What's Behind the Wall — Companion Guide 02

Every wall is a sandwich. Know the layers before you cut into one.

A house is made of perhaps a dozen repeating assemblies. Behind the paint there is a fixed order of layers, and in those layers run the cables, pipes and ducts that make a drill bit expensive.

This 23-page guide draws each assembly in section with the layers numbered from outside to inside, then tells you what you'll hit when you cut, the stop signs that mean a problem, and where the full drawing lives in Ching's book. It opens with eight rules for opening anything and closes with where every service runs and how to find things through the finish.

What's inside

• Eight rules before you cut. Power, the other side of the wall, bearing, studs, depth, inspection holes, old materials.
• Twelve assemblies, layer by layer. Exterior wall, partition, bearing vs non-bearing, floor/ceiling, slab, foundation wall, pitched roof, low-slope roof, window, door, wet wall, brick veneer.
• Where the services run. Cable, supply, drain, gas, duct and data habits, with the heights that are nearly law.
• Finding things. Studs, cables and pipes through drywall, plaster, tile and masonry — and which fastener holds what.
• Fire blocking and the load path. The one question to ask anyone who proposes removing a wall.
• Older houses. Plaster and lath, balloon framing, knob-and-tube, galvanized pipe, lead, asbestos.
• The before-you-open-it checklist.

A note on scope. Typical North American residential construction; assemblies, service heights and materials vary by region, era and builder. Nothing here replaces an engineer's opinion on a bearing wall, a licensed electrician or plumber, or a hazardous-materials survey on an older house.