There are many different ways to expand your house to include more rooms. A simple addition is one option, but it can be very expensive. An addition also requires that you have extra space on your property. If you have that space and you want an addition, a good builder will be able to build one to your specifications. If you want a faster and more economically-friendly solution, however, you should consider converting your garage into a flat. A garage is hopefully already waterproof, and some are even connected to your current HVAC system.
Insulating the Garage
The first step will be hiring builders in PL7. Many of them will recommend that you insulate your garage. That insulation can be installed in the actual walls of your garage or it can be built between the concrete walls and the cladding. Many people choose to install insulation on top of the concrete and then drywall on top of that, which is the fastest and simplest way to insulate the garage walls. There are also some options for installing insulation in the floor.
HVAC System
Your heating, ventilation, and air conditioning (HVAC) system will likely need to be extended to your garage. If you want to go a simpler route, a builder can install a space heater and a window air conditioner if you need one. Extending the HVAC system will simplify the process but will likely take a little more building. You should work with a qualified builder to determine which method would be right for you.