Mountain Bigfoot HD is a heavy-duty synthetic roofing underlayment engineered for extreme weather conditions. With 365-day UV exposure rating and 50-year limited warranty, it addresses Montana’s unpredictable construction schedules better than standard synthetics that offer 90-180 days of protection. For contractors dealing with weather delays, permit holdups, or labor shortages, this extended exposure window changes the game.
Superior Performance in Montana Conditions
The numbers tell the story. Mountain claims 35x to 1236x stronger tear and tensile strength compared to 30# felt. Testing shows tear strength at 42 lbs machine direction and 38 lbs cross direction. Burst strength hits 240 PSI — numbers that matter when chinook winds rip through the Flathead Valley or ice builds up on Mission Mountain slopes.
Temperature range runs from -70°F to 300°F. That covers everything from January arctic blasts in Great Falls to August heat on south-facing metal roofs. The material is highly water-repellent and reduces warping, wrinkling, and cracking in cold weather — critical when freeze-thaw cycles can destroy lesser underlayments.
Weight matters on the roof. At 38 pounds per roll covering 10 squares, it’s 8x lighter than 30# felt. Crews haul fewer rolls up the ladder and cover more area per trip. Coverage increases 17% per course compared to standard 30# felt.
Technical Specifications
| Specification | Value |
|---|---|
| Roll dimensions | 48” × 250’ |
| Coverage per roll | 10 squares (1,000 sq ft) |
| Weight per roll | 38 lbs |
| Tear strength MD/CD | 42 lbs / 38 lbs |
| Tensile strength MD/CD | 108 lbs / 95 lbs |
| Burst strength | 240 PSI (1650 kPa) |
| Permeability | 0.05 |
| Temperature range | -70°F to 300°F |
| UV exposure rating | 365 days |
| Warranty | 50-year limited |
Certifications include ICC-ESR 5197, ASTM D8257, ASTM D226, AC 188, FL 42105, CAN/CSA A123.3, ASTM E-108, and Texas Department of Insurance compliance.
Installation and Practical Considerations
The Gripwalk surface provides skid-resistant traction — valuable on steep pitches or morning dew. Cool grey surface reduces heat absorption during installation, keeping crews comfortable during summer projects.
Installation follows standard practices with specific requirements. Recommended for slopes 3/12 or greater. For slopes under 4/12, use double coverage with 50% overlap plus 1 inch. Not suitable for slopes under 2/12. Horizontal laps require 4 inches, vertical laps 6 inches.
Fasteners must be corrosion-resistant plastic-cap or metal-cap nails with minimum 1-inch diameter. Miami-Dade approved ring-shank nails with 1-5/8 inch cap work. No staples allowed. Using staples or fasteners without 1-inch caps voids the warranty.
Valley treatment requires specific attention — don’t install continuously over valleys. Use 36-inch wide adhered leak-barrier membrane first, then overlap by 6 inches. Keep fasteners at least 8 inches from valley center.
The material is 100% synthetic/inorganic — it won’t rot or mold. It’s also 100% recyclable, meeting green building requirements for contractors working on LEED projects.
The Bottom Line
Mountain Bigfoot HD solves real problems Montana contractors face. The 365-day UV exposure rating means projects can weather delays without compromising the underlayment. The strength specs handle whatever Montana throws at it — wind, snow, ice, temperature swings.
Applications include mechanically attached asphalt shingles, metal roofing systems, tile, and slate on wood decks including plywood, OSB, and dimensional lumber. It replaces both 15# and 30# felt.
For contractors tired of rushing to dry-in before standard synthetics degrade, or dealing with felt that tears in the wind, Bigfoot HD delivers measurable advantages. The 50-year warranty backs up the performance claims. Not the cheapest option, but for Montana conditions, the extended UV rating alone justifies consideration on projects where timing matters.
FAQ
Q: How long can Mountain Bigfoot HD stay exposed before final roofing?
Mountain Bigfoot HD offers 365-day UV exposure rating — a full year of protection. Final roof covering must be installed within this UV exposure limit to maintain warranty coverage. This extended timeline beats standard synthetics that typically offer 90-180 days.
Q: What fasteners work with Bigfoot HD underlayment?
Use corrosion-resistant plastic-cap or metal-cap nails with minimum 1-inch diameter. Miami-Dade approved ring-shank nails with 1-5/8 inch caps are acceptable. Never use staples — staples or fasteners without 1-inch caps void the warranty.
Q: Can Mountain Bigfoot HD handle low-slope roofs?
Bigfoot HD is recommended for slopes 3/12 or greater. For slopes less than 4/12, install with double coverage using 50% overlap plus 1 inch. The product is not suitable for slopes under 2/12.
Q: How much area does one roll cover?
Each roll measures 48 inches by 250 feet and covers 10 squares (1,000 square feet). This provides 17% more coverage per course than standard 30# felt.
Q: What makes Bigfoot HD better for cold weather than felt?
The synthetic material is highly water-repellent and reduces warping, wrinkling, and cracking in cold weather. It operates from -70°F to 300°F, handling Montana’s temperature extremes. Being 100% synthetic/inorganic, it won’t rot or mold like organic felt can.
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