Which home improvements are the most cost effective while improving value?

[Dana Anghel]

I can finally originate Fannie Mae HomeStyle Renovation Loans, and I'm really excited!

But.

From my understanding at this point, there is one major thing that can be a deal breaker: if the appraiser concludes that the contractor bid will cost more then the actual value that would be added to the property. 

So my question for rehabbers/appraisers/general contractors out there: which home improvements are more likely to cost less then the actual after-renovation value? (ex: Tearing down walls to create more space, adding an extra bathroom..?)

Also, what are the worse renovations that don't add as much value in proportion to the actual cost? (pretty sure pools are right in that category).

Keep in mind that the work needs to be performed by a licensed and insured General Contractor - self help is not allowed.

Thank you for any input. [edited]

[Matt Sicignano]

Here's a great link that I have used from Remodelers Magazine. What I like about it is that it's trending, and also gives you area specific information.

http://www.remodeling.hw.net/cost-vs-value/2014/