How to Determine if a Wall is Structural
As you plan a remodeling job, you'll begin to see your house in a new light. Things that appeared permanent before — walls, for example — may not seem that way anymore. You'll soon realize that almost any alteration is possible if you are willing to do the work and bear the expense. Before you get carried away and start knocking down walls, however, you need to understand that there are two kinds of walls in a house: bearing (or structural) and nonbearing (or partition) walls.
Bearing walls help carry the weight of the building and its contents to the ground. Partition walls simply divide interior space. It is far easier to remove or relocate a partition wall than it is to do the same to a bearing wall. In many cases you may want to rethink your project before deciding to remove or modify a bearing wall.
How to Spot the Difference Between Bearing and Nonbearing Walls
The next step in planning is to determine whether an interior wall is a bearing wall. This book deals with interior remodeling only, so discussion is limited to interior walls.
If the wall runs parallel to the ceiling and floor joists, it is probably not a bearing wall. Short closet walls, for example, usually are not bearing. If the wall runs perpendicular to the ceiling and floor joists, there is a good chance it is a bearing wall.
How can you tell which way the joists run? Most of the time joists run perpendicular to the roof's ridgeline. If the wall is under an attic, go up and see if the joists cross over the wall. If joists end on top of a wall, it definitely is a bearing wall. If the attic has floorboards, they run across the joists; you'll see the lines of nails where they are fastened to the joists. If your roof is supported by trusses, the answer is simpler. Trusses have diagonal pieces that run from the attic floor to the rafters. They transfer the weight of the roof to the outside walls, so all the interior walls in the story directly below are probably partition walls.
If you can't check above, check below. Is there a wall directly under the one you want to remove or modify? If there is, they both are probably bearing walls. If there is a basement or crawlspace below the wall you want to change, go there and see if a beam supported by posts or piers is directly under the wall. If so, you can assume the wall above is bearing.
If you still have doubts, hire a carpenter or a structural engineer to help you.