| A study of failed foundations (ADSC 2000) estimates the cost of foundation
repair at over 12.5 billion dollars annually. The most common cause of
foundation failure/problems is poor maintenance, which can normally be
prevented. Considering that most remedial action will not completely keep a
foundation from moving, it becomes even more important that the homeowner
complies with the required maintenance procedures to reduce movement and allow
the house to function as originally intended. This is just as important after
repairs have been complete because the house may move in an area that has not
been repaired or is still dependent upon bearing soil stability for continued
performance. Since many foundation repair companies require homeowner
maintenance as a condition of their warranty agreement, compliance is also good
business and one of the best insurance policies available.
The following categories of maintenance are the most common problem areas and
should be addressed in a scheduled sequence to reduce movement before and after
foundation repairs to minimize distress in the foundation and the structure it
supports.
Slope Maintenance The foundation should have been
installed sufficiently above site grades to allow proper post-construction
surface drainage. It is the homeowner's responsibility, however, to maintain
these positive drainage conditions. The primary function of good drainage is to
prevent ponding near, or intrusion of water, under the structure, which would
increase seasonal moisture fluctuations, or migration of water.
Much of the damage caused by expansive soils is due to lack of timely
maintenance by the homeowner and is in some part preventable.
Under ideal conditions the slab will maintain its original position.
Unfortunately soil is not consistent and the moisture content is seldom at an
optimum ievel in the support soil when the slab is constructed. Many slabs are
poured on drier than normal soil that later becomes wet from capillary rise of
water from below, causing the thin floors to lift. After repeated drying and
rewetting of the support soil, small amounts of soil are squeezed from the
interface of the concrete base and the soil base to lower the wall into the
ground, much like a car tire miring into a rut. If the soil has a high amount of
clay content, it wilf also deform under pressure, much like children's putty
during the swelling stage.
Earth Perimeters
The
excavated area outside the foundation is usually filled with loose soil fi!l
when a house is constructed. This is usually called the "backfill area".
Maintaining a positive slope in the backfill area next to the house is the most
critical aspect of slope maintenance. During the first few months or years, this
material often settles. In many cases settlement is severe enough to reverse or
flatten the slope next to the foundation. Reverse or negative drainage will
cause ponding of water during precipitation or heavy irrigation. Ponding allows
an excessive amount of water to percolate into the ground" next to the
foundation, which may accelerate this settlement. To avoid this, the homeowner
should periodically compact the backfill area by tamping with a heavy piece of
wood such as a 4 "x 4 ". Hand compaction works best after a rain or snow melt
has dampened the ground or with the careful addition of small amounts of water
by the homeowner such as with a drip line. Additional soil should be added as
necessary to maintain a positive slope away from the foundation. This soif
should always be clay, not sand, so moisture can be better maintained and water
will run off instead of soaking in spotty high concentrations.
The minimum slope requirement should be 5% for the first 5' away from the
foundation (3" of drop) and then at a minimum discharge slope of 1%
(approximately 1/8" drop for every foot of distance) from that point on. The
type of vegetation may dictate a greater slope to avoid over saturation of the
critical perimeter soil. Some type of ground cover is recommended, however, to
reduce erosion and lower the frequency of slope maintenance work.
Flat Work
One of
the beneficial functions of Hat work {sidewalks and patios that are not part of
the foundation) adjacent to foundations is the prevention of evapotranspiration
and fluctuation of water intrusion to the bearing soils. Therefore, every
homeowner should conduct a yearly inspection of concrete flat work and do any
maintenance necessary to improve drainage and minimize infiltration of water
from rain, snow melt and lawn watering This is especially important during the
first five years for a newly built house because this is usually the time of
most severe adjustment between the new construction and environment The process
of inspection and maintenance should continue over the years, but, cracking,
settling and other problems should become less common.
Because perimeter fill material may not have been compacted in 4" lifts at
optimum moisture (as is normally recommended by engineers), settlement is
greater along the house A negative slope may occur that will allow ponding This
concentration of water will allow permeation through cracks in the concrete and
over- saturation of perimeter bearing soils This deeper saturation will often
times cause damage to the foundation and/or basement floors Because evaporation
is limited by the flat work, the ponded water may dramatically increase moisture
levels at the crucial perimeter beams and/or piers.
When this tilting of flat work occurs, the concrete should be replaced or
mudjacked to reverse the negative slope If a minimum of 1% slope (again about
1/8" for every foot of distance) is maintained, however, it will only be
necessary to seal all cracks and ports of entry to prevent vertical water
migration This will include the perimeter joint around the foundation grade beam
A urethane or other flexible sealant should be used that will allow some
movement but prevent water passing below the slab
Flower Beds Changing the site by the addition of
flowerbeds, patios, fences, swimming pools, etc , may cause water ponding, which
will exacerbate the wet cycles. Therefore, proper drainage considerations during
such additions must be made
Nurserymen will specify peat, bark, sandy loam and other planting substances,
which, in conjunction with bed borders, will increase moisture levels above that
desirable Therefore, flowerbeds must have some provisions for elimination of
excess water. This may be in the form of weep holes, drain barriers or other
removal systems. The problems created by flowerbeds are not a popular subject
since homeowners will resist good engineering to beautify their house. There
should be a balance between vegetation utilized for aesthetic demands and
harming the bearing soils.
One
of the primary problems in flowerbed design is installation of a concrete or
steel barrier that will resist normal water run-off. If these barriers are
desired, they should have openings cut to ailow water passage and avoid
over-saturation.
The use of highly permeable materials such as peat, bark, etc., should only
be used if topography allows installation of subsurface drainage to collect
excess wafer and discharge it away from the foundation. This will also require
installation of an impermeable barrier at the bottom of the flowerbed to help
collect water for removal by the drain medium.
Shrubs planted in the flowerbed should be chosen for their compatibility to
the shallow barrier of the bed. Short and very contained root growth will be a
plus to proper health and maintenance of the bed vegetation.
In the flowerbed, the slope should be a minimum of 5% (5/8" for every foot of
distance), unless ample subsurface drainage can be created to discharge water
away from the foundation.
Gutters And Downspouts Gutters should be inspected twice
a year, once in the spring and again in the fall. All debris should be cleaned
out and metal gutters checked for rust. If there are trees near the roof,
gutters may have to be cleaned out more often.
Check the slope of the gutters, since poor slope causes water to accumulate
in low spots, building up debris and accelerating rusting. Slope of the gutters
should be a minimum of 1" of fall for each eight feet of length. The gutter can
be installed so that it drains in one direction. If, however, any single length
of gutter is more than 35' long it should be installed to drain both ways from
the center or have downspouts at a spacing of not more than 20' on
center.
The
easiest way to check the slope of a gutter is to use a garden hose or pour a
bucket of water into ii and see if the water flows out smoothly or ponds in low
spots. The gutter should then be adjusted to remove any high or low spots that
prevent the smooth flow of water.
Downspouts should be checked for clogging at the same time the gutters are
checked. Clogging often occurs at the elbow where downspout and gutter meet. The
elbow can be removed for cleaning, but it may be necessary to use a plumber's
snake to clean the down- spout. If there is a problem with leaves, a leaf
strainer or leaf guard is a good buy as long as neither prevents proper function
of the gutter.
Spiash blocks should be long enough and sloped enough to carryall water well
away from the foundation and beyond the backfill area. Water should be
discharged no closer than 5' from the foundation. Usually it is necessary to add
a downspout extension in order to get the water far away from the foundation. It
is possible to purchase extensions that have flexible elbows that can be bent up
to make it easier to mow the lawn. The extensions should be left down at all
times. Special roll-up type down- spout sheets (plastic tubes) that attach to
the end of the downspout are also available. These plastic tubes extend when
filled with water and roll up when empty. If erosion is a possibility, splash
blocks can be placed at the discharge point to prevent associated problems.
Because the materials deiineated above are readily accessible at most
hardware and do-it- yourself stores in a variety of makes and colors, they can
add to the aesthetic qualities of a house.
Sub-Surface Drains Subsurface drains will many times be
utilized when topography, vegetation or construction does not make it possible
to drain at the surface. These may consist of drain inlet basins, trench drains,
funnel drains, etc. If correctly installed, subsurface drains should require
little maintenance. The most important thing to remember is to avoid
covering or obstructing the drain where it discharges and to maintain adequate
slope. It may occasionally be necessary to clean out roots, nests or other
debris from inlet basins or discharging ends of the pipe.
Inlet basins should be inspected every 6 months to ensure these do not become
clogged with leaves, grass, soil or other debris, which would negate
function. The bottom of these inlets normally has a sedimentation
basin that requires removal of dirt as fill adds up over time. It may also be
necessary to back wash (main lines when discharge becomes a noticeable
problem. If problems persist, running of a (mechanical snake may be
necessary to remove the obstruction.
Settlement problems in a yard will many times crush piping and reduce the
discharge flow, which will cause sedimentation to occur and subsequent closure
of the drain lines. Damage may also result from the driving of heavy trucks
across the surface. In any case, repair will normally require excavation and
replacement of the drain line. This may be an even greater possibility if clay
tile is used in lieu of heavy duty PVC.
Location of clean-outs and discharge lines will be a plus to locate problems
and tnitiate corrective action. Therefore, a drawing of lines and locations
should be made during installation for future reference.
Capillary/French Drains
Capillary drains are installed to intercept and collect moving
subsurface water and discharge it away from the structure. Unless the slope
allows, this will many times require installation of a deep sump and pump to
collect water and discharge it through a shallow drain line.
The pumps utilized in this operation may malfunction and unless an alarm
system is installed there will be no warning. Therefore, it is advisable that
the home-owner inspect the sump at least every 6 months to make sure trash,
debris or pump failure has not occurred. If a solid sump well cover is used,
there will be less potential for debris, but the horneowner will not be able to
view the sump and determine if it is functioning. Therefore, the addition
of an alarm is recommended to provide a warning to the horneowner prior to
the onset of other problems, such as upheaval or water intrusion into the
structure.
Discharge lines should have cfean-outs to allow removal of
obstructions by use of a snake or by jetting. Because effectiveness of these
systems is largely unknown until problems occur, it is wise to also backwash the
system from the discharge end and/or at the sump at least every 2 years. The
effectiveness of this backwash will normally be seen by a discharge of debris,
which may have clogged the system.
Capillary drains are many times utilized as moisture
barriers along the perimeter of a foundation to shed water and stabilize sub
slab moisture. This will include extension of an impermeable barrier drain
material under flower pipe beds and up along French Drain grade beams.
Therefore, it is important for the home-owner to avoid any planting action that
may puncture the barrier material. If this damage occurs, it will be necessary
to patch the hole with materials that maintain the integrity of the
barrier.
Irrigation/Sprinkler Systems Watering of lawns and house
perimeters must be regulated to maintain consistent moisture content under the
foundation. Therefore, allowances for shrubs, plants and trees must be regulated
for each segment of the yard. It is advisable that watering along foundation
perimeters should be on a maintenance basis in corroboration with seasonal
needs. This should be in conjunction with plant and tree requirements so
that added water will not be siphoned from under the foundation.
Seasonal monitoring will necessitate different watering for the sides that
receive added and hotter sunlight (south and west sides), which increases
evaporation. This monitoring will also take into consideration time of day
for watering. Most authorities recommend early morning watering so that less
evaporation will occur.
It must be understood that over watering can be just as damaging to the
foundation as under watering. If an electronic sprinkler system is installed,
each of the factors listed above must be incorporated into the sequence and
timing. Visual observations must also be included in the process to make
adjustments beyond the capacity of normal programming.
A variety of watering heads and systems are on the market that can be
customized to a homeowner's needs. There are bubble sprays, side sprays or angle
sprays that discharge from riser heads or pop-ups and can be mixed to provide
complete coverage. Where evaporation is a concern, however, a drip system will
provide necessary watering very efficiently. A close inspection of the ground
surface is necessary to ensure appropriate volumes and consistency. The goal is
to keep the soil near and under the foundation a consistent moisture (neither
wet and/or muddy nor dry and cracked).
An inspection of the sprinkler system should be performed at least twice a
year to determine if zones are functioning properly and if heads are improperly
discharging/broken or if leaks have occurred that will provide uneven watering.
This will, in the case of electronic watering systems, require running through
the system to determine if times, duration and frequency have been
maintained.
Vegetation And Trees
Studies from England and the United States have proven conclusively
that trees can cause damage to foundation stability and in more severe cases
complete foundation failure. Engineering studies map the effect of moisture
withdrawal, which can severely damage a slab- on-grade foundation and cause
movement in a pier and beam foundaiion system." Even when the perimeter of slab
has been underpinned, the interior slab will often deform as moisture migrates
to the perimeter as a result of root capillary action.
Planting of shrubs, flowers and trees should be with the understanding of
mature growth. Since additional moisture withdrawal will occur, distance and
watering patterns must be planned. If distance away from the foundation cannot
be maintained, root barriers may be necessary to reduce and/or eliminate
penetration under the slab and subsequent moisture withdrawal during times of
drought. The depth of this barrier may vary according to tree or plant root
expectations. These barriers, if properly constructed, can also serve as a
moisture barrier, which will add stability to moisture contents under the
foundation. Several agriculture agencies have material available which provides
projected root and moisture requirements for different types of vegetation.
Trees should not be planted closer to the foundation than approximately the
mature height of the tree. Some studies also indicate the tree limbs should not
invade the footprint of the house at maturity. There is a variance with
different types of trees that will necessitate their planting even further away.
If the proper distance cannot be maintained, it may be necessary to install a
root barrier to reduce the risk of future problems. Pruning of tree branches so
that they do not extend over the structure can also be an effective way to limit
root growth under the foundation.
The plants should fit the environment. In areas where droughts frequently
occur, it may be necessary to substitute drought resistant plants and trees to
incur less action on the foundation and provide easier maintenance of the
foliage.
Plumbing Leaks Leaks in water and sewer lines will change
the soil equilibrium under a foundation and can lead to differential
movement/damage. Therefore, it is necessary to recognize signs that indicate
problems exist.
If sewer lines are frequently stopped-up and roots are observed when
clean-out rooters are used, a sewer test should be conducted to determine the
presence and location of the break. Repair of a break should be made immediately
to avoid damage and future problems.
If abnormally high water bills indicate a sudden surge in water usage, wet
spots occur that can- not be explained or the owner should hear the sound of
water running in a bathroom (note: The bathroom nearest the water supply line
will provide the best indication of a water leak), a test of the pressure Sines
should be conducted. If leaks are found, they should be repaired
immediately.
If hot spots occur in the floor or unexplained water should pool, it is a
good idea to call a plumber. Catching leaks early will many times avoid
extensive foundation damage that may be very difficult to repair.
Plumbing Leak Repairs Leaks will often occur under a
slab-on-grade foundation that require breakout of a segment of the slab to gain
entry and repair the plumbing. Care should be taken to perform proper compaction
of the soil when repairs have been completed. This will require adequate
moisture in the utilized soil and compaction of layers no thicker than 3" to
restore soil bearing to as it existed prior to excavation The vapor barrier
should be repaired with piastic and a bonding material to provide a vertical
moisture stop from vertical capillary action or water migration that may enter
the living space. Even in the case of post tensioned slabs, a minimum of #3
reinforcing steel bars, at a spacing of 12" on center, should be utilized by
drilling into the existing slab horizontally and epoxying the reinforcing steel
bars to provide integrity. A bonding agent should be utilized at the edges to
provide the necessary bonded joint between existing and newly placedconcrete. It
is normally advisable to install a moisture shield at the surface to prevent
migration of water through the concrete This same procedure should be employed
if it was necessary to break through a grade beam to repair a plumbing line
except that non-shrink grout or epoxy concrete should be used to remold the
beam.
Reinforcing Steel Exposure Many times concrete will
blister or peel along the grade beam and reveal post tensioning cable ends or
conventional reinforcing steel bars If left unprotected, corrosion will slowly
reduce the originally intended strength of these reinforcing steel members
Therefore, it may be necessary to properly clean the steel and remove all bond
and then install an epoxy grout or non-shrink grout to build back the beam and
protect reinforcement In more severe situations, it may be necessary to drill
and epoxy reinforcement dowels/ stirrups to build out the grade beam and provide
adequate coverage of the reinforcing steel.
Brick, Rock Or Cladding Cracks Movement weathering and
freeze damage will often times create cracking in the brick veneer or mortar
that will allow passage of moisture into the vulnerable wall material Because
this will often lead to deterioration of wood members, it is advisable to seal
these cracks with a urethane. mortar or caulk that will prohibit weathering
problems Where obvious structural problems are visible such a lateral
displacement of veneer, lateral shields Of other retainers will be required to
prevent additional movement damage.
Vent Covers The original purpose of vent covers is to
provide adequate circulation of air under the floor of a pier and beam
foundation so that moisture will not build up and cause deterioration of wood
members Although coverage of these vents will save money in reducing heating
bills, it will often provide the unwanted environment for wood rot Therefore, it
is not advised that these covers be utilized unless other means of air
circulation are available such as a sub floor vent fan(s).
Recent revelations of houses where the growth of bacteria was so invasive and
so deadly that the houses could not be salvaged, have led to anew examination of
detection and prevention of such growth.
Animal Damage Dogs, skunks, armadillos, snakes etc will
many times burrow under a slab or pier and beam foundation This will undermine
the bearing soil and may provide entry for water that was not possible prior to
the excavation Therefore, it is necessary to back fill the segment and/or place
an impenetrable shield to prevent further entry It is also important to restore
positive drainage to prevent foundation moisture instability.
Termite Damage Wood should not touch the ground at any
place near a foundation This will only invite termites and provide avenues for
their passage to more appetizing segments of the structure Therefore, the
homeowner should take care to avoid laying, placing or constructing wood that
engages the ground This includes removal of any wood pieces that may exist in
the crawl space of a pier and beam foundation When you add moisture to wood on
the ground, you provide a perfect environment for growth of termites and other
wood eating insects
Interior Doors
It is
a known fact that most slab-on-grade foundations will move differentially, which
can cause misalignment of interior doors Therefore, some flexibility in the fit
of the doors will reduce the inconvenience of this movement
Interior doors should have a minimum 1/8" to 3/16" clearance between the top
and side with the frame This will allow some seasonal movement prior to sticking
It is also a good idea to provide adequate clearance off the carpet or floor to
further buffer movement and allow for different heights of carpet and/or
flooring.
Tom Witherspoon President of SiW Foundation Contractors. Richardson
TX M S M A S. University of Texas at Dallas. Doctoral Engineering
Studies at Southern Methodist University "Residential Foundation
Performance", * book published 2000
Posted by admin on Monday, January 2, 2006
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