Foundation Crack Monitors

Foundation Crack Monitors

A crack monitor is a diagnostic tool that is used to determine whether or not there is active foundation movement. 

Active Movement Versus Past Movement

Believe it or not, there is an acceptable amount of past foundation movement that home inspectors will allow.  The amount is 1/2” of inward deflection on a load bearing exterior foundation wall.  As long as the wall is not actively moving, this will pass inspection.  With that being said, there is no amount of acceptable active foundation movement that is allowable.  So let’s ask the question; “Why is that?”

There are some scenarios where stress was present a long time ago that is no longer being applied to a wall.  Some examples are:

• Backfilling the wall too soon when it is not fully hardened or is still “green”
• A large tree that once applied load to the wall but was cut down
• Changes in the percentage of water in the soil over time
• A large vehicle or machine that once operated too close to the foundation wall

All of the above examples represent a situation where a stress was applied to a wall, but was subsequently removed.  In these cases, if the wall has less than 1/2” inward deflection, nothing needs done...but a monitor should be applied to ensure there is no active movement.  If the movement measures more than 1/2”, reinforcement is recommended.  

In the event you are able to determine that the wall is actively moving, monitoring is not needed.  This is a case where reinforcement is required.  Remember, there is no amount of acceptable active movement of a load bearing foundation wall.  

Here are some common visual cues that can show whether or not active movement is present:

• Previously repaired mortar joints that have opened again
• Previous generations of paint lines that show the wall was in a different position in the past
• Past repairs on wall that are still allowing movement
• New cracks 

When To Use A Crack Monitor

In some cases it may be difficult to determine whether or not a wall is “actively” moving.  Most wall movement is very slow and almost imperceptible to the inhabitant.  Much like watching your children grow, you rarely take notice until you see a past picture to benchmark where they are now versus where they once were.  This is why a crack monitor is the best instrument to determine whether movement is occurring.  The monitor is installed at the current state of a crack and over time we have an established benchmark for reference.

If you have a crack that concerns you, a crack monitor is always recommended.  The monitors are relatively inexpensive and can save tens of thousands of dollars by catching structural deficiencies before they manifest into serious foundation problems.  At a cost well under $200 installed per monitor, it only makes sense to install them on any crack that concerns you.

Many of our clients who are having structural repairs done on one wall, will have us install monitors on all of the other walls for peace of mind.  They are prudent in doing this because it will allow for quick diagnosis of a problem should one occur.  Like most other problems in life, when you catch them early they are more manageable and less expensive to deal with.  This is no different.

Monitoring Period

Once a monitor is installed, we recommend waiting 1-2 years before determining whether or not a wall is actively moving.  This allows all of the seasonal forces to be audited and accounted for in addition to soil load and other factors.  The monitor can be checked quarterly by the homeowner.  With that said, should movement be observed, we recommend contacting us immediately at (800) 771-3244 for remediation.  Once active movement has been determined, the situation must be addressed as soon as possible.  

Beyond Monitors 

There are some walls that are so badly manipulated that monitors make no sense.  If a wall has more than 1” of inward deflection at the midsection, is leaning in at the top or has bottom shear, the wall should be reinforced as soon as possible.  In these cases the accrued damage warrants repair, regardless if active or not.

To learn more about foundation movement or Keystone, visit www.keystonebasementsystems.com