To get it permitted you have to pay for an architect, engineer, permit fees, and possibly open up walls to make sure the correct beams, plumbing, electrical, etc. is present. 

A good cost segregation study is engineering-based, the IRS' preferred methodology.

Each property is so different that that is why a good engineering based study with on-site property review is the IRS' preferred methodology and keeps you out of IRS audit territory. 

I use the short-term rental rules to turn my depreciation into active losses, and I had an engineered study done to make sure everything was defensible.

An engineering backed modeling study might be good for this type of property.

STRs can benefit from engineered cost segregation studies but it can be a case by case basis.

Always hire an engineer first, then send the engineer's recommended scope of work to foundation companies and have them bid based on that report. 

There are two types of cost segregation study companies.1 - An engineering firm where a professional will stop by to analyze the property and provide you a report based on his/her findings.2 - An engineering firm that will send you a questionnaire.

It's like a development deal in considering your engineers and architects as partners.

Now to be fair the company we are funding is a Civil engineering firm with deep experience..