Can you put a new roof over an old roof? The simple answer is, yes. It is possible to put new shingles over old ones, but when it comes to maintaining your home, and literally the roof over your head, it is important to consider all options. Let’s dig a little deeper into the new roof over old roof question and look at all the ins and outs of roof on roof construction, so you can make an informed decision about over roofing your home.
The Difference Between Roof Replacement and Re-Roofing
Putting a new roof on your house can be expensive, but no roof lasts forever. Inevitably, it will need to be replaced to maintain the integrity of your home. There is a difference though between replacing your roof and installing a new roof over an existing one.
Roof Replacement
A roof replacement is when you tear off the old roof to install a new one. This involves removing the old roofing materials and cleaning the roof bed. It might also include repairing the roof bed and frame, if necessary. Then, a new underlayment is installed, followed by a new roof covering, such as shingles, tiles, or wood shakes. A roof replacement also includes disposing of the old roofing materials.
On average, a roof replacement can take anywhere between a day to a week, depending on the weather, roof size and design, the roofing materials used, and if any structural repairs need to be done to the roof deck.
Re-roofing
Re-roofing is a way to renew a roof by installing a new roof over existing shingles. There is no tear off with this roof redo, which cuts down on installation time. Since a re-roof does mean laying shingles over existing ones though, it can only be done with asphalt or composite shingles. You cannot mix materials with a re-roof. There is no re-roofing over slate tiles or wood slats.
When Can You Put a New Roof Over an Old Roof
Even if you have an old asphalt shingle roof over roofing it with new asphalt shingles can only be done under certain conditions. A certified roofing contractor will inspect your roof for a number of factors to determine if re-roofing is possible. If these factors are met, then you may want to consider a re-roof.
Even if these conditions are met though there are other factors you will want to consider before putting new shingles on top of old ones.
Re-roofing can be a suitable option if your roof is:
- At the end of its life but the underlying sheathing and underlayment is still in good condition
- Worn to the point of your shingles losing granules, but not causing any leaks
- Aged but in fair shape, with no curling or missing shingles
- In good condition but you want a different roof color or design without the costs of a full replacement
When Not to Put New Roofing Over an Old Roof
Putting a new roof on top of an old one is not advisable when your roof inspection reveals certain factors. A roof inspector will determine if over roofing is an option for your home by looking at the following factors:
- Quality of roof surface
- Number of existing layers
- Local building codes
- Integrity of the roof structure
Quality Matters
Roofing shingles are designed to be installed on a flat surface. Your old roof needs to be completely flat and level for an over roofing project. Existing shingles that are curling, bumpy, or gap-filled can make securing new shingles difficult or old shingles can push through the new shingled layer. Either way your new roof will not be properly installed, causing further problems. Missing shingles on the old roof can be replaced before proceeding with over roofing your home, but determining the cause of the missing shingles is vital. Otherwise, an underlying problem may go unaddressed and cause damage down the road.
Too Many Layers
Installing a new roof over an old one adds to the overall weight of your roof. If you have two layers of shingles already installed on your roof, adding yet another layer is not recommended. Most building codes will only allow two layers of shingles to be added to a house.
Local Building Codes
Most building codes allow two roof layers, but building codes are geographic. Some areas only allow a single layer of roofing, which automatically prohibits re-roofing in favor of replacement. It is important to check specific local codes and regulations for the roof layer limit in your area.
Roof Integrity
If your roof inspection reveals any spongy areas or other signs that the integrity of your roofing structure has been compromised, then a roof replacement is necessary. Covering an old roof with a new one when there are signs of damage to the underlying structure can cause significant problems. A re-roof only covers the problem, it does not solve it.
Benefits of Putting New Roof Over an Old One
There are advantages to roof over roof construction, including cost, time, and convenience.
Less Expensive
Re-roofing is less expensive when compared to a roof replacement because most of the roof layers, including the decking, weatherproofing, underlayment, and shingles, remain intact. This cuts down on both labor and material costs. You are also not paying for the tear down or disposal costs. Short term, this all adds up to over roofing your old roof with a new one as a less expensive option than a roof replacement. Long term costs though can add up.
Less Time Consuming
Since a re-roof does not include the time and labor involved in a complete tear down, it is one of the fastest ways to redo your roof. Depending on your roof size, re-roofing can take between 1-2 days.
More Convenient
Roof tear downs are messy and a significant part of a roof replacement project. This can make it harder to fit into your schedule. With its faster installation, a re-roofing project can be much more convenient.
Extra Protection
Re-roofing over shingles adds an extra layer to your roof, which can provide more insulation and moisture prevention to protect your home.
The Disadvantages of Installing a New Roof Over an Old One
Re-shingling roof tiles is quick and less expensive when choosing to do an over roofing project, but installing shingles over shingles can have significant drawbacks too.
Warranty Violation Concerns
Each manufacturer has unique warranty conditions for their shingles. Many will void the warranty on new shingles that are installed over old ones. Old shingles can cause issues that cannot be directly attributed to the new shingles, which are the ones covered under a warranty. Before starting a re-roofing project, check the manufacturer’s warranty conditions.
Weight Strain
Re-roofing adds weight to your roof, which can significantly strain its integrity. Composite shingles weigh between 350-450 pounds per square. If your roof is designed to hold only one layer of roofing, you can overload it with over roofing your home. Putting added pressure on your home’s construction can cause additional problems down the line. The smaller your house the bigger the risk. If you live in a climate that receives a lot of snow, this added strain is compounded and can lead to roof collapse.
Incomplete Inspections
If you do not tear off the old roofing materials it is impossible to do a full Inspection on the sheathing boards and weatherproofing layers of your roof. You can miss what you can’t see. Over roofing prevents your roofer from doing a visible inspection, which may lead to underlying problems being overlooked. A full tear down can reveal areas where your roof may be compromised. Repairs can then be done during the roof replacement process. This is impossible with a re-roofing. When needed repairs are missed, it can cause costly problems later.
Difficult to Fix Leaks
An extra layer of roofing can make identifying and fixing a leak complicated and costly. The re-roofing process also prevents roofers from installing water and ice dam barriers. This can be especially important in areas that experience harsh winters or strong storm damage.
Difficult to Replace Underlayment
Since there is not a tear off with a re-roof, the underlayment cannot be replaced. If the protective layer between the sheathing and the shingles wears out it is very difficult to replace. This can lead to water intrusion and leakage, which can cause costly damage.
Home Devaluation
Since re-roofing can be more of a quick fix option instead of a thorough, long term repair, it can decrease your home’s value. Since the roof will need to be replaced at some point, a re-roofing can be seen as a liability to a home buyer. They will have to tear off and dispose of two-layers when replacing the roof, making it more expensive, and your home more difficult to sell.
Over Roofing Your Home: The Last Word
When it comes to maintaining your home, the roof over your head is one of your most vital considerations. When it comes to doing a re-roofing project or a full roof replacement, it is important to weigh all your options to make an informed decision. Hire a professional roof inspector and get recommendations from a certified roofer, like those at Summit Construction. Ensuring the integrity of the roof over your head deserves no less.
