Key Takeaways
- Surface Tension Matters: Shrink wrap creates a drum-tight, slick surface that sheds snow, whereas woven tarps create friction and trap accumulation.
- The Weight of Water: Wet snow can weigh 20+ lbs per cubic foot. Blue tarps with “ponding” pockets can easily exceed their burst strength at grommet points.
- Seamless Strength: Heat-welded seams in shrink wrap maintain 100% structural integrity, unlike sewn or taped tarp seams that leak under standing snow.
- Preventing Collapse: High-tensile 12-mil shrink wrap distributes load evenly, preventing the point-load failures common with nailed tarps.
As winter settles across the country, property owners with damaged roofs face a critical question: Will my temporary protection hold up against the weight of snow? For those relying on standard blue tarps, the answer is often a disastrous “no.”
At StormWrappers, we engineer solutions that withstand the elements. Understanding shrink wrap snow load capacity is essential for anyone protecting a residential or commercial asset through the winter months.
What is Shrink Wrap Snow Load Capacity?
Shrink wrap snow load capacity is the structural ability of heat-sealed, low-density polyethylene (LDPE) to withstand the static and dynamic weight of accumulated snow and ice. Unlike standard tarps, 12-mil shrink wrap is installed to be “drum-tight,” creating a high-tensile surface (up to 3,000 PSI tensile strength) that actively sheds snow rather than trapping it. This capacity is defined not just by the material’s breaking point, but by its ability to prevent the ponding that leads to structural failure.
The Physics of Snow: Calculating the Weight on Your Roof
To understand why temporary covers fail, we must first look at the load they are asked to carry. Snow is not just fluffy white powder; it is heavy, suspended water.
- Light, Fluffy Snow: ~3-5 lbs per cubic foot.
- Settled/Packed Snow: ~12-15 lbs per cubic foot.
- Wet, Heavy Snow: ~20+ lbs per cubic foot.
- Ice: ~57 lbs per cubic foot.
If you have a 20×20 foot section of damaged roof covered by a tarp, and you receive just one foot of wet snow, that tarp is suddenly supporting 8,000 pounds of weight (400 sq ft x 20 lbs). This is where the difference between a “cover” and an “engineered enclosure” becomes a liability issue.
For a deeper dive into how winter weather impacts structural stability, read our analysis on Structural Integrity in December: 12-Mil Shrinkwrap vs. The Weight of Snow.
Why Blue Tarps Fail: The Mechanics of Collapse
We often see “blue tarp nightmares” in January. The failure of a blue tarp under snow load is rarely due to the plastic dissolving; it is a mechanical failure caused by design flaws.
1. Point-Load Failure (Grommets)
Blue tarps are secured using grommets spaced every 18-36 inches. When snow accumulates, the weight pulls against these specific points. A single grommet cannot withstand hundreds of pounds of tension, leading to tears. Once one grommet fails, the load shifts to the next, causing a zipper-effect failure.
2. The “Ponding” Effect
Because tarps are mechanically fastened (nailed or tied) rather than heat-shrunk, they inevitably sag. This sag creates a depression where melting snow collects. This water re-freezes into ice, increasing the weight density from 20 lbs/ft³ to nearly 60 lbs/ft³. This is a primary cause of secondary interior water damage.
3. Friction and Surface Texture
Blue tarps are woven. This texture creates friction that holds snow in place. In contrast, the smooth surface of virgin resin shrink wrap encourages snow to slide off, especially on pitched roofs.
For more on the risks of traditional methods, see Why Blue Tarps Fail When You Need Them Most.
The Engineering Advantage: Shrink Wrap Snow Load Capacity
StormWrappers uses 10 to 12-mil LDPE shrink wrap, which offers a fundamentally different approach to handling snow loads.
Heat-Sealed Integrity
Our installation process involves heat-welding seams to create a single, continuous sheet of plastic. There are no grommets to tear out. The load is distributed evenly across the entire surface area and the perimeter attachment, reducing stress concentrations.
Drum-Tight Tension
When we apply heat, the material shrinks by approximately 20-25%. This creates a “drum-tight” fit over the roof structure.
- No Sagging: Prevents water pockets from forming.
- Aerodynamic: Reduces wind whip, which prevents the material from cracking in freezing temps.
- Shedding: The slick, tensioned surface allows gravity to clear the roof of snow more effectively than loose tarps.
Data Comparison: Shrink Wrap vs. Blue Tarp
The following table illustrates the material differences that contribute to snow load capacity:
| Feature | Standard Blue Tarp | StormWrappers Shrink Wrap |
|---|---|---|
| Material Construction | Woven Polyethylene strands (Permeable over time) | 100% Virgin Resin LDPE (Solid membrane) |
| Thickness | 2 – 5 Mil (Typical) | 9 – 12 Mil (Heavy Duty) |
| Snow Shedding | Low: Woven texture traps snow; sagging creates pockets. | High: Slick, tensioned surface promotes sliding. |
| Seam Strength | Weak (Sewn or Taped); leak prone. | Heat-Welded (Monolithic strength). |
| Load Failure Mode | Grommet tear-out; zipper failure. | High tensile stretch (up to 600% elongation before break). |
| Winter Lifespan | 30 – 90 Days (degrades rapidly in UV/Cold) | 6 – 12 Months (UV Inhibited) |
Preventing Ice Dams and Secondary Damage
One of the hidden dangers of low-capacity roof covers is the formation of ice dams. When a tarp sags and collects water, that water freezes at the eaves, blocking drainage. This forces water to back up under the tarp and into your home.
Because StormWrappers installations are seamless and tight, they eliminate the ridges and valleys where ice dams typically form on temporary covers. For specific tips on managing ice, check out 5 Comprehensive Steps to Prevent Ice Dams This Winter.
Commercial Considerations
For commercial building managers, the risk profile is even higher. A failed tarp on a warehouse or apartment complex can lead to massive liability claims and inventory loss. Commercial insurance policies often favor or fully cover shrink wrap because it mitigates the risk of further loss. Learn more about why risk managers prefer our solution in Why “Blue Tarps” Are a Red Flag for Commercial Risk Managers.
FAQ: Snow Loads and Roof Protection
How much weight can shrink wrap hold?
While specific “pounds per square foot” ratings depend on the underlying framing structure, 12-mil shrink wrap has a tensile strength of roughly 3,000 PSI. In practical terms, a properly framed and tensioned shrink wrap roof can support heavy snow loads (20-30 PSF) without tearing, provided the underlying structure is sound.
Can you shrink wrap a flat roof for winter?
Yes. However, on flat roofs, we often build a wooden substructure or “pitch” to ensure water and melting snow run off. Without this pitch, even shrink wrap can hold standing water, though it will not leak like a woven tarp. See The Science Behind Shrink Wrap for more details.
Will the shrink wrap crack in freezing temperatures?
No. Our premium shrink wrap contains UV inhibitors and is designed to remain flexible in extreme cold. Unlike cheap tarps that become brittle and crack, virgin resin LDPE retains its elasticity.
Don’t leave your property vulnerable to the crushing weight of winter. If your roof is damaged, a blue tarp is a gamble you can’t afford to take. Contact StormWrappers today to secure your property with a solution engineered to handle the load.
