In many houses, a well-planned garage conversion can create a new room or rooms that blend seamlessly with the existing house. The process should begin with a careful assessment of the garage and the problems and promises it holds.
The biggest question facing most garage conversions is what to do about the garage door. Once the door is removed, the resulting space needs to be filled in so that it both blends in with the rest of the house and provides a useful service to the new living space. Possible options include installing a patio door or framing a new wall that includes a large window.
A typical garage sits on an uninsulated concrete slab, which may be several inches below the floor level inside the house. The slab may well be sloped toward the garage door or a floor drain. With these circumstances, you will want to consider filling the bottom of the garage door opening with a curb that will keep water out of the converted space and protect wall framing from moisture. You will also need to decide if the floor should be leveled.
Heating and Cooling
If the garage is attached to the house, you may be able to extend the existing heating and cooling system into the new space. If that is not possible, look into an independent system (heat can be supplied by electric baseboards, gas space heaters or woodstoves, for example, while a room air conditioner can handle warm weather). Add insulation to walls, floor and ceiling before deciding how to heat and cool the space.
If you expect to substantially increase electrical usage in the converted space, consider adding at least one new 20-amp circuit. Wiring to a detached garage can be run through an underground conduit.
This can be the biggest headache of a garage conversion. Getting water supplied to the garage may be easy, but drainage could present major problems. Check with a plumber about your options. If you are lucky enough to have a laundry/utility room connecting the garage to the house, you might be able to turn it into a bathroom.
Loss of Storage and Parking
Much of what is currently stored in your garage could go into a new shed, the basement or attic, or be sold at a garage sale. To protect your vehicle from the elements, consider building a carport.
Think hard about to make the exterior of the converted space look like it has always been a part of the house, rather than an afterthought. Try to match the siding, colors, window and door styles and the landscaping.