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 adding layers to their roof installation.

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:

1. 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.

Considered bad practice and an opportunity for roofers to take advantage of less informed customers.

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.

1. 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.

2. 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.

3. Gets hotter

If you have multiple layers of shingles on your roof, the trapped heat between the layers could cause the shingles to not allow the attic to ventilate like it should. Resulting in premature aging of a roof. This effect is particularly significant if you've installed new shingles over warped ones, as it further increases the heat retention between the layers.

4. 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.

5. 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.

6. 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.  

7. 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.

8. 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. 

9. 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.  

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