SIGA Majcoat® 350 Thermally Weldable Breathable Roof Underlay (1.5 x 33.4 m; 50 m²)

SIGA Majcoat® 350 is a diffusion-open, thermally weldable roof underlay that withstands driving rain and protects roof structures from the outside on pitches from 5° and in extreme conditions. One roll is 1.5 x 33.4 m and covers 50 m².

The membrane has a 3-layer structure: a carrier fleece with a special TPU coating on both sides. It is extremely sturdy, tearproof and waterproof, and the overlaps are welded with hot air instead of taped, which gives high security at all joints. A printed cutting and laying aid saves time on site.

Majcoat® 350 can be used as a temporary roof covering for up to 16 weeks and meets ZVDH classes UDB-A and USB-A for underlay and sub-roof membranes.

Roof underlay main features

• Roll size: 1.5 x 33.4 m (50 m²)
• Roll weight: 19 kg
• Structure: 3 layers, carrier fleece with TPU coating on both sides
• Joints: thermally weldable (hot air)
• Integrated adhesive strip (SOB): no
• Thickness: 0.8 mm
• Mass per area: 380 g/m²
• sd value: 0.3 m (EN ISO 12572)
• Water tightness: class W1 (EN 1928)
• Max. tensile force: 440 N/50 mm lengthwise, 500 N/50 mm crosswise
• Nail tear resistance: 245 N lengthwise, 235 N crosswise
• Temperature resistance: -40 to +90 °C, short-term up to +120 °C
• Fire class: E (EN 13501-1)
• ZVDH class: UDB-A / USB-A
• Temporary roof covering: up to 16 weeks
• Minimum roof pitch: 5°

Applications

SIGA Majcoat® 350 is designed as an underlay and sub-roof membrane where a fully welded, highly secure roof layer is needed.

• Low-pitch roofs from 5°
• Roofs exposed to extreme weather or long construction periods
• Sub-roofs where all joints must be fully welded
• Prefabricated roof elements

How to install the roof underlay

Install the membrane on the outside of the roof structure before the counter battens and battens.

1. Lay the first sheet with the printed side facing you.
2. Lay the second sheet with an overlap of about 10 cm, using the printed laying aid.
3. Make a test weld before starting.
4. Weld the overlaps with a hot-air welder at about 200 °C.
5. Fix the membrane above the welded joint.
6. Fix the counter battens directly to the load-bearing structure (e.g. rafters) with suitable screws, such as full-thread screws.

• Tip: SIGA recommends nail sealing tape under the counter battens for effective weather protection.
• Tip: for details and connections SIGA lists Wigluv® 100, 150 & 300 and nail sealing tape as related products.
• Tip: Majcoat® 350 can also be prefabricated and delivered as finished roof sections.