How to Distinguish Shrinkage, Expansion, & Settlement Cracks in Foundations
SHRINKAGE vs EXPANSION vs SETTLEMENT - CONTENTS: Foundation crack types: how to distinguish between foundation shrinkage, expansion, & settlement cracks & why it is important to tell the difference. Photos of types of foundation crack & movement damage.
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Masonry structure crack types:
This chapter of the "Foundation Crack Bible" discusses in detail the process of distinguishing types foundation damage
due to shrinkage, expansion, or settlement, for all types of masonry foundations: concrete, masonry block, wood, stone, pre-cast.
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.
Foundation cracks, which are signs of foundation damage, can mean very different things
depending on the material from which a foundation is made, the location, size, and shape of the foundation crack, and other site observations.
SHRINKAGE vs EXPANSION vs SETTLEMENT - Distinguishing Among Shrinkage, Expansion, and Settlement Cracks
General Comments about foundation expansion or shrinkage
Cracks will occur in masonry structures: Most solid materials may both expand and contract in response to temperature variations.
Solid materials may be cracked by pressure from loading. In masonry foundations, bricks actually expand indefinitely, though probably
at a decreasing rate. Poured concrete shrinks after pouring. Masonry blocks may shrink and expand.
All of these materials respond
to changes in moisture and temperature. A long brick wall exposed to sunlight and cold weather and built without expansion joints
will crack and fail. Concrete block walls shrink but don't normally expand (below grade). Poured concrete shrinks during curing
but may also expand or contract in response to moisture.
Determining when action is needed: All cracks need to be separated into those which are expected to require no further repair except possibly cosmetic (which can help future monitoring), those which merit ongoing monitoring for change and possibly signs of worsening conditions, and those which are so significant as to require repair.
Setting priority of action: Repair work needs to be identified with respect to urgency, ranging from immediate (risk of collapse or other unsafe conditions) and less urgent.
To the extent that the inspector can see the extent of movement and the potential for damage to a building, and to
the extent that the inspector can make a reasonably confident guess about the cause of foundation damage or movement, s/he can
estimate the chances of its continuance and thus help set a priority for further evaluation or repair, as well as setting the specifics
of outside repairs to reduce further damage such as keeping water or vehicles away from the building.
A variety of site conditions can lead to cracks in a concrete or other masonry foundation walls or floor slabs.
generally, foundations may be damaged and cracks may appear from innocent causes unlikely to affect the
structure such as concrete shrinkage cracks, initial settlement, or from potentially more serious causes such as
ongoing settlement, unusual pressures or loading, or from improper construction.
Identification of Shrinkage Cracks in Poured Concrete Foundations or Slabs
Shrinkage cracks in poured concrete are easily recognizable and can be distinguished from other types of cracks that occur
later in the life of a foundation wall or floor slab.
Concrete shrinks as a natural process during its curing.
You can see the shrinkage of even a perfect concrete floor slab with no visible cracks in its surface if it was poured inside of an existing
foundation. Notice the gap between the edges of the slab and the foundation wall? Notice the stains or concrete debris on the
wall at the slab level? These indicate that at the time the slab
was poured it was touching the wall. A poured concrete wall shrinks as well.
Concrete curing is a chemical reaction, not just "drying" or loss of water. But depending on
the concrete mix, amount of water, portland, aggregate type, temperatures, humidity, groundwater, sun exposure, groundwater, and
other conditions, the amount of shrinkage that will occur in concrete as it cures varies.
In any case, this concrete shrinkage process causes the concrete to develop internal stresses.
To relieve those stresses, unless control joints were included in the wall or floor slab design, the
wall or floor is likely to crack in a classic "concrete shrinkage pattern" as the concrete cures.
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 and stop entirely, which are usually discontinuous in the crack's finest or hairline area (the crack "stops and starts"
in the same area), are usually shrinkage cracks and should not be ongoing nor of
structural significance, though they may invite water entry through the wall. [See our article on
POLYURETHANE FOAM INJECTION]
Shrinkage cracks in concrete
range in length from a few inches to the entire height of the concrete wall, extending from
wall top to bottom. Concrete shrinkage cracks virtually always extend through the full thickness of
the foundation wall, which means they can provide a ready path for water entry into the building.
Common areas for a shrinkage concrete crack to develop
are under a basement window, above a doorway in the middle of a long
wall or where the foundation "steps down." Shrinkage cracks also often occur near the middle of a large poured
concrete wall [or floor] if no control joints were used. [Concrete control joints are very often omitted in residential
construction. Shrinkage cracks and how to recognize and diagnose them are discussed further at
SHRINKAGE vs EXPANSION vs SETTLEMENT.
Evidence of Foundation Expansion
Brick, in particular, whether used in a foundation or as a building wall, expands over time and as moisture, temperature, and other conditions vary.
Dave Wickersheimer, P.E. and R.A., who is a masonry failures expert from the SHC, informs us that brick "grows" or expands
indefinitely. However if we exclude heating effects of sun exposure (discussed below), most brick expansion from its internal chemistry
probably occurs early in its life.
Thermal expansion of brick:
Thermal expansion cracks in brick are often nearly vertical, maybe passing right through the bricks not just
at the mortar joints, and tend to be near the building corners.
In any long brick wall, whether it's veneer or structural, if it's real brick,
look for expansion cracks if the wall design did not include vertical expansion joints. Southern exposure, walls exposed to more sun,
take more heat and may show more expansion due to the added thermal effects of sunshine.
Although it's natural state causes brick to expand or "grow" slowly in size continuously,
more often, brick walls exposed above-grade are subject to more rapid and more significant heating gains from sunlight.
These brick walls may expand (when heated) and contract (when cooled)
sufficiently to cause major damage if proper control joints are not used during construction. If you observe long expanses of brick masonry
walls above grade and without expansion joints, look for expansion cracking. When caused by thermal expansion, brick walls may show most
movement at the two ends of the wall most-exposed to sunlight.
The author, using a simple plumb line and measuring tape, has measured as much as
4" of expansion found at the top of a brick structure whose wall corners leaned out 4" over the wall bottom from this force
over the height of a two story structural brick wall.
Brick masonry walls below-grade are of course not exposed to heating and expansion from sunlight, but instead are exposed
to earth pressure (look for horizontal cracking), moisture gain, and in freezing climates, frost damage too. Look for horizontal cracks in
brick walls at or near the frost line, and look for stair-stepped cracks at corners of the building from frost heave or settlement.
Foundation Settlement: crack patterns, other evidence
The photograph shows a significant settlement crack in a poured concrete foundation of a new (modular) home.
This crack appeared first as a fine hairline crack. The owner monitored the crack as it expanded to a significant width over
the ensuing year.
A combination of poor site preparation of soils below the building footings (un compacted fill), portions of
footings sitting on bedrock, and nearby blasting led to differential settlement that produced this damage. We suspected that
also some reinforcing steel may have been omitted from construction of the foundation wall.
A settlement crack is more likely to be wider at top than its bottom as the foundation "bends" over a single point (or
as one section of footing tips downward from its neighbor), allowing differential settlement; it is possible for a settlement crack to appear fairly uniform however if a foundation breaks vertically and then pursues differential settlement.
Settlement cracks need to be separated into initial settlement due to construction or site factors and ongoing settlement due to site factors.
Settlement cracks are usually wider at the top of the crack, usually continuous, and may occur multiple times in a wall
Direction of downwards movement: If you draw an imaginary line orthogonal (at a right angle to) the line of a diagonal foundation crack, usually the
line you've drawn points to the direction of downwards movement in the wall. However a diagonal crack may also indicate upwards wall-lift
such as by frost or expansive clay soils which are more active under one portion of a foundation wall than another.
Sink holes and foundation cracking: Settlement cracks may appear at the opposite end of a wall when a reinforced masonry foundation is settling due to presence of
a sinkhole (for example in Florida). In this case the diagonal crack can fool the inspector if s/he looks for downwards
movement at the corner closest to the crack. Instead, the main portion of the building can be sinking! This condition can be
distinguished by observing or measuring the directions of floor or wall slope.
Multiple settlement cracks in walls: Multiple cracks of either type (settlement or lifting) may occur in a given area. Usually
settlement cracks are visible both outside and inside of the foundation wall if the wall material is exposed to view at all.
Watch out: To be used properly, this information must be combined with specific
on-site observations at the particular building in order to form a reliable opinion about the condition of that building's foundation. Anyone having
concern regarding the structural stability, safety, or damage of a building, foundation or other components, should consult a qualified expert.
[The photograph shows severe foundation damage discovered during construction of a new home.]
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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, professor, school of structures division, UIUC - University of Illinois at Urbana-Champaign School of Architecture. Professor Wickersheimer specializes in structural failure investigation and repair for wood and masonry construction. * Mr. Wickersheimer's engineering consulting service can be contacted at HDC Wickersheimer Engineering Services. (3/2010)
*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.
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 used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cobeen, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328 This book is an update of a long-established text dating from at least 1988 (DJF); Quoting: This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the California PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
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Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
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