Knowledgebase - Building
Science
"Building scientists
have learned that buildings work as a system of interrelated
elements."
--EPA, Montana
State University, USDA
Building Sciences is the study of how buildings
function under various environmental conditions. Some of the
key elements to understanding how a building works are listed
below:
Moisture movement
Relative
Humidity
Pressurization
Air Leakage
Temperature
Building Envelope
Ultimately, structure, ventilation and filtration
all influence the performance of the entire system. Indoor air
quality can be greatly improved by using the proper design strategy
and good building materials. Mechanical systems should be designed
and installed by trained experts aimed toward protecting the
health, quality of life and productivity of the building occupants.
Moisture Movement
Moisture problems are the number one source
of residential concerns. Excess moisture generated within the
home needs to be removed before high humidity levels lead to
physical damage to the home or mold growth. The ideal interior
relative humidity levels to maintain on a seasonal basis would
be 40% - 50%RH. The key to controlling relative humidity levels
in a home is to maintain a moisture balance. Too much moisture
can cause problems, but some moisture in the air is necessary
for human health and comfort.
Relative Humidity
Relative humidity is the ratio of the amount
of water in the air at a given temperature to the maximum amount
it could hold at that temperature; expressed as a percentage.
Pressurization
Maintaining buildings under positive pressure
relative to outdoors can help to maintain indoor air quality
by limiting the infiltration of outdoor air that may adversely
affect thermal comfort and may contain moisture and pollutants.
Allowing air to move freely and unimpaired from room to room
in the conditioned areas of a home is essential. Balanced pressure
helps maintain consistent temperatures without placing abnormal
stress on the envelope.
Many normal household items can work against
your ventilation system. Some of these include the stove vent,
clothes dryer, and bathroom fan. The function of each these is
to remove air from the home and push it to the outside. This
can create a negative pressure in the home. If the proper amount
of make up air is not supplied by the design, the negative pressure
in the home will draw the air from uncontrolled areas. The uncontrolled
make-up air can be from a crawlspace, cracks in the foundation,
leaky window seals, the water heater flue and the chimney. When
air is pulled in through the water heater flue, chimney or furnace
flue, carbon monoxide is also being pulled into the home. This
is called "back-drafting". Uncontrolled air from the crawlspace
or foundation cracks can contain radon, moisture, and other contaminants.
The proper system design will take into account
household items that could create a back-drafting situation.
Air Leakage
Air leakage is the unintentional movement
of air from one area to another. Air leaking from the ductwork
(air being pushed out of the ducting system), will have a negative
impact on your comfort level, heating and cooling system efficiency,
and indoor air quality. To alleviate air leakage from the ducting
system, all connections and transitions on the ducting system
should be properly sealed and insulated.
Air leakage can also occur because of the
home's natural 'stacking effect.' As warmer air in the home rises,
a negative pressure is created in the lower areas of the home.
If mechanical ventilation is not used to create a pressurization
balance, the negative pressure will be equalized by drawing unconditioned
air (air leakage) through cracks, piping access holes, and porous
building materials.
Temperature
Internal and external temperatures play a
role in building sciences. Temperature can determine the pressurization
of the home, hence affecting the comfort levels and efficiencies.
In most cases, internal temperature is controlled through mechanical
methods (air conditioners and furnaces). Attention must be given
to selecting the right equipment,
the right size, and the right contractor.
Building Envelope
The building
envelope refers to all external building materials, window
and walls that enclose the internal living space. Homes are
built tighter to control air leakage and improve energy use,
but tighter construction limits much-needed air exchanges.
If the envelope isn't constructed of "breathable" materials,
stale air and pollutants tend to be retained and re-circulated
via the HVAC duct system.
| 
