Can You Install A Roof Over An Existing Roof? – Family Roofing

Posted on by David Reid

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Can You Install A Roof Over An Existing Roof?

It is not uncommon for homeowners to roof over existing shingles; this is called reroofing.  New shingles can be installed or laid over the old ones when a new roof replacement comes instead of tearing off the existing roof.  You should only reroof over existing shingles if the roof decking is in good condition and there is presently only one layer of shingles on your roof.  Adding more than two layers of shingles can cause the roof structure to sag under the weight.  It’s best to replace flashings when reroofing.  A roof replacement would typically involve tearing off the old roof down to the decking to remain only with the roof’s trusses or rafters, which sometimes need to be reinforced if damage or rot exists. In reroofing, none of this happens. 

You can install a roof over an existing roof.  To be clear, installing a new roof over an old one is a purely exclusive process for roof materials in the form of shingles, like asphalt, wood, and metal.

Installing a new roof over an old one is also known as reroofing.  Reroofing dates back a few decades ago where a homeowner, after a thorough roof inspection of the roof, decides that well, the top is worn out but is generally still in good condition and:

  • The decking is not leaking,

  • The roofs framing is intact

  • The roof itself does not bear substantial damage

When a homeowner decides to reroof, he will be trying to avoid:

  • The labor expenses of tearing off the old roof,

  • The cost of disposing of the waste materials

  • The mess and clutter of damaged roofing materials

In the aftermath of a reroof, the home and the roof will benefit in the following ways:

  1. The home’s interior will enjoy the advantage of having the extra layer of roof add value to the home’s insulation, where air conditioning will be at its best.

  2. The roof will benefit from an extra layer of barrier against the climate and its elements.

How Do You Tie In Shingles To An Existing Shingles?

Tying into an existing roof shingle that needs the expertise of a licensed roof contractor who will deliver a professional and flawless result.

Things to consider before you opt for a reroof:

  1. Make sure to check if the building code in the area you reside in allows the process of laying a new roof on top of an existing one, and if it does, how many layers are acceptable.

  1. The roof is an integral part of the building that keeps the home in general safe and warm all year round.  For this reason, ensure to pay attention to the roof deck, the eaves edge, and the valleys when you begin the project.

  1. Because you will not be removing the roofing material, ensure that the roofing accessories, for example, the flashings and valley liners march up with the quality with roofing material so that the entire roof will age correctly.

  1. With an extra layer of shingles in place, more heat will be trapped in the attic, ensuring that the air vents in the area are sufficient because the roof will be preserved with a sound venting system and will rot with too much moisture.

Like many common home improvement questions, the answer is you can, but you need to decide if layering shingles is the best course of action for your home.  It isn’t uncommon to layer a second roof right over the first and then tear everything off before you put a third layer down.  Building codes and most municipalities will usually allow you to overlay a second (though never a third) layer of asphalt shingles over an existing shingled roof. You will need to check with your building inspections department to be sure.

Common Problems with Layering Shingles

Layering shingles has a few drawbacks that you should take into consideration before you decide to lay new shingles over the old.

  • If there’s any curling of the old shingles, the new shingles will not lay flat.

  • Moisture can get trapped under the heavy layers and cause premature rotting of the wood.

  • You do add excess weight to the roof framing, which can cause the decking and/or roof joists to bow and cause a ripple effect in the roof.

  • Overlay will not work well at all with dimensional shingles, only three tab.

  • If you do overlay, you have to cut off the tab of the first course which will give you a “bump” about 6″ up the roof all the way around the shingle roof.

  • You must pull off both layers before you roof the next time. Many times the cost for a double tear-off is more than doing it two separate times.

  • Tear-off will give you the opportunity to examine the decking for any rot and make repairs now before it gets worse (and more costly).

  • If you do remove the old shingles, you will end up with a nice fresh layer of felt on the roof deck.

Re-Shingle Roof as Part of a Larger Plan

Despite these drawbacks, layering shingles can still be the best plan for your roof.  One of the situations, where this option can make the most sense is for a temporary fix as part of a long term plan. Many of the common problems listed above can be avoided if you end up replacing your new roof in the next five or ten years.  This sounds like an unwarranted expense, but simply layering shingles can make for a reasonably priced project.  You can then invest your money and invest in a high-performance, energy-efficient roof in ten years that will last for the rest of your life.