A roof overlay is the installation of a new layer of roofing over an existing roof without first removing the old roof covering. It is also sometimes called a roof layover or reroof-over.
A roof overlay can reduce tear-off labor, disposal, and project time, but it is not appropriate for every roof. The condition of the existing roof, the roof deck and structure, the type and number of existing roofing layers, local building requirements, and the roofing manufacturer’s installation instructions all need to be considered.
If you are deciding between a roof overlay and a complete roof replacement, here are the most important differences, advantages, limitations, and Los Angeles requirements to understand.
What Is a Roof Overlay?
A roof overlay involves installing a new roof covering directly over an existing roof instead of tearing the old roofing off down to the roof deck.
Roof overlays are most commonly associated with asphalt shingle roofs, although whether an overlay is allowed depends on the existing roofing system, proposed new material, local building code, and manufacturer requirements.
The terms roof overlay and roof layover are often used to describe the same general process. Building departments may also use terms such as reroofing or reroof-over.
How Does a Roof Overlay Work?
Before installing a new roof over an existing one, a roofing professional should evaluate whether the existing roof is suitable for an overlay.
This typically includes checking:
- The type and number of existing roofing layers
- The condition of the existing shingles or roof covering
- The condition of the roof deck and structural components
- Whether there is evidence of leaks, trapped moisture, rot, or deterioration
- Whether the structure can support the additional weight
- The condition of valleys, edges, vents, penetrations, and roof flashing
- Whether local building requirements allow another roof covering to be installed
- Whether the proposed roofing manufacturer permits the installation method
If the roof qualifies, the existing surface is prepared and the new roofing system is installed according to applicable code and manufacturer requirements.
The exact installation process depends on the roofing system. A new roofing underlayment, flashing components, edge materials, or other accessories may be required depending on the project.
Roof Overlay vs. Roof Replacement
The primary difference between a roof overlay and a full roof replacement is whether the existing roofing material is removed.
With an overlay, an approved new roof covering is installed over the existing roof. With a full replacement, the existing roofing is removed so the roof deck and other underlying components can be exposed, inspected, repaired if necessary, and covered with a new roofing system.
A roof overlay can involve less demolition and disposal, but a full replacement provides much better access to the roof deck and underlying structure.
That makes a complete replacement the better choice when there are concerns about water damage, deteriorated decking, structural problems, multiple existing roof layers, or other concealed conditions.
What Are the Pros of a Roof Overlay?
Less Tear-Off Labor
Because the existing roof covering is not completely removed, an overlay can reduce the amount of demolition required at the beginning of the project.
Less Roofing Debris
A full tear-off can generate a significant amount of old roofing material that must be removed from the property and disposed of. Keeping an allowable existing roof covering in place can reduce that waste.
Potentially Lower Upfront Cost
Eliminating some tear-off labor and disposal can make a roof overlay less expensive than a complete replacement in certain situations.
However, there is no universal percentage savings. Actual roof overlay cost depends on the roof size, roofing material, labor, repairs, access, permit requirements, and condition of the existing roof.
Potentially Shorter Project
Because less material must be removed, an overlay may take less time than a complete tear-off and replacement. The actual project length still depends on roof size, complexity, weather, repairs, and the roofing system being installed.
What Are the Cons of a Roof Overlay?
Hidden Roof Deck Problems
One of the biggest disadvantages of an overlay is that the existing roof covering remains in place. That can limit access to the roof deck and make concealed deterioration harder to identify.
If a roof has experienced ongoing leaks, trapped moisture, rot, or damaged sheathing, installing another roof covering over it does not correct those underlying problems.
Additional Weight
A new roofing layer adds weight to the roof structure. Before an overlay is approved, the structure must be capable of supporting the additional load.
This is especially important when heavier roofing materials are involved or when an existing roof already has multiple layers.
Future Tear-Off May Be More Involved
An overlay can postpone removal of the existing roofing, but those additional layers may eventually need to be removed during a future replacement.
That can increase the amount of tear-off and disposal required later.
Limited Ability to Inspect the Entire Roof Deck
A complete tear-off exposes the decking across the roof, giving the installer an opportunity to identify damaged or deteriorated areas before the new roof is installed.
An overlay does not provide the same level of access.
Manufacturer Requirements May Limit Overlay Installation
Roofing manufacturers establish installation requirements for their products. Whether a roofing material can be installed over an existing roof, and whether doing so affects warranty coverage, depends on the specific manufacturer and roofing system.
Check the applicable installation and warranty requirements before selecting an overlay solely to reduce project cost.
When Can You Put a New Roof Over an Old Roof?
A roof overlay may be an option when the existing roof is in relatively good condition and the building, roof structure, roofing materials, and local code all permit another roof covering.
Conditions that may support an overlay include:
- The roof structure can support the additional weight
- The roof deck is structurally sound
- The existing roofing is securely attached
- There is no significant moisture damage or deterioration
- Roof drainage is adequate
- The existing roofing material is compatible with the proposed new roof
- The number of existing roof layers is within applicable limits
- Local building requirements allow the installation
An inspection by a qualified roofing professional can help determine whether those conditions exist.
When Is a Roof Overlay a Bad Idea?
A complete tear-off and replacement is generally more appropriate when the existing roof has significant problems that should be exposed and corrected.
A roof overlay may not be a good choice when:
- The roof has active or recurring leaks
- The roof deck is soft, rotted, damaged, or otherwise questionable
- There is evidence of trapped moisture
- The roof structure cannot safely support another layer
- The existing roof already has the maximum number of allowable layers
- The existing and new roofing systems are incompatible
- The roofing manufacturer does not allow the proposed installation
- Local building requirements prohibit the overlay
If there is uncertainty about the condition of the roof deck, removing the existing roofing provides the best opportunity to inspect and repair the underlying structure.
How Long Does a Roof Overlay Last?
There is no single lifespan that applies to every roof overlay.
How long an overlay lasts depends on the roofing material, condition of the original roof, quality of installation, ventilation, climate, maintenance, and whether the installation follows manufacturer and building-code requirements.
A properly installed overlay on a suitable roof may provide years of additional service, but it should not automatically be expected to perform exactly like a complete roof replacement installed over a fully exposed and inspected roof deck.
If long-term performance is the main priority, compare the expected life of an overlay with the cost and benefits of a complete replacement rather than choosing based only on the initial price.
How Much Does a Roof Overlay Cost?
Roof overlay cost varies significantly by project. Important factors include:
- Total roof area
- Roof pitch and complexity
- Existing roofing material
- New roofing material
- Condition of the existing roof
- Necessary repairs
- Flashing and penetration work
- Labor costs
- Permit and inspection requirements
An overlay can sometimes cost less than a full replacement because there is less tear-off and disposal. However, homeowners should compare complete estimates rather than assuming a fixed percentage of savings.
You can read more about the factors affecting replacement pricing in our guide to whole roof replacement cost versus partial repairs.
Roof Overlay Requirements in Los Angeles
If your property is located within the City of Los Angeles, reroofing is regulated by the Los Angeles Department of Building and Safety (LADBS).
LADBS allows existing roof coverings to remain in certain situations when inspection or other evidence shows that:
- The roof structure can support the additional weight
- The roof sheathing is solid and structurally sound
- Roof drainage is sufficient
- The existing roofing is securely attached
- Existing insulation is not water-soaked
- Applicable fire-retardant requirements are maintained
The exact number of existing roof layers that may remain depends on the roofing material and applicable requirements.
For composition shingles, LADBS states that shingles may be installed over solid sheathing or over a maximum of two existing layers of composition shingles that were installed over solid sheathing.
However, reroofing over existing wood shakes or wood shingles is not permitted in the City of Los Angeles. Those materials must be removed before new roofing is installed.
LADBS also imposes specific fire-classification requirements, including additional requirements for properties within designated fire districts.
You can review the current requirements on the LADBS reroof information page.
Keep in mind that City of Los Angeles rules do not automatically apply throughout Los Angeles County. Properties in other incorporated cities may fall under their own local building departments.
Do You Need a Permit for a Roof Overlay?
A roof overlay may require a building permit depending on the jurisdiction and scope of the project.
Within the City of Los Angeles, LADBS requires permits for applicable reroof work and provides specific reroof permitting and inspection requirements.
Before beginning an overlay, verify which building department has jurisdiction over the property and confirm the permit requirements for the proposed roofing system.
For a broader explanation of reroofing, replacement, repair, and permitting requirements, see our guide: When Do You Need a Permit for Roof Work?
Frequently Asked Questions About Roof Overlays
What is a roof overlay?
A roof overlay is the installation of a new roof covering over an existing roof without completely removing the old roofing first. It is also sometimes called a roof layover.
Is a roof overlay the same as a roof layover?
Yes. Roof overlay and roof layover are commonly used to describe the same general method of installing a new roof covering over an existing one rather than performing a complete tear-off.
Is a roof overlay cheaper than a roof replacement?
It can be. An overlay may reduce tear-off labor and disposal costs, but the actual savings depend on the roof, materials, repairs, labor, and permit requirements. There is no fixed percentage by which an overlay will always cost less.
How long does a roof overlay last?
The lifespan depends on the roofing material, existing roof condition, installation quality, ventilation, climate, and maintenance. An overlay should not automatically be assumed to last as long as a complete replacement installed over a fully exposed and inspected roof deck.
Can you put a new roof over old shingles?
Sometimes. Whether new roofing can be installed over existing shingles depends on the condition of the roof, number of existing layers, roof structure, local building requirements, and manufacturer instructions.
Can you install a roof overlay in Los Angeles?
Yes, in some situations. LADBS permits certain existing roof coverings to remain when structural, sheathing, drainage, attachment, insulation, fire, and other requirements are satisfied. Some existing roofing materials, including wood shakes and wood shingles, must be removed before reroofing.
Do you need a permit for a roof overlay?
A permit may be required depending on the jurisdiction and scope of the project. City of Los Angeles reroof projects are subject to LADBS permitting requirements.
Choosing Roofing Materials for an Overlay or Replacement
Whether you are planning a roof overlay or a complete replacement, choosing a roofing system that is compatible with the property, roof structure, local requirements, and installation method is essential.
LA Roofing Materials supplies roofing and waterproofing materials for residential and commercial projects throughout the Los Angeles area, including asphalt shingles, tile roofing materials, slate roofing materials, underlayment, waterproofing products, metal roofing, and related roofing accessories.
If you are planning a reroof or replacement and need help sourcing materials for the project, contact LA Roofing Materials.
Roofing, permit, and building-code requirements vary by jurisdiction and can change. This article provides general information and is not a substitute for guidance from the building department, roofing manufacturer, engineer, or contractor responsible for your project.