryer vents that go into the attic, rather than directly outside. Instead, bathroom vents should continue up though the attic space and out of the roof via a roof vent.
While kitchens are not as notorious as bathrooms for moist, hot air, hood vents that are routed into and stop in the attic, rather than continuing through the roof and going outside, can cause the same issues. Moist, warm air will encourage the growth of mold and mildew and can damage insulation and roof structure. If you are unsure where your hood fan vents, ask your contractor to check the attic for correct venting before they begin your roof replacement.
It seems obvious—intake vents take air in, exhaust vents let it out. But for some reason, even experienced roofing contractors can switch up the two, leading to poor ventilation and all of the problems it poses. That is why it is important for your roofing contractor (or you, if you are installing your own roof) to understand the difference and take care to install the right vent type in the right location.
Incorrect, missing, insufficient, or damaged attic insulation can cause a roof to deteriorate. When done right, attic insulation keeps hot and cold air from coming through the attic walls and entering the attic space; it regulates the temperature. But if an attic gets too hot, the heat can rise into roofing materials above, warping and damaging the roof deck and shingles. It can also increase snowmelt, which results in shingle-breaking ice dams.
All roofs need an underlayment between the roofing material and the wood roof deck. This underlayment provides a barrier against water and weather, and it can make your roof last longer. If you choose the wrong underlayment for your roof or climate, try to reuse old underlayment materials, improperly install the underlayment, or choose not to install one at all, your roof will face an increased risk of leaks, water damage, mold, dry rot, and other moisture-related problems.
Improper underlayment is also one of the most common metal roofing mistakes. Underlayments are important for metal roofs to prevent heat transfer and to insulate against noise that can come through the roof, including loud rain sounds.
Shingle exposure is the length of exposed shingles between layers. Each manufacturer has a recommended shingle exposure for their products, and it is imperative to follow those directions. Shingles that are installed too close together have too short of an exposure, which can keep water from running off, leading to pooling water or water seeping underneath the shingles. When the exposure is too long, with an excess of each shingle showing, wind can blow up under individual shingles; this causes them to flex, bend, crack, and even blow off.
Unless your roof is flat, your contractor (or you, if it is a DIY job) needs to consider the slope when installing new roofing. That is because different roof slopes require different materials and methods. For example, you can cover flat to low-slope roofs with roll roofing, while pitched roofs are better served by shingles and tiles. If you choose the wrong roofing material or installation methods for your roof slope, you will end up with leaks and damage.
Gutters should never sag, flex, or fit loosely against your roof. They need to be the right size for your area’s weather and they need to hold the weight of rainwater as it flows through and out of the downspouts. If gutters are incorrectly attached to the roof, or if screw placement is wrong, they can sag or come loose. Not only does this look bad, but it can create even worse problems; water may back up and tear off or leave holes in your roofing and fascia. For these reasons, make sure you have correctly sized gutters and that they are installed correctly.
Valley flashing is a V-shaped metal strip that roofers install over the junction where two sections of roof meet. It directs rainwater off the roof and protects against water seeping into the crack between sections. Since roof valleys see a lot of water and runoff during rainstorms and snowmelt, it is very important to have new, solid, secured flashing. If you or your contractor do not secure the flashing correctly, it can allow water to seep down into the roof; over time, this may cause the entire roof to buckle or collapse.
Flashing is a metal, plastic, or composite material that is used as a protective barrier for your roof against water intrusion. It is the defensive line between your roof and serious water damage caused by leaks that leads to rot and mold. Flashing works by directing the flow of water away from your home to keep it from absorbing into the roofing and underlayment.
Flashing accounts for just a small sliver of a total roofing project, but its importance is immense. Bad flashing is one of the biggest causes of water damage in homes. Do not assume that flashing is good for a second round just because it looks fresh. When possible, contractors should always install new flashing to ensure that it will last as long as all of the other new roofing materials that are being applied during the job.
“However, if the flashing is behind the siding or rock work on the home, replacing it might be cost inhibitive and even detract from your home’s aesthetics,” says Feller. “This is a great conversation to have with your contractor—ask them how they are going to handle the flashings, especially on sidewalls, headwalls, chimneys, and skylights.”
Using recycled flashing is bad enough, but leaving out flashing altogether is even worse. When a roof lacks flashing around chimneys, vents, skylights, and other openings in your roofing, water can get in and compromise the shingles, roof deck, and other roofing components. Eventually, this leads to rot, mold, insulation damage, roof truss damage, water damage throughout the home, and foundation issues.
If you live in a climate where it snows in the winter, you need a plan for preventing ice dams. An ice dam occurs when snow melts on your roof and then refreezes, creating a wall of ice that prevents meltwater from draining off your roof. Over time, ice dams and the water behind them can break apart shingles and get through the roof decking in the form of leaks.
Attic insulation and ventilation are major components in preventing ice dams, since warm inside air will heat up your roof, melting snow and creating the conditions for damming. For this reason, new roofing should include a plan for insulation and ventilation systems, along with well-designed gutter systems and even adhesive barriers that strengthen roof edges against damage.
Drip edges are strips, usually made of aluminum, installed on the edge of a roof and meant to direct water away from the home and into the gutter or, if there is no gutter, off the roof. It can be tempting to reuse old drip edge strips from your previous roof; however, even if they look good, that is still a risk. Reusing drip edges can compromise their fit and function, leaving your roof open to water damage.
Even worse than reusing old drip edge material is failing to install one at all. Drip edges prevent water from getting under your shingles and can protect against wind-driven rain. It might seem like skipping this step will save time and money at installation, but it can have long-term ramifications. If you do not have a drip edge, you are risking water damage, mold, dry rot, warping, and leaks over time.
Roofing might look deceptively simple, but it has a lot of complicated, nuanced installation requirements. All quality roofing manufacturers have specific instructions for how to install their products, and you or your roofer need to follow those directions exactly in order for your roof to perform correctly. You can also forfeit warranties if you skip steps or ignore directions. For this reason, you must read and follow directions when installing your new roof, or verify that your roofing contractor knows, understands, and agrees to follow all manufacturer guidelines.
Most cities and towns require a permit for all roofing jobs, but many people do not think about permits when doing DIY jobs because they are used to contractors taking care of that detail. In other cases, homeowners or roofing contractors (including unlicensed operators) try to cut costs by skipping the permitting process. But this is never a smart move; you may be stuck with ramifications like fines, removal of your newly installed roof, or a loss of home insurance if you fail to pull the proper permit.
The perk of doing your homework to find a reputable roofing company is that the crew will show up with documentation of an insurance policy that gives you peace of mind. When proper contractor insurance is not in place, you could be responsible for paying for property damage that occurs during your project. In some locations, if your contractor does not have active workers’ compensation insurance coverage on all of their employees, you can also be held financially responsible if a worker is injured while on your property.
Nobody wants to create new roofing problems with uninformed or improper installation. There is a reason why roofing contractors go through training, apprenticeships, and certifications before they are allowed to touch your roof. Roof installation is hard, complicated work that impacts the integrity of your home's structure.
Each roofing manufacturer uses very specific regulations regarding how their roofs should be installed. Roofing pros know about warranty information, correct flashing techniques, the right number of nails per shingle, and other necessary installation details.
The list above is just a start. There are hundreds of ways a roof replacement can go wrong, from inferior materials and methods, to leaving the roof open too long, to skipping the permit. Be aware that negligence or intentional errors can completely derail the job.
One of the biggest culprits is trying to do work in the most inexpensive way. Reusing materials, buying mismatched or discounted materials that are not part of a cohesive roofing system, or choosing materials that are not the right fit for your roof and climate are sure ways for a roof replacement to go wrong. While it is good to stick to a budget because roof replacement costs can be high, cutting corners is more likely to cost you money and possible heartache in the future.
Not fully understanding the job or details is another common roofing mistake. The person planning the job, purchasing the materials, removing the old roof, and installing the new one must be detail-oriented, with a firm understanding of the exact job and its requirements. One small mistake—such as ordering the wrong nails or incorrect shingle overlay—can compromise the entire job and leave your home vulnerable.
Because installing a new roof is such a hard thing to do right, it is best to let a pro handle this complicated job unless you have experience in roofing. Hire a licensed, insured, experienced, local roofing contractor near you who prioritizes quality and value. Checking references, seeing examples of their work, and asking good questions about their methods and what you can expect from them give you the best chance of getting a reliable, durable roof that is installed the right way.
Whether you are installing your own new roof or hiring a contractor to do the heavy lifting for you, knowing the most common roofing mistakes will better equip you for this project.
