Use Rigid Foam Underneath Sidewalk to Control Water
I wouldn't go forward with that plan.

Diverting the water three feet away from the foundation won't stop the water from getting to your foundation. You need to put a french drain in and ensure that there is an outlet for the water to go somewhere where it won't damange anything. 

You can buy premade french drain material at your local home improvement store of you can building your own with gravel and perforated pipe. It's generally  pretty cheap either way. 

Also, ensure that you have proper slope for your french drain or you won't have flow like you need to ensure that the water gets moving.