When it comes time to replace your shingle roof, you need to decide between replacing the existing shingles or installing a new layer of shingles on top of the existing layer. However, installing new shingles on top of an existing layer — a process known as a roof-over — is only possible if there is only one existing layer of shingles on your home.
Before you can determine whether this option is a possibility, you’ll need to figure out the number of shingle layers currently on your roof. This guide will get you started and help you decide whether a roof-over is the best option for your situation.
Overview of Layers of a Roof
Shingles are the most familiar component of roofs because they’re the only part you actually see. Underneath the shingles are a number of other components, all of which are necessary to form a reliable barrier between your home and the elements. Moving from the bottom up, these layers include:
- Decking: Commonly consisting of plywood, the decking layer is installed on top of the framing in most applications. It provides strength and structure by tying the rafters and trusses together. The underside of the decking can usually be seen from the attic.
- Ice and water barrier: This self-adhering, self-sealing, waterproof membrane is applied to the decking of the roof. It’s made to protect against infiltration of water as a result of wind-driven rain and ice accumulation.
- Flashing: Flashing is a thin material that serves to direct water away from areas where elements of the roof intersect, like the chimney and the siding. Flashing is often made of metal, such as steel, copper or aluminum. It often fails before shingles do, so it should be regularly inspected to ensure the home has a seal that is watertight.
- Starter strip: These specialized shingles line every edge of the roof of your home. They are installed after the roof decking but before the underlayment. Their purpose is to seal your roof’s edge, which will significantly increase your roof’s ability to stand up against wind-driven rain and strong winds.
- Underlayment: The underlayment consists of a rubberized or felt asphalt sheet, and it provides an additional protective layer between your roof deck and your shingles. It helps to reduce blow-off by letting your shingles lay more uniformly and flatly. The underlayment also keeps wind-driven rain from getting under the shingles, which can damage the structure of your roof or even the inside of the house.
- Shingles: Shingles are the part of the roof that everyone recognizes. This layer is visible from the outside, and it serves an important aesthetic purpose. There are two main types of asphalt shingles — 3-tab and architectural. 3-tabs cost less but are also less durable. They are not as resistant to wind and have a flatter appearance. Architectural shingles are used for the majority of roof replacements today. They cost only slightly more than their 3-tab counterparts, and the specifications and warranties are much better.
- Ridge caps: Shingles don’t cover ridges very well. Ridge caps, which are specialized long shingles, are installed along the ridgeline of the roof. They fit over the joints between two edges, keeping rain and snow out of your home while letting hot air escape. Ridge caps also give roofs a finished look by making a tightly sealed joint on both sides.
What Does It Mean to Have Multiple Layers of Shingles?
In the construction industry, adding an additional layer of shingles over an existing one on a roof is known as a roof-over. Roof-overs offer a number of advantages compared to replacement:
- Lower cost: Price is usually the primary reason homeowners opt for a roof-over rather than having their shingles replaced entirely. In addition to the cost of re-roofing, you can also save some on disposal expenses and dumpster rentals.
- More convenience: Roof-overs are generally less messy than replacement, as you’re not ripping off the entire shingle roof. This difference translates into a quicker, easier cleanup job.
- Faster completion: If you skip the part where the old shingles are torn off, it’s usually faster for roofers to complete the job.
- Less risk: Much less can go wrong with a roof-over compared to roof replacement. There isn’t a risk of an unexpected storm interfering with the dry-in process, and there’s no debris that could fall and damage your property.
That said, homeowners should be aware of potential problems with two layers of shingles. For one, a roof-over job generally doesn’t last as long as a roof replacement. When you do end up replacing multiple layers of shingles, the costs for the tear-off and disposal are both higher. Other disadvantages include:
- Extra weight: Installing a new roof over the existing one means adding weight that can put more stress on the decking. The extra weight can be an issue down the road, especially during heavy rains or snowfall.
- Difficulty detecting leaks: When you have two layers of roofing, it is generally more difficult to inspect its sheathing. It can be more challenging to find problems like leaks, mold growth and rotted or damaged wood, keeping you from fixing the damage.
- Lower quality: For your roof-over to be as reliable as a tear-off, the existing roof would need to be in a condition that is near-optimal. Without removing the existing shingles, the roofer cannot examine the roof properly and therefore cannot know what the condition of your roof is. An experienced roofer may be able to detect signs of hidden damage, but they would have a much better idea if the existing shingles were removed.
- Not as visually appealing: There’s a good chance your existing shingles have gone through a considerable amount of wear and tear, leaving some of them curling, uneven or torn. These damaged shingles do not provide a reliable base for the installation of new shingles, so the new roof may end up looking noticeably flawed regardless of the skill of your roofer. You’re even more likely to end up with imperfect results if the roof was made using something other than the common 3-tab shingles.
- More difficult maintenance: An additional shingle layer can make it more challenging to detect issues and perform the necessary maintenance. If a leak develops, for example, the water will move through both shingle layers, changing direction and hiding the source of the leak.
- Shorter life span: A new shingle layer over an old, damaged layer won’t last as long as it could otherwise. Roofing with two shingle layers also holds more heat in, which accelerates deterioration.
- Impact on inspection reports: If you plan to put your home on the market, take note that inspectors often see roof-overs as a negative factor.
- It can only be done once: Most building codes only permit a maximum of two shingle layers, meaning you can only opt for a roof-over once before needing replacement. If you want to know how many layers of shingles you can put on a roof in your area, consult your local codes.
How to Tell How Many Layers Your Roof Has
If you’ve bought your home recently, you may not know whether it already has a double layer of shingles. One easily observable clue that a home has had a roof-over is that the roof has an overall lumpy appearance, especially at the roof penetrations, like gas appliance flues and plumbing vents. You can usually notice these details from the ground.
If you want to be absolutely certain that you’re looking at two layers of shingles, you will have to get up on a ladder and examine the shingles on the edge. You may want to ask a professional to do so. A normal roof has a starter row of shingles and then a single layer above it, giving it a total of two shingle layers. Roof-overs, on the other hand, will have four layers.
Which Number of Layers Is Best to Have?
Simply put, the right number of layers for your roof depends on your situation. If your shingles are starting to fail but the underlying structure and sheathing of your roof are in a generally good state, you might want to consider a roof-over. Your existing shingles may be worn out due to weather or age and losing granules, but if they are not causing leaks and are not missing or curling, you may not need to remove them before adding a second layer.
When a Roof-Over Is a Good Idea
If weight isn’t a concern, adding another high-quality layer of shingles to your roof actually adds an additional layer of defense. Together with the decking, underlayment and original shingle layer, this second layer can provide protection from damage and prevent any leaks from entering your home. In this situation, the additional layer can be seen as an upgrade that enhances leak protection. It will also help direct rainwater from the roof and into the gutters and downspouts, preventing the issue of pooling.
A roof-over may also be a good idea if:
- You want to change the look of your roof: A roof-over offers the opportunity to change the look of your home. You might want to go with another color or design. If you’re renovating your entire house, maybe you’d like the roof to match the new look. Even if your main objective is not to redesign your roof, a roof-over will provide a new aesthetic appeal. The second layer will be slightly raised as a result of the existing shingle layer underneath, giving the appearance of more depth.
- You have a limited budget: A roof-over is without a doubt less costly than a roof replacement in the short term. There’s no need to tear off an existing roof, so less labor is required. Your roofer can start installing the new roof right away without having to remove and dispose of the existing shingles.
When a Roof-Over Isn’t Such a Good Idea
A professional, reputable roofing contractor will always let you know if your roof isn’t a good candidate for a roof-over. A roofing inspection is essential before you take any action on your roof.
Following a thorough roof inspection, the roofer will let you know whether they recommend a roof-over or not. Feel free to ask several roofing contractors for opinions and estimates so you can pick the best roofer for your home.
You might decide against a roof-over if:
- You don’t have asphalt shingles: A roof-over is not a possibility is if you don’t have asphalt shingles already. Mixing materials is not possible, and neither is installing a new layer over wood tiles or slate.
- Your shingles are curling: Roof-overs are also not possible if your shingles are curling. The installation of a new layer will only be successful if the existing one is completely level and flat. Shingles are known to curl over time, so if you do want to do a roof-over, you should speak with your roofer about replacing the curling shingles first.
- You already have two layers of shingles: If your roof already has two layers of shingles, you will not have the option to add another one. Most building codes do not allow more than two layers. If the codes in your area do allow another layer, you should still keep in mind that the extra weight can be dangerous.
- Your roof has extensive, visible damage: If your roof has damage, you shouldn’t cover it up with an additional layer. Instead, you should tear everything off completely and deal with the source of the problem.
How Scro’s Roofing Can Help
We at Scro’s Roofing have been providing customers in Raleigh, North Carolina, and the Triangle with full-service residential and commercial roofing solutions since 1995. We strive to provide the best possible customer experience. From our first phone call to the completion of the job, we’ll make sure that you, the customer, are the focus.
Our experienced roofers have been expertly trained to repair and install a wide variety of roofing systems, and our GAF Master Elite® certification sets us apart from competitors. If you’d like top-notch roofing services, competitive warranties and a variety of financing options, go with Scro’s Roofing Company. To request a free estimate or find out more about our services, you can call us at 919-551-5104 or contact us online.
Last updated: 12/23/2021