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How to Recognize Building Site Factors Affecting Foundation Condition or Foundation Cracking StructAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com How to identify site or terrain factors affecting foundation condition Building site factors contributing to foundation movement, cracking, or damage Visual inspection of foundations Photographs of foundation crack patterns

This document describes how to recognize and diagnose building site factors that contribute to or perhaps cause various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls. Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

1. SITE FACTORS AFFECTING FOUNDATIONS - in Foundation Damage Diagnosis: How to Observe Site Factors Which May Damage a Building Foundation

• Area History in Foundation Damage Diagnosis: Is there evidence of a history of earthquakes, landslides, mud slides, soil settlement, sink holes, construction on fill, or buried debris on or at sites in the area?
  
  
• Constructed on fill, or on organic/site debris used as fill or buried for disposal, risks future settlement. In some cases, burying site debris or trees, or construction over an old landfill, can result in dangerous settlement or even sudden ground openings occurring years or even decades later.
• Constructed over or close to a ravine: Ravines, ditches, filled areas, or underground streams can result in later earth movement, slides, and foundation damage.
• Neighborhood history; cracks in other houses in the area. If other homes in an area are observed to have settlement, leaning, or foundation damage, watch for those conditions on the property being inspected. In an area of one Northeastern U.S. city, all of the homes in a hilly neighborhood lean consistently to the right and have suffered major settlement damage.
  
  
• Area geology in Foundation Damage Diagnosis:
  
  
• Sink holes: sink holes can appear suddenly and be a catastrophe; they are more prevalent in certain areas of the country. Sink holes, collapsing soils, voids open suddenly after heavy rains identify by history of area; insurance is available and limited "free" Geotechnical analysis may be available from local state or county government in problem areas. A homeowner should tell insurance company if there is a sinkhole, evidence of one, or suspicion of one. 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
• Lakes and Streams: surface drainage, water & earth loading: observe nearby lakes for evidence of the probable level of the high water table in the soils on which a building has been constructed. Is the basement below lake or stream level? In areas of Long Island, NY, some homes are constructed with a basement floor below the level of nearby waterways, and survive only by having continuously operating sump pumps. One such home collapsed during an inspection by the author.
• Solid rock or rocky construction sites: may mean that foundation construction required blasting. Unusual cracking in a poured concrete foundation of a modular home in New York State was traced to a combination of inadequate footing preparation and blasting at an adjoining site as a second house was being built.
  
  
• Soils in Foundation Damage Diagnosis: Are there problem soils such as wet, expansive clay soils, scree, bedrock, boulders, buried debris, evidence of fill? Problems having soil characteristics as their origin can show up years later.
• Fill: Is there evidence of construction on fill: Look at the surrounding land, its slope and shape. Look for covered tree boles
• Expansive soils - are more serious extensive and more common in certain areas: e.g. Colorado, North & Central Florida Ocala/Gainsville, and in Canada, Ottowa, Winnipeg, Ontario & Manitoba. Expansive soils shrink and expand significantly as ground water levels vary. In some areas homeowners must install a system to maintain water in the soil below the home to prevent soil shrinkage, settlement, and building damage.
• Tree bole is the bottom of a typical deciduous tree where the tree roots begin to leave the trunk and spread underground. Normally the bottom of a tree widens and slopes down away from the tree. If you observe a deciduous tree trunk which is simply vertical, going straight into the ground, you may have found evidence that fill has been added to a site.
  
  
• Original and Surrounding Slopes: show the original direction of excavation-sequence used in constructing a building. For example, the foundation for a home constructed on a steep hillside will normally be constructed by excavating into the hill from the down-hill side of the foundation footprint.
  
  The excavation process cuts into the hillside and moves earth from the "uphill" side of the foundation footprint to the "downhill" side where it serves as fill. If the filled-portion of the foundation area is not adequately compacted or stabilized, a result is that building footings are constructed on virgin soils at the "uphill" portion of the home but on filled soils at the "downhill" portion of the home's footprint. It is common to find evidence of footing and foundation settlement cracking occurring over the on-fill portions of the foundation, and perhaps beginning just at the transition point where the footings moved from being poured on virgin soils to being poured on filled-soil. Observing the site shape tips-off the inspector to watch out for evidence of such movement.
  
  
• Stepped foundation footings: are a normal practice on steep slopes. But where a site has a combination of intermittent bedrock and steep soils, differential footing settlement and movement often occurs at transition points, such as where a footing steps off of rock and onto soils. Similarly, because a house with a basement and a garage often has footings at two very different depths (8' down for the basement and 3'-4' down for the garage) differential settlement may occur between those structures.
  
  
• Exposure of foundation to mechanical or vehicle damage: A driveway close to the foundation wall, common in older cities, e.g. NYC & Toronto, exposes foundations to damage when heavy trucks such as an oil tank truck or a cement delivery truck pass close to the building to make a delivery. Horizontal earth loading cracks (in a masonry block wall) are likely to appear in a pattern similar to earth loading cracks but higher up than from simple earth loading, perhaps at the center or bottom 1/3 of the wall.
  
  
• Water, Foundation Leaks, Wet Basements in Foundation Damage Diagnosis: Trees (their roots) and rocks which are near the foundation define areas to watch out for both root damage to a foundation and, more subtle, water entry from ground water (or roof spillage) which is directed towards the building foundation wall by a combination of these factors:
  
  
• Poor site drainage and improper routing of surface runoff, roof runoff, or ground water are very common sources of both basement water entry and foundation damage.
• Water follows underground passages in soils created by tree roots, digging animals, earth worms, excavations for underground utilities such as water lines and buried electrical lines. If these lead towards a foundation, particularly from an uphill slope, watch for foundation leaks inside such locations.
• Water follows underground bedrock which slopes towards a building, and is difficult to keep out. Leaks often are observed in a basement or crawl space where bedrock is exposed and one can see the building footing sitting on (and hopefully pinned-to) bedrock or on large boulders.
• Frost heaving (in freezing climates) - recurrent wet soil freezing, due to poor site drainage or gutter defects, tends to cause horizontal cracks in the upper 1/3 of a foundation wall, always below-grade level, and typically at or just above the natural frost line depth of the soil.
  
  
• Nearby Roadways: may expose a building foundation (or other components) to damage from traffic-induced vibration.

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FOUNDATION DIAGNOSIS Chapter Index

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Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - principal author/editor of the InspectAPedia ^TM Website
• "Quality Standards for the Professional Remodeling Industry", National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987. See our books at "Structure" at the InspectAPedia Bookstore
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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
• 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
• www.inspect-ny.com - The Free Home Inspection & Construction Diagnosis Public Information Website

NOTE: 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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