Analyzing Foundation Cracks

Crack Appearance

Vertical or Diagonal Cracks in a foundation wall. Cracks start at floor and run to ceiling. Cracks are wider at the top or the bottom.

Possible Cause

Vertical movement between the two pieces of foundation. Crack is the hinge. Poor fill, soil creep, erosion, etc. are possible causes.

Crack Appearance

Horizontal Crack in a foundation wall. Commonly seen in concrete block walls. Crack is usually 4 to 5 feet off the floor.

Possible Cause

Poorly designed foundation wall. Wall is actually a retaining wall trying to hold back dirt from falling into basement. Can be fixed with beams or helical piers.

Crack Appearance

Stair stepped cracks in a block foundation or in brickwork above a foundation. Cracking often begins at a window or door corner.

Possible Cause

Foundation is either settling or heaving. Vertical displacement between two or more sections is occurring. Must be stabilized before masonry repair begins.

Crack Appearance

Hairline cracks around basement windows or in basement walls. Cracks appear not to get larger. Usually occurs weeks or months after foundation is poured.

Possible Cause

These are likely shrinkage cracks caused by water loss when foundation was curing. Usually not a structural problem unless foundation begins to move.

Crack Appearance

Interior plaster or drywall cracks above doors, windows or archways. No apparent foundation cracks.

Possible Cause

These are most likely seasonal cracks caused by lumber shrinking and swelling. Structural problems are probably not present.

Related Column: Foundation Cracks

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Literature for Foundation Problems

The two books listed are excellent resources for those who really want a good understanding of soil movement and foundation problems. Check your local library for availability.

• Residential Foundations
  by Jim Carr
• Has Your House Got Cracks? A Homeowner's Guide to Subsidence and Heave Damage
  by T.J. Freeman, G.S. Littlejohn, and R.M.C. Driscoll

Steel Pipe Piers and Helical Anchors

The following two companies are very familiar with solving foundation settlement problems. One uses helical anchors (A.B. Chance Co.) while the other (United Structural Systems, Inc.) uses steel pipe piers. However, at the time of this publication, United Structural Systems, inc. was only servicing the Midwestern States. If you want to compare the two systems, there is a good likelihood that a company exists near your town that does use the steel pier method. Simply check the Yellow Pages under "Foundation Repair."

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Ways to Stabilize Your House Foundation

Years ago, when I first got into the construction business, we used to fix failed foundations by "underpinning" them. This simply involved digging a round or square hole underneath the failed portion of the foundation. After we reached solid ground, we would fill this hole with concrete. This new pier would support the foundation. This method is still used today, however, it is quite labor intensive. Much of the digging is performed by hand.

Newer methods have been developed that allow you to not only stabilize the foundation, but also lift it back up (to varying degrees.) These methods involve either driving steel pipes into the ground or installing a giant screw called a helical pier. Once these things are driven or drilled into solid ground, a large steel bracket is attached. The bracket slips under the foundation and footer. Machinery then is able to lift the bracket up the pier or the steel pipes. If you are lucky, you can bring the foundation back to its original position.

Artificial Rain

Let's talk about expandable clays. These soils can cause big problems, especially for people who live in a house on a slab or who have room additions or garages with shallow foundations (those four feet or less in the ground.)

Periods of extended, severe drought can dry a soil to deep levels. Large trees near a house can suck vast amounts of moisture from the soil. You can combat these problems if you install (during construction) a water injection system. It's easy to do.

Have you seen foundation drainage pipe? You know, the pipe with holes in it. Imagine if your builder is installing this to drain water away from your foundation. Great! But what about when your foundation needs water? Well, simply have the builder install two or three Tee fittings around your house. Extend a vertical pipe from these fittings up to the surface. In periods of dry weather, you can run a garden hose into the pipes. The soil, down by your footer, will think that everything is normal back at the surface! Nothing like smoke and mirrors!

Phantom Settlement Cracks

Sometimes people think that their house is settling when, in fact, it is not. They are victims of lumber shrinkage and swelling. The framing lumber (wall studs, floor joists and roof rafters) all absorb humidity from the air.

Here in Cincinnati, we have very humid summers. Cracks around windows and doors disappear or get very small in the summer months. Six months later, these same cracks look like the Grand Canyon. The drier winter air sucks the water from the lumber.

The wood acts like an accordion. It moves back and forth with the changes in seasons. Be sure to consider this possibility before you initiate expensive foundation repairs! You may not have a foundation problem.

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Foundation Settlement

Numerous homeowners have told me about instances that happened in the middle of the night. The stories are all very similar. They are awakened by a loud "crack" or "pop". Yes, part of their house cracked like a dry piece of kindling wood. However, often the part that cracked is the foundation!

Other stories speak to doors and windows that work perfectly one day and stick the next day. Sometimes the sticking is seasonal. That is, the doors and windows work fine for three to four months and then trouble begins. Magically, the doors and windows work fine four to six months later.

In all these cases, the common denominator is some form of major structural movement. The movement can be within the house (lumber swelling and shrinkage) or it can involve the entire house (settlement or some other force which is stressing the entire structure.)

All too often, however, the term 'settlement' is used to describe any movement. This can be misleading, as settlement is really just one form of movement which can affect the way the inside and outside of your house looks. Cracks can develop in your house from other forces such as landslides, heaving (frost or soil swell), soil shrinkage, erosion of soil from beneath your foundation, earthquakes, construction blasting, soil creep, etc. You see, lots of things can be happening! Sometimes, two or more at once.

Common Causes

It is not uncommon for a house to be built on fill dirt or on a hillside. Have you seen huge earth-moving machines working on a new subdivision? They scrape dirt from the high spots and deposit it on the low areas. The dirt that is used for fill is supposed to be compacted. However, it may not always be. Gravity and water entering the soil over time compacts the loose fill. If the compaction is not the same under the entire foundation, your foundation may fracture.

Hillside construction is a simple matter of high school physics. Gravity is constantly pulling the soil down the hill. I learned this in my first geology class. This soil creep, as it is called, takes place at a faster rate the closer one is to the surface of the ground. So, houses dug into a hillside basically have their backsides exposed! The part of the foundation that is shallow and is near the surface is subject to movement, while the remainder of the foundation is quite stable where it is dug deeply into the hillside. Perhaps you have seen foundation failures like this.

Hillsides also pose another problem. The soil creeping down the hillside can exert huge forces on the uphill part of the foundation. These walls can crack or tilt inward from the force of this pressure.

Water, or the movement of water in soils, can cause foundations or slabs to crack as well. For instance, imagine if a sewer line or water line that runs beneath your house develops a leak. It erodes soil from beneath your house and floor. Eventually the foundation footer, wall, and/or floor cracks in response to the absence of the support. Remember, your foundation was designed to work with adequate support beneath it. Remove this support and.......CRACK!

Certain parts of the nation have clay soils. Some of these clay soils shrink and swell (like an inexpensive sponge) in response to the amount of water they contain. This movement can be dramatic. As the soil beneath your foundation dries out, your foundation drops. In wet weather the clay swells and lifts your foundation. This is no problem if the movement is the same at every point along your foundation. In more cases than not the movement is not equal. Stress builds and your foundation cracks.

Solutions

If your foundation develops a crack or a fracture, it usually can be stabilized. If the crack is vertical or diagonal, it may require a support from beneath that cradles the footer or foundation. If your foundation develops a horizontal crack, it can be stabilized in several ways as well.

In all instances, it would be wise to consult with a licensed structural engineer who specializes in residential problems. If you try to solve the problem yourself, or merely trust the workmen, you may have a problem occur at a later time. Some of the solutions can actually transmit the stress of the problem to another portion of your foundation. These cracks may happen months later. The contractor will generally say that those are not his fault, when, in fact, they may be! Have a structural engineer develop the solution. Then hire a contractor to perform the work.

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Using Transits, Laser Levels and Optical Builder's Levels

Can you imagine how you might go about trying to determine the differences in elevation between two points which are approximately 100 feet apart? Using a four foot wood or aluminum level would be very impractical. A water level might also be tough to use, as the 100 plus feet of tubing would be very tough to maneuver. Surely, one would think, there has got to be an easier way.

Well, as you might expect, there is a much easier way to determine elevation differences. You simply use a transit or a builder's level. These highly sensitive and accurate instruments (that's what they are often called in the field - instruments) are the only way to go. They are easy to set up and can be used in any weather that you can stand being in.

What is the difference between a level and a transit, you might ask? A level basically does just one thing - it establishes a level line when set up on a tripod. A transit can do a little more. It not only can establish a level line, but also a plumb line when looking through the scope or sight. Also, a transit has the full 360 degrees of a circle marked on its base. This means that when you rotate the sight around on the tripod you can do basic surveying.

How Do They Work?

Have you ever seen one of those old World War II submarine movies? Or, how about the movie Hunt for Red October? In just about every submarine movie or show, there always seems to be a scene where you are looking through the periscope. That is what it looks like when you peer through an optical level or transit. The only difference is that the crosshairs in levels and transits don't have all the markings that you sometimes see in the periscopes. In fact, when I'm in a good mood and using my transit, I'm often heard saying "Flood torpedo tubes 1 & 4! Bearing 245 degrees! Range 3,000 yards!"

Back to reality. Optical levels and transits operate in a very easy manner. Once they are placed on a tripod and adjusted (made level themselves), they project a level line as you look through the instrument. This means that any spot that you look at which is right in the middle of the crosshairs is at the same elevation as the thing you just looked at a moment before.

OK, so how can they tell the difference between two points? No problem! When used in conjunction with a grade pole (a stick or pole that is marked in feet/inches or metric units), a level or transit enables you to determine elevations with great accuracy. The method is very easy.

Here is the challenge. Let's say you want to measure the difference in elevation between two points on a hill. The first thing to do is set up the level or transit in a location so that after it is adjusted, the line of sight through the crosshairs is higher in elevation than the two points you are trying to measure.

Now, you look through the instrument while a second person takes the grade pole and places it on one of the two locations. Making sure they are holding the pole in a plumb position, take a reading. For our example, let's say the first reading is 2 feet 6 inches. Now, send the person to the second spot and take a reading. Let's say that the crosshair hits the grade pole at 10 feet 9 inches at this location. OK, what is the difference in elevation between the two spots? The difference between the two points is 8 feet 3 inches. Which spot is lower than the other? Obviously, the second location is lower in elevation than the first (assuming that the markings on the grade pole start at zero on the bottom of the grade pole.)

Turning in a Circle

The neat thing about optical levels and transits is their versatility. When placed on a tripod, these devices can rotate a full 360 degrees on top of the tripod, just like the submarine periscopes. This function allows you to set up a level and take readings in any direction. The speed of operation depends only on two things: how quickly the person with the grade pole can move from location to location; and how quickly you can locate the grade pole in the cross hairs, focus and take a reading.

Durable but Delicate

Levels and transits are made to withstand dusty construction site conditions. They can withstand getting wet. Heat and cold conditions do not bother them. However, if you drop one, you are in trouble.

These instruments are delicate with respect to impacts. The optical lenses can be knocked out of adjustment, as well as the leveling screws which are used to level the instrument on the tripod. Only professional service centers can realign an instrument.

Use Tips

Using a level or transit takes some practice. The method of setting up the tripod is somewhat tricky, especially on sloped surfaces. Muddy or unstable soil can be a problem. You may adjust the level and begin using it, but several minutes later, because of your moving around the tripod, the soil may move slightly. The level may now be out of adjustment and who knows how many readings might be in error.

There are some tricks that will help you achieve highly accurate readings. For example, let's say that you need to take measurements for points all in a straight line. The best place to set up the level or transit is at one end of the line, not in the middle. Levels can begin to make slight errors, if slightly out of adjustment, when you begin to rotate them on the tripod. If you are at one end of the line of points, you shouldn't have to rotate the level. All that you will need to do is focus the lens as the grade pole moves.

Checking for Errors

Checking a transit or level that is suspected of being out of adjustment is fairly easy. Locate a small 1/4 or 1/2 acre pond on a windless day. Set up your level and ask the grade pole individual to go around the pond and set the bottom of the pole right where the water hits the shore. Since the water in the pond is level, all the readings should be the same.

Labor Layoffs

Let's say that you need to do some of the things we talked about, but can't find that necessary person to hold the grade pole. Once again, no problem. Within the past five years, laser levels and transits have become reliable and affordable.

These devices are great because they are designed for one person use. You set up the instrument in virtually the same fashion as an optical instrument. The difference lies in the fact that you simply turn on the laser and BINGO, a fine, thin, red beam of light begins rotating.

You take the special grade pole, which has a sliding target, and move around from point to point. The only thing you need to do is slide the target up and down the grade pole and take the readings when the laser hits the center of the target. It's that easy.

Does any of this sound like fun? If so, just about every tool rental store rents levels and transits. Go get one for an afternoon and sink some ships! Happy hunting!

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Optical Levels, Laser Levels & Transit Manufacturers

• Laser Reference, Inc.
• Macklanburg-Duncan
• Sokkia
• Stanley Tool Works
• Topcon Laser Products Division
• David White Company

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Tips on Residential Foundations

Give serious consideration to installing vertical reinforcing rods in your foundations. Most building codes insist that you install horizontal steel bars near the top and bottom of your walls. However, virtually no code (except earthquake areas) requires the placement of vertical steel. In the event that your foundation cracks, I guarantee that it will cost you many times more money to repair the crack than to have installed the steel in the first place.

NEVER backfill a foundation until both the basement slab and the first floor subfloor assembly are in place. These two elements are critical. They are the top and bottom of the "box."

Wait as long as possible to backfill. Concrete or concrete blocks develop strength over time. In fact,under ideal conditions, they often achieve only 75% of their design strength after 28 days!

Negotiate with your builder or foundation contractor to leave forms in place for three to four days if possible. Removing forms the day after the pour subjects the fresh concrete to rapid moisture loss. The concrete needs water for it to gain its maximum strength. During hot or windy weather, consider applying a curing compound to the walls immediately as the forms are removed.

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Basement Walls

Many parts of the nation enjoy soil and topography which favors the installation of basements or partial basements (crawl spaces). Areas which have very little soil cover, marshy land, or high water tables make frequent use of concrete slabs. However, those people or builders who do build basements often overlook an important point. Basement walls, be they poured concrete or concrete block, are also retaining walls. They retain, or hold back, the dirt which surrounds your house.

Retaining walls which exceed four feet in height often are engineered. They require special footers, specific wall thickness, and the prolific use of steel reinforcing. Many residential basement walls often have seven feet of backfill against them! However, there is a difference between a free standing retaining wall and a residential foundation wall. A residential foundation wall has two things that help it structurally. The basement slab and the wood subfloor assembly which is bolted to the top of foundation walls are important structural elements. The basement slab stops the bottom of the wall from sliding inwards, while the subfloor assembly helps to keep the top of the wall from tilting inwards.

However, these two elements are not enough to totally withstand the forces of soil and water against a poured concrete or foundation wall. These walls must be constructed in such a way as to resist the forces which will be placed against them. To further complicate the issue, no two building sites are exactly the same. For example, a foundation constructed at the bottom of a hillside will have greater forces against it than a foundation built at the top of the hill. A foundation which will last 100 years in areas of little or no seismic activity might crumble in a moderate earthquake in southern California. All foundation system plans should be checked for the particular building site by a competent structural engineer. The $200 - $300 fee may equate to a lifetime insurance policy. It is money well spent.

Tension Headaches

The strength of concrete and concrete masonry products (block) is usually measured in the amount of weight they can support before failure. This weight squeezes or compresses the concrete or masonry materials. Thus it is called compressive strength. However, concrete or concrete masonry is not always squeezed. Often it is stretched or pulled. These forces are referred to as tension. Non-reinforced concrete or concrete masonry products generally are only 1/10th as strong in tension than in compression. That means that if a concrete wall is rated for 3,500 pounds per square inch in compression, it will only be able to withstand 350 pounds per square inch when subjected to a tension force.

Foundation walls are subjected to tension forces as they try to hold back the soil around them. The dirt wants to push in or bulge the wall. You can illustrate this very easily with a thin piece of cardboard. Stand the cardboard up straight just like your foundation wall. Using your finger, push the center of the cardboard. The cardboard bows inward. When this happens to a foundation wall, the inside face of the wall is actually being stretched or pulled. This is tension. The resulting crack is a measurement of just how much it was stretched!

Steel, on the other hand, can withstand tremendous tension forces. In fact, the average steel used in reinforcing rods for residential construction will fail only after 60,000 lbs per square inch of force is used to pull it apart! Fortunately, steel is very inexpensive. If you decide to build anything with concrete or concrete masonry and you do not include reinforcing steel, I guarantee that you will develop a massive headache when that first jagged crack appears! Be smart, insist on the use of reinforcing steel anytime you build with concrete or concrete masonry products. You will not be disappointed.

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