How to increase rents and capital gains on Professional HMOs? Two sure and tested ways are loft conversions and extensions. We are doing this extension in Greater Manchester to add a large ensuite room. We will generate an additional 650 a month added rents by doing so. This also adds to the value of the property and if we decide to sell it, the value of the property is based on the yearly rents. Make sure you get your permitted development with the council as well as building regs to sign off the project upon completion. Watch our progress.