How to Diagnose & Evaluate Diagonal Foundation Cracks InspectAPedia® -
How to Evaluate Diagonal Foundation Cracks
Photographs of types of foundation cracks
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This chapter of the "Foundation Crack Bible" discusses in detail the process of evaluating foundation
diagonal foundation cracks, step cracks, and signs of foundation damage. Foundation cracks and movement are discussed by type and location of foundation cracks,
vertical foundation cracks, horizontal cracks, and diagonal foundation cracks, and shrinkage cracking.
DIAGONAL FOUNDATION CRACKS - Diagonal & Step Crack Patterns in Building Foundations
This settlement crack probably occurred during initial footing settlement.
Notice that it is wider at the top than the bottom of the
crack. This suggests that the footing to the left or right of the crack has moved downwards, with further downwards movement as we move
further from the crack itself.
If this is new construction and the crack does not change in width the site conditions may have stabilized.
Clues to help diagnose the probable cause of diagonal foundation cracks in buildings:
From corner towards adjacent opening, wider at top than bottom - often due to foundation settlement, expansive clay soil, frost damage, or
damage from a shrub/tree close to the foundation wall.
Under a ground floor window, from sill to ground, sill bowed up - often due to foundation heave, clay soil, frost, shallow or absent footings
In the foundation wall anywhere, wider at bottom than top - settlement under building
At building corners in cold climates - frost heave, frost lensing, shallow footings, water problem, or insufficient backfill. In a typical
raised ranch with a garage located in part of the basement, and with the garage entering at one end of a home, we often find step cracks
in the front and rear foundation walls only on the garage-end of the home. These cracks may correspond to some related observations: (1) there
may be less backfill against the front and rear foundation walls where a garage entry is located between them; (2) the reduction in backfill combined
with an un-heated garage may expose these building corners to more frost damage; (3) if a building downspout or gutter defect spills roof
drainage against the building wall, these forces will often combine to make more severe frost cracks appear on the garage-entry end of the home.
Vertical or diagonal crack which over a short time - settlement over sink holes- serious, open suddenly after rain; or ravines, mulch, fill,
organic debris (later rots and settles).
Over window/door, straight or diagonal - loading/header defect - may appear as horizontal along top or bottom of header, vertical at ends of header
(possibly due to differences in thermal expansion of different materials of header vs. wall) or vertical/diagonal at center of header (loading failure)
or at corners (possible point-load failure)
Cracks in a poured concrete foundation which are diagonal or vertical and which are generally uniform in width, or which taper to an irregular hairline
form, usually in fact a discontinuous crack in the hairline area, are usually shrinkage cracks and should not be ongoing nor of
structural significance, though they may invite water entry through the wall.
Note that often at these foundation failures cracks are visible both outside and inside, but outside they may be covered by backfill.
For detecting evidence of sink holes in an area by visual inspection see Sink Holes:
Can X-Ray Vision [Advanced Building & Building Site Inspection Techniques] Warn of Sink Holes? in Florida or elsewhere
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Sal Alfano - Editor, Journal of Light Construction*
Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and some of the foundation inspection photographs cited in these articles
Terry Carson - ASHI
Mark Cramer - ASHI
JD Grewell, ASHI
Duncan Hannay - ASHI, P.E. *
Bob Klewitz, M.S.C.E., P.E. - ASHI
Ken Kruger, P.E., AIA - ASHI
Bob Peterson, Magnum Piering - 800-771-7437 - FL*
Arlene Puentes, ASHI, October Home Inspections - (845) 216-7833 - Kingston NY
Greg Robi, Magnum Piering - 800-822-7437 - National*
Dave Rathbun, P.E. - Geotech Engineering - 904-622-2424 FL*
Ed Seaquist, P.E., SIE Assoc. - 301-269-1450 - National
Dave Wickersheimer, P.E. R.A. - IL*
*These reviewers have not returned comment 6/95
Technical Edits, Changes, Amendments to This Document
06/07/2007 adding text, illustrations, content
9/23/2006 editing to clarify text and add content; Technical review (partial) by Arlene Puentes.
4/17/2006 editing to clarify text in several sections.
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