On timber, fascias are often installed on new builds on top of a tanalised timber bacit. uPVC Fascias Soffits Technical information. RAL lour: White 9010. Product Length Tolerance: +-5mm. All Sizes Available: 100mm, 125mm, 150mm, 175mm, 200mm, 225mm, 250mm, 300mm or 405mm, Measured externally add 9mm.