Causes of Foundation Failure

Posted on 22. May, 2011 by in blog

There are many, many things that can cause a foundation to fail.   We put together a list of usual suspects.  Let us know in the comment section below if you have any questions.

Design
Poor design from the drawing stage is a major contributor to heightened foundation deterioration.

Materials
Proper material selection for a home’s foundation is important. Once selected, the materials must be used in a manner that they were designed for. Modern building materials are usually fabricated under controlled conditions, reducing the risk for failure.
Older materials may have been made onsite, using improper base materials or incorrect proportions. Old poured-in- place concrete is an excellent example of a great idea that was often incorrectly made. Improper amounts of cement powder and the wrong types of sand are examples of incorrect proportions, eventually leading to product failure.

Environment
Whatever the foundation is constructed of, it should be protected from the environment it resides in. Freeze-thaw cycles and water are two critical factors that have to be properly dealt with.

Workmanship
Poor mixing, incorrect water-cement ratios, inadequate strength or durability, poor curing techniques, premature form stripping, poor compaction (honeycomb voids), and very permeable concrete put weakness and lowered durability as results for all.

Weathering
Weathering cannot be stopped, though it can be significantly slowed. It is important to address the foundation system as a whole and not just divert a problem from one area to another.

Other Things That Can Go Wrong That Can Cause Foundation Failure

Surface Voids
Surface voids are the cavities or slight holes that materialize on the exterior of concrete. Surface voids are caused by decaying mortar and cement, water damage, improper installation or burrowing animals.

Soil Conditions
Foundation problems can be caused by constantly shifting conditions of the soils that surround the home. Clay soil for example, contracts and expands with varying levels of moisture. Clay expands when exposed to greater moisture and contracts as it dries. This will ultimately cause foundation cracks.

Foundation wellness is a delicate balance of proper soil conditions. Large trees and plants have the ability to extract too much moisture from the soil and improper drainage can cause heavily saturated soil to cause problems as well.

Surface Drainage
A proper and well thought out surface drainage plan cannot be stressed enough. It is critical to keep as much surface water away from the foundation as possible. This specifically includes downspouts. The City of Toronto has promised to begin enforcing their 2010 downspout disconnection directive. As these downspouts are disconnected, it is critical that the collected water from a home’s roof is diverted away from a home’s foundation. Bear in mind, it is illegal to divert the water towards a neighbour’s property. No matter how well a home is waterproofed, it will not be able to sustain itself against a constant head of water pressing against it. Link to the city of Toronto website on disconnecting downspouts

Penetrations
Traditionally, great care has not been applied when installing water, gas and drainage pipes through the footing or foundation. In many cases they are shattered through without adequate repair from both sides.

Roots
Tree roots can negatively affect a home’s foundation. It is important to gauge the distance between the tree and the foundation wall, as the closer the proximity, the greater the risk. It must be noted that not all tree roots damage foundation walls. Some roots simply turn away when confronted with the challenge. The less moisture present in the soil surrounding your foundation wall, the more likely a tree root will look elsewhere for a water supply.

Tree roots though can find their way into vacant cracks in a wall and gradually compel the opening to spread. It is at this point when water can enter the home.

Downspouts
The main function of a downspout is to divert water away from the home. Downspouts are critical in protecting the home’s roof, siding and foundation from water damage. Attaching connectors and extenders to your downspout will aid in the prevention of soil erosion, foundation damage and flooding near the house.

Legislation imposed by Toronto City Council in 2007 approved mandatory downspout disconnection for the combined sewer service areas of the City of Toronto. This bylaw requires homeowners who live within the affected areas to disconnect their home’s downspout from the City’s sewer system by 2010.

The benefit to disconnecting downspouts, most notably to ones at the rear of the house, is that they tend to collect organic material. Leaves, maple keys, acorns, etc. travel down the downspout and into the sewer lines beneath the basement floor, and can create a blockage over time. In many older homes the downspout connects to a clay pipe which is part of the home’s sewage system.  The clay pipe is particularly susceptible to the freeze-thaw cycle as it travels through the ground frost area. Over time the pipes tend to break down, providing access for roots and deposits collected from the roof.

The problem in disconnecting downspouts is that most properties have not been designed to accommodate the load of water that has been collected from their roofs and will be deposited on their properties. It is critical that when the downspouts are disconnected that they are redirected away from a home in an appropriate manner.

Differential Settlement
Differential Settlement is loosened or previously disrupted soil consolidating over time due to weight. The most famous example is ‘The Leaning Tower of Pisa’, whose foundation is composed of saturated clay soil, therefore causing the ‘tilt’.

In urban settings, differential settlement is usually caused by building on unsound soil or by disrupting soil underneath a foundation or where a foundation is to be built.

Ad Freezing
Ad freezing is the method whereby an entity adheres to another through the action of ice fastening. As soil around a home freezes and expands, it is possible for the ice to grab the surface of a foundation and damage it.

Backfill
Backfilling is the replacement of the excavated material. Any backfill material should be free of roots, stones and debris that could prevent proper compaction. If the excavated material is contaminated, it should not be used and replaced with material that properly drains and does not store water.

It is important to replace any excavated fill in layers that are compacted, so as to reduce the amount that the fill settles. This helps maintain the grading around a home and prevent depressions that direct water towards a homes foundation.

Repairing the Repair
Repairing work that others have previously done is unfortunate, though very common. In most cases the work was done by the well intentioned, though unpracticed. Most failures stem from a good product being used in the wrong situation or in an incorrect way.

Thermal Shocks
All untreated masonry and concrete absorbs water. Water naturally expands as it freezes, close to 10%. As the water freezes, it stresses the brick or concrete that it resides in. It is the expansion of various amounts that causes difficulties in the concrete’s stability. Eventually, this pressure overcomes the strength of the material, causing cracks to form and eventually overall failure.

Vermin
The potential of damage to a home’s foundation as a result of vermin is a very real scenario. Nesting and gnawing of mice, rats, insects and fungi can cause damage to foundation walls and the insulating system surrounding it.

Expansive Soils
Often referred to as ‘Bentonite’, expansive soils possess high clay content that is able to absorb large quantities of moisture and thereby swell. On the other hand, with a lack of moisture the process can contract. The drastic progression of contraction and expansion can cause a structure’s foundation to shift unevenly and lift.

Hydrostatic Pressure
This is the pressure point in a liquid at rest, resulting from the load of the fluid which sits on top of it. Hydrostatic pressure forces water into the foundation through any cracks or masonry decay. When water seepage gets deep in a basement, there is a good chance that a high water table exists. This is the level whereby standing water exists underground.

Increases and decreases in precipitation will change the water table levels. Typically, builders install drain systems to help prevent the water table from rising higher than the beginning of the foundation. This also provides reprieve of hydrostatic pressure. If the water table can be controlled, there is a good chance you can prevent water from leaking into the basement.

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