The 1/3 rule for wall stability

Structure · Problems · printed page 43 (PDF page 44)

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Book index entries

One-Third Rule for Wall Stability Stability – The One-third Rule Footings – and Foundations Foundation – and Footing

Text in the illustration

middle third of the wall
force
center of gravity
procedure
measure the amount that the wall is out of plumb
make a scale diagram - drawing a line representing the force of gravity through the center of the structure
if this line does not lie within the center 1/3 of the wall, the wall is unstable
the same concept applies to bowing or leaning walls
if there are joists resting on the walls, even less lean is allowed before the wall is unstable
stable
borderline
unstable
(the center of gravity for the wall extends outside the middle third)

Generated explanation

Four wall profiles illustrate the one-third rule for wall stability, comparing a plumb wall, two increasingly leaning walls, and a bowed wall. Each profile marks the wall's middle third, its center of gravity, and a vertical gravity line extending to the base. The plumb wall is labeled stable, the slightly leaning wall borderline, and the more severely leaning and bowed walls unstable because their gravity lines extend outside the middle third at the base. Horizontal arrows indicate forces acting on the displaced walls. The procedure instructs the reader to measure the out-of-plumb displacement and make a scale diagram, and notes that walls supporting joists allow even less lean before becoming unstable.

Components

wall wall base

Defects shown

out-of-plumb wall leaning wall bowed wall wall instability gravity line outside the middle third of the wall base

Related illustrations

0287

The 1/3 rule for wall stability

· p. 47

The illustration compares an upright wall, two progressively leaning walls, and a bowed wall using the middle-third rule for stability. Each wall has its middle third shaded, a center-of-gravity marker, and a vertical do