Pros & Cons of Multiple Layers Roof Shingles

The "Pros & Cons of Multiple Layers Roof Shingles" would make for a valuable blog post that could inform our readers who are considering re-roofing their old roofs.

To begin with, the term "multiple layers of shingles" refers to the practice of installing a new asphalt shingle roof on top of an existing one, as opposed to completely stripping the roof down to the sheathing and replacing it with new shingles.

Although most building codes permit this approach, it's worth considering whether it's a good idea or not. Let's explore the advantages and disadvantages:

Pros to Overlaying a Shingle Roof

The pros of layering roofing shingles help the roofer to sell their service to the homeowner:

• Cheaper, faster and less messy; A roofer can pass the cost savings of skipping the time intensive tear-off step and disposal of old shingles to the homeowner; Depending on the size of the roof, this can potentially shave off a day of work for the roofer.

Cons to Overlaying a Shingle Roof

The cons of layering roofing shingles show how layering roofing shingles is a short-term fix at best, and will result in long-term problems that could be expensive.

• Can’t detect leaks or other damage. If you simply add a new layer of roofing material on top of the old one, you won't have the chance to thoroughly examine the roof's sheathing. This means that issues such as leaks, faulty flashing, deteriorated or damaged wood, and algae growth may go unnoticed, and it's difficult to address or prevent problems that you're unaware of.
• Added weight. By installing a new layer of roofing material, you are essentially creating a second roof for your house. This extra weight places strain on the roof decking, which is particularly concerning in areas that experience heavy rainfall and snowfall, such as our climate. It's worth noting that an average 30-square roof requires 90 bundles of shingles, and each bundle of asphalt shingles typically weighs around 100 pounds. Therefore, adding a new layer of shingles could add approximately 9,000 pounds of weight to your roof.
• Gets hotter. If you have multiple layers of shingles on your roof, the trapped heat between the layers could cause the shingles to age prematurely. This effect is particularly significant if you've installed new shingles over warped ones, as it further increases the heat retention between the layers.
• Affects inspection reports. If you're attempting to sell a house that has multiple layers of shingles, a home inspector may view this as a drawback, as it suggests potential issues for the prospective buyer. Additionally, in some cases, having multiple layers of shingles could shorten or even nullify the shingle warranty.
• Roof becomes Bumpy and Aesthetically Displeasing; Installing new shingles over old buckled or warped shingles will make a roof lose its curb appeal, uneven and bumpy. If the new shingles are of a different size like 3-tab shingles are 5” and architectural shingles are 5 ⅝”, this will result in bumps every 8 shingles. These bumps allow water and wind to get underneath the new shingles, eventually causing leaks.
• No Opportunity to Fix the Roof Deck; This ignores any damaged roof decking, flashing, and ice and water barriers that need repairs due to not tearing off the old shingles and exposing the roof deck. Allowing any existing leaks or water damage to continue happening without the roofer and the homeowner knowing, until it becomes a real problem for the homeowner.  
• Disqualifies Manufacturer’s Warranty on New Shingles; Disqualifies material warranty, pro rated enhanced warranty and contractor’s workmanship warranty. For example, 3-tab asphalt shingles come with a 25 year warranty, architectural 30 year warranty that’s pro rated 10 years after coverage ends. Further, if a roofer uses all components from one manufacturer the homeowner receives a 50 year non pro rated warranty and contractor’s workmanship warranty.
• Disqualifies Insurance Coverage for Damages; Depending on the provider, any layering of shingles will not be paid for by the insurance company. Reason being, there is an additional cost of labor to tear off each layer of shingles and replace each layer of shingles. 
• Lowers Home’s Value when Selling; During home inspections, multiple layers of shingles on the roof is a red flag (negative) on their assessment of the home’s value because it indicates potential problems for the new homeowner.  

FAQ

Is it OK to put two layers of shingles on a roof?

Yes, it is generally acceptable to have two layers of shingles on a roof, provided it doesn't violate local building codes or exceed your roof's weight capacity. Consult a roofing professional for guidance.

What are the cons to 2 layers of shingles?

Cons of having two layers of shingles include reduced ability to inspect roof decking, potential warranty limitations, possible uneven appearance, and increased weight on the roof structure.

Is it OK to layer shingles?

Layering shingles is usually acceptable, as long as it adheres to local building codes and your roof's structural capacity can handle the additional weight. Consult a roofing expert before proceeding.

Is overlaying shingles bad?

Overlaying shingles is not inherently bad, but it can have drawbacks such as limited inspection access, potential warranty issues, and increased roof weight. Consult a roofing professional to determine if it's the best option for your home.

What is one of the drawbacks to adding a second layer of roofing over a first?

One drawback of adding a second layer of roofing over the first is the inability to inspect the roof decking for damage, potentially leading to undetected issues that could worsen over time.