🧾 Underlayment Calculator & Ice and Water Shield Calculator – Roofing Roll Estimator
Calculate roofing underlayment rolls required by area, slope, and coverage for shingles or synthetic felt
Use this underlayment calculator and ice and water shield calculator to estimate the number of rolls you’ll need based on roof area, coverage per roll, and waste.
Calculate how many underlayment rolls your roof project requires. This tool accounts for roof area, roll coverage, waste buffer, pitch factor, roof sections, and optional cost per roll. Proper underlayment is essential for waterproofing, protecting against wind-driven rain, and extending roof life.
Measure the total roof deck area in square feet (length × width × pitch). A typical asphalt felt roll covers ~400 sq ft. Synthetic rolls may cover 1,000+ sq ft. Add extra for overlaps, valleys, hips, and cutting waste. Typically 5–15%. Steeper roofs have more surface area. Use a pitch factor (e.g., 1.2 for 7/12 slope). If the roof has multiple sections, enter count. Each adds to total area. Enter roll price to calculate project cost.Result will appear here
💡 Tip: Always order 10–15% extra rolls for valleys and overlaps.
📐 Guidance will appear here after calculation.
✅ Best Practices:
• Start installation from the eaves and work upward.
• Overlap horizontal seams at least 4 inches.
• Overlap vertical seams at least 6 inches.
• Use cap nails or plastic cap staples per manufacturer instructions.
• Install ice & water shield at eaves in cold climates.
• Synthetic underlayment resists tearing better than felt.
• Avoid leaving underlayment exposed longer than manufacturer allows.
• Roll out in straight lines to avoid wrinkles.
• Check local code for required type (felt vs synthetic).
• Store rolls flat and dry before use.
❓ FAQ - Underlayment Questions
Q: What is roof underlayment?
A protective barrier installed between roof deck and shingles to resist water infiltration.
Q: Felt or synthetic — which is better?
Felt is traditional and cheaper, but synthetic is stronger, lighter, and more resistant to UV and tearing.
Q: How much overlap is required?
Typically 4" horizontal, 6" vertical, or as per manufacturer specs.
Q: Do I need underlayment if using metal roofing?
Yes — most codes and warranties require it, even under metal roofs.
Q: Can underlayment be left exposed?
Only temporarily. Felt: 1–2 weeks. Synthetic: up to 3–6 months depending on product.
Q: How much waste should I plan for?
Usually 10–15%, more if the roof has many valleys, dormers, or hips.
Q: Is ice & water shield the same as underlayment?
No — it’s a peel-and-stick membrane used in valleys and eaves for extra waterproofing.
Q: Do warranties require underlayment?
Yes, most shingle manufacturers void warranties if underlayment is missing.
Q: What nails/staples should I use?
Cap nails or cap staples for synthetic; standard roofing nails for felt.
Q: What thickness is typical?
Felt comes in 15# and 30#. Synthetic thickness varies by brand.
Q: What is an underlayment calculator?
An underlayment calculator estimates how many rolls you need from your roof area, coverage per roll, pitch factor, and waste buffer, with optional cost totals.
Q: How do I use an ice and water shield calculator?
Measure linear feet of eaves and valleys where ice & water shield is required, convert to square feet based on roll width, add overlaps and waste, and compute rolls needed. Our estimator supports these inputs alongside standard underlayment.