Material

Fiberglass base

Grades / Types

• 1F Felt: Thin, lightweight, often used under slates
• 3B Felt: Heavier, more durable, commonly used under tiles
• Torch-on / SBS modified: For flat roofs

Roll Size

Width: 1 m
Length: 8–15 m per roll (varies by manufacturer)

Thickness

3–5 mm (depending on grade)

Weight

~3–5 kg/m² (depending on type and thickness)

Fire Rating

BS EN 13501-5: typically Class BROOF(t1) for pitched roofs

Fixing

Nailed with clout nails or staples;
Overlapping typically 75–100 mm along length and 150 mm across width

Usage / Application

Underlay for pitched roofs beneath slates or tiles;
Provides secondary water protection;
Breathable variants available for ventilated roofs