RussFast LR Underlay

RussFast LR Underlay provides a high level of vapour permeability – helping to avoid the risk of harmful condensation, whilst remaining completely airtight. Manufactured using high-quality material, the underlay offers a high performance in all UK locations, providing resistance against wind uplift on the roof and acting as a reliable secondary barrier against wind-driven rain and snow.

Roll Size: 50m x 1m

Resistance to wind pressure – 1676Pa, tested to BS5534.
Fully independently certified by BM Trada.
UKCA marked.

Key features

• Can be used in all UK locations (zones 1-5)
• Excellent nail tear strength
• Fully watertight and airtight
• Helps to alleviate condensation risk in the roof space in accordance with BS5250
• Easy to cut and lightweight for handling
• No tapes required

Technical Information
Weight184 (-8) gsm
Resistance to water penetration
Before artificial ageing:
After artificial ageing:

Class W1
Class W1
Maximum tensile strengthMD
320 (-20)N/50mm
330 (-20)N/50mm
300 (-30)N/50mm
290 (-20)N/50mm
Before artificial ageing:
After artificial ageing:

90 (+15)%
70 (-25)%

90 (+15)%
70 (-25)%
Tear Resistance (nail shank)190 (-15)N200 (-15)N
Flexibility at Low
Water Vapour
Equivalent Air Layer
Reaction to Fire(NPD)