Ross Kirkland
There could be multiple reasons for this, here's a couple to give you an idea but you would need to get someone out to have a look and could do so by posting in the job section. 1) Water is getting into the rendered substrate from higher up behind paint, or water is getting sooked up into the render if it continues down to ground level without any dpc or break. This dampness would cause the paint to flake due to the wetting/drying cycle of the surface its adhered to and/or expansion contraction. 2) The substrate was never properly prepared, or was in poor state when first painted. You can improve adhesion of paints by removing all loose paint and using a stabilising solution. This binds the surface layer and allows the fresh paint to properly adhere to the surface.
