Roofing Ice and Water Shield Calculator
Estimate ice-and-water membrane area, full rolls, purchased coverage and material cost for eaves and valleys using editable widths, overlaps and product coverage.
Default project preview
4 rolls
Protected eave area
504 ft²
Protected valley area
72 ft²
Base membrane area
576 ft²
Purchased coverage
780 ft²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Building length
Enter this project assumption in ft. The current imperial default is 40 ft.
End overhang
Enter this project assumption in ft. The current imperial default is 1 ft. Minimum: 0.
Protected eave lines
Enter this project assumption in a unitless value. The current imperial default is 2. Minimum: 1.
Membrane width at eaves
Enter this project assumption in ft. The current imperial default is 6 ft.
Total valley length
Enter this project assumption in ft. The current imperial default is 24 ft. Minimum: 0.
Membrane width at valleys
Enter this project assumption in ft. The current imperial default is 3 ft. Minimum: 0.
Overlap allowance
Enter this project assumption in %. The current imperial default is 10 %. Minimum: 0. Maximum: 30.
Cut and waste allowance
Enter this project assumption in %. The current imperial default is 10 %. Minimum: 0. Maximum: 30.
Coverage per roll
Enter this project assumption in ft². The current imperial default is 195 ft².
Price per roll
Enter this project assumption in a unitless value. The current imperial default is 95. Minimum: 0.
How to read the outputs
Protected eave area
2 eave lines. Default preview: 504 ft².
Protected valley area
entered valley dimensions. Default preview: 72 ft².
Base membrane area
before allowances. Default preview: 576 ft².
Purchased coverage
full rolls. Default preview: 780 ft².
Coverage remaining
above calculated order. Default preview: 88.8 ft².
Material cost
membrane rolls. Default preview: $380.00.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Base area = protected eave length × eave count × membrane width + valley length × valley width. Overlap and waste percentages are added before rolls are rounded up.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Estimate self-adhered roof membrane from eaves, valleys, penetrations and local coverage rules.
Calculation steps
- 1Measure eave length and required upslope coverage.
- 2Add valleys, walls and penetration zones.
- 3Include side and end laps.
- 4Divide by actual roll coverage and round upward.
Worked numerical example
Two 60 ft eaves with a 6 ft membrane width require 720 ft². Adding two 20 ft valleys at 3 ft wide adds 120 ft², for 840 ft² before laps and waste.
Purchasing and rounding
Use the exact roll width and net coverage, and verify substrate, temperature and primer requirements.
Interpret the result
The calculator estimates membrane area; required locations and extent depend on climate, code and roofing-system instructions.
Page-specific assumptions
- Simple rectangular membrane zones.
- Net roll coverage reflects laps.
- One membrane product.
Common mistakes
- Using gross roll area.
- Stopping short of the required interior-wall line.
- Applying over wet or incompatible substrate.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Roofing Ice and Water Shield Calculator questions
Does every roof require the same membrane width?+
No. Required protection depends on roof design, climate, product instructions and local requirements.
Why include overlap separately from waste?+
Overlap is consumed in installed laps, while waste covers cuts, starts, ends and damaged material.
Does this include underlayment for the full roof?+
No. It estimates only the entered eave and valley protection zones.