A bump-out addition can be a room added onto your home, on the back of your house or even the front of your house. A patio deck can also be considered a bump-out addition. An added garage is also considered to be a bump-out.
Find out the floor height of your home's regular floor level. To find out this height, you must pull siding off of a spot on the outside at the bottom of your home. This exposes your floor system band and your sub-floor. You can either build your bump-out floor to match your existing floor level, or you can raise or lower your bump-out floor.
Determine the size area you need for the type of bump-out addition you are going to install. You might need to clear some trees and make room in your yard to accommodate the addition.
Decide if you want to install your bump-out addition on a crawl space or just an expanded floor system. You can use either. A crawl space will require footings and block laid. An expanded floor system will require pier holes filled with concrete for the uprights to support the floor system. You can also simply pour a concrete slab for your bump-out addition, if your terrain will allow for it.
Consider the example of using a concrete slab to install a bump-out addition. When your slab is ready, raise your outside walls. Then, put your ceiling joists in. Your roof system must come next. Put plywood and felt on your roof system. Finish with shingles.