Photograph of - cracked  masonry block foundation wall, probably from earth pressur at original construction - notice the wavy mortar. Drop a plumb line to measure total inwards bulging of this block foundation wall. Foundation movement: how to detect & diagnose active or ongoing movement in a building foundation
     

  • FOUNDATION MOVEMENT ACTIVE vs. STATIC - CONTENTS: Foundation movement: how to detect & diagnose active movement or movement cracks in a building foundation. Types of foundation damage as a function of movement activity; how to assess the extent of foundation damage. Photographs of foundation movement crack patterns
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Determine active vs. old building foundation or structural movement: This article explains the difference between active & static foundation movement: how to detect & diagnose active movement or movement cracks in a building foundation.

This article series describes how to recognize and diagnose 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.

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MOVEMENT ACTIVE/STATIC - Foundation Movement: Determining Active or Dynamic (ongoing movement) vs. Static (no ongoing movement)

The photo at the top of this page shows a bowed masonry block foundation wall with horizontal cracking that occurred due to earth loading at the time of construction, probably by vehicles driving too close to the foundation wall shortly after it was constructed. At this website we explain how it is sometimes possible to be confident about the cause of foundation damage which in turn helps assess the risk presented to the building.

Photographs of types of foundation cracks and other foundation damage: we have a large library of photographs which we're in process of adding these photographs to this website. Pending completion of that work, contact the author if assistance is required.

How to evaluate the extent and importance of building foundation movement

How to determine the age of foundation cracks

Look for clues indicating old vs. new cracks and active vs. static cracks. For example, evidence of repeated repairs (patched, re-cracked, re-patched) is clear indication of recurrent movement. Evidence that a crack occurred at time of construction (in an older house, such as wavy mortar which "bent" in the mortar joints as a wall was loaded) is clear indication of an old condition which may or may not be accompanied by other evidence of later movement.

How to look for evidence of horizontal foundation movement or wall displacement

Horizontal wall movement: Look for evidence of horizontal wall displacement, lateral displacement such as frost push of a masonry block wall. The bottom block course, held in place by the floor slab, may be in the original location while the first course above or higher courses may have been pushed horizontally inwards.

How to evaluate foundation wall leaning, tipping, or bulging

Wall tipping or leaning: Look for evidence of wall tipping or leaning - the entire wall has remained flat but leans inwards at the top.

Wall bulging: Look for evidence of wall bulging, locate the center of the most bulged-in section and note its height above the bottom of the wall and its relative position to the top of grade outside.

How to measure the amount of lean or bulge in a foundation wall

Photograph of our sketch of a simple way to use a plumb line and measuring tape
to determine the amount of lean or bulge in a foundation wall

Measuring foundation wall tip, lean, or bulge: is simple: drop a plumb line near the most-bulged area (usually the center) of the wall, perhaps fastening it to a nail in a floor joist overhead, about 4" in from the wall. Measure from the string in to the wall at various heights up the wall.

You'll be able to easily pinpoint the height of the most bulge or lean. This is not engineering. It's simple a simple mason's method to measure a wall or chimney during construction to keep it plumb.

[You may need to hire the services of a licensed professional engineer, one who is experienced with foundation troubleshooting and repair, especially if there is need to design a special building repair method or if there is apparent risk of possible building instability or collapse.]

  • Wall most-bulged in near the outdoor ground surface (commonly occurs in the upper 1/2 of the wall), perhaps at a depth equal to the frost line in climates where freezing occurs or in the top 1/3 of the wall if we suspect water or frost loading on the wall, or possibly vehicle traffic driving too close to the wall.
  • Wall most-bulged in at its center height - the center of the overall height of the wall (common) - we suspect vehicle traffic or possibly water/earth loading
  • Wall most-bulged in near its bottom (unusual) - we suspect earth loading or wet earth loading.

Details: a plumb line, that is a string suspended by a weight, gives a perfectly vertical line from which to measure back to the wall surface. We don't care about the absolute value of the various measurements, we care about the difference between these measurements. Usually the very bottom of a building wall will not have moved inwards, particularly if a concrete floor has been poured against the foundation.

The entire building floor slab is acting as an "anchor" to hold the bottom of the foundation wall in place. So we take the distance between the foundation wall and the string at the bottom of the wall as our "home base" or point of assumed "zero movement".

We compare this measured value with the other measurements between the wall and the string. If the foundation wall or any part of it higher than the floor has moved, tipped, or bulged inwards, those measurements from wall-to-string will be less than the distance, wall-to-string measured just above the floor level. That's because the wall has moved inwards, towards the string.

An example of measuring the amount of foundation wall bulge inwards

  1. We "eyeball" the "bulged" foundation wall and guess at the point at which it is bulged inwards the most - perhaps close to the center of the length of the wall (right-to-left dimension)
  2. We hang our string or plumb line from the nearest floor joist, keeping the string a few inches away from the foundation wall
  3. We measure 4.00 inches between the foundation wall surface to our vertical plumb-line string at 1" above the concrete floor - this is our "zero point" or "home base" measurement
  4. We measure 2.00 inches from the same foundation wall surface to our vertical string at a height of 5' from the floor
  5. We measure 3.25 inches from the same foundation wall surface to our vertical string at the very top of the wall just under the sill plate.
  6. We check that we've measured at the area of greatest inward bulge in the wall by moving our plumb line to our left, then to our right on either side of the ceiling joist we used to hang the string for our first measurement. If the distances we measure, wall to string, are greater than the distances we measured at our first trial, then that one is the point of greatest inwards foundation wall bulge.
  7. Finally we do the math: subtract our "higher on wall" and "closer to string" measurements from our "at the floor" and "farthest from string" measurement. We see these results:
  8. Foundation Wall Bulge-in at floor = 0 inches
  9. Foundation Wall Bulge-in at 5'up from floor = 4" - 2" = 2" of inwards bulge
  10. Foundation Wall Bulge-in at the top of the wall = 4" - 3.25" = .75" of inwards lean

How to distinguish between a "bulged" foundation wall and a "leaning" foundation wall, and why we care

Characteristics of a leaning foundation wall

If all of our measurements of inwards movements in the foundation wall increase in distance (wall to string), from floor up towards the top of the wall, the wall is leaning inwards. In this case we'd expect to not see horizontal cracks (if the wall is masonry block, for example).

Characteristics of a bulging foundation wall

If our measurements anywhere between the floor and the top of the wall is greater than the distance measured (wall to string) at the floor bottom and at the wall top then the wall is "bulged" inwards at that point. If the wall is masonry block in construction we'd expect to see horizontal cracks in one or mortar joints in the bulged area, with the widest horizontal crack at or close to the point of greatest inward bulge.

Even a concrete wall which is bulged is going to be cracked horizontally, though perhaps not in such a straight line. But a bulged reinforced concrete wall would be very rare unless perhaps the concrete wall bulged, or its forms bulged, during the time that the concrete was being poured and was still wet.

Other cases of leaning or moved foundation walls may produce different measurements

Horizontal foundation wall movement, creep, non-leaning lateral shift

On less frequent occasions we've found that an entire masonry block wall (or portions of it) were pushed horizontally inwards by some outside force, without causing the wall to lean or bulge. In a pure example of such a case, all of the differential movement measured (wall to string) between the wall bottom point (held in place by the floor slab) and the inwards-pushed wall section, will be a horizontal movement of that portion of the wall, and if it's masonry block, you'll see that the inwards-moved blocks are "hanging over" or projecting past the surface of the masonry blocks that did not move.

Combinations of foundation wall movement

You may encounter a foundation wall which has moved inwards in a combination of forms, both bulging at its most-pushed-in point (with horizontal cracks in the foundation wall) and the wall may have also been pushed inwards sliding some of the masonry blocks inwards past others which have remained in place.

In this case you'll see both that some masonry wall blocks will overhang or protrude past others in the wall (usually upper inwards pushed blocks hang over lower more stable blocks closer to the floor), and there may be bulging and cracking at another elevation of the wall.

Step cracks in building foundations may also be present in bulged, leaning, or horizontally pushed foundation walls if they were constructed of brick or masonry block, or possibly (though less common) of stone.

In fact since the building foundation corners are stronger than the center portions of the foundation wall (the opposing wall at right angle resists movement of the wall being pushed), wall bulges, leans, and cracks tend to occur towards the center of the wall, resulting in step-cracking closer to the ends of the same wall.

Other step cracks will of course also occur in building masonry block foundation walls that are not leaning or bulging particularly, where frost or settlement have been causing an "up and down" movement in the foundation or footing.

Other vertical cracks can occur in a masonry block or concrete or brick or stone foundation wall without leaning or bulging if the wall is moving due to footing settlement or frost.

Questions about active (dynamic) foundation movement

When we find visual or measured evidence of cracking and movement in a masonry foundation wall of any type, there are some diagnostic questions we can ask that help assess the cause of the problem and the urgency of repair actions:

  • Constant rate of foundation movement: Does the evidence suggest that cracking and foundation movement are occurring at a constant rate?
  • Accelerating rate of foundation movement: Is there evidence that the wall movement is accelerating?
  • Decelerating rate of foundation movement: Is there evidence that the wall movement is decelerating?
  • Seasonal rate of foundation movement: Is there evidence that the wall movement is seasonal or intermittent? One of our associates has a masonry block garage foundation wall which heaves and moves up and down every spring.
  • Site-Work-Related of foundation movement: Is there evidence that the wall movement is related to ongoing site work?

NOTE: without historical data these causes can be difficult to confirm without monitoring. Active movement requires at least monitoring; present or future repair steps likely.

 

Continue reading at FOUNDATION MOVEMENT COMBINATIONS or select a topic from the More Reading links shown below.

Or see FOUNDATION DAMAGE SEVERITY

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FOUNDATION MOVEMENT ACTIVE vs. STATIC at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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