Can You Shingle Over Existing Roof Shingles: Complete Guide

old roof lg

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.

Here’s what inspecting houses for decades have taught me:

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 re-roofing.

On a typical day, a roof replacement would 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. 

Can You Build A Roof Over An Existing Roof?

You can build a roof over an existing roof. But, 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, and 
  • 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, and 
  • 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 an ardent roof contractor who will hack the job and deliver a 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 mind the roof deck, the eaves edge, and the valleys when you begin the project.
  1. Because you will not be changing 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 in style.
  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.

Requirements needed before embarking on a reroof:

  • New shingles
  • Roofing nails.
  • Valley liners
  • Roof vast
  • Roofing Adhesive
  • Hammer
  • Ladder
  • Strip lines

How Do I Reroof My House?

The following is a step by step procedure of handling a reroof;

Step One

Ensure that all the roofing materials and tools are on site.

Step Two

Climb up the roof and remove any curled or broken shingle that might get in the way of achieving an even roof surface.

Step Three

Standing on the climbing ladder on the edge of the eaves, begin from the roof’s edge by installing a starter strip that fits in place and flashes with the existing outer roof shingle.

Step Four

Cut/remove 4” of the end of the starter strip shingle. As such, the joints between the shingles will be covered when the first course of shingles is installed.

Step Five

Trim enough material from the bottom of the full-length shingle to allow them to fit between the bottom of the tubs of the existing shingles and the new shingles.

Step Six

Use four long nails to penetrate through the existing asphalt layers and the decking, install a full-length shingle covering the starter strip and nail it into place.

Step Seven

Apply the starter strip and the full-length shingle all around the roof edge of the house.

Step Eight

First, the valleys build up the exposed gap using roof vast and the roof adhesive to level up with the old roof before installing a valley liner.

Step Nine

Install the remaining regular-sized shingle to the rest of the roof like you would in a normal roofing process.

Is It OK To Roof Over Existing Shingles?

It is not OK to roof over existing shingles most of the time. Roof replacement is a tough decision to make because it requires a lot of money plus time to carry out the job comfortably and delivers a befitting result.

The answer to whether it is acceptable to roof over an existing roof could be a skeptical “maybe” or a “maybe not.” Roof replacement is a tricky and challenging project for many homeowners, and it all depends on your budget.

This question is not definite because roofing over another is wrong on so many levels as much as we would love to. 

Let us look into the main reason why reroofing is not suitable for your household and your property.

The Extra Weight

When a new roof is laid over another, the new rooftop adds additional weight to the current weight. In some areas, reroofing is done not once but up to three times.

The thing is, the roofing includes trusses and roof sheathing, and the general structure of the house is designed to carry a certain weight. 

Therefore, having an unplanned roof layover contradicts the housing and building code because shingles are generally heavy.

As much as reroofing is a practice that has gone on for hundreds of years, the National Housing Code has recently restricted this old method of roof replacement, terming it as a safety hazard for people residing in that home.

Should Old Shingles Be Removed?

The importance of having a proper roof over your head is to provide shelter, but an adequate roof goes ahead to also protect the overall building from damage. Roofs get old, and when they do, a replacement should be on the offing.

Because reroofing is not a foreign idea, many may choose to take that route, but if you are still undecided, here are reasons why tearing off the existing roof before installing a brand new one is good:

  1. Proper Installment

The advantage of tearing off a damaged roof is that your new roof will benefit from a proper installment. 

When the old roof is out of the way, the new top starts from scratch and has the potential of being laid on a flat surface with no obstructions; therefore, it will be firmly attached, and the entire roof will have an even surface.

  1. Saves Money

The biggest reason behind reroofing is that homeowners have this fancy idea that they are saving money in labor, shortening the time needed to complete the project, and finding it easy to manage the roof replacement process.

The truth is that reroofing is a bad idea because the layers of roofing materials stalked on top of each other will need to be dismantled at the end of the day. The homeowner will pay more money to have it torn apart as it will involve more than tearing off one layer after another.

It also goes to the cost of disposing of the waste material. Many layers of roofing material will have grown two-fold or three-fold. As such, you will be charged according to the amount of waste to clear out.

Overall, reroofing in the name of cost management is just a delay tactic.

  1. Obstruction Of Roof Inspection

A home inspection is carried out at least once or twice a year. In this visit, a home inspector is expected to thoroughly inspect the roof for any damage or leaks and certify whether the top is in good condition or not.

With a roof overlay on the way, an inspector will have no way of determining whether the old roof material that is not visible is holding up or deteriorating silently.

It is a life where you live not knowing what to expect, just hoping for the best and not preparing for the worst.

  1. General Outlook

Often, the new roof is laid on top of an old one; chances that the old one was damaged and had bumps and missing shingles in other places are high.

All these abnormalities will determine the final outlook of the new roof. You will not be surprised when an uneven surface characterizes the new top.

When selling off your property, a dire physical outlook is not good to the eye or a potential buyer.

  1. Product Warranty

A majority of new roofing products come with a warranty. It signifies that their product is of good quality and will last for long and withstand any challenge.

But because another product is already in place, the ability for their product which they have performance confidence in will have interfered. 

The manufacturer will be hesitant to guarantee their responsibility to cater to any damage that their product might face because the exclusivity for their product to perform is now questioned.

In summary, tearing off the old roof has many advantages besides being expensive upfront. It is because a tear-off will address the challenges and damage the old top had.

For example, the roof was susceptible to leaks and wood rots; roof tearing will address the problem. 

The roofing contractor will replace all rotten and damaged trusses and frames before installing new underlayments and shingles.

Removing old shingles plus the sheathing and replacing them with new roofing materials will make your roof appear as good as if your building was new. It will give your roof a good appearance and will impress buyers as well.

Finally, a roof tear-off will add more life to your roof, unlike in the case of a reroof where the existing damages are not addressed.

How Many Times Can You Shingle Over A Roof?

As much as the Building Code and City Code allow reroofing as an accepted way of roof replacement, it limits the number of overlays to only 2. You are required to tear the roof down to the decking and replace it with new roofing materials.

That aside, some homes have dared the roofing requirement by laying new shingles on top of another four times, which is wrong and very dangerous.

If you must, use the highest quality of asphalt roofing material to carry out a reroof. High-quality asphalt is slightly lighter in weight than other roofing materials such as wood, rubber, and metal shingles.

Why Are Multiple Layers Of Shingles Bad?

Multiple layers of shingles are bad because it makes the roof prone to cracks and breaks and leads to more renovation costs.

During the reroofing process, the roofers will attach the ladder to the roof’s edge, as they carry the heavy shingles one at a time and place them on the rooftop for easy access when they start roofing. 

As this process goes on, it may put untold stains on the layers of the existing shingle, and something may crack or break somewhere, leading to more damage and uncertainty.

Let us agree that reroofing is taking the shorter but most uncertain route to a place. As much as your roof will have to be replaced, you will eventually incur a heightened renovation cost.  

Reroofing Tips

Over the years of working as a Master Inspector, I have heard many roof renovation ideas from hundreds of homeowners. The following tips are ideas I can vouch on that will help a homeowner in his quest to have his roof replacement but by having the new one laid over the old one:

  1. If you have decided that reroofing is the way to go, it will be wise to have any loose or damaged shingle removed. It ensures that the incoming roof has a tight and firm foundation to hold and settle on.
  1. When reroofing, it is also wise to maintain the original roofing material. Taking on a different material could cause a problem as the two might not be compatible as far as roof and attic ventilation is concerned and might end up trapping heat instead of letting it out.

Aside from that, a roof bearing different roofing materials might end up being listed as low value, and a homeowner will find it hard selling it off in its excellent value.

Final Thought

As discussed earlier, installing a new roof over an old one is a purely exclusive process for roof materials in the form of shingles.

The only way to know if your existing roof and the building’s fabric will be able to take on the incoming weight from the shingles is to have a home inspector carry out a survey of the entire house and certify its safety.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.