Where to use
Where a new lean-to extension meets an existing building, the original external wall becomes an internal partition below the roof line and must be protected from dampness and the penetration of rainwater. Similarly, when a flat roof is resurfaced with added insulation, or is reconstructed as an inverted roof with top paving, the roof level may be raised and thus require the skirting and its corresponding damp proof course to be lifted.
In addition, existing cavity trays which have been poorly constructed or have rotted allowing water to leak through must be replaced.