Diagnose & Evaluate Step Cracks in Concrete Block Walls / Foundations
Angular cracks / step cracking in concrete block, brick or other CMU walls
DIAGONAL CRACKS in BLOCK FOUNDATIONS, WALLS - CONTENTS: How to Evaluate Step Cracking, Stair-Step or Diagonal Foundation Cracks in concete block, masonry block, "cinder block", brick or other concrete masonry unit (CMU) walls & foundations. What are the typical causes of diagonal step cracking in concrete block foundations? What is the impact of diagonal foundation cracks on a building's stability? Are repairs needed? Photographs of types of diagonal foundation cracks
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Diagonal foundation or wall cracks in concrete block or other CMU walls & foundations, diagnosis & repair:
This chapter of the Foundation Crack Bible discusses in detail the process of evaluating stair-stepped or diagonal cracking and related signs of foundation movement or damage in concrete block walls. Similar terms to "concrete block" used by some include "cinder block" or masonry block or concrete masonry or CMU walls and foundations.
Diagonal foundation cracks and movement are discussed by type and location of the cracks and their common causes. 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.
Diagonal Step Cracking in Concrete block or Brick Walls Caused by Vertical Movement - Structural Damage vs Minor Damage
[Click to enlarge any image]
The stair-stepped block wall crack shown above has been "repaired" using mortar but without more information we don't know if the cause of this cracking has been properly identified and cured. We will discuss the crack pattern and location and what they mean in this photo later in this articvle. A more thorough inspection of the entire foundation, site, building age, construction methods and other details are needed.
Hairline Step Cracking in Block Foundations or Walls
Below is hairline step cracking observed in a concrete block foundation near the corner of a home just a few years old.
The hairline (less than 1/16" wide) stair-step cracking following the mortar joints in this foundation wall and located near a building corner will often be found at corners on buildings in a climate subject to freezing or where there expansive clay soils. Frost heave or expanding soil heave and subsidence may cycle seasonally to produce this damage.
A structural engineer or masonry engineer will usually call any crack in his foundation wall a "failure". But not all "failures" are equally scary. At the time of inspection of the foundation above the amount of movement suggested by a hairline crack like this is very unlikely to (alone) present much risk of a catastrophic collapse, but conditions may worsen if the cause of cracking is not found and corrected. Start by controlling roof runoff and getting it away from the building. Further inspection inside would be useful too.
I'd need to look inside the foundation wall shown just above to better assess the amount of movement that is going on, but I figure that by the time I see diagonal stair step cracking appearing through the foundation coating or parging on a foundation wall, if I pick away some of the loose coating around the crack I'm going to see a wider crack (and thus more movement) than was evident before.
A typical cause of diagonal or "step" cracking in a concrete block wall (and some brick or other CMU walls) is frost heave or settlement, but as you can see in the photo below, a collapsing masonry block foundation may also show diagonal cracking near wall corners. That's because the intersecting wall is resisting movement in the collapsing wall while more movement and damage occurs towards the wall center.
Moderate Step Cracking in Block Foundations or Walls
The step cracks in this block foundation wall are more than 1/8" wide and there have been (bungled) prior repair attempts, probably to try to stop water entry through the crack. When I see a repair that has re-cracked I've got pretty good evidence that there is ongoing or cyclic damage to the wall, perhaps from frost or seasonally expanding soils. I'll say more below about why step cracks in block walls usually occur near the building corners.
I don't think this wall threatens imminent collapse but leaks and damage will increase until we find and fix the cause of this step cracking.
Above we see a different type of step cracking or diagonal cracks in a concrete block wall as well as a horizontal crack a bit above mid-wall height (right side of the photo). This cracking is caused by earth pressure on the outside of the wall, most likely due to a combination of wet soils and frost-push if this building is in a freezing climate. We might see similar block foundation wall damage from heavy vehicle traffic passing close-by a wall too.
Shown above is fairly-typical stair-step cracking near the corner of a building's block foundation wall. Click to enlarge this photo and you'll see that the top of the foundation footing is showing - at grade level. If I see that the step crack extends down through the footing then the footing, too, has been damaged. This New York home's foundation will continue to do its's annual frosty weather dance but it might quiet down if the owner extends that downspout about six feet further away from the building and into an area where the water keeps going away.
Very Serious Step Cracking Damage in Block Foundations or Walls
Vertical movement in a concrete block or brick wall might appear as either vertical cracks but more often as step cracks in which the crack pattern follows the
mortar joints between the masonry units in a stair stepping pattern. Our next collapsing concrete block wall photo (below) was shared with us by Carson Dunlop Associates, a Toronto home inspection & Education firm.
In both of these photographs, major vertical dislocation, foundation settlement,
has caused large step-cracking in the concrete block foundation wall. In addition to diagnosing and correcting the reason for
this settlement or foundation movement, this section of wall will have to be rebuilt.
Step Cracks Caused by Impact on a Block Wall
The step cracked block wall above was damaged by impact by a large truck that was pulling into the area of a loading dock. Below I show a larger view of the same wall, making the point that you have to use some common sense when interpreting foundation cracks: look at what's going on.
This wall needs to be re-built and the truck drivers who smash(ed) into the wall ought to get a life.
List of Typical Diagonal Crack Patterns in Building Foundations & Walls
These crack patterns form 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:
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
How to Trace the Direction of Foundation Wall Movement From a Diagonal Crack
Where step cracks are present, if you draw an imaginary line at right angles (orthogonal) to the diagonal formed by the stair stepped cracking,
the downwards direction of the line will generally point to the center of the point of downwards (or up and down) movement in the structure.
But unfortunately even this "rule" has exceptions. In Florida we observed a concrete block home with step cracking high in some of its walls.
The cracks were traced to settlement at the other end of the building which was responding to soil subsidence over a sinkhole.
Typical repairs for diagonal cracks in a concrete block foundation wall include the following steps
1. Assess and confirm the type of foundation cracking that has occurred in the block foundation so that we understand its cause - since knowing the cause of a crack helps understand the probability of future movement or damage. For the foundation damage shown in our photo above we suspect severe frost pressure on the wall combined with footing heaving or settlement, but we won't be confident about that analysis before inspecting the rest of the building and the building exterior and site.
2. Assess any impact of the diagonal foundation crack on the structure or its stability. For the concrete block foundation diagonal crack above there is no question that the crack involves significant structural damage, and it's likely that an expert on site will recommend reconstruction of the wall.
But before supporting the structure, removing the wall, and rebuilding this section of the foundation, it makes sense to form a complete picture of the sources of movement and damage. For example, the foundation footings may have been set on poorly prepared soil or on fill, there may be roof or surface runoff problems to correct, and we may also need to install a working foundation drainage system.
3. Repair (or rebuild) the foundation. A crack such as the block wall damage shown above should not simply be sealed with caulk or epoxy. Repairs are needed.
Watch out: even if a masonry block wall is rebuilt, as for the concrete foundation discussed at DIAGONAL CRACKS in CONCRETE FOUNDATIONS, WALLS, all foundation waterproofing solutions should begin with an identification of the source of water entry and steps to correct it outside if at all possible. The most common sources of foundation leaks are improper handling of roof runoff or surface runoff - problems that can often be corrected without digging up the foundation.
At WATER ENTRY in BUILDINGS we provide a series of articles detailing approaches to basement waterproofing, starting with the simple, inexpensive basics but also including the use of excavation, geotextiles, etc.
For evaluating the seriousness of foundation damage see
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"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
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
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"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
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
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)
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.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. 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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