How To Install Metal Roofing Over Shingles The Right Way?

29 August 2025

Today’s topic: How to install metal roofing?

If you’ve been thinking about upgrading your roof without tearing everything off first, you’re not alone. One of the most common questions I hear as a roofer is: “Can you put a metal roof over shingles?” The answer is yes—you can, and when it’s done right, it can save you time, money, and a whole lot of mess.

I’ve spent years working on both residential and commercial roofing projects, and I can tell you there’s a right way and a wrong way to tackle this job. Let me guide you through the process step by step, with a few pro tips and common mistakes to avoid along the way.

Why Should You Consider Installing Metal Roofing Over Shingles?

Metal roofs have gained significant popularity over the past decade, and for good reason. They’re durable, energy-efficient, and they look sharp on just about any home or building. By installing metal roofing over shingles, you:

Save on tear-off costs (no dumpster rentals or labor for removing shingles).
Add an extra layer of insulation, which can help with energy efficiency.
Reduce installation time, since you’re working over an existing roof deck.

That said, this method isn’t right for every roof. Before you start, it’s essential to ensure that your roof structure can handle the added weight and that your local building codes permit this type of installation. Additionally, you may want to consider checking out Cleveland roofing companies, thanks to their reputation and expertise, especially if you are located in the United States.

How To Install Metal Roofing Over Shingles?

So, without wasting time, let’s find out how you can install metal roofing over shingles.

Step 1: Inspect Your Roof Before Doing Anything

Here’s the truth: the success of your metal roofing project depends on the prep work. Before laying down panels, conduct a thorough inspection.

Inspect the decking for signs of rot or soft spots. If your roof sheathing is compromised, it needs to be replaced.
Look for more than two layers of shingles. Most codes don’t allow more than two layers total.
Check flashing, chimneys, and vents for proper installation. Any existing leaks must be repaired before the new roof is installed.

Pro Tip: Walk the roof carefully. If you feel any spongy areas underfoot, you have decking issues that must be addressed first.

Step 2: Lay Down A Moisture Barrier

Although shingles already provide some protection, you’ll want to add a layer of underlayment before installing metal panels. This extra layer protects against condensation that can form under the metal.

I usually recommend using a high-quality synthetic underlayment. It’s lightweight, tear-resistant, and holds up better in the long run compared to traditional felt paper.

Step 3: As An Optional Step, Add Furring Strips

This is one of those “pro versus DIY” differences. Many homeowners skip this step, but furring strips (also called purlins) create a flat, even surface for the metal panels to sit on. They also improve ventilation, which helps reduce moisture buildup under the roof.

Install the strips vertically, spacing them every 2 feet or so.
Make sure they’re fastened securely into the rafters, not just the shingles.

Pro Tip: Furring strips are especially important if your shingles are uneven or curling. Without them, your new metal roof could end up looking wavy.

Step 4: Choose The Right Metal Panels

Not all metal roofing is created equal. The most common options are:

Corrugated panels: Budget-friendly and great for sheds or garages.
Standing seam panels: Sleek look, hidden fasteners, and very durable—perfect for homes and commercial buildings.
Metal shingles or tiles: Designed to mimic traditional roofing but with the strength of metal.

Your choice ultimately depends on your budget, style preferences, and the desired lifespan of the roof. Personally, I recommend standing seam if you’re planning to stay in your home for the long haul.

Step 5: Install The Metal Roofing Panels

Now comes the main event. Installing metal roofing over shingles isn’t overly complicated, but it does take precision.

Start at the bottom edge (eaves) and work upward.
Lay the first panel square with the edge of the roof. If your first panel is crooked, the entire roof will appear uneven.
Overlap panels properly—follow the manufacturer’s guidelines for overlap distance.
Fasten with the right screws. Use screws with rubber washers to seal holes, ensuring they penetrate solid decking or furring strips.
Continue up the roof, checking alignment every few rows.

Pro Tip: Don’t overtighten screws. If the rubber washer is squished too flat, it won’t seal properly and may crack over time.

Step 6: Flashing And Trim Work

This is where many DIY jobs go awry. Flashing around chimneys, skylights, and valleys is critical for keeping water out. Trim pieces at the ridges and edges give the roof a finished, professional look.

If you’re unsure about flashing details, this is the step where you may want to consider hiring a professional. A metal roof is only as good as its weakest point, and improper flashing is the most common cause of leaks.

What Are The Common Mistakes To Avoid?

I’ve seen many metal roofs fail due to simple errors. Here are the top mistakes to watch out for:

Skipping the underlayment. This leaves your roof vulnerable to condensation.
Using the wrong fasteners. Nails or cheap screws won’t hold up—always use roofing screws with rubber washers.
Poor alignment. Once panels are on, it’s tough to fix crooked lines. Take your time.
Ignoring ventilation. Without proper airflow, you risk moisture damage and reduced lifespan of your roof.

How To Maintain Metal Roofs? Tips

Now that you know how to install metal roofing, the next issue is: how to maintain it? One of the perks of a metal roof is its low maintenance, but that doesn’t mean zero maintenance is required.

Inspect screws and fasteners yearly. Tighten or replace any that have loosened.
Keep gutters clean. This prevents water from backing up and damaging flashing.
Trim overhanging branches. Metal roofs are tough, but falling limbs can still cause dents or scratches.
Wash occasionally. A simple rinse with a hose keeps the roof looking sharp and removes debris.

Know How To Install Metal Roofing In 2025!

If you’re handy and comfortable working on a roof, installing metal over shingles is a doable task. But here’s my honest advice: it’s not for everyone. Working on a roof is inherently dangerous, and even a minor mistake can result in significant financial consequences down the road.

As a roofer, I’ve fixed plenty of DIY jobs that started with good intentions but ended up leaking or looking crooked. If you’re unsure about any part of the process—especially flashing and sealing—don’t be afraid to call in an expert.

Installing metal roofing over shingles can be a smart move if it’s done right. You’ll save money, boost curb appeal, and enjoy a roof that could last 40–50 years.

If you’re ready to take the next step, don’t hesitate to reach out to a professional roofer. Whether you just need advice, an inspection, or a full installation, we’re here to help. After all, a roof isn’t something you want to gamble on—it’s what keeps your family, your business, and everything inside safe and dry.

Read More:

Barsha Bhattacharya

Barsha is a seasoned digital marketing writer with a focus on SEO, content marketing, and conversion-driven copy. With 8+ years of experience in crafting high-performing content for startups, agencies, and established brands, Barsha brings strategic insight and storytelling together to drive online growth. When not writing, Barsha spends time obsessing over conspiracy theories, the latest Google algorithm changes, and content trends.

View all posts

Cybersecurity Fundamentals: A Complete Guide For Beginners

Today’s topic: Cyber security for beginners Almost every company that uses computer systems is facing threats coming from the cyber world. If you have data that you keep or you go online, then you are a potential target. Besides, I am well aware that cybersecurity jargon has a tendency to give one a headache. On top of that, technical instructions confuse the business owners and managers who are newcomers to the subject. That is exactly why I made this guide to help you understand the concepts more easily. In this blog, I will help you grasp the main points you have to know. Additionally, I will highlight the main threats to your business today. So, if that’s what you want to know, keep reading! What Is Cybersecurity? Cybersecurity ensures the safeguarding of your digital assets by protecting your systems, networks, and data from any unauthorized access or interruption. Also, according to most experts, the preservation of the CIA Triad should be your top priority when building a security program. And this includes: Confidentiality. Integrity. Availability. So, one can trace any security forecasting made about these three attributes. And TBH, understanding the fundamentals of modern cybersecurity for businesses requires more than just grasping the technical dimensions. After all, security is not merely the concern of the ICT department. Rather, it is a comprehensive risk management objective that needs the contribution of people, processes, and systems combined. The Most Common Types Of Cyber Threats I have often seen beginners ask about what they are actually protecting their organizations against. And that is something most guides on cyber security for beginners miss out on - clarty! The global threat landscape is broad. Nevertheless, a few attack categories account for the vast majority of successful corporate security incidents. Phishing One of the ways phishing works is through sending deceptive messages that appear to come from legitimate sources to exploit human behavior and emotional urgency. For example, criminals can make a message look like it is from your bank and ask your employees to click on a link that contains viruses. They might download a file that carries malware, or give away their corporate login details on websites that are staged to look real but are actually fake. As a result, phishing is still the major way through which attackers break into modern enterprises. Malware And Ransomware Then again, malware aims to use your very computer to extract sensitive data or allow external unauthorized access. Ransomware is a type of malware that can cause significant damage. It works by encrypting files on your computer as well as those on the network. The attackers then ask for a ransom in exchange for the decryption key. In the end, these kinds of cyberattacks lead to long-term standstill of operations, huge financial losses, and serious regulatory punishments across all sectors. Trend Analysis: I strongly advise against paying ransoms. Federal agencies like CISA echo this warning. Paying does not guarantee that you will get your data back, and it directly funds global cybercrime syndicates. Credential-Based Attacks In these attacks, hackers obtain, guess, or purchase valid usernames and passwords. Then, they use them to gain unauthorized access to your internal corporate accounts. Weak user passwords and password reuse across multiple services allow these attacks to succeed. Furthermore, the absence of secondary validation makes your systems vulnerable. Once an attacker gains valid credentials, their behavior inside your network looks completely identical to a legitimate corporate user. Therefore, detection becomes incredibly difficult. Insider Threats Insider threats arise from your own employees, contractors, or trusted partners. They misuse their authorized network access. Sometimes they do this intentionally for financial gain. Other times, they cause harm unintentionally through sheer negligence. I find that data breaches caused by insiders are much harder to detect than external attacks. This happens because the malicious activity blends seamlessly into normal daily business use. Cyber Security For Beginners: Core Security Concepts Every Beginner Should Know Several foundational concepts appear repeatedly across modern cybersecurity guidance. I believe that mastering these principles is essential if you want to build a logical understanding of the field. Defense in Depth This architectural principle states that you should build security controls in distinct layers. If one security control fails, other redundant barriers remain in place. As a result, you limit the lateral damage. If you rely on a single line of defense, like a traditional network firewall, you leave your organization completely exposed whenever that single boundary fails. The Principle of Least Privilege (PoLP) This principle dictates that you grant users, systems, and individual applications only the minimum access rights they need. They should only have the permissions required to perform their baseline business functions. External adversaries consistently exploit over-privileged accounts. They use them to move freely across your network once they establish an initial entry point. Zero Trust Architecture The traditional concept of a secure perimeter no longer works. Hybrid remote work and cloud-hosted data have dissolved that boundary. Consequently, the industry has shifted to Zero Trust Architecture. This framework relies on a core mantra: "Never trust, always verify." Under this model, you never grant access implicitly based on a user's physical location. Instead, you must continuously authenticate and authorize every single request. Patch Management This is about regularly and consistently patching your software, firmware, and operating systems with security updates. Almost all the successful cyberattacks are based on exploiting vulnerabilities that are already known. In most cases, vendors have made public that they have rolled out patches to these security loopholes. When you quickly run after these patches, you drastically lower the chances of getting hit by automatic hacking tools. Security Awareness You must recognize that your personnel are both a critical vulnerability and your most powerful line of defense. When you teach your employees how phishing operations function, they learn why strong passwords matter. Consequently, they can report suspicious activity and contribute meaningfully to your overarching security posture. Building A Basic Security Foundation For Cyber Security For Beginners If you are just beginning to develop your security program, you can deploy a few high-priority actions. They provide massive protection without requiring significant technical expertise or massive capital investment. The NIST CSF 2.0 small business security guide resource is specifically designed to help organizations with little or no existing cybersecurity program begin building a structured approach. I highly recommend using it as your baseline standard. Priority 1: Multi-Factor Authentication (MFA) First, you must enable MFA across all corporate accounts. Focus especially on email, administrative dashboards, and remote access systems. MFA disrupts standard credential-based attacks. It requires a secondary verification factor, such as a mobile authenticator app token, which remote hackers cannot easily replicate. Priority 2: Automated Patching Second, you need to configure all operating systems, applications, and browsers to update automatically. Automated update settings minimize the manual burden on your internal staff. In addition, they guarantee that you close critical vulnerabilities before threat actors can target them. Priority 3: The 3-2-1 Backup Strategy Thirdly, having regular backups of your essential data is a must. Let me explain why I always stick to the classic 3-2-1 formula: 3 Copies: You need to have at least three different copies of your business data. 2 Media Types: Backups should be done on two separate types of media, for example, a local server and cloud storage. 1 Isolated Location: Make sure you have one copy kept completely offline or very separate from your main corporate network. If you fully isolate your backups from the main environment, ransomware cannot reach or encrypt them. Thus, you ensure a reliable recovery route. Understanding Risk In Cyber Security For Beginners: The Foundation Of Smart Security Many beginners mistakenly believe that cybersecurity is an all-or-nothing race to achieve absolute, unbreachable protection. In commercial reality, the goal is always risk management. You must identify the specific threats that matter most to your distinct organization. Then, you assess the operational consequences and make informed decisions about where to invest your resources. Evaluating Risk Levels Not every business faces identical risks. To allocate your resources effectively, I suggest looking at how impact and likelihood intersect: High Impact / High Likelihood: A ransomware attack hitting unpatched public servers. You must invest defensive resources here immediately. High Impact / Low Likelihood: A targeted, state-backed espionage attack against a small local retail store. The probability is too low to justify a massive budget. Low Impact / High Likelihood: Routine spam and automated bot probing. These are highly common, but you can easily mitigate them using standard filters. Low Impact / Low Likelihood: Minor issues that require minimal ongoing monitoring. For example, a localized small business handling limited customer contact information faces entirely different liabilities than a healthcare provider managing patient medical files. A small creative firm manages risks differently from a large bank handling daily digital payments. People's risk levels aren't fixed. They shift when teams go remote, new tech is used, market steps are taken, or rules change. A security plan built for today's setup will leave big holes in a year unless checked and improved regularly. The Human Element In Cybersecurity Technical controls are essential, but they cannot entirely compensate for a weak internal culture. If your employees use weak passwords, succumb to basic social engineering, or bypass security rules for temporary convenience, your technology will fail. I regularly review the Verizon Data Breach Investigations Report (DBIR). Expert analysis of fundamental security priorities in this report finds that about 60% of confirmed breaches include a human factor. That factor covers mistakes, weak passwords, or being tricked by advanced social engineering tactics. Therefore, you should invest in continuous security awareness training. Run realistic phishing simulations. Finally, build a transparent culture where your employees feel comfortable reporting accidental clicks. This approach will make a material difference in reducing your organization's exposure. Read Also: Cybersecurity Threats In Asset Tracking And Strategies To Mitigate Data Security In The Cloud: Strategies For A Safe Migration

3 Top Tips To Help You Increase The Lifespan Of Your Ratchet Straps

Tie-down straps are an invaluable part of any cargo hauler’s arsenal. I can assure you that they are excellent for securing loads efficiently and safely. Additionally, they’re also easy to use on just about anything. That said, using your tie-downs every day usually means they face the toughest weather conditions. You know, these can often lead to extensive wear and tear. Now, some of you might buy your Ratchet straps online. Or, some of you, like me, have a local supplier. No matter what, it’s essential to always invest in quality tie-downs and accessories. You must know how to increase rachet straps lifespan. Additionally, you must ensure proper care practices. They are very important for ensuring that your straps function efficiently. In fact, this will ensure that they last a long time. This post takes a closer look at the most effective ways to keep your ratchet straps in mint condition. What Are Ratchet Straps? Okay so are you planning a move or a quick trip? If yes, I have got to tell you something. If you are moving a few items around town, you may not be all that familiar with ratchet straps. In fact, I am expecting you not to know how they work. Essentially, ratchet straps, or tie-downs if you prefer, are heavy-duty straps. These are designed to restrain all types of loads during transport. For the most part, the straps are designed using a strip of long, robust webbing material such as polyester or nylon. Then, Ratchet mechanisms and end fittings complete the rest of the ratchet strap design, such as: Loops Hooks If you’re a first-time ratchet strap user, here’s what you need to know: Firstly, you have to place the loose end of the tie-down strap into the metal mandrel part of the ratchet. Secondly, you need to gently pull the strap securely through the slot in the mandrel. Thirdly, you ned to tighten the strap. You can do this by pulling the slack out. Then, you need to gently crank the ratchet. This important for you to reach the desired tightening. Also, you must keep the strap in line with the other one. This one step will ensure avoiding locking or tangling. In addition, you need to tighten the strap to secure it. Additionally, you have to lock the handles down. At the end of the trip, reverse these steps. This will help you to avoid damaging or tearing the straps. Finally, you must ensure your straps are dry. Also, you need to check if they are undamaged before you put them away for storage. How To Increase Rachet Straps Lifespan: Some Real Tips Now that you know what the product is, the next probable question will be: How to increase rachet straps lifespan? Well, I am here to tell you just that! Quality ratchet straps will last a long time if you take proper care of them. Fortunately, there’s no complex maintenance attached. Here are a few tips to help you care for your tie-down straps. 1. Always Inspect Your Ratchet Straps Before Each Use The first tip to know is to inspect your ratchet straps before every use. This is because little issues, such as damaged hardware or frayed webbing, can affect the integrity of the straps. This can lead to them snapping or tearing loose during the trip. The general rule of thumb is that if 10% or more is torn, the strap should be replaced. Check for damages in the following ways: Hardware: Check the ratchet and hooks for bends, deformation, and rust. Hooks can be bought separately if they need to be replaced. Webbing: Inspect the webbing material for tears, fraying, or signs of excessive wear. Stitching: Run your hand over the stitching and check for broken threads. Labels: Quality straps should have a Working Load Limit (WLL) tag. Check that this is legible and intact. 2. Straps Should Be Kept Clean The frequency and types of cargo you’re loading can leave your straps dirty. In fact, it can even damage them. This is because oil, dirt, and chemicals can seriously degrade webbing material over time. So, not only does this reduce flexibility, but it also affects the strength of the straps. You should aim to clean your tie-downs and all their accessories after each use. Additionally, this rule applies especially if you’ve used them for loads containing chemicals. Here’s what you need to know: Always use a solution of warm water and mild soap to remove debris and dirt. Additionally, you must avoid harsh solvents. Also, you cannot use any chemicals as these can weaken polyester fibres. You need to gently scrub the webbing with a soft-bristled brush. This will effectively remove stubborn dirt. Finally, you have to rinse thoroughly. Also, you must air-dry it completely before storing. 3. Proper Storage Is Crucial If you are wondering how to increase rachet straps lifespan, this step is very important. Once you’re done with your straps for the day, it’s essential to store them properly. Improper storage exposes the webbing to UV rays and moisture, which can weaken or damage it. Here’s how you should do it: Firstly, you need to roll the straps neatly. This step comes right after cleaning and drying. You have to roll the straps to prevent kinks and tangles. Then, you need to store it in a dry and cool place. I suggest that you always avoid storage areas. This is where the straps will be exposed to dampness or direct sunlight. Finally, I will suggest that you opt for storage containers or bags. You need to use good-quality air-tight storage containers. Additionally, you can go for sealable bags to keep your straps safe and dry. Also, I feel like it’s a good idea to place them in a cupboard. How To Increase Rachet Straps Lifespan: Explained No matter how often you’re using your ratchet straps, it’s always a good idea to use our care tips to keep them in mint condition. This not only reduces the likelihood of having to buy new straps every time you need to use them, but it will also give you peace of mind that your straps will remain efficient every time you need to use them. This will keep your cargo and everyone around your vehicle safe! Read Also: The Importance of Packaging Design in Small Business Success Incredible Ways To Minimize Network Downtime For Business Top 3 Dropshipping Marketplaces: Pros And Cons Of Each

Importance Of COVID-19 Coverage Under Group Health Insurance Policy

India has come a long way from fighting COVID-19 to rising above it. However, just after the lockdown was lifted and companies start urging employees to return to the workplace, a concern remains: who would protect employees against COVID-19 at the workplace? That is why COVID-19 coverage under group health insurance policy. Before the pandemic, companies often purchased group health insurance without this coverage; however, COVID-19 changed everything. Thus, it becomes crucial to understand the exact benefits of this coverage for employees and organisations. COVID-19 Coverage Under Insurance Policy COVID-19 is a communicable disease that spreads through air and human contact. Although the spread of COVID-19 is now containing and people are more aware of precautionary measures, the disease has not eradicating. That is why, to safeguard the welfare of employees who are most exposed to COVID-19, the Insurance Regulatory and Development Authority of India (IRDAI) made it mandatory for every organisation to provide COVID-19 coverage under their group health insurance policy. Benefits Of COVID-19 Coverage Under Insurance Policy Here are some of the benefits of COVID-19 coverage under the group health insurance that employees can take advantage of. IRDAI Mandatory As per the orders from the Insurance Regulatory and Development Authority of India (IRDAI), it has been made mandatory to provide COVID-19 coverage to every employee of an organisation. Without this coverage, companies are not allowed to start their in-office operations. Medical Expense Coverage Under the group health insurance policy, employees are covered for medical expenses relating to COVID-19. It means that all financial expenses incurred, from diagnostics to treatment and medicines, will be covered by the policy. Employee Dependent Coverage Several group health insurance policies extend their coverage to employees’ dependents; the same applies to COVID-19 coverage. The policy provides COVID-19 coverage to the employee's spouse, children, and dependent parents. Provides A Sense Of Security COVID-19 is a life-threatening disease, and providing coverage for this disease gives employees a sense of security. They feel safe and secure coming to the office premises to do their work. Employee Loyalty When employers buy medical insurance for their employees, they establish a good rapport and loyalty in their minds. This loyalty reflects in the work of employees and the productivity of their outputs. Inclusions And Exclusions Of Coverage When we refer to health insurance for COVID-19 coverage under insurance policy, we need to know what's covered and what's not. It is always best to know this in advance to avoid unpleasant surprises at the time of a health emergency and ensure that you make the most of your policy benefits. Just like any other medical insurance policy, the COVID-19 cover also has some inclusions (what is included) and exclusions (what is excluded). Let me break these down to you in detail so that you have a crystal clear understanding well in advance, even before you make a claim. Inclusions The inclusions detail all the medical expenses and services you'll cover for with your COVID-19 cover. The following is what you can generally expect: Pre And Post-Hospitalisation Cover - The COVID-19 cover provides coverage for expenses incurred during pre- and post-hospitalisation treatment. It includes expenses such as diagnosis, doctor’s appointments, and medicines. Pre-Hospitalisation: The costs of medical examinations, specialist visits, COVID-19 tests, and medication before hospital admission are eligible. For example, if you had to undergo blood exams, a PCR exam, or a CT scan to confirm the infection, the cost would be eligible. Post-Hospitalisation: You can be ill for a few days, and you will require follow-up consultations, medication, or physiotherapy. These are also covering for a few days after discharge (likely 30 to 60 days). Second Opinion - The COVID-19 coverage under the group health insurance policy also provides coverage for expenses related to a second medical opinion. For example, if you are not satisfied with the diagnosis from your first doctor’s visit, you can always seek a second medical opinion without worrying about finances. You may consult with another physician or specialist to confirm your treatment regimen. The cost of this consultation, either face-to-face or by telemedicine, is paid for. Daycare Treatment Cover - The group health insurance policy also provides coverage for expenses incurred during COVID-19 daycare procedures. Even some antiviral drugs, oxygen therapy, or even other minor procedures associated with COVID can be done without overnight admission. Your group health insurance cover for COVID-19 pays for these charges just the same way it would pay for inpatient care. Ambulance Cover - In case you need ambulance services from your resident to the hospital or from one hospital to another recommended hospital, then the COVID-19 coverage will also cover its cost. Exclusions While the cover is extensive, there are certain conditions and medical costs that are not included. Understanding these exclusions allows you to have realistic expectations and avoid claims rejection. Pre-Existing Diseases - The COVID-19 coverage under the group health insurance policy is limited to treatment for coronavirus disease 2019 (COVID-19). If the insured is suffering from a pre-existing illness, there will be no coverage for treatment of that illness. Maternity Or Newborn Cover - There is no coverage for maternity or newborn treatment under the COVID-19 cover of the group health insurance policy. Waiting Period - Several health insurance policies have a waiting period; similarly, there is a 30-day waiting period for getting coverage under COVID-19. Thus, if you make any claim before the waiting period, you will not get a claim. Summing Up The COVID-19 pandemic has changed the way the entire medical and insurance field operates. Before the pandemic, group health insurance policies typically provided coverage for most medical emergencies; however, with the addition of COVID-19 coverage under insurance policies, the policies have become more comprehensive. As employees, one must check for this coverage in their group health insurance policy. Employers have the responsibility to find a trusted insurer, such as TATA AIG, which includes this coverage in their group health insurance, to comply with the IRDAI orders. Moreover, organisations can buy business insurance online, such as fire and burglary, marine, and workers' compensation, to safeguard their other assets.

How To Install Metal Roofing Over Shingles The Right Way?

Why Should You Consider Installing Metal Roofing Over Shingles?

How To Install Metal Roofing Over Shingles?