Load bearing walls in houses almost always assist the structure in the support of the roof. The best way to identify a load bearing wall is from underneath the house or in the basement. Sometimes load bearing walls are identifiable from the attic or by examining the exterior of the house.
Interior load bearing walls can be identified by noting how the trusses are constructed to carry the weight. If there are diagonal braces that push some of the weight of the roof to a central or other interior wall, this is a load bearing wall. Underneath the house or in the basement these interior walls will rest on a central beam of wood or steel. This beam will support the floor joists and the load bearing wall. It will rest either on concrete piers or a combination of steel or wood and concrete.
Outside walls almost always are load bearing in any house. Overhead trusses distribute the weight of the roof to the walls that run parallel to the peak of the roof. On the walls that stand perpendicular to the peak or ridge of the roof, the end trusses sit with their weight as if they were a special add on to the top of the wall.
If there are unique architectural features such as a large gable extending over an open area of the structure, special interior walls may be constructed with a significant beam to bear the weight of truncated trusses. The studs at each end of this wall will be at least doubled to help convey the weight to beams in the basement or piers place beneath them into the ground below the frost line.
Exterior load bearing walls will have a double top plate constructed from the same size lumber as the wall studs. Usually these are either 2x4 or 2x6 timbers. The plate will run the entire length of the wall. While the wall will generally rest on the subfloor, it is ultimated placed directly over the foundation. This lets the wall utilize the strength of the foundation to prevent cracking and settling under the best circumstances.
Not all houses have interior load bearing walls. If the roof trusses are properly constructed, they can often span a distance of 40 feet or more without having a central support wall. These trusses are able to shift the entire weight of the roof to the exterior walls. In larger buildings, the walls need to be constucted with at least 2x6 studs. In some cases it is advisable to set the studs on twelve instead of sixteen inch centers.
All openings in a load bearing wall must have headers over the opening to carry the weight for that portion of the span to double studs on either side of the opening. These headers are usually 2x10 or 2x12 in size and are cut the length of the opening plus the width of the studs on either side of the opening. The header boards are laminated together to make the width match the size of the studs.
Load bearing walls can only be removed if support posts and beams are put into place to replace the capacity of the studs that were removed. Often jacks and other bracing is necessary until the new support system can be completed. This keeps the roof from caving in or developing sags.
Almost all walls that are not load bearing can be removed, remodeled, and relocated without incident at the whim of the builder or home owner. This walls serve only cosmetic purposes to define the dimensions of various rooms and architectural features of the building or home.
