Oscar asks: What is the simplest way to identify different types of interior wall structures and whether it is safe to remove some of the studs? Also, what are the telltale signs that reveal different roof structures?
Steve Bliss, of BuildingAdvisor.com, responds: As for figuring out wall and roof structures, it takes a bit of detective work and knowledge about residential construction techniques in your area. Are you planning to remodel and wondering what you will encounter under the drywall or plaster?
Clues include the age of the house, regional building techniques, and the type of building – single-family vs. multi-family.
For interior walls in a single-family home in the U.S., 2×4’s at 16 in. on-center are the most common construction. For party walls in a townhouse of multifamily home, you might find concrete block. You can determine the thickness of the framing by measuring a door jamb or sometimes by removing an electrical switch plate. You can determine stud locations with a stud finder. With drywall, an inexpensive magnetic version works fine, but for older plaster walls, you will need an electronic stud finder. For a definitive answer, you may need to cut away a small section of drywall or plaster.
If you are removing some or all of an interior wall, you will need to determine whether the wall is load-bearing. All structural loads in a house follow “load paths” from roofs and floors, down though walls and posts to the foundation. In a simple house with a gable roof, the floor and ceiling joists generally run from eave to eave and are supported at mid-span by an interior supporting wall. This wall will be running parallel with the eaves of the roof. In more complicated designs, it is more difficult to identify which walls are load-bearing. And occasionally, you will be surprised by illogical, incorrect, or unusual construction patterns. With owner-built homes, anything is possible.
Again, the only definitive way to tell is by removing a small piece of ceiling finish and looking to see whether the ceiling joists above end on the wall, making it load-bearing. It’s possible, but uncommon, for continuous joists to be supported mid-span by a bearing wall. The size of the joists and length of the span would be clues. On a particularly puzzling three-story Victorian mansion I was working on years ago, the architect told me to cut part-way though the studs, and if the saw blade bound (indicated a load above), to call him. Turns out the wall was supported from above by steel rods, something I’ve never seen before or after. I’ve also seen an exterior wall framed like a spider web. The older the building, the less predictable the framing you’ll encounter.
If you are removing part of a load-bearing wall, you will need to temporarily support the ceiling above (see photo), and install a header or support beam. When in doubt, ask a consulting structural engineer to take a look.
Roofs are move complicated to analyze. In general there is an attic hatch that allows you to poke your head up into the roof structure and take a look. The three main types of roof structures are trusses (in more modern homes), rafters with ties, and rafters with a structural ridge. Ties are either ceiling joists of other structural members that connect to the bottom of the rafters, creating triangles that keep the joists from spreading. If there are no ceiling joists or cross ties connected to the rafters, then you probably have a structural ridge beam. This is often the case with cathedral ceilings. There are many possible configurations. When in doubt, consult an engineer as roofs can be tricky to modify without causing structural problems.