Metal Roofing can be expensive, so it makes sense that you may want to save money where you can and install a metal roof directly over your existing asphalt shingle roof. There are two questions that should be asked before attempting to put a metal roof over shingles. The first is “Can I put a metal roof over shingles” and the second is “Should I put a metal roof over shingles.”
Can I Put a Metal Roof Over an Existing Roof?
Hypothetically speaking, it’s possible to put a roof over a roof. There are several reasons you shouldn’t do it, but it can be done.
Disclaimer: If you have a roofer recommending a roof over a roof, you should choose a different roofing company. Most professional roofing companies won’t put a metal roof (or a shingle roof) over a shingle roof. Some municipalities will not approve a roof-over-roof installation. It may void your roof warranty.
Should I Put a Metal Roof Over an Existing Roof?
Now that we’ve answered the question of if it’s possible, here are some reasons that it’s not a great idea. Stop and consider having your current roof removed before you put a new one on your home.
Two Roofs Will Increase the Weight on Your Home
Your home wasn’t designed for the weight of two roofs. You may not see structure damage immediately, but over time, you could do severe damage to your attic and the structure of your home. Repairing such damage is likely to be more expensive than having the roof removed in the first place.
There’s No Chance To Repair The Decking (or Anything Else)
Lifting, curling, and missing shingles or leaks are some of the common signs that may indicate a problem with your decking, due to exposure. If your decking is damaged or rotting, there’s no way to see it with shingles on top. A rotten deck could mean anything from a leaky roof to a collapsed one.
Difficulty Finding Leaks
If water gets under your metal roof, it will become almost impossible to track the leak, since the water will simply take the path of least resistance down the shingles, and leak at any previous points of weakness.
Underlayment for Metal Roofs
Your roof currently has an underlayment meant for asphalt shingle roofs. Metal roofs use an entirely different underlayment that’s specially designed for metal roofs. By applying the roof over a roof, you’re not able to use the underlayment that’s recommended by the roofing company. Not using the proper underlayment or having a proper installation can void your metal roof warranty.
Covering Up a Bad Roof with a Good Roof
If you’re thinking about replacing your roof, you likely either have a damaged roof or an old roof that’s beyond its life expectancy. Putting a new roof over the old one doesn’t do enough to fix the damage that’s lurking underneath. Leaking, ventilation problems, and even roof collapse are all possibilities in the future.
Metal Roof Over a Shingle Roof
A metal roof over a shingle roof may seem like a good idea. You may be tempted to save money and think that, because a metal roof has a longer lifespan, it would be a good enough protectant over an older shingle roof. However, like all roofing systems, a metal roof is meant to be the only roof installed. Installing it over a second roofing system is more likely to cause problems down the road and could lead to everything from having to replace your metal roof sooner than you expected to roof collapse.
Metal Roof Installation
When properly installed, a metal roof has one of the longest lifespans of any roofing material. It has several advantages over shingle roofs. Although it can be expensive to initially install, a metal roof can give you the security and satisfaction of a quality roof for a long time.
Read more about Metal Roof Myths.
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