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Underlays

Standard Underlay

BLM Standard Underlay and Grade A1F Building Paper conform to Lead Sheet Association recommendations and if laid correctly will protect the Lead from imperfections in the roof decking and allows the underside of the Lead some breathing space.

Standard Underlay

  • Sold in rolls of 25m x 1.0m.
  • Manufactured from non-woven polyester to 220g/M2.
  • All Lead Sheet over 600mm wide should have underlay fitted.
  • BLM Standard underlay will not rot or become adhesive in hot weather.

Building Paper

A traditional, reinforced bitumen-bonded building paper laminate manufactured with wet strength kraft paper conforming to BS1521, Class A.

  • Sold in rolls of 25m x 1.0m.
  • Must be fitted over the whole substrate area.
  • Ideal for use on plywood substrates.
  • Protects Lead against alkalis from concrete, stone and screed surfaces.

Technical Data Sheets (Printable PDF's)

Standard Underlay

Grade A1F Building Paper 

  • When fixing Underlay avoid using nails. Use staples on a timber substrate.
  • Underlays should be laid across the fall of a roof.
  • Avoid forming joints above Underlay. Close proximity of a flame may cause damage.
  • When joining adjacent sheets, overlap the material. Use a sharp knife or shears to cut the Underlay.
  • Wood Rolls should be fitted over the Underlay.