installation...
Weathertight Durable Roof Underlay should be fixed in accordance with BS 5534 and BS 8000 Part 6.
Weathertight Durable Roof Underlay should be installed by laying it horizontally across the rafters with the logo-side containing the lap lines laid upwards and visible.
Each horizontal lap should be draped over the rafters or counter battens without sagging and not pulled taut. Horizontal and vertical laps must be laid in accordance with BS 5534.
Horizontal laps should be secured under battens. Where laps are made that are between the batten gauges then it is essential that additional fixings are used to secure the lap. These fixings should be no more than 25mm from the edge of the overlap.
At the hips of the roof, Weathertight Durable Roof Underlay on both sides of the hip should be draped over with a minimum overlap of 150mm. Alternatively, a strip of Weathertight Durable Roof Underlay that is a minimum 600mm wide should be laid along the hip rafter and draped equally on both sides.
At the ridge of the roof, Weathertight Durable Roof Underlay should be lapped by a minimum of 150mm from each slope of the roof apex.
Weathertight Durable Roof Underlay should not be permanently exposed to UV radiation. At the Eaves of the roof, Weathertight Durable Roof Underlay should be lapped over and onto an Eaves Protection System that is fitted into the eaves gutter system.
In Roof Valleys, a minimum 600mm wide strip of Weathertight Durable Roof Underlay should be laid over the valley bed / board, under the valley lining. The main roof underlay feeding into the valley from each roof plane should then be secured over the valley lining in accordance with BS 8000 Part 6.
If Weathertight Durable Roof Underlay is damaged during installation, repair can be carried out by over-laying an additional layer over the damaged area ensuring that the repairing section is overlapped by a minimum 150mm.