Synthetic vs. Felt Roof Underlayment
ComparisonComparing synthetic polypropylene roof underlayment against traditional #15 and #30 asphalt-saturated felt — tear strength, weight, UV exposure, and cost.
Comparing: Synthetic Roof Underlayment
Quick Comparison
| Criterion | Synthetic Roof Underlayment | Material 2 |
|---|---|---|
| Material | Woven or non-woven polypropylene/polyethylene | Organic felt saturated with asphalt (#15 or #30) |
| Weight | 3–8 lbs/square | 15–30 lbs/square |
| Tear Strength | 20–50 lbs (MD) | 5–10 lbs (MD) |
| UV Exposure | 4–6 months | 30 days maximum |
| Water Resistance | Does not absorb water; lays flat when wet | Absorbs water; wrinkles and buckles when wet |
| Coverage per Roll | 10 squares (48" × 250') | 2–4 squares (36" × 72'/144') |
| Cost per Square | $5–$12/square | $3–$7/square |
| Slip Resistance | Non-skid surface — safer for crew walking | Slippery when wet — safety concern |
| Code Compliance | ASTM D4869 | ASTM D226 Type I (#15) / Type II (#30) |
Our Recommendation
Synthetic underlayment is the clear winner for new construction and re-roofing projects. The faster installation (larger rolls, lighter weight), superior tear resistance, and extended UV exposure justify the modest cost premium. Use #30 felt only when matching an existing underlayment layer for overlay installations, or when the roofing manufacturer specifically requires felt.
Detailed Analysis
Synthetic underlayment has become the industry standard for good reason — it installs faster, lasts longer on the roof during construction, and provides a safer working surface for the roofing crew.