Can You Put New Shingles Over Old Ones
Can You Put New Shingles Over Old Ones
Short answer: Technically yes for one layer, but generally NOT recommended.
Installing new shingles over an existing layer -- called an overlay, re-roof, or layover -- is one of the most frequently asked roofing questions. While building codes in most jurisdictions allow a maximum of two total layers of asphalt shingles, the fact that you can does not mean you should. Understanding the risks will help you make the right choice for your home and budget.
Why Overlaying Is Allowed
Building codes generally permit homeowners to install one additional layer of asphalt shingles over an existing single layer, provided:
- There is only one existing layer -- a third layer is never permitted
- The existing roof is in reasonably flat condition (no severe curling, cupping, or buckling)
- The decking is structurally sound
- The roof structure can handle the additional weight
- Local codes have not adopted stricter single-layer-only requirements (an increasing trend)
Why Overlaying Is a Bad Idea
Despite being code-legal in many areas, roofing professionals overwhelmingly advise against overlays. Here is why:
It Hides Damage Underneath
The most important reason to tear off old shingles is to inspect the roof deck. Water damage, rot, mold, and deteriorated sheathing hide beneath old shingles. An overlay covers these problems without addressing them, allowing them to worsen for years until they become structural failures. You cannot assess or repair what you cannot see.
It Adds Significant Weight
A standard square (100 square feet) of asphalt shingles weighs 200-350 pounds depending on the product. A second layer adds 600 to 700 pounds per square (accounting for shingle weight plus the trapped old layer) to the roof structure. For a 2,000 square foot roof, that is an additional 12,000-14,000 pounds. Older homes may not have structures engineered for this load, especially in areas with heavy snow.
It Traps Moisture
Two layers of shingles with old underlayment sandwiched between them create conditions where moisture can become trapped. This moisture has no way to dry and accelerates decay of the decking and supporting structure.
It Shortens the New Roof's Lifespan
Shingles installed over an existing layer run hotter because the old layer prevents proper heat dissipation. The uneven surface beneath causes the new shingles to conform to the texture of the old ones, creating stress points. Both factors reduce the lifespan of the new shingles by an estimated 20-40% compared to shingles installed on a clean, flat deck.
It Prevents Proper Underlayment Installation
Modern underlayment -- especially ice and water shield -- must be applied directly to the roof deck to function correctly. An overlay installs over old shingles and old underlayment, bypassing this critical waterproofing layer.
It Can Void the Warranty
Many shingle manufacturers void or significantly reduce warranty coverage when their product is installed over an existing layer without explicit written approval. See What Voids Your Roof Warranty.
It Is More Expensive to Remove Later
When the double-layer roof eventually needs replacement, the tear-off cost is significantly higher. Crews must remove two layers instead of one, doubling the tear-off labor and disposal fees. A double tear-off adds $1,000 to $3,000 to the next replacement.
It May Violate Updated Local Codes
An increasing number of jurisdictions are moving to single-layer-only requirements, even for asphalt shingles. Check your current local building codes before assuming an overlay is permitted.
When an Overlay Might Be Acceptable
In limited circumstances, an overlay may be a reasonable choice:
- Budget is extremely tight and a tear-off is genuinely unaffordable, and the alternative is leaving a failing roof in place
- The existing layer is flat and in decent condition -- no curling, cupping, buckling, or significant granule loss
- There is no evidence of moisture damage (check the attic for water stains, mold, or soft spots)
- There is only a single existing layer
- The roof structure can handle the additional weight
- You accept the reduced lifespan and warranty limitations
- Local codes permit the overlay
Even when all these conditions are met, a tear-off and clean installation is still the superior approach.
The Right Approach: Tear Off and Start Fresh
The professional recommendation is always:
- Tear off all existing roofing material down to bare decking
- Inspect the decking thoroughly for water damage, rot, mold, and structural issues
- Repair or replace any damaged decking (typically OSB or plywood, $50-$75 per sheet)
- Install proper underlayment -- ice and water shield at eaves, valleys, and penetrations, then synthetic or felt underlayment over the field
- Install drip edge at eaves and rakes in the correct order
- Install new shingles on a clean, flat, properly prepared surface
This approach ensures maximum shingle life, full warranty coverage, and catches hidden problems before they become emergencies.
Cost Comparison
| Factor | Overlay | Tear-Off and Replace |
|---|---|---|
| Upfront cost savings | $1,000 - $3,000 cheaper | -- |
| New roof lifespan | 15 - 20 years (reduced) | 25 - 30 years (full life) |
| Warranty coverage | Often voided or reduced | Full manufacturer warranty |
| Deck inspection | Not possible | Full inspection and repair |
| Next replacement cost | Higher (double tear-off) | Standard single tear-off |
| Cost per year of service | Higher over time | Lower over time |
The overlay saves money today but costs more per year of roof life when you factor in shorter lifespan, reduced warranty, and the future double tear-off. For most homeowners, the tear-off is the better long-term investment.
