So, you’ve decided you’d like to replace your current roof with a metal one. Great idea.
But you have to consider what’s already there, and if you already have shingles on your roof, is it possible to put a metal roof on top of that? Fortunately, the answer is “yes,” but it comes with stipulations.
If you have shingles on your roof and would like to install a metal roof on top of it, it will only work if you have no more than four layers of shingles remaining on the roof.
Otherwise, you’ll have to remove all of them before installing your new roof.
Can You Lay Metal Roof Over Shingles?
As a general rule, installing one type of roof over another type isn’t recommended, but just like everything else in life, there are exceptions to this rule.
Unless you have too many layers of shingles on your roof, you can go ahead and install a metal roof on top of those shingles.
Why is this the case? When you install one roof on top of another, you might not notice any damages that are located on your old roof, and this can cause problems in the future.
The reason why is simple: unnoticed problems will likely only get worse over time, and if you have a brand-new roof on top of one that has problems, things can get complicated.
Indeed, by the time the problems come to a head, so to speak, it will be much more difficult to repair the old roof because you’ll likely have to remove the new roof first before anything else is done.
The more layers of shingles you have, the more likely you’ll have problems once you place the metal roof on top of those shingles.
Still, it can be done if there are only a few layers of shingles in the first place.
Some of the damages you can miss include everything from water spots to mold and mildew and maybe even rot, and when you remove the shingles or old roof first, you can take the time to inspect and notice these things so that they can be repaired first.
Another potential problem is the possibility of trapping moisture and water vapor in between the new metal roof and the shingles from the old roof, which greatly increases the chances of rot and other problems.
Nevertheless, if you do decide to install a metal roof over a few layers of shingles, there are some things you need to keep in mind first.
How to Install Metal Roofing Over Shingles
The first thing you need to do when placing a metal roof over shingles is check local building codes because they can vary quite a bit from one area to another.
In fact, some codes specify you cannot have any shingle layers on the roof, while others limit the layers to a certain number.
You’ll also want to choose a lighter method such as aluminum or steel and not a heavy metal such as copper.
Why? The lighter ones are simply easier to install over an existing roof, including shingles, so you’ll have a much easier time making sure the metal roof is placed on correctly and without any problems.
Of course, the easiest thing to do is go ahead and remove the old shingles from the roof before you install the metal roof, but even that option has its disadvantages.
It is much more time-consuming and even more expensive of a job, particularly since you have to count the amount of labor involved.
Once you decide to install your metal roof over your shingles, it’s good to know you have a few different ways to do this.
Option 1: Underlayment
The simplest and least expensive way to protect your new metal roof when you wish to install it over existing shingles can be summed up in one word: underlayment.
Underlayment is essentially a barrier between the shingles and your new roof that protects the metal roof when temperature and humidity changes in the weather cause that metal to expand and contract, which causes the shingles to act like sandpaper when it rubs against the metal part of the roof.
If this happens, the bare steel that is part of the metal roof might be exposed, opening up a whole new set of potential problems.
The simplest solution to this problem is to just go ahead and install the underlayment so that you don’t have to worry about this happening.
While this is the fastest and least expensive way to install a metal roof over older shingles, there are some disadvantages.
First of all, you might miss potential problems in the shingles unless you conduct a thorough inspection before you install the underlayment, and it also doesn’t make for the flattest metal roof in the end.
This is because as a general rule, each layer of shingles is going to be 1/8” higher than the course located below it.
Option 2: 1×4 Purlins
This is a very common method of installing a metal roof over shingles because it involves laying down 1×4 purlins directly over the shingle roof before starting to install the metal one.
All you have to do is make sure the plywood located underneath the shingle roof is in good condition. If it is, this option will work out favorably.
This method is a little more expensive than the underlayment method, but it is very efficient and does a great job.
Do I Need Underlayment for Installing Metal Roof Over Shingles?
No. While underlayment is probably the cheaper/easier option, you’re other option is installing 1×4 purlins over the shingles, and then installing the metal roofing over the purlins.
Although many experts recommend removing shingles completely before installing a metal roof, the truth is that it can be done this way as long as there are no more than three layers of shingles already in place.
Each of the methods mentioned above has its own advantages and disadvantages, so you’ll have to know your own roof well before you decide which one is right for you, which shouldn’t be that difficult.
Metal roofs are great for a variety of reasons, including the fact that they last a very long time and are very attractive to boot.
Placing one of these roofs over shingle roofs is a bit of a challenge, but nothing says that it cannot be done.