A PRIMER ON LOAD BEARING WALLS... CAUTION IS THE OPERATIVE WORD!!
Before any modifications are made to a wall in your home, it is important to have a basic understanding of how that change could affect its structural integrity. Here is a brief but to the point essay on this heavy subject!
There are two types of walls in a home... load bearing and non-load bearing.
Homes are over engineered with good reason. Do you really need 2x4 wall studs
every 16" (center to center) to prevent your house from collapsing? Under
most circumstances, the honest answer is no. Then, why is this an accepted
construction standard? Why not 18"? Or 24"?
Engineers design structures to be able to handle loads and forces greater than what they could ever be expected to handle under real world conditions. Based on the current sizing of lumber, and modern construction practices, 16" was determined to be the right spacing between wall studs for residential load conditions.
This over engineering allows you to put a large cabinet or waterbed in your upstairs bedroom, or a grand piano in the living room, and not having to worry about your home collapsing on you! This margin of safety designed into structures via enforcement of building codes is something for which we should be thankful.
Even so, we can't think in terms of cutting wall studs willy-nilly! If we are engaged in a project that requires cutting of wall studs, we must try to understand something about how weight or the structure above a wall, or load, is distributed. Only then can we proceed safely and with the confidence that comes with being prepared!
How do you determine whether a wall is load-bearing? This can be difficult to determine even for an experienced carpenter. Analyzing the wall loads in large, complicated homes is tough enough to understand. When there have been renovations, this determination can become nearly impossible. Even building inspectors rely on the "when in doubt" principle... when in doubt, assume the wall is load bearing and act accordingly.
It is easy to understand how renovations can cause weight to be transferred onto formerly non-load bearing partition walls. For example, the addition of exhaust fans and attic stairways often requires cutting of ceiling joists, which can also transfer loads from the original walls... the main (center of the house) beam and the outside wall, onto non-load bearing walls that are in between them. Adding a room in an attic can change the entire load bearing status of the walls below.
To confuse matters further, some types of construction, such as post and beam or steel girder, may not have any bearing walls at all except for the outside walls. What's a mother to do??
Look at the structure of the house and ask the following questions:
- Is there a significant load above, such a built-up (multi-board) carrying beam or another wall? Is there a full floor above it, or just an empty attic?
- If you can view the joists in the attic, is the wall parallel or perpendicular to them? Generally, load bearing walls are perpendicular to the joists they support. If two separate floor joists or ceiling joists intersect over a wall, that wall should be considered load bearing.
- Is it an outside wall? You should consider all outside walls load bearing. If the house has been remodeled, a former outside wall could now be an inside wall. Examine the foundation to find these "stealth" outside walls.
- Look at the beams and posts in the basement. In multi-floor dwellings, posts and beams in the basement indicate bearing walls above them, even up two floors. Be aware that these multi-floor bearing walls may not be directly above each other.
- In complex, large homes, the basement can be a jungle of carrying beams and posts, crisscrossed and interlocked. Careful inspection is necessary to determine how this maze of beams supports the house, and its effect on the walls above.
If you have any doubts about the strength or loading status of the wall, GET PROFESSIONAL ASSISTANCE! You may even be able to get your local town building inspector to stop by and take a look around!