Hello,
The short answer: there's no easy way to identify load-bearing walls; even professionals sometimes have difficulty determining if a wall is or is not load-bearing. So if you're asking this question because you're about to knock down a seemingly light wall, consider hiring a structural engineer to check it first.
OK, now that the lecture is over, answer the question already, right? OK: most but not all exterior walls are load-bearing (might be just the front and back walls that are load-bearing). Then there are hip-roofed homes, where the second floor is smaller than the first floor, meaning all exterior walls carry some of the load.
Now for interior walls. Most frequently, interior walls that run perpendicular to the floor joists are load-bearing. But, again I stress, this might not be the case with your home. Moreover, bearing walls are not always stacked on top of one another, so even finding a bearing wall on one floor doesn't make its sister wall a sure candidate. Also, don't assume that all the floor joists run in the same direction; you may have a situation in which two walls that meet at right angles are both supporting walls.
Still want to take a stab at locating the load-bearers? Here are three starting points, but again, do not rely on these alone.
1. If the house has a basement, go downstairs and find out what's below the wall. If the wall above has a wall or beam below it, the wall above is probably load-bearing.
2. If the wall is below an attic, go to the attic and determine whether its floor joists are running perpendicular to the wall below. If they are, the wall is supporting the attic floor and shouldn't be touched.
3. If the floor joists are hidden by a floor above or a ceiling below, you may need to chip away some of the ceiling to determine whether the joists run perpendicular to the wall.
I hope this helps.
Jay Somerset
http://www.homerenovationguide.com/
