Difficulties That Arise with Multiple Shingle Layers
Installing a second layer of shingles may seem like an easy way to upgrade your roof without undergoing a full replacement, but this shortcut often causes more problems than it solves. From reduced lifespan to invalid warranties, doubling up on shingles leads to all kinds of issues for homeowners down the road.
Before deciding to layer new shingles over your existing ones, it's important to understand the potential downsides. Learning what can go wrong helps you make an informed choice about your roof's future.
What Are the Problems of Having Two Layers of Shingles
Adding a second tier of shingles may appear convenient initially, but it causes complications over time.
Higher Risk of Water Damage and Leaks
The more layers installed on your roof, the higher the risk of moisture issues. Shingles contain small spaces between each piece, leaving room for water to sneak through. Additional tiers exaggerate this problem, with water getting trapped between layers.
Extra weight from double shingles also causes fastener points to loosen. This allows water to penetrate vulnerable spots, causing leaks that damage roof sheathing and internal structures.
Makes Future Roof Repairs Difficult or Impossible
While installing a fresh layer seems straightforward, removing shingles during later repairs grows extremely difficult with multiple tiers in place. The demolition process takes longer, since workers must pry up 2+ levels of roofing.
In some cases, the roof becomes impossible to rescue. Weight and connection issues prevent repairs, forcing full replacements. This costs homeowners more money in the long run.
Causes Faster Deterioration, Mold, and Rot
Trapped moisture from leaks leads to faster decay of roofing materials. It also accelerates mold growth, which spreads quickly between double shingle layers. This deterioration compromises structural integrity much quicker than usual.
Wet shingles experience loose mineral granules, excessive curling, and increased wind uplift. Extra shingle weight also presses on vulnerable areas, causing premature cracking or holes.
Can Invalidate Roof Warranty Protections
Most roofing warranties only cover leaks and defects if shingles are installed properly per manufacturer guidelines. Adding a second tier often voids these protections since it goes against recommended procedures.
Multiple shingle layers also make leak origin identification difficult. When technicians cannot pinpoint exact damage sources, the warranty claim gets denied.
Weakens Roof Stability and Resilience
Doubling up shingle weight stresses the entire roof structure. Extra mass strains framing, decking, rafters, and trusses not designed to handle excess loading.
This added burden deteriorates resilience against weathering and impact. It also magnifies vulnerability against high winds, storms, snow, and seals. Weakened stability escalates tear-off risk.
Potential Damage Problems from Multiple Shingle Layers
Increased Chance of Leaks and Moisture Damage
Applying shingles atop one another multiplies risk for water infiltration. Extra layers create additional seams and edges for moisture to exploit. More avenues mean more ways for water to penetrate and become trapped.
Exterior temperatures also impact shingles differently when multiples overlap. Heat, cold, and humidity fluctuations cause uneven drying, curling, and gaps.
Trapped Water Causes Rotting and Wood Decay
Leakage feeds fungus growth and accelerates rot damage. Fungi colonies bloom underneath shingles where moisture gets caught between layers. Once wood rots, repair complexity escalates.
Since soft damp wood cannot support new shingles, plywood or OSB decking might need partial or full replacement. This exponentially grows project scope and costs.
Higher Chance of Mold and Algae Formation
Standing water and moisture become breeding grounds for mold, mildew, and algae. Spores take advantage of hospitable areas under multi-tiered shingles. Cleanup difficulty amplifies once colonies establish.
When left unchecked, microscopic roots dig into roof sheathing. Removal processes require potent cleaners, extensive scrubbing, and sometimes decking replacements.
Leads to Premature Granule Loss and Shingle Failure
Mineral granules protect shingle asphalt from UV rays while adding color. But granules erode faster when excessive water exposure weakens bond. Multiple tiers mean faster deterioration as leakage accelerates wearing.
Bare patches cause asphalt to dry out, shrink and crack prematurely. With makeup compromised, multi-layered shingles lose effectiveness quicker.
Structural Issues from Too Many Shingle Layers
Added Weight Stresses Roof Framing
Standard shingles weigh 235-340 lbs per square stack. Doubling layers doubles weight. This burdens structural framework not designed for such heavy loads.
Trusses, rafters, and decking suffer overstress damage like splits, fractures, and warps. Repairs become necessary before new roofing installation.
Vulnerable to Wind and Storm Damage
Extra shingle mass makes roofs more vulnerable against weather events. Without reinforcement, the structure gets overwhelmed by heavy winds, hail, snow or rainfall.
Added weight also reduces wind resilience. Multi-layer roofs suffer blow-offs, uplift, and tears more frequently during storms. Fastener failure grows more likely as well.
Compromises Structural Stability
Excess weight taxes all connection points, including fasteners, adhesives, vents, and flashings. Weaknesses manifest as extra pressure loosens anchored spots.
Gaps then form as shifting allows wind, rain and moisture to penetrate. This deterioration snowballs into instability issues and escalated repairs.
Creates Uplift Pressures and Fastener Failure
Wind flowing over roofs generates uplift forces along the exterior. Added shingle weight makes structures more prone to peeling from these winds.
The amplified upward pressures also bear down on fastening points. This either pries up nails and staples or withdraws them from decking. Both instances allow blow-offs.
Impacts on Roof Life Expectancy and Longevity
Prevents Uniform Weathering and Aging of Shingles
Single-layer roofs experience even heat, light, and moisture exposure across shingles. But multiple tiers age differently with uneven weathering from leaks, moisture traps and lift gaps.
Bottom layers lose granules first while shielding top layers. This causes patching and streaking as materials degrade non-uniformly across roof planes.
Leads to Premature Brittleness, Cracking and Tears
Trapped moisture, leaks, and uneven weathering degrade shingle composition, durability and pliability faster. Asphalt binders dry out, become brittle and develop cracks sooner.
Top layers also abrade base layers during expansion/contraction and wind flutter. This accelerates surface wear and tear failure.
Causes Uneven Thermal Expansion or Contraction
Temperature fluctuations cause shingles to expand and contract. But layered materials react differently, with bottom layers hindering top layer movement.
Warping, buckling and loosening result as restraints build internal shear stresses. Bond release then allows blow-offs in wind storms.
Extra moisture exposure underneath accelerates mineral stripping, revealing vulnerable asphalt. Ultraviolet rays then degrade petroleum-based binders, causing brittleness, shrinking and cracking.
These effects multiply exponentially when combined with abrasion from upper layers shifting. Granule loss then leads to advanced aging.