Hi Stephanie,
It really depends on the house. If you are living in your house for 30 years and add a new kitchen and bathrooms over the years your not going to add the amount you spent on these renovations to your home price.
However, as a investor the swing works a little different. We buy discounted properties that a lot of the time have unusable or very dated kitchens and bathrooms which decrease the value. From there we calculate a number for all needed repairs and upgrades to get the full asking price. So as far as many parts of the process your really restoring maximum value to the house that once lost all value.
Adding value to me is much different. Adding value would be changing the features of a house with an addition for instance, or possibly a garage, or just about anything that would be "added on" could also be adding value. Even adding a half bath or full bath would add value. So basically layout changes and additions could add value. Remodeling and updating basically restores value.
Also last but not least zillow gives you inflated retail prices on renovations, you can normally do much better than they say price wise
