Are you sure its rising damp. I had damp at the front of my house which appears from the ground up the first floor outside wall, I assumed rising till i actually watched the rain come down, flood over my gutter and bounce off the ground outside and then hit the front of the house. It had clearly been happening for several years. A quick trip up a ladder and i adjusted all my gutter and thats stopped that. Ive got to rip the render off to the first floor level, but thats not a major job as I will rip it off and my builder will re render for me.
As mentioned take a builder and also go on a rainy day and watch carefully.
