What Is Behind Drywall?
Drywall is the rigid gypsum-based board that forms most walls in homes. Often called wallboard, drywall is usually 1/2 inch thick. It is either screwed or nailed directly to the wall studs. If you could see behind the drywall or remove it, you might see any of the following:
Insulation
Exterior walls usually will have fiberglass, cellulose, mineral wool, or foam insulation. Older homes’ exterior walls may not have insulation behind the drywall. Interior walls usually do not have insulation but sometimes will have it as a soundproofing device.
Window and Door Headers
Headers are horizontal members that run across the top of doors, windows, and entryways. Headers are important because they support weight that ordinarily would have been supported by vertical studs in that space. One reason to care about headers is that they give you air and light. The wider the header above the window, the larger the window. Thus, you receive more air and light. Also, within the house, a sturdy header above the door between kitchen and living room can help tie the two rooms together.
Wires
Electrical cables are usually behind drywall, either running horizontally through holes in the studs or stapled vertically up the sides of studs. Outlet cables tend to be about 12 inches high. Light switches are around 48 inches high, so expect to see electric cables around that area. You should not find loose electrical wires: only wires bundled together as either metal- or plastic-sheathed cables. Loose wires are not allowed by most electrical codes. In some older homes, though, you may encounter loose wires called knob-and-tube wiring.
Plumbing Pipes
Plumbing pipes of PEX, copper, or galvanized steel are found behind walls mainly to serve kitchens and bathrooms. Pipes will run vertically more than horizontally through walls. A common example would be a blue PEX and a red PEX pipe running vertically up from the water heater and main water supply in the basement.
Other Possible Features
Fireblocks: You may encounter short horizontal pieces of studs that act as fireblocks to slow the movement of fire.Insects: Even the tightest wall may end up with spiders and thus cobwebs.Dead vermin: Sometimes, rats and mice die within a wall and remain there until found during a remodeling project.Debris: Sometimes builders let construction debris fall down wall wells.Sharp screws and nails: If the wall on the other side is drywall, there is a good chance that you will encounter a number of screws or nails that did not hit the studs.Plaster keys: If the wall on the other side is made of plaster, plaster will have squeezed through the metal or wood lath to create necessary knobs called keys.
How Far Apart Are Studs?
With stud spans, a type of measurement called on-center applies. Studs are measured from the center of one stud to the center of an adjacent stud. A load-bearing wall, sometimes called a partition wall, supports the weight of the house above it; a non-load-bearing wall supports only its own weight. Before removing any wall, consult a licensed contractor or structural engineer. Even the fee for a structural engineer is far less than the cost of repairing a collapsed wall or roof.
16 Inches On-Center
Load-bearing wall studs are usually 16 inches apart, on-center. This predictable spacing lets you easily find studs when trying to hang a picture, install shelves, or put in new kitchen wall cabinets, among other projects.
24 Inches On-Center
Non-load-bearing walls can have vertical studs spaced as far apart as 24 inches, on-center. Since non-load-bearing walls only bear the weight of drywall and some electrical and plumbing work within, it is possible to have wider apart studs. In some homes, load-bearing walls are 24 inches apart, on-center.
