The invention relates to a flat roof structure comprising a water attenuation layer comprising at least one water attenuation layer comprising at least one water attenuation element formed of man-made vitreous fibres bonded with a cured binder composition. The flat roof structure further comprises a water reducing layer below the water attenuation layer, and at least one drainage point in fluid communication with the water attenuation layer and arranged to direct water from the flat roof structure towards the ground. The binder is an aqueous composition free of phenol and formaldehyde comprising:



a component (i) in form of one or more lignosulfonate lignins having a carboxylic acid group content of 0.03 to 2.0 mmol/g, based on the dry weight of the lignosulfonate lignins,
a component (ii) in form of one or more cross-linkers.