Central Ohio Home Inspection Pros ®
Foundation Cracks
The word foundation is a timeless metaphor of strength and
security, and people quite naturally have genuine concerns about
the foundations on which their homes rest. For this reason,
people need to be educated about foundations in general and
specific types in particular, and I include such information in
every report. This is what I include about slab on-grade
foundations, and you are welcome to use all or any part of it
that you might find useful.
This residence has a bolted, slab foundation.
Such foundations are the most modern, but they can vary
considerably from older ones that have no moisture barrier
beneath them and no reinforcing steel within them to newer ones
that have moisture barriers beneath them and adjustable
reinforcing steel within them. This type is called a
post-tension slab, but is often impossible to distinguish one
slab type from another in which even the size and spacing of the
bolts can vary, although most are concealed. Our inspection of
slabs conforms to industry standards. We examine the visible
portion of the stem walls on the exterior of the structure for
any evidence of significant cracks or structural deformation.
However, we do not move furniture or lift carpeting and padding
to look for cracks, and we do not use any specialized tools or
measuring devices to establish relative elevations or determine
any degree of differential settling. Significantly, many slabs
are built or move out of level, but the average person would not
realize this until there is a difference of more than one inch
in twenty feet, which most authorities describe as being
tolerable. Interestingly, many slabs are found to contain cracks
when the carpet and padding are removed, but there is no
absolute standard for evaluating them. However, those that are
less than 1/4" and which exhibit no significant vertical or
horizontal displacement are not regarded as being structurally
threatening. They typically result from common shrinkage, but
can also be caused by a deficient mixture of concrete,
deterioration through time, seismic activity, adverse soil
conditions, and poor drainage, and if they are not sealed they
can allow moisture to enter a residence, and particularly if the
residence is surcharged by a hill or a slope, or if downspouts
discharge adjacent to the slab. However, in the absence of any
major defects, we may not recommend that you consult with a
structural engineer or a foundation contractor, but this should
not deter you from seeking the opinion of any such expert, and
we would be happy to refer one.
A similar narrative appears with raised foundations. Such
narratives not only educate clients but also sensibly limit the
responsibility of inspectors, who are not geo-technical
specialists and should not be expected to accept the
responsibilities of a specialist. For instance, how many
inspectors are likely to be aware that American builders
continued to use an inferior sand-lime mixture for many years
until the development of pressure testing at the turn of the
twentieth century proved that Portland cement, which was
invented by an Englishman in 1824, was vastly superior. It was
simply a case of a cultural bias. All foundations are not equal.
I have poked my finger into some that were built at the turn of
the twentieth century that had the consistency of a crumb cake.
This is why informative narratives are essential, and why any
defect in the components of a foundation needs to be carefully
documented, and why I favor the use of computer-generated
narrative reports, in which an inspector can store endless
amounts of narratives that can appear with a simple click of a
mouse. And these same narratives can also be used as a reference
library in which inspectors can look up information that they
could not possible hope to remember. But let’s consider the
common issue of cracks in a slab foundation.
Some inspectors may be inclined to believe that
small cracks, which are typically the result of shrinkage, are
not worth noting. However, consider the following case involving
a house with slab on-grade foundation in a neighborhood with no
apparent geological issues, no cracks in the streets, no broken
curbs, nothing. The house had been completely renovated, and
appeared to be in perfect condition. It was tastefully
furnished, and had a new roof, new windows, new doors, and new
carpeted and tiled floors, to name the major improvements. The
only visible blemishes were cracks in an old patio slab that
could have resulted years earlier, due to the absence of
expansion joints, the installation of which was not in common
practice when the house was built.
A year later, a specialist evaluation of the same property
confirmed that expansive soils were raising and lowering the
house as though it were floating on water, and in a sense it
was. Doors had shifted out of square, and cracks radiated from
every opening. Some cracks in patio slabs, walkways and
driveways, are not necessarily a cause for alarm. They result
from moderate ground movement, which builders try to accommodate
by cutting in expansion joints at every eight feet or so, but
inspectors should never make assumptions about such things. They
should at least inform their clients about them, and recommend
that they seek a second opinion.
Vertical cracks in foundation walls are
relatively common, and typically result from shrinkage. However,
those in the above pictures that were taken from inside a garage
are probably seismically related, but not everyone agrees on the
significance of such cracks. And when money is involved,
opinions can range from rational to ridiculous. A veteran
foundation contractor that I once knew paid little attention to
such cracks unless there was a significant degree of rotation,
but that was in a less litigious era. He would explain how they
occur and sometimes pacify his nervous clients by explaining
that he had to crawl through an eighteen inch crack in the stem
wall, meaning the screened foundation access hatch, to enter the
crawlspace. However, there are issues besides cracks that
inspectors need to be concerned about. For instance, if the
soils around a foundation extend above the footing and do not
slope away for a distance of at least six feet, structural
problems could result, as you can see from the picture of a
foundation wall that was taken from inside a crawlspace. Soils
were piled high on the outside of the stem wall that allowed
moisture to pond, penetrate, and eventually deteriorate the
concrete to a point that exposed the rebar, as you can see from
the picture.
Shrinkage cracks are common in slab foundations, and are usually
quite small. However, it is not unusual to find larger ones
where the slab meets the footing. These are referred to as
cold-joint separations, and are usually not discovered until
carpeting and padding are being replaced. Because of their size,
they can seem structurally alarming but they’re really not and
are easily repaired with non-shrink grout. However, people have
been reported to become hysterical, believing that their house
is about to fall down, or that the seller had deliberately
concealed defects that the inspector should have magically known
existed. It’s a recurrent nightmare for those inspectors who
have tried to convince a disgruntled client that such cracks
have little significance. The truth is that all cracks are
structural but not all of them are structurally alarming, and
people really do need to be educated and cautioned about them,
no matter how small, in which case their response is likely to
be rational instead of hysterical.
We should not leave the subject of foundations
without talking about sloping floors. Some floors are built out
of level, and some are caused by differential settling, which is
a result of weight bearing down on footings situated in soils
that are either inherently unstable, inadequately compacted, or
have become destabilized by moisture. Significantly, most
builders pay little attention to weight, and could only guess at
the weight of a house, whereas a shipwright could tell you down
to the last pound what a ship weighs. Consequently, houses do
have a tendency to settle, usually listing to one side, or
settling more or less equally on opposing sides, which leaves
floors crowned in the center. Similarly, many structural
engineers agree that one inch of slope in twenty feet is
tolerable, and report that differences in elevation are
typically not noticed until it exceeds this.
Contents
PATCH
Independent Home Inspections, LLC
Serving Columbus and Central Ohio
Rick A. Harrington
13514 Falmouth Ave
Pickerington, Ohio 43147
(614) 565-4962
(614) 768-1190 fax
Home Inspections
Thermal Imaging (Infrared)
