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This document describes how foundation or slab cracks can be monitored for evidence of movement and what general advice makes sense for building owners or buyers where foundation damage is found and/or where further foundation inspection, testing, diagnosis, or repair appear warranted based on a general field inspection. We include discussion of methods used to perform ongoing monitoring of building foundations for cracking and movement.

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Methods for Monitoring Foundations for Evidence of Ongoing or Episodic Movement

Building foundations may be moving, either continuously or episodically. Most movement is episodic, that is, the movement is not a simple and continuous creep but rather foundation movement or cracking occurs in fits and starts. Our sketch (left) shows a bulged masonry block foundation wall that has bowed in two inches at its innermost point.)

Usually foundation movement and further cracking occurs in response to occurrences of what has caused the cracking in the first place.

See FOUNDATION DAMAGE SEVERITY and then FOUNDATION MOVEMENT ACTIVE vs. STATIC for distinguishing severe and also ongoing foundation movements.

Examples of Causes of Ongoing Foundation Damage/Movement

• Continuous vehicle traffic too close to the foundation (weight) or even in a nearby roadway (vibration)
• Continuous blasting and nearby site work
• Continuous overloading or point loading on the foundation due to construction or building design

On occasion a foundation cracked or damaged by an event (drove a heavy vehicle too close to the masonry block foundation wall) may later move, crack or bend, buckle, lean, bulge, etc. in response to other site conditions that it was previously able to resist before it was weakened by the original damage (frost, water, other vehicles).

Examples of Episodic or Discontinuous Causes of Foundation Damage/Movement

• Seasonal area flooding of surface water or subsurface groundwater
• Seasonal freezing weather - frost heaving and frost lensing

List of Simple Methods to Monitor a Masonry Foundation for Evidence of New or Ongoing Movement

• Crack Pins to monitor masonry structure movement: a metal pin is secured to the masonry surface on either side of the crack. Periodic measurements are made of the distance between the two points of the pins.

• Crack monitor slide devices: such as a glass slide, a more complex set of moving glass slides that include fine markings can be epoxied (or mechanically fastened) across a building foundation crack. These devices provide accurate indication of any additional movement in the foundation wall. Beware: small amounts of foundation movement occur in masonry materials as a normal effect of temperature and moisture changes. Don't mistake these causes for ongoing building movement.
  
  The Avongard crack-monitoring device, a $16.00 U.S. device measuring 1.25" x 5.75", is an example of this product. "The Avongard Crack Monitor consists of two overlapping acrylic plates. One plate is white with a black millimeter grid, while the other is transparent with red cross hairs centered over the grid. Once the Crack Monitor is in position across a crack, the cross hairs shift vertically or horizontally on the grid if movement occurs,so that anyone can easily see and track crack movement." (Photo above courtesy of Avongard.)
  
  The Avongard crack monitor can identify masonry wall movements down to 0.5mm and can handle total movement of 30.75" in crack width and 0.375" upwards movement (one side of the surface lifting or protruding past the other, such as on a concrete floor). For longer term monitoring of a cracked masonry wall or floor we like this device. The monitor can also be used to measure movements in foundation corners by incorporating an angle bracket. Avongard provides a movement progress chart that permits logging of observations over time.
• Masonry Crack Fillers: if a horizontal, vertical, or diagonal masonry crack is filled with hard masonry patching compound, any substantial future movement is likely to show up as a new crack in the patched area (or nearby). Beware: some masonry products shrink when they dry and cure - don't mistake a patch shrinkage crack for building movement. But if a foundation crack is leaking you'll want to seal it, not just monitor it.
• Masonry Crack Caulks: filling a foundation crack with a masonry caulk is a quick, inexpensive, and effective way to seal the crack; some caulks, such as pourable sealant used to close floor cracks during radon mitigation work, are easy and effective to use. Beware: flexible materials won't show small amounts of future building movement.

• Measure and Document Foundation Movement: masonry foundation cracks alone may not be the only nor even the most critical evidence of foundation movement. If a foundation wall is leaning, bending, or bowing, that stress may have resulted in several small width cracks that do not adequately describe the total amount of foundation movement.
  
  A written and photo inventory of foundation cracks, simple measurement of foundation crack length and width as well as documenting their location, may be combined with simple measurements of the total lean or bulge in a foundation wall. (Photo courtesy Carson Dunlop). See FOUNDATION BULGE or LEAN MEASUREMENTS for details.
• A foundation inspection & diagnostic report: a thoughtful inspection of the building and site as well as an inventory of existing cracks permits a diagnosis of the causes of foundation damage as well as its extent. If there is evidence of significant foundation movement, we recommend that you take this more costly step. See FOUNDATION CRACK EVALUATION for guidance.
• Other foundation movement monitoring devices are used by professional engineers, including load cells or pressure cells, extensometers used with a borehole and tape, tilt meters that measure angular change or lean, strain meters, beam sensors, and soil movement sensors. Companies such as Slope Indicator sell these and other sensing and measuring devices.

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FOUNDATION DIAGNOSIS & REPAIR
FOUNDATION INSPECTION METHODS
SITE FACTORS AFFECTING FOUNDATIONS
FOUNDATION CONSTRUCTION TYPES
FAILURES by FOUNDATION TYPE & MATERIAL
FOUNDATION DEFECTS OF OMISSION
FOUNDATION CRACK EVALUATION
  CRACK MONITORING Methods
  DIAGONAL FOUNDATION CRACKS
  HORIZONTAL FOUNDATION CRACKS
  SHRINKAGE vs EXPANSION vs SETTLEMENT
  Sinkholes & Building Damage
  Thermal Expansion Cracking of Brick
  VERTICAL FOUNDATION CRACKS SLAB CRACK EVALUATION
FAILURES by FOUNDATION MOVEMENT TYPE
FOUNDATION BULGE or LEAN MEASUREMENTS
FOUNDATION MOVEMENT ACTIVE vs. STATIC
FOUNDATION DAMAGE SEVERITY
FOUNDATION DAMAGE REPORTS
FOUNDATION REPAIR METHODS
ADDITIONAL READING
FOUNDATION INSPECTION STANDARDS

• "Concrete Slab Finishes and the Use of the F-number System", Matthew Stuart, P.E., S.E., F.ASCE, online course at www.pdhonline.org/courses/s130/s130.htm
• Avongard crack monitors, Santa Monica, CA 90406, 800-244-7241 can be reached by email to info@avongard.com
• Slope Indicator Company, 12123 Harbour Reach Dr., Mukilteo, WA, USA 98275 425-493-6200 can be reached by email to solutions@slope.com
• 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. *
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Bob Klewitz, M.S.C.E., P.E. - ASHI
• Ken Kruger, P.E., AIA - ASHI
• Aaron Kuertz aaronk@appliedtechnologies.com, with Applied Technologies regarding polyurethane foam sealant as other foundation crack repair product - 05/30/2007
• 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

ADDITIONAL READING about Foundation Failure Diagnosis & Repair

• Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but reprints available from some inspection tool suppliers)
• Design of Wood Structures, Donald E. Breyer, McGraw Hill, 1988 ISBN 0-07-007675-8
• Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
• Forensic Geotechnical and Foundation Engineering, Robert W. Day, McGraw-Hill Professional, 1998, ISBN 0070164444, 9780070164444, 460 pp. Mr. Day discusses the Avongard crack monitors and other foundation monitoring methods - p. 48-49.
• Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
• ASHI Training Manual - not recommended: incomplete, inaccurate, overpriced--DF
• The Home Reference Book and other Manuals from Carson Dunlop, Home Pro, T.I.E., Inspection Training Associates (Home Inspection training/report firms)
• "Avoiding Foundation Failures," Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
• "A Foundation for Unstable Soils," Harris Hyman, P.E., Journal of Light Construction, May 1995
• "Backfilling Basics," Buck Bartley, Journal of Light Construction, October 1994
• "Inspecting Block Foundations," Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
• "When Block Foundations go Bad," Fine Homebuilding, June/July 1998
• inspect-ny.com - The Free Home Inspection & Construction Diagnosis Public Information Website
• Journal of Light Construction articles are available on CD ROM from the Journal of Light Construction, www.bginet.com, 802-434-4747

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