Causes of Foundation Movement

Expansive soils have a relatively high percentage of clay minerals and are subject to changes in volume with changing moisture conditions. Two of the most common expansive soils are the adobe soils found predominately in the Southwestern U.S.. and Lea (highly frost-susceptible) soils, found mostly in Eastern Canada. Furthermore, all types of clay soils are found throughout North America and may cause significant damage to a structure. It is estimated that 50% of the land in North America contains expansive soil.

The soil under a house swells and shrinks with the seasons. This movement is not a problem as long as it is uniform or not enough to damage the foundation and/or house. Damage to the house may appear and disappear on a regular basis as the seasons change. Significant defects occur when the movement is uneven or localized.

Movement in foundations is caused primarily by; isolated movement or uneven settlement of sections of the structure, additional lateral pressure at foundation walls, sliding surface layers of soil, vibration or additions to the structure.

Moisture can move under the foundation through suction (similar to dry sponge absorbing water). Under moist conditions water moves vertically and horizontally through the soils under the foundation – as the clay soils draw water, they grow in volume (swell or heave). The opposite is true as the soils around the foundation dry out – the moist soils lose volume (shrink) as the moisture moves out from under the foundation.

Movement occurs because the soils expand so forcefully.   Foundations can actually be displaced by the forceful movement.   In a structure, cracks are usually caused by this movement at different rates and distances. Changes in the water content of clay soils cause up to 90% of the cracking problems in a house. Uniform changes in soil moisture are less damaging than localized changes. These cracks are evident as:

 

  •  CRACKS IN THE EXTERIOR OR INTERIOR WALL COVERING AND CEILINGS
  •  CRACKS IN GARAGE OR BASEMENT SLAB, DRIVEWAY, PATIO, OR WALKWAY
  •  SEPARATION OF DRIVEWAY, PATIO, OR WALKWAY FROM FOUNDATION
  •  BOWING, DISPLACEMENT OR ROTATION OF EXTERIOR WALLS
  •  SEPARATION OF WOOD TRIM AT CORNERS
  •  TILTING OF FENCES AND RETAINING WALLS
  •  BINDING DOORS AND WINDOWS
  •  UNEVEN FLOORS/SEPARATION OF WALLS FROM FLOOR

 

There are things you can do to protect your foundation and home from movement.  Tune in to next week’s blog for some tips and things to pay attention to.  If you are thinking of selling your home and you have some of the items listed above, it would be a good idea to have a structural engineer come and take a look.  It is much better to take care of issues before your home is listed than to deal with them under the pressure of a real estate contract.

Attic Insulation

Since the weather has been bitterly cold, you may be wondering about your attic insulation.  During the winter, attic insulation prevents heat within the house from escaping through the ceiling and into the unheated attic space. During the summer, it reduces outside heat from radiating downward through the attic and into the house. All insulating materials work on the principle of trapping. They have millions of tiny air pockets to restrict heat of trying to pass through.

TYPES OF ATTIC VENTILATION:
The maximum heat difference between the air in the attic and the outside air should be approximately 10º F (6º C) to avoid reducing the life of the roof covering. Never block off vents in winter, since moisture from the house will condense and cause problems. In a properly insulated attic, the ventilation will not lower the temperature in the house. The general rule of thumb is one square foot of free vent area for each 150 square feet (with no vapor barrier), or 300 square feet (with a vapor barrier) of attic floor.
SOFFIT VENTS – are provided on the underside of the eave either as grills or the preferred continuous type. Soffit vents are used in conjunction with roof, gable or ridge vents.
ROOF VENTS – are either round or rectangular and are cut in the roof near the top of the roof. The higher the better to allow hot air to rise and dissipate out through these vents.
GABLE VENTS – are louvered openings commonly used at the gable ends of gabled roofs.
RIDGE VENTS – are cut into the ridge of a roof and are popular with a cathedral ceiling.
POWER VENTILATORS and GABLE VENTILATORS – are equipped with a thermostat that turns on the unit when the attic temperature reaches a certain point and turns off when the attic cools.
TYPES OF ATTIC AND ROOF CONSTRUCTION:
Gable and Hip Roofs – These are common and can be easily insulated by placing the insulation between the
ceiling joists or bottom chords of trusses. A polyethylene vapor barrier must be placed under the insulation (warm
side of insulation) to reduce any moisture entering the attic from the house. A provision should be made for
unblocked adequate airflow from the eave of the roof (soffit vent) to the open attic portion of the structure. This is
achieved by using air chutes or channels between insulation and the rafters or top chord on roof trusses.
Cathedral Ceilings –  It is very important that adequate ventilation be provided in these roof structures. The
best ventilation system is one that uses continuous ridge and soffit vents to vent each rafter bay.  This airflow is
necessary to remove any condensation and reduce the build up of heat.
One and One Half Story Houses and Mansard Roofs – These types of attics have several small sections that
must be properly insulated on the vertical knee walls, on the floor of the attic, on the sloping ceilings and on the top flat portion of the 1½
story area. The outer attic is treated as a non-heated area and it must be insulated and ventilated. Air can be allowed to enter through the soffit vents and exit up above the slopping ceiling to the attic space above the 1½ story portion. The top portion of the attic can be vented using roof or gable vents.
Note: If using the older batt insulation with a paper backing (vapor barrier) make sure that the paper is on the warm side of the insulation or facing the finished wall or ceiling surface.

What is CSST and do you have it in your home?

If you have a newer home or just recently added gas, there is a good possibility that Corrugated Stainless Steel Tubing, or CSST was used.  This is a relatively new material that is approved for distribution of natural gas inside homes.

The most common issue with CSST is that it has not been properly bonded.  When CSST is installed without being properly bonded to current standards, there is an increased risk for damage to the material from a nearby lightening strike. When CSST is damaged, it can leak gas and cause a fire or explosion. Weather conditions in Oklahoma make our homes highly susceptible to lightening strikes.  The Governor of Oklahoma has just implemented an emergency order with regards to CSST and bonding.

The new emergency rule, at OAC 158-70-1-3(f), adds a requirement to a home inspection if the inspector observes yellow CSST.  The emergency rule directs all home inspectors to notify their client in writing that only a licensed electrical contractor can determine if the yellow CSST is properly bonded and grounded as required by the manufacturer’s installation instructions.

How would you identify CSST in a home?

Look for flexible tubing with a yellow jacket that covers the ridges.  It does not have to be yellow, Counterstrike has a black jacket, but the majority of the CSST in Oklahoma has a yellow jacket.  You would be able to see it in your attic connecting to your furnace and/or water heater.

What should I do if I have CSST?

If you think your home or business may have CSST, the Oklahoma Construction Industries Board recommends contacting a licensed electrician for an inspection.  CSST that has not been properly grounded should be bonded to the building’s electrical grounding system according to the manufacturer’s instructions and National Electrical Code.

For CSST or any home inspection questions, call our office at 405-301-3321 or send us a message at jan@nsohi.com.