BPI Test
solar heat gains through windows depends on
the angle of the sun overhangs and shading weather conditions the physical properties of the window
off-gassing of materials
the evaporation of volatile chemicals in certain materials (such as carpeting) into the air
windwashing
the flow of air through soffit vents into attic insulation, reducing the insulation's effectiveness
air flow
the movement of air; air transfer
Heat transfer
the movement of heat
Air exchange Rate
the number of time the interior volume of air changes over in one hour (air changes per hour, or ACH). Formula: ACH = CFM x 60 / volume
Infrared thermography
the practice of using a camera like an infrared camera and interpreting the images it produces
wind effect
the pressure-related effect of wind on a house. Air leaks in the envelope allow air to infiltrate, and that in turn pushes air alread inside the house out. The amount of wind-driven infiltration depends on the liakiness of the home and the direction and strength of the wind
Pressure boundary
the same area where the thermal boundary occur, but where we need to stop airflow
Bay
the space between and the size of the wood influence the cavity or bay (indicates the amount of insulation)
dew point
the temperature at which air reaches 100% relative humidity
Whole-building home performance contractors
those professionals whose job is to improve home performance - need to understand building science.
Thermal Barrier for SPF
to comply with International Building Code a thermal barrier is applied b/w the foam and the interior space to provide some protection during a fire. The most common thermal barrier is 1/2" drywall.
electronic standby losses
uses energy and gives off heat, enven when they are turned off.
relative humidity increases when
we lower the temperature and leave the amount of moisture unchanged
internal heat gains
windows, appliances, and occupants
average R-value
you must convert the $-value to a U-value. R-values and U-values are inversely proportional to one another: as $-values increase, U-values decrease and vice versa. U=1/R (and R= 1/U)
condensation occurs at
100% relative humidity
Four general categories of building science:
Building Mechanicals Environment Occupants
Building Envelope:
Foundation Walls Roof Windows Doors
two primary types of framing in homes:
balloon (before 1940s) and platform (after 1940s)
soffit chute
prevents windwashing
Building Science
taken from physics chemistry and thermodynamics
Delta T
Change in temperature; the greater the temperature difference (delta T) between the two spaces, the faster the heat will move
BTU
1 BTU is equal to the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit (sensible heat)
Rigid foam board
Air barrier: Covers large holes Structural strength: thermal break Exterior sheathing: resists heat transfer
Attached garage
BPI first priority for air sealing between the garage and house bc of occupant health and safety
Typical Insulation R-Values
Cellulose, loose-fill - 3.7 - Attic floor Cellulose, high-density - 3.2 - Walls, enclosed cavities, framing, transitions Fiberglass batts - 3.0 - Basement ceiling, open stud walls, attic floor Rigid board, polyiscoyanurate - 7.0 - Foundation walls, attic access doors
Delta P
Change in pressure Air moves from high pressure to low pressure It follows the path of least resistance
Common Types of foam board insulation
EPS (expanded polystyrene) XPS (extruded polystyrene) Polyisocyanurate
Assessing Existing Insulation
Good: no gaps or imperfections are present Fair: there are gaps in over 2.5% of the insulated area; this equals a 3/8-inch space along a 14.5-inch batt Poor: there are gaps in over 5% of the insulated area; this equals a 3/4-inch space along a 14.5-inch batt.
Cathedral ceiling
Has the same pitch as a roof
The Big 3:
Heat, Air and Moisture Difference in temperature and humidity between areas inside the house, and between the inside and the outside of the house, are exerting some sort of subtle influence on the conditions in the home.
Mechanicals:
Heating and cooling and ventilation Electrical Systems Lighting and appliances Plumbing Systems
Spray Foam Insulation
High-density (closed-cell) SPF: adheres well, very durable, and resists moisture Low-density (open-cell) SPF: not as resistant to heat transfer as high-density SPF, but it offers a greater yield and may be more cost-effective. Low-density SPF is also resistant to moisture, but less so than high-density SPF.
Importance of Occupants at a component of buildings
Home performance primarily deals with existing, occupied homes. Occupants are the beginning and the end of the system: they may do things in a house that affect the other components, and they are certainly on the receiving end when things like comfort and indoor air quality are affected
Fiberglass Batt Insulation
Insulation help together with adhesives. faced: with paper backing or Unfaced: without paper backing
Types of insulation
Loose-fill/blown Fiberglass batt rigid foam board spray foam
Cellulose Insulation
Made of ground-up newspaper that has been treated with fire retardants
Home Performance also includes:
Occupant health and safety Indoor air quality and occupant comfort Durability of materials
Potential vs. Kinetic Energy
Potential energy is stored energy. Think of firewood, or a battery. Kinetic energy is the energy of motion. Burn the firewood, and its potential energy is converted to kinetic energy in the form of heat.
Recommended R-Value for attics
R-38
Insulation performance is measured by:
R-value: measure of thermal RESISTANCE U-value: measure of thermal TRANSMITTANCE
Relative humidity
The actual amount of moisture in the air relative to the total amount of moisture that the could hold, at a give temperature and pressure. Expressed as a percentage
Thermal boundary
The boundary between those conditioned and unconditioned spaces
Pascals (Pa)
Units of air pressure 250 Pa/1"column of water (of any diameter)
Factors that affect airfow velocity:
Volume of the space Temperature and moisture content of the air Presence of gaps or holes through which air can leak
Before attempting any of the air sealing work, it is important to:
Walk through the home and map out the sites as you discover t hem Move aside existing insulation Clean the area; otherwise, the foam or chalk will not adhere to the surfaces
Infiltration
When air unintentionally flows into a home from outside. This occurs when the pressure inside the home is lower than outside (negative pressure)
Exfiltration
When air unintentionally flows out of the home. Happens when the pressure inside is higher than the pressure outside (positive pressure)
Rafter
a sloped framing member that supports the roof
ridge vent
a slot cut through the roof at the peak of the house
soffit vents
a vent on the underside of a roof that allows cooler air to enter an attic; works with a ridge vent to provide attic ventilation
Stud
a vertical framing member that supports an interior or exterior wall
Interacting relationship
an action taken on one component causes reactions or changes in other components, or worsens certain pre-exiting conditions (and increases their likelihood of producing negative effects
Thermodynamics Definition
an are of science that looks at the relationship between heat and other kinds of energy
Thermal Bridge
an area of high heat flow compared to an adjacent insulated area can be minimized with advanced framing techniques, adding continuous insulation, or using thermal breaks (such as rigid foam board) to slow down conduction.
building envelope
any part of the building assembly that creates a boundary between indoor and outdoor space including: foundation roof exterior walls attached porch attached garage exterior doors and windows
Two primary types of spaces inside the building envelope
conditioned and unconditioned
Three ways heat is transferred
conduction, convection, and radiation
Unconditioned space
consist of areas you do not heat or cool. In many homes, this includes the attic, basement, and/or crawlspace.
Conditioned spaces
consists of areas that you heat and cool. So, your living spaces, but also any other areas that you may not necessary 'live' in, but where you want to control climate.
Fiberglass/mineral wool
cotton candy like fiber
Mechanical ventilation (bathroom fan)
could cause air pressure differences between the inside and outside of the home. If air leakage is present, this could cause the house to leak air at a faster rate, which, in turn, would create the need for the thermostat to be adjusted more often
convective loops
describe the tendency of air to circulate around a space as the air is heated and cooled
Mechanical effect
describes air movement resulting from mechanical systems such as: Heating and cooling ventilation (bath and kitchen fans) dryer exhaust
vaulted ceiling
does not have the same pitch as a the roof; can consist of one or two straight slopes, or it can be arched. in the case of straight slopes, one wall of the room is taller than the opposite wall, and the ceiling slopes downward toward the shorter wall.
Overall R-Value
looks at the entire assembly including wall, floor or ceiling
Stack effect
driven by buoyancy force. Indoor and outdoor air have different temperatures and moisture content, and thus, different densities. This density difference creates either a positive or negative buoyancy force. The greater the density difference, and the higher the structure, the greater the buoyancy force; this is why chimneys are typically tall and narrow. It is also why the stack effect is more pronounced in taller buildings. * warmer air exfiltrates at top, equal amount of cooler air infiltrates at bottom to replace it
2nd Law of Thermodynamics
energy flows naturally from high concentrations to low concentrations HEAT moves from warmer to cooler; AIR moves from higher pressure to lower pressure; MOISTURE moves from wetter to drier
1st Law of Thermodynamics
energy moves from place to place; energy changes form one form to another; energy cannot be created or destroyed Energy moves around and changes form.
Overall U-Value
entire window assembly: pane, framing, sash, even the locks *the lower the U-Factor the better
Moisture cycle (in a house)
evaporation <> condensation
Factors that affect fiberglass batt performance
gaps and voids, compression, and poor contact
Polyisocyanurate
good for application where space is at a premium. Rigid polyisocyanurate boards are typically covered with a foil facing to protect the surface
Drawbacks to noon-standard types of ceilings
hard to clean, pain, and change light bulbs cost more to heat and cool expensive to install
balloon framing
has continuous wall cavities from the basement to the attic
House-as-a-system:
holistic view: the whole-house approach and it's another way to define building science
Joist
horizontal framing member that supports a ceiling or floor
Velocity
how fast air is moving - measured in cubic feet per minute (CFM)
Transmittance (U-value)
how fast heat move through a material; tells us how much heat is transmitted though a one-foot square section of a building component (like a wall) in one hour, when there is a one-degree temperature difference across the two opposite
Resistance (R-value)
how well a material resists heat transfer
Environment:
in this context, refers to managing the indoor environment as the exterior environment is changing (keeping the interior temperature and relative humidity within acceptable levels, and ensuring indoor air quality with an adequate amount of fresh air and little to no pollutant concentrations
Radiant Barrier
insulation that reflects heat back to the heated side typically made of aluminum foil bonded to paper or sheathing. Reflective foil or shiny side must face an air space. *only effective for radiant heat transfer (line of sight). Not effective at controlling heat transfer due to convection (air) or conduction (surface to surface).
Home performance
is the systematic approach to improving the comfort, health, safety, energy efficiency, and durability of a home.
low-e windows
low-e stands for 'low emissivity' emissivity is the ability of a materiel to absorb and radiate heat. To counter the internal gains that occur when sunlight shines through window, a low-e coating can be added to the outside surface of the windows. glass, by its nature, has a high emissivity. that means it's really good at soaking up heat from the sun and radiating it into the home. adding the low-e coating to the windows reduces their emissivity, meaning that instead of absorbing and radiating heat, they reflect it. besides reducing internal gains, low-e windows can enhance occupant comfort.
dry-bulb Temperature (ambient air temp)
measure the amount of heat in t he air
XPS (extruded polystyrene)
more expensive than EPS, XPS provides excellent moisture resistance, and is a good option for underground applications
Ice dams
occurs when warm air melts snow on the roof directly above, but does not melt snow on the overhangs. Water from the melted snow flows down into the gutters, where it freezes. This prevents any further melting snow from draining properly. Ice dams can damage the roof and everything beneath it.
wet walls
one of the more common places where you will find an open wall top is the wall in the bathroom that contains the majority of plumbing and venting pipes
Chases
openings through the attic floor to accommodate pipes, ducts, chimneys and flues
IAQ (indoor air quality) pollutants from the outside
pollen smoke air pollution
Infrared (or IR) camera
produces thermal imaging as a tool that is used to assess the level and performance of insulation in the home
EPS (expanded polystyrene):
same material used for foam coffee cups and packing peanuts cam be molded into sheets and used as insulation.
How insulation works
slows heat transfer by trapping air in small pockets; it is this trapped air that acts as the insulator. The heat is forced to conduct through the tiny air pockets, rather than the fiberglass itself; this is a much slower process
moisture may appear in a house in these ways
standing water in the basement condensation on windows and other surfaces mold and mildew
wet-bulb temperature
takes moisture into account; usually lover than dry bulb bc of moisture content
relative humidity increases as
temperature decreases b/c cooler air cannot hold as much moisture as warmer air.
Latent heat
the amount of energy absorbed or released by a substance as the substance changes its state
Sensible heat
the amount of energy added to or removed from an object that causes a change in the object's temperature.