Metal Roof Over Shingles Problems: 8 Things You Need to Know

Installing a metal roof over shingles is a popular option in Canada, especially in provinces like Ontario and Alberta, where homeowners want durability without the mess of a full tear-off. This approach can save time, reduce labor costs, and even provide extra insulation.

But it also comes with challenges — from structural strain to moisture issues. In this guide, we’ll cover:

✅ Advantages of metal over shingles,
✅ Common problems to watch out for,
✅ Solutions that minimize risks,
✅ FAQs Canadian homeowners ask.

👉 Ready to see if this method fits your home? Get your Free Estimate today.

Why Choose a Metal Roof Over Shingles?

While it’s a practical option for many, there are specific metal roof over shingles problems you should be aware of. We usually decide that we will go with a metal roof instead of shingles because it’s more convenient, more efficient and less expensive. Here are the main reasons this approach works:

Cost Savings

Homeowners often ask about metal roof over shingles problems, especially when weighing costs against long-term durability. You save on labor and disposal from shingle removal and lower the cost of the project. While cost-saving, this method can lead to metal roof over shingles problems if not done correctly.

Time and labour cost are reduced, and this is a realistic choice for a lower-budget homeowner.

Faster Installation

Since the shingle layer is already applied, the work is done in a short amount of time, and the project can be finished faster.

Perfect for homeowners that need protection immediately or who have a project deadline.

Added Insulation

Installing a metal roof over shingles can be efficient, but understanding common metal roof over shingles problems is crucial for a successful project. If shingles are left intact, they add an extra layer of heat and noise insulation that can make your home more energy efficient.

This can be especially useful in places where the temperature is high.

Environmentally Friendly

Leaving the shingles on eliminates construction waste from ending up in the landfill, which is a greener option.

Reuse the current roof structure, it saves the project as much ecological resources.

These benefits alone are why a metal roof over shingle roof is a nice choice, but you’ll also need to know what you can expect when doing so to make sure you get a long lasting solution.

metal roof over shingles problems starts with understanding the challenges

Metal Roof Over Shingles: 8 Main Issues

Before committing to this roofing method, it’s important to evaluate the potential metal roof over shingles problems that might arise. Although shingles are the benefit of having a metal roof, there are some problems that homeowners should understand. From moisture issues to structural concerns, this guide addresses key metal roof over shingles problems you should consider.

Structural Concerns

Metal roof over shingles problems can impact your home’s integrity. Adding metal to a layer of shingle just adds extra weight to the roof system. Metal roofs are light in comparison to other roof types, but when multiple roof layers are stacked together, they strain older or compromised roof decks. This may result in structural failure in the long run, especially in dwellings that weren’t built to carry this load.

Trapped Moisture

Knowing the potential metal roof over shingles problems ensures you’re prepared for any challenges during installation. The biggest hazard when you leave shingles up is the possibility that water will get caught between the shingle and the metal roof. This can happen if your shingle roof is leaking or if ventilation is bad. Microbial, mould and rot growth could be caused by confined moisture that can compromise the roof deck and other supporting structure.

Uneven Surface

Curled, cracked or old shingles are going to provide an adobe basis for the metal roof. This makes installation more difficult and may cause visible defects (waviness, sags) in the finished metal roof. Uneven finishes also destroy the watertight bond of the metal panels and increase the chances of leaks.

Decreased Longevity

A metal roof’s lifespan will be impaired if it’s laid over shingles and the bottom layer is already ruined or moisture-ridden. In the long run, these problems can affect the functioning and the life of the metal roof and you may need to repair or replace it sooner than anticipated. If you’re planning to install a metal roof, knowing the metal roof over shingles problems can help you make an informed decision.

Ventilation Issues

Keeping a roof properly ventilated can save any roofing from heat infiltration and condensation. If you simply stick a metal roof over shingles without venting it, heat and moisture will sit on the roof and cause energy waste and damage to the roof deck. If there is not enough airflow, space between shingles and metal panels will cause wear on both.

Warranty Limitations

There may be certain types of installation requirements by the manufacturers of metal roofs for their warranties to hold. : Putting a metal roof on top of shingles that is not up to these requirements will void the warranty and you will be held liable for any future repairs or replacements. Remember to read the instructions of the manufacturer before you try it.

Noise Amplification

And while metal roofs are meant to be quiet, their lack of a flat, well-insulated base will make you more loud during the heavy rains or hail storms. This is especially true if your existing shingle layer has gaps or voids that aren’t good at keeping noise out.

Aesthetic Challenges

When you add a metal roof on top of an existing shingle roof, it can change the look of the roof and give it rolls or an uneven appearance. This won’t affect functionality but can affect curb appeal especially in contemporary or luxury home architecture where a professional finish is desired.

For a long-lasting roof, it’s important to address common metal roof over shingles problems during the planning stage. If you manage these potential issues during the planning stage, you will prevent a lot of them and still get an install job done right that offers the best of both worlds.

How to Avoid These Problems

✔ Full Tear-Off
Best long-term solution. Exposes the roof deck, removes hidden damage, and maximizes lifespan.

✔ Underlayment or Battens
Creates a flat surface, improves ventilation, and reduces moisture risks.

✔ Hybrid System
Partial tear-off in problem areas + new underlayment. Balances cost savings with safety.

✔ Professional Installation
Hire experienced roofers who follow Ontario and Alberta building codes and manufacturer guidelines.

Metal Roof over Shingles Problems:

Aspect	Benefits	Costs
Cost Savings	– Eliminates tear-off and disposal expenses, reducing project costs.	– Potential for higher long-term repair or replacement costs due to underlying issues.
Installation Speed	– Faster installation process without removing shingles.	– Faster installation may overlook detailed inspections or prep work, increasing future risks.
Insulation	– Adds an extra layer of thermal and sound insulation, enhancing energy efficiency.	– Poor ventilation or moisture buildup can negate insulation benefits and lead to damage.
Environmental Impact	– Reduces waste sent to landfills, making it eco-friendly.	– Underlying shingle issues can result in frequent maintenance, impacting overall sustainability.
Aesthetic Concerns	– Can be done without compromising visual appeal if underlying shingles are even.	– Uneven shingles may create visible ripples or bumps in the metal panels, reducing curb appeal.
Warranty	– Cost savings from skipping tear-off may outweigh risks if warranties remain valid.	– Manufacturer warranties may be voided if installation doesn’t meet specific requirements.

How to Install Metal Roof Over Shingles To Avoid Problems?

FAQs — 2026 Canadian Edition

Is it legal in Canada to install metal over shingles?
Yes, usually over one layer only. Check local codes in Toronto, Ottawa, Calgary, or Edmonton.

How long will it last?
Up to 40–70 years — but underlying shingle issues can reduce lifespan.

Will it void my warranty?
Some manufacturers may cancel warranties if proper installation steps aren’t followed.

Can I install metal over multiple shingle layers?
Not recommended. Extra weight can damage the roof deck.

What underlayment should I use?
A synthetic underlayment improves durability, moisture resistance, and finish.

Why Choose Professional Metal Roofing?

At Professional Metal Roofing, we offer tailored solutions:

Install Over Shingles – with thorough inspection and quality underlayment,
Complete Tear-Offs – when structural issues exist,
New Construction Roofs – custom-designed for your project.

We provide:

Year-round installation in Ontario & Alberta,
Skilled crews with decades of experience,
Premium materials with 50-year transferable warranties.

👉 Explore our Our Works gallery or request your Free Estimate today.

Conclusion

A metal roof over shingles can save time and money, but it’s not a one-size-fits-all solution. By understanding potential issues — and addressing them with proper planning, ventilation, and expert installation — Canadian homeowners can enjoy a durable, efficient, and attractive roof for decades.