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Koratech Classic Roof Underlay 50 x 1m


Sandtoft Koramic VPM Classic underlay will provide temporary protection against rain for up to a month prior to the installation of the tiles or slates. If the exposure period exceeds one month then advice should be sought from Sandtoft Technical Department.

Can be used as a secondary line of deference against wind, driven rain and snow. Sandtoft Koramic VPM Classic underlay will reduce the wind loading on the roof tiles and slates.

  • Suitable for use with all Sandtoft tiles and slates.
  • Can be used in both warm and cold roof designs on any roof shape and building type.
  • Highly vapour permeable, but entirely watertight.
  • Helps to avoid condensation risk in the roof space in accordance with BS 5250
  • UV and heat resistant, tough and durable.
  • Does not generate nuisance noise under wind loading.
  • Easy to cut and lightweight to handle.
  • Can be used in cold roofs without restriction for wind uplift in all exposure conditions in the UK and Ireland.
  • Can be used as a temporary roof covering.
Technical Info
Technical Info
Technical data   Koratech Classic           Koratech Super
Roll size 1.5 x 50m 1.5 x 50m
Material weight   142 g/m2 160 g/m2

Water vapour transmission at
25 °C/75%RH (grams/m2/day)

1112 1166
Water vapour resistance (MNs/gm)  
(Meganewton seconds per gram)      
0.18 0.18
Tensile strength unaged (N/50mm)    
Longitudinal 247 389
Transverse 197 349
Tensile strength aged (N/50mm)(1)    
Longitudinal 179 -
Transverse 147 -
Wet strength (N/50mm)(2)    
Longitudinal 240 -
Transverse 205 -
Nail tear strength (N)                      
Longitudinal 194 389
Transverse 260 395
Wind uplift resistance (KPa)                      
Batten spacing 350mm 0.5 1.0
Batten spacing 330mm 0.5 1.0
Batten spacing 300mm 1.0 2.0
Batten spacing 250mm 2.5 2.0

(1) UVA aged for 336 hours at 50 °C & heat aged for 90 days at 70 ± 2 °C
(2) Wet strength soak at 23 °C for 24 hours €“ tested surface wet            

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