The first line of defense for your home, shingles shield your interior from costly leaks. When properly installed, quality shingles can last decades. Over time, however, even the best shingles will need to be replaced. But what if you decided to simply add a second layer of shingles? Here’s what you should know about this risky decision. 

Why Do Some Homeowners Do it?

Despite what you might have heard, adding a second layer of shingles will not make a new roof more waterproof; in fact, it often creates extra problems. Still, many homeowners choose to do it in an attempt to save money and time. 

By leaving the existing shingles in place, they are able to skip the labor-intensive process of tearing them off. Unfortunately, while this decision may save you a little money in labor costs, you will still need to do plenty of prep work (removing warped shingles, ridge caps and vents, among other things). You will also have to replace or add brand new flashing, which can sometimes be difficult over old roofing. 

Eliminating the tear-off and disposal steps can save a decent amount of money depending on the size of a roof. That said, most homeowners discover that they are only delaying the cost since they will have to remove two layers of shingles the next time they have their roofs replaced. That’s usually twice the expense for labor costs and disposal.

Why it’s Not Recommended

As we’ve already explained, the potential disadvantages of a “roof over” tend to outweigh the advantages, but it all really depends on your unique situation. Below, we’ve outlined some reasons not to shingle over an existing roof to help you make an intelligent roofing decision.

Shingles are made for flat surfaces. Asphalt shingles are designed to be applied over a plywood deck. When adding another layer of shingles, the old roof’s bumps, seams and imperfections will transfer to the fresh layer. In the end, your roof won’t look nearly as good as it would if you did a full tear-off.

installing shingles on roof with nailgun

More shingles mean more weight. Roof structures are usually designed to handle a dead load of just one layer of shingles, along with some extra snow and a reasonable safety margin. Adding new shingles will effectively double the weight of the roofing, so you will have to make sure your structure can endure the extra load. This is why building codes typically limit roofing to just two layers. On certain homes, the added weight of extra layers will cause the decking to sag between the trusses and rafters.

It prevents visual inspections. There’s simply no way to thoroughly inspect your roof decking and correct any potential issues without removing the existing layer of shingles.

You can’t replace underlayment. The underlayment between the shingles and the roof decking helps prevent water from entering the attic. If your underlayment is damaged or worn out, it will not protect your deck from any water that happens to get past the shingles.

It may void your warranty. Some warranty plans will not allow you to add a second layer of shingles. Be sure to check with the shingle manufacturer, so you will understand every installation requirement and any potential warranty issues before adding a second layer.

It could be a red flag for buyers. If you are planning to sell your home in the near future, a second layer of shingles may sound like a great idea. After all, why pay to have the existing layer stripped away if you’re not going to live in the home? Ultimately, however, it’s the new homeowners who will end up having to pay the extra expense of a two-layer tear-off down the line They will also have to accept the risk of sagging, leaks and underlayment damage. 

Due to these issues, home inspectors often warn prospective buyers about common issues associated with roofs with two layers of shingles. This can make it harder for you to sell your home at the price you’re looking for. Many buyers will walk away when they learn about the roof, while others will use this sort of issue as a negotiating tactic to drive down your asking price. 

If you’re weighing the pros and cons of adding a second layer of shingles, the experts at A to Z Roofing can help you make an informed decision. For decades, A to Z Roofing has specialized in residential roofing, restoration and repair. A locally owned Colorado business, we’ve operated continuously throughout the Denver metro area and the entire Front Range for nearly a quarter of a century. During this time, we’ve served the needs of homeowners and local businesses, providing expert service using top-quality products. Contact our team of attentive professionals to learn how we can restore, repair or replace your damaged or aging roof.