If you plan on buying an old house in a geographical area with a known propensity for differential foundation movements, then it is always wise to seek the advice of a qualified geotechnical engineer. It becomes necessary to evaluate the occurrence of foundation-related problems and to determine the root cause of such problems.
The cause is the most important factor as repairs will be futile if the original cause of the distress is not recognized and eliminated. It becomes difficult to detect the problems if the signs of distress are concealed through cosmetic attempts. Such activities commonly involve painting, patching, tuck-pointing, addition of trim, installation of wall cover, etc.
The main concern in all cases is to decide whether the degree of distress demands a foundation repair. This decision requires extensive experience and some degree of compromise. Therefore, we have discussed the general signs of distress for foundation stability and ways to detect these signs of distress.
- 1. Checklist to Inspect the Foundation Stability
- 1.1 Check for Irregularities in Doors
- 1.2 Check for Irregularities in Floors
- 1.3 Check for Cracks in Outer Surfaces
- 1.4 Check for Irregularities in Walls and Ceilings
- 1.5 Check for the Exterior Surface of the Foundation
- 1.6 Check for Drainage Adjacent to the Foundation
- 1.7 Check for Trees Planted near to the Foundation
- 1.8 Check for Exposed Concrete Surface
- 2. Example to Check the Foundation Stability
1. Checklist to Inspect the Foundation Stability
The following is a simple checklist of structural irregularities for evaluating the stability of a foundation. If the structural irregularities, mentioned below, are observed then the foundation of the structure is in need of repair. If you are still uncertain regarding any of the points listed below, then you should consult a qualified geotechnical engineer.
1.1 Check for Irregularities in Doors
- Inspect interior doors for proper fit and operation. Check for evidence of prior repairs and adjustments such as shims behind hinges, latches or keepers relocated, tops of doors shaved.
- Check the plumb and square of the door and window frames. Look if the doors are square in the frames or not.
- Check to see if the strike plates have been adjusted to accommodate the strikers, relocation might indicate movement.
- Measure the length of the door at the doorknob side and the hinge side. A discrepancy suggests that the door may have been shaved.
- Also, feel the top of the door above the doorknob. If it is smooth, the door may have been sanded or shaved. If the door rubs slightly at the top, shimming the hinge plate might provide alignment without altering the door.
1.2 Check for Irregularities in Floors
A simple method for checking the level of a floor (without carpet) is to place a marble or small ball bearing on the surface and observe its behavior. A rolling action indicates the construction of foundation on a differential grade, which can be the problem for the stability of foundation.
1.3 Check for Cracks in Outer Surfaces
- Check the exterior foundation and masonry surfaces for cracks and look for evidence of patching.
- Look for the irregularities in siding lines or brick mortar joints.
- Look for the separation of brick veneer from window and door frames.
- Check for the trim added along with door jams or window frames.
- Observe the separation or gaps in cornice trim.
- Check for the separation of brick from frieze or fascia trim (look for original paint lines on brick).
- Look for separation of the chimney from the outside wall.
- Observe the irregularities for sight ridge rafter, roofline, and eaves.
1.4 Check for Irregularities in Walls and Ceilings
Inspect wall and ceiling surfaces for cracks or evidence of patching. Any cracking should be evaluated based on both extent and cause. Mostly, hard construction surfaces tend to crack. Often, this can be the result of thermal or moisture changes and not the foundation movement. However, if the crack exceeds 0.6 cm in width, the problem is possibly structural.
On the other hand, for example, if a 0.3 cm wide crack is noticed, it could be a sign of impending problems. A simple check to determine if a crack is still growing is by marking at the apex of the existing crack and then making a horizontal and a vertical mark along the crack using a straight edge.
If the crack changes even slightly, one or more of the marks will no longer match in a straight line along the crack, and the crack will extend past the apex mark. A slight variation of this technique is to mark a straight line across a door and a matching door frame. If any movement occurs, the marks will no longer form a line. The continued growth of the crack or displacement of the door marks would be a strong indication of foundation movement.
1.5 Check for the Exterior Surface of the Foundation
On foundations, check floors for firmness, inspect the crawl space for evidence of moisture, deficient framing support, and ascertain adequate ventilation. The crawl space should be dry with adequate access. As a rule of thumb in geotechnical engineering, 1 ft2 of the vent is suggested for each 150 ft2 of floor space.
1.6 Check for Drainage Adjacent to the Foundation
Check exterior drainage adjacent to foundation beams. Any surface water should quickly drain away from the foundation and should not pond or pool within 2.5 to 3 m. More attention should be given to planter boxes, flower bed curbing, and downspouts on gutter systems.
1.7 Check for Trees Planted near to the Foundation
Look for trees that might be located too close to the foundation. The safe planting distance from the foundation is preferably 1.5 times the anticipated ultimate height of the tree.
More importantly, the distance should be 1.5 times the canopy width. Consideration should be given to the type of tree. Also, remember that the detrimental influence of roots on foundation behavior is grossly underrated and it should not be neglected.
1.8 Check for Exposed Concrete Surface
Check for the cracks in exposed concrete surfaces. Hairline cracks can be expected in areas with expansive soils. However, larger cracks approaching or exceeding 0.6 cm in width require a detailed consideration and can be due to foundation movement.
2. Example to Check the Foundation Stability
Foundations are often constructed out of level (i.e. on grade elevation). The differences between grade elevation, deflection, and differential movement are very confusing to many people. For foundation stability and repair purposes, the primary concern is a differential movement. The following example will bring clarity to the confusion.
The figure below illustrates the location of different doors in various situations.
Door-A will not latch and clearly does not properly fit frame, an example of differential movement. Also, the cracks are extended into the sheetrock (panel made up of gypsum). This represents a potential for foundation leveling.
Door-B fits and latches properly although the floor is not leveled. This door was framed square on an unleveled floor. This situation does not represent a potential for foundation repair.
Door-C and Door-D will not latch and are low on the hinge side. The sheetrock is badly cracked. The center slab has settled and requires a strong foundation repair.
Door-E shows no evidence of differential movement since it is located outside the area of differential movement.
Door-F will not latch, clearly does not fit the frame, and is high on the inside (doorknob). The sheetrock is severely cracked, this type of distress needs repair.
Door-G shows no distress since it is not subjected to differential movement.
Door-H shows minor distress, which on its own may not require repair. However, this door is situated along the peak of the heave. Doors perpendicular and on a plane with Door-F may show similar movement. However, all doors parallel with the slope of heave will appear similar to Door-F. Thus, this foundation is in urgent need of repair.
Foundation is a structural element that provides the support for various loads acting on the superstructure.
When certain parts of a building move down relative to the remaining parts of the building, then it is called a differential foundation settlement.
Maximum acceptable foundation movement is 0.3%. For example, for a span of 10 ft between the support, acceptable movement is 0.36 inch.
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What are the construction practices which are used to avoid differential settlement in foundation?