At the same time demand for terraced houses from landlords to rent out has fallen to almost half their previous level, says Paragon Mortgages.
The firm says that the proportion of landlords who are expressing an interest buying semi-detached BTL properties has risen from 23% in the final quarter of last year to 35% in the first three months of 2015.
The figures come from a survey they undertake which tracks landlord confidence - which also reveals that demand for terraced properties has dropped from 67% to 35% over the same period.
The specialist lender says that this drop in demand has led to landlords now being interested on an even basis across the broad spectrum of property varieties.
Landlords want to buy flats and semis
When landlords were asked which properties they were hoping to buy, 30% said they wanted a flat, 35% expressed an interest in semi-detached, while 35% opted for a terraced property.
The remaining 22% said they were only interested in HMOs and multi-unit blocks.
A director of Paragon, John Heron, said: “The growing proportion looking to buy rental property soon points to a steady and continued growth in the private rental sector.
“Looking at the interest levels for different types, it suggest that landlords are taking a broad perspective to cater for a wider variety of households needing a suitable home to rent.”
The survey, which has been undertaken for the past 13 years, also reveals that landlords are increasingly optimistic about the future for rental properties in the UK with 27% say they are feeling positive.
There's also been a growth in landlords looking to invest in BTL property soon, which has risen to 18% from 15%.
Thousands of landlords in Scotland sign petition
Meanwhile, a petition opposing a Scottish government law to introduce rent controls has been signed by more than 3,000 landlords.
The petition was launched at the beginning of May by the Council of Letting Agents and the Scottish Association of Landlords (SAL).
The aim of the petition is to get the government to recognise the importance of Scotland's private rental sector.
The new legislation also aims to remove the right of a landlord to terminate tenancy when the agreed lease term ends.
Those behind the petition say the legal moves will discourage new landlords from investing in property to help meet rising demand and the chief executive of SAL, John Blackwood, said: “Some changes to the regime are necessary but we are urging the government to consider the implications of their proposals.”
