Short Answer is yes, via interest tracing rules. 

Is there any good rules of thumb to estimating the cost of a boiler?

My dad and I (both with access to VA loans) are about to get into the multifam game and how we proceed is really going to depend on the true occupancy rules for the VA and our lender.

I ended up with some rules, couple here:1.Discrimination - Never Rent to Attorneys, Law students or Law Professors.Learn all you can about the Housing Laws i.e.

Over time, rents may increase, improving your cash flow, and you’ll gain equity and valuable experience managing tenants and property operations.

You want to be able to demonstrate that your intent in purchasing, subdividing, and improving was to hold for investment use. 

My question is why you want to bring it up to code, other than just to feel good or improve your exit strategy?

Improved, not made worse.

These methods include:Detailed Engineering Cost ApproachDetailed Engineering Cost Estimate ApproachSurvey or Letter ApproachResidual Estimation ApproachSampling or Modeling ApproachExperience or “Rule of Thumb” ApproachFor further details on the methodologies, refer here.WHAT ARE THE BEST AND WORST PROPERTIES FOR COST SEGREGATION STUDIES?

Using the 30% affordability rule, the monthly rent affordability for most households would be around $1,545.