Can I Install New Shingles Over An Existing Roof?
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Can I Install New Shingles Over An Existing Roof?

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Posted By: Roof Troopers

If the circumstances are right, yes, it is possible. The industry term for this type of installation is called “re-roofing.” However, it is not recommended and most professionals would strongly advise against this practice. When possible, a full roof replacement is the best option.

In this post, we’ll first go over the certain circumstances in which re-roofing is possible. Then, we’ll go over the reasons why you wouldn’t want to do this to your home’s roof.

When is Re-Roofing Possible?

  • When you have asphalt shingles
  • If it meets the manufacturer’s requirements and will stay under their warranty
  • If it is allowed by your area’s building code
  • If the HOA or other related organization approves it
  • If the structure can handle the weight (for the most part, code allows you to have two layers of shingles)

If you do decide to re-roof, here are some of the key aspects you need to cover (Note: There may be more items depending on your situation):

  • Check to see that the existing roof isn’t leaking
  • Check to see that the roof decks aren’t damaged. This is difficult without the roof being torn off but you can try to check from the attic.
  • The old shingles are flat
  • The roof is dry
  • Check to make sure the old shingles are not curling or in bad shape/missing shingles
  • Reflash all necessary parts such as a chimney, skylights, where the roof meets with a wall, etc
  • Replace pipe flashing, box vents, etc

Why You Shouldn’t Install New Shingles on to an Existing Roof

We would not recommend installing asphalt shingles over an existing roof. If a client asks us to do so, we inform them that we do this type of installation and explain the reasons why. Here are some of the few issues you should consider:

  • Without tearing off the existing roof, you can’t fully assess the condition of the roof deck
  • Shingles are just one aspect of the roof system. While shingles are very important, how the entire system is assembled is even more important. For example, how the flashing is done, underlayment, ventilation, etc.
  • You are not able to accurately assess how the previous roof was installed or the type of system that was used.
  • Asphalt shingles are designed to be installed over flat surfaces. When they are installed over an existing roof, there are bumps, grooves, and gaps. Often times it is noticeable when a second layer is installed.
  • Re-roofing may affect the warranty on the new shingles or even void the warranty
  • Building codes and energy efficiency have improved with technology. For example, now many areas require ice and water shields where water can penetrate. If you are installing over a roof that is 20 years old or more, It is likely your system will be inefficient.
  • Re-roofing may not look good on an inspection report if you are planning to sell your home.
  • Re-roofs are more prone to leaks and issues

These are just a few of the many reasons why we would advise against doing a re-roof.

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