While rent represents the biggest expense each month for many consumers, the payments rarely are reported to credit bureaus, meaning they don't help people improve their credit scores.

It's one of the largest segments that still isn't reported to credit bureaus. That lack of reporting works against most consumers, something TransUnion set out to show with an empirical study.

"Following the mortgage crisis during the last recession, home ownership rates have declined to 20-year lows as many consumers choose to rent. In fact, there are now 40 million American renter households in 2013, which is up nearly 5 million since 2007," said Tim Martin, executive vice president at TransUnion. "Despite millions of more renters, most rental payment histories are not provided to credit bureaus, and renters looking to improve their credit standing cannot do so."

Eight in 10 renters with a subprime credit score would get an immediate boost with just one timely rent payment reported, according to research that TransUnion presented Thursday at the National Apartment Association's Education Conference & Exposition in Denver.

The subprime segment of the population, consumers who may be viewed as higher credit risks, could experience positive effects with only one month of on-time rental payment information.

The analysis found that approximately eight in 10 subprime consumers (79.1% of those with a VantageScore 2.0 credit score lower than 641 on a scale from 501 to 990) saw an increase in their score one month into their new apartment lease. Nearly 41% of subprime consumers saw their VantageScore increase by 10 points or more after one month.

TransUnion’s research also compared the credit score impact of being a first-time homebuyer (where the mortgage payment is reported to the credit bureaus) versus being a renter (where the apartment rental payment is not reported). The research found that, on average, those who became first-time home buyers in early 2012 saw a 5.2% increase in their credit score over the next year. However, the average renter actually saw a slight decline (-0.4%) in credit score during this same timeframe.

Logistics seems to be the biggest issue preventing wider reporting of rent payments, and some work is needed to set up systems to send out the data each month. Renting in the past was also perceived as a transition to owning a home, although the downturn is reshaping that attitude.

While the owner of a small apartment building or a single-family rental may not participate, TransUnion is making an aggressive push to get larger property managers to join its "ResidentCredit" service and start reporting.

The service encourages property managers to report the payment performance of their apartment residents. Through it, property managers will submit data about their residents to TransUnion each month, reporting the amount and timeliness of their last payment, and any balance owed.

The information will appear on consumers' files alongside their other financial obligations such as auto loans, credit cards and student loans. TransUnion will not charge any fees to report rental payment information via ResidentCredit, company officials said. Also, if a property manager who furnishes the data requests it, TransUnion will share the information reported with other national credit reporting companies to be included in their consumer credit files and scores.

Credit bureau Experian includes positive rent payment information in its credit reports. Larger property management companies report directly through Experian’s RentBureau service.