A survey of around 900 landlords showed that nearly 80 per cent invested in upgrading properties after purchases, spending around £8,720 each.
The total spend is £839m a year.
This included work such as general painting and maintenance, electric or plumbing and new flooring. Other actions included installing a new kitchen or bathroom or upgrading windows and installing a new boiler.
The report continued that the quality of homes in the private rented sector (PRS) had improved over the past decade with homes classed as decent growing from 53 per cent in 2006 to just over 76 per cent currently.
The proportion of non-decent properties in the sector has also nearly halved to around 23 per cent since 2006.
The improvement has been partially driven by expansion of the sector, which has led to the addition of better-quality homes, as well as improved buy-to-let funding.
According to the report the number of private rented sector homes has nearly doubled between 2009 to date, going from 509,000 to 1 million.
There have also been significant improvements in energy efficiency with just under 40 per cent of homes in the private rented sector having an Energy Performance Certificate (EPC) rating of C or above. This is up from around 13.5 per cent in 2009 and higher than the owner-occupied sector.
However, despite the progress there are still some aspects of private rental properties which are in need of improvement such as overcrowding, damp and other hazards.
According to the report around 7 per cent of private renters live in overcrowded accommodation, the highest level it has ever been.
Almost 7 per cent of homes reported damp problems, however this has fallen from 15 per cent in 2009.
Paragon Bank’s managing director of mortgages Richard Rowntree said: “Overall homes in the sector are newer, larger, warmer and more energy efficient than they were 10 years ago and tenants have more choice.
“Whilst we recognise more needs to be done to improve standards, since 2009 there are nearly three times the number of properties with an energy rating of C or above, a 100 per cent increase in the number of homes built after 1990 and a substantial expansion in the types of property available to rent in the PRS.”