Property Watch: Problem of foundation crack

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By Will Decker

One of the biggest concerns for home buyers, and many homeowners, is when they see cracks in their house’s foundation.  If you have a crack, or cracks, in your house’s foundation, you have a problem, but the problem is very often not a big one.  Foundation cracks, usually, only mean that you may get a little water seepage into the basement during a heavy rain, but they can also be a symptom of severe and dangerous structural problems.

 Types of foundations

Before we begin explaining foundation cracks, let’s first understand the different types foundation buildings can have.  I live and work in the Chicago area where the foundations are usually poured concrete and most houses have basements.  In the southern United States, most houses have crawlspaces instead of basements.  In Florida, most foundations are just slabs of concrete poured on the ground (the water table is too high in Florida and basements would just fill up with water).

Different areas have different soil conditions and climates, calling for different types of construction.  All foundations, however, serve to provide the structural base for the building.  All types of foundations begin with a wide base, called a footing, upon which the foundation wall rests.  The footing provides a wide area resting on the ground to distribute the weight of the building evenly.  The footing is usually placed deep in the ground (in this area, footings should be at least 4 feet deep) so they will not be moved by water or freezing ground in the winter.  The foundation wall, what most people think of as the house’s foundation, rests on the footing and extends upwards to where it meets the house’s exterior walls.

The foundation wall can be constructed of different types of materials, again depending upon local conditions and construction requirements.  Some areas use concrete blocks, also referred to by their old name of cinder block.  Some older houses have brick foundations.  There are even some areas, usually dry, desert states, where the foundations are constructed out of wood.  In my area, most foundations are poured concrete with a few concrete blocks and bricks and I will limit this article to those types.

Types of foundation cracks and how to fix

Foundation cracks have many causes, but the cause of the crack can usually be determined by the type of crack.

Vertical crack

A vertical foundation crack is a crack that goes straight up and down or slightly diagonal, within 30 degrees of vertical. Vertical cracks are of least concern and are commonly seen  in almost all houses.  They occur because concrete is very strong under compression but cracks easily  occur under tension.  Most houses will see one, two or even three vertical cracks form within the first couple of years after construction.  These cracks are not a real structural concern, but they can allow seepage of water through the foundation wall during heavy rains.  Again, this is normal.  The solution to vertical cracks is usually simple, inexpensive and permanent.

We recommend that you have the crack repaired by urethane or epoxy injection.  A material is injected into the crack, through small holes drilled into the crack face from the basement.  A sealing material is injected under pressure and the crack is sealed.  The material is also flexible so that the crack does not re-open if there is future foundation movement.  Almost all these types of repairs are warranted for 50 years.  Fixed once and fixed forever.

Diagonal cracks

A diagonal foundation crack is one that runs from about 30 to 75 degrees from vertical on the wall.  Many times, diagonal cracks will be wider at one end than at the other and sometimes the crack will be very narrow (also called a hairline crack).  Diagonal cracks are usually caused by differential settling of the foundation and can occur when the house is new or old.  Differential settling is caused by a change in the ground conditions under the foundation footings.  One part of the house’s foundation, say one corner, settles a little lower into the ground while the rest of the foundation stays fully supported.  This causes a tension on the foundation just like described above.  But this tension is not in a straight horizontal vector, but horizontal and vertical.  The foundation cracks, are but cracks at an angle rather than straight up-and-down.  This is also why many diagonal cracks have the crack wider at one end.

Because the foundation is moving in two directions, a part of the crack is also wider and will indicate the exact settling area.  This differential settling could be caused by the house being built on a hill (left) or because of changes in the soil conditions because of excessive rain or drought.  It can also be caused by simple things like having your gutter downspouts drain too close to the house’s foundation on one side or at one corner.

Diagonal cracks can be repaired in the same manner as vertical cracks, but more injection material is usually called to account for any additional future movement.  Repairing diagonal cracks also calls for determining the cause and position of the differential settling.  This is where a certified Home Inspector, one who has specialized training in structural and foundation issues, can be of help.

Horizontal cracks

Foundation cracks that run sideways are the most serious types of cracks.  They are sometimes seen in poured concrete foundations but more commonly in concrete block and brick foundations.  Horizontal cracks are caused by a bowing foundation.  The foundation wall’s exterior is usually covered by a backfill of dirt and gravel.  If this backfill is improperly done, or does not get proper drainage or gets overly compressed (many times by the construction equipment that was used to build the house) the excessive pressure against the foundation wall causes it to bow inwards.

Sometimes there is excessive rain, which can also be followed by a freeze.  This can increase the hydrostatic pressure behind the foundation wall and cause it to bow inwards (right).   Bowing foundations are serious and can lead to structural failure of the foundation and collapse of the house.

There are a couple of different techniques for fixing horizontal foundation cracks.

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