Five layers, five lifespans
A building is not one thing that ages at one speed. Keep its fast parts from being trapped behind its slow ones, and most demolition never has to happen.
long life, loose fitWhen a pipe leaks inside a wall, a plumber cuts the wall open. When wiring is replaced, holes are bored through the frame. Each time, something that should last a century is damaged to reach something that lasts fifteen years.
The writer Stewart Brand gave this problem its clearest picture in How Buildings Learn in 1994.1 A building, he said, is several layers that change at different speeds. We treat that idea as a drafting rule, not a metaphor.
The layers
| Layer | Typical life | The rule it must obey |
|---|---|---|
| Structure | 60 to 300 years | Never pierced by pipes or wires. Other layers attach only at planned, recorded points. |
| Skin | 20 to 60 years | Fixed to the structure through battens or brackets, never glued straight to it. |
| Services | 7 to 20 years | Pipes, wires and ducts live in their own cavity, floor or ceiling space. |
| Space plan | 3 to 30 years | Inner walls and ceilings fix to tracks and clips, not to the structure with glue. |
| Stuff | 1 to 10 years | Furniture and fittings stand free or hang from rails. Nothing is glued in place. |
One sentence covers all five rows: nothing may be fastened through a layer that should outlive it.
Where houses break the rule
Almost everywhere. Take an ordinary outside wall. The cladding is nailed through the weather barrier into the sheathing. The window is sealed to the barrier. Wires are stapled to the studs and insulation is sprayed around them. To change the window, you tear the barrier. To reach a wire, you cut the wallboard and dig out foam.
Nobody sees this on the drawings, because drawings show a building going together. The trap only appears when you draw it coming apart, and almost nobody draws that.
What we do about it
- Draw the reverse order. Every standard detail gets a second sheet: step one, step two, which tool, what is destroyed. It takes about an hour a detail.
- Set a limit. Five steps to free a window. Ten to free a stud. If a detail fails, it is redrawn.
- Give services a room of their own. A shallow inner wall, a raised floor or a dropped ceiling carries every pipe and wire. Nothing punctures the airtight layer, so the house is also less drafty.
- Put short-lived layers on the outside of long-lived ones, in the direction you will reach them from.
Every time a short-lived part is trapped behind a long-lived one, a future demolition has been drawn.
The honest cost
A service cavity takes a few inches of floor area. Drawing the reverse sequence takes design time. Neither is large, and both are paid once.
The saving is harder to show, because it arrives decades later as demolition that didn’t happen. We build homes to keep, so that saving comes back to us. For a builder who sells and leaves, it never would, which is most of the reason houses are built the other way.
Sources and notes
- Stewart Brand, How Buildings Learn: What Happens After They’re Built, 1994. Brand listed six layers, beginning with the site itself. ↩
Drafted with AI assistance from Viridian's working papers and detail guides, then read, corrected and approved by Keith Cash, co-founder. Found a mistake? Tell us.