We advise anyone who is building parapet walls (walls that the roof does not cover) that special attention must given made to sealing the tops of the walls, otherwise water may seep down through the walls and wet the plaster sheet on the internal part of the walls, resulting in mould.
Water seepage can also loosen the render on the outside of the walls, and the resulting damage can be very expensive to repair.
We suggest that the top of the wall be flashed properly, and recommend the use of polystyrene capping sprayed with polyurethane for a permanent finish. These cappings can also be decorative.
Contact us for any other advice.