Excavation
With the architectural drawings an excavation contractor lays out the boundaries for the site.  The hole is made 2 – 3 feet wider than the walls to allow space for the masons to work.  Typically a skid loader is used to remove soil from the hole.  The excavator calculates how much material is required for backfilling.  The rest of the excavated material is used for fill on the site or trucked away.

Footings
The masons build forms for the footings.  The footings provide support for the block walls. Bleeder tubes are laid perpendicular to the wall location within the forms.  These allow water to drain from the exterior drain tile to interior drain tile.

Wall construction
Wall construction begins at the corner of a block wall.  Strings are run from corners as a guide for block placement.  If the corners are off plumb the center of the wall is likely to be off plumb.  The exterior of the wall is “damp proofed” using a spray on sealer.  These are usually very thin and dissipate over time. 

Drain Tile
Drain tile is PVC perforated plastic flexible tubing 3 – 4 inches in diameter. Masons helpers lay the exterior drain tile – usually on the footing.  Holes should be cut in the drain tile at the bleeder tubes to allow proper drainage.  Normally 18 inches of gravel is placed over the exterior drain tile.  Interior drain tile is usually laid next to the footings and is pitched toward the sump crock. The interior drain tiles are covered with 4 to 6 inches of gravel to prevent concrete from the floor from clogging them.  The gravel is covered with a plastic vapor barrier. If the tile is not placed correctly water will accumulate around the bottom of the basement walls.  Proper investigation of possible drain tile blockages is essential before costly, messy repairs are planned.

Floor Construction
With the walls complete the floor is poured and finished with pitch toward a floor drain.  It rests on the footings and gravel covering the interior drain tile.  It anchors the bottom blocks but is not otherwise considered a structural component

Backfill and finish grade
The foundation structure is now complete.  There is a 2 to 3 foot space between the exterior of the wall and the dirt.  This space is usually filled with material left over from the excavation.  If the back filling process is overly aggressive or the walls are not properly braced the walls may be pushed out of plumb.  This may result in costly repairs if evaluated by a contractor that wants work or a structural engineer who is often unfamiliar with backfill movement issues.

The final step is finish grading.  The grade must slope away from the house to divert water away from the foundation.  A rule of thumb is that the slope should be 6 inches of pitch in 10 feet. The slope away from the house may change over time as the backfill around the foundation settles.  Short drain spouts can contribute to problems.  These are relatively easy to correct provided they are implemented before excessive pressure builds and causes the walls to move and become unstable.  The single most important way to decrease the probability of foundation damage is to divert surface water away from the perimeter of the structure. 

In Conclusion

The purpose of a foundation inspection is to diagnose the condition of the foundation and develop a plan for corrective action – while you can control the situation.  

If you see any of the following indicators in a property you should have the problem diagnosed to quantify the extent of the problem – before a buyer forces your hand. You will add more value to your client if you are proactive rather than reactive!

• Dark spots on walls, floor, and carpeting, evidence of mold or fungus.  There will likely be a musty smell.

• Efflorescence is a white chalky substance on walls and is caused by moisture leaching the mortar that holds the walls together.

• Peeling paint or lose floor tiles can indicate that moisture is entering the home and causing the adhesive to fail. Wood becomes stained or rotten.

• Rust on the base of furnaces, water heathers and other appliances indicate that water is or has been present.

• Cracked or bowed walls may indicate that fill around the foundation is exerting pressure on the walls causing them to move or the foundation is settling due to poor soil or dry soil conditions.

• Water stains of bottom blocks and or floor cracks.

Many foundation problems can be corrected by the homeowner and may include longer down spouts, additional fill at grade level or monitoring the condition of walls found to be out of plumb but stable at the time of inspection. These are relatively inexpensive and easy to do and can be implemented quickly to keep the property sale on track.

Mike Shadid, January 30, 2013

The facts, information and opinions contained in this newsletter should not be construed as a warrantee or guarantee of any type.  They are based upon observations and information obtained over 30 of doing basement inspections.  Equally qualified persons may come to different opinions based upon similar facts and observations.  Any person relying on opinions contained in this newsletter do so at their own risk.  Each basement is unique and general opinions contained in this newsletter may not apply to all basements.  If you have a problem with your basement you should have it inspected and not rely on general opinions in this newsletter.