K
P Property Improve Roof calculator Methodology About Reviewed by a Texas-licensed GC

Property Improve · Roofing

Ice & Water Shield Calculator

Count the rolls of self-adhering membrane for eaves, valleys, low-slope sections, and penetrations — in the South it's for wind-driven rain, not ice.

Where I&W shield goes

The bottom edge of every roof slope. Wraps the entire perimeter of the dripline.
Code: at least 24″ inside the heated wall plane. With overhangs that's typically 36″ total height. Cold-climate code may require 48″+.
Code requires full coverage over any low-slope area when shingles are used.
Eaves coverage330 sqft
Valleys coverage120 sqft
Low-slope coverage0 sqft
Penetrations54 sqft
Total with waste554 sqft
Rolls needed
3
~200 sqft per roll · material cost $330–$525
Why I&W matters in the South. The "ice" part is misleading — Texas, Florida, and Gulf-coast roofs almost never see ice dams. But I&W shield is also the best defense against wind-driven rain, the actual enemy in our markets. Eaves, valleys, and around penetrations are the three places where rain pushes uphill against the shingle pattern. I&W seals around the nails and fasteners; standard underlayment doesn't.
→ Underlayment Calculator
For the field underlayment that goes ON TOP of I&W shield.

More about this estimate

What "ice & water shield" actually does

It's a peel-and-stick membrane that self-seals around nails and fasteners. When you penetrate it with a roofing nail, the membrane closes back around the shaft instead of leaving a hole. That's the magic — and why it matters.

In cold climates the use case is ice dams: snow melts, refreezes at the eave, and water backs up under the shingles. I&W shield seals the deck so backup water can't penetrate.

In Texas, Florida, and Gulf-coast markets the use case is wind-driven rain during tropical storms and thunderstorm fronts. Same underlying physics: water pushed sideways past the shingle's intended water-shed pattern. I&W shield is the seal of last resort.

Code requirements (IRC R905.1.2)
  • Eaves in regions with average January temperatures of 25°F or less: I&W shield required to extend 24″ inside the heated wall. Texas and most of the Gulf are exempt by raw temperature, but many local codes still require eave protection.
  • Valleys on all asphalt-shingle roofs: required.
  • Low-slope (under 4:12): required full coverage when shingles are used.
  • Around penetrations: best practice; not always code-required but always smart.
Why coastal / hurricane markets specify more

Florida HVHZ (High Velocity Hurricane Zone) code requires expanded I&W coverage. Some Texas Gulf coast counties have similar requirements. If your insurance carrier offers a wind-mitigation discount, full I&W coverage of the entire roof (not just edges) is one of the qualifying upgrades — typically 5–15% premium discount.

Standard install order
  1. Decking installed
  2. Drip edge at eaves (under)
  3. I&W shield at eaves, valleys, low-slope, penetrations
  4. Field underlayment over the rest of the roof
  5. Drip edge at rakes (over underlayment)
  6. Shingles
About this calculator

Reviewed by Eurocraft, a Texas-licensed general contractor. Roll coverage assumes standard 36″ × 65′ rolls (~200 sqft).