ARE 5.0: PPD key terms

The local weather conditions of a specific site, shaped by topography, vegetation, water, and nearby buildings. It can differ noticeably from the broader regional climate and affects heating, cooling, and daylight design decisions.

A graph showing the relationships among air temperature, humidity, and energy content at a fixed pressure. Designers use it to plot comfort zones and to understand heating, cooling, humidification, and dehumidification processes.

A measure of how much and how often outdoor temperature falls below a reference base, usually 65 degrees Fahrenheit. Annual totals indicate climate severity and help estimate seasonal heating energy use for a building.

The ratio of interior illuminance at a point to simultaneous exterior illuminance under an overcast sky, expressed as a percentage. It quantifies how much usable daylight reaches a space independent of sun position.

The tendency of dense built areas to be warmer than surrounding rural land because dark surfaces absorb solar radiation, vegetation is scarce, and waste heat is released. It raises cooling loads and can worsen outdoor comfort.

The rotation of a building on its site relative to true north and prevailing conditions. It determines which facades receive morning or afternoon sun and strongly influences daylighting, solar heat gain, and wind exposure.

The direction from which winds most often blow at a site during a given season. Knowing them helps designers place entrances, ventilation openings, and windbreaks to improve comfort and natural ventilation.

The ratio of a building's total floor area to the area of its lot. Zoning codes use it to cap development density, so it directly constrains how much building program a site can hold.

The minimum required horizontal distance between a building and a property line, street, or other reference. Setbacks come from zoning and fire codes and shape the buildable footprint on a site.

The calculated number of people a space is designed to hold, based on floor area per occupant or fixed seating. It drives egress width, exit count, plumbing fixture counts, and ventilation requirements.

The clear width provided along exit access, exits, and exit discharge, sized so occupants can evacuate safely. Codes set minimums based on occupant load and may require additional width for sprinklers or stairs.

The time in hours that a building assembly resists fire under standardized test conditions, such as one hour or two hours. Ratings apply to walls, floors, and shafts and increase with building height and occupancy risk.

A code classification, such as Type I or Type V, describing the combustibility of structural elements and the fire ratings required. It sets limits on building height and area for a given occupancy.

A continuous, unobstructed path connecting accessible elements, spaces, and exits that meets standards for width, slope, surface, and turning space. It must serve every part of a building open to people with disabilities.

A portion of a building served by one thermostat or control point, ideally grouping rooms with similar loads and schedules. Good zoning keeps temperatures comfortable and avoids heating one area while cooling another.

An air-handling system that keeps supply air temperature roughly constant and varies airflow to each zone in response to load. It saves fan energy at part load and allows simultaneous control of many zones.

A control strategy or damper assembly that brings in cool outdoor air when conditions permit, reducing mechanical cooling. It lowers compressor energy during mild weather and improves indoor air quality through added ventilation.

A ventilation approach that adjusts outdoor air intake based on measured occupancy, often using carbon dioxide sensors. It saves energy in intermittently crowded spaces while maintaining acceptable indoor air quality.

A measure of a material's resistance to heat flow; higher numbers mean better insulation. R-values add in series for layered assemblies, though framing and other thermal bridges reduce the effective total.

The overall rate of heat transfer through an assembly, equal to the inverse of its total R-value. Lower U-factors indicate better performance and are used for windows, walls, and roofs in energy code compliance.

A path of high heat conductance through an assembly, such as a steel stud or concrete slab edge. Bridges bypass insulation, lower effective R-value, and can cause condensation and cold interior surfaces.

A material that restricts the movement of water vapor through an assembly. Correct placement depends on climate and assembly type, and mistakes can trap moisture and cause mold or decay.

A single-number rating of how well a partition blocks airborne sound; higher values mean more privacy. It is used to compare wall and floor assemblies and to meet acoustic requirements between rooms.

A continuous layer that limits uncontrolled air leakage through the building envelope. Sealing it improves energy performance, moisture control, and comfort, and it must be detailed at joints and penetrations.

A grid used in programming that rates how strongly each pair of spaces should be near or separated from every other. It translates functional relationships into a diagram before rooms are arranged on a floor plan.

A schematic drawing of circles representing spaces and lines or arrows representing required connections. It tests program relationships and circulation before size, shape, and structure are fixed.

The ratio of usable net floor area to total gross floor area, including circulation, walls, and mechanical space. It measures planning efficiency and helps test whether a program fits within a given building envelope.

A diagram that arranges program spaces vertically by floor to test relationships, structure, and building height. It reveals conflicts such as heavy loads or noisy uses above quiet ones before design develops.

Designing environments usable by the widest range of people without adaptation, including those with disabilities, older adults, and children. Principles include equitable use, flexibility, simple operation, and adequate clear space.

The total cost of a building element or system over its useful life, including initial construction, operation, maintenance, repair, and replacement. Comparing alternatives on this basis often favors efficient systems despite higher first cost.

A structured review that seeks the required function at the lowest total cost, often after design is well advanced. It can cut waste but risks removing features that owners value if applied too aggressively.

A reserve of money included in a budget for costs that cannot yet be precisely defined. It shrinks as design progresses and should not be confused with scope changes requested by the owner.

An allowance for increases in construction cost between the time an estimate is prepared and the time work is actually bid or built. It reflects inflation and market conditions.

A price per unit of construction, such as dollars per square foot, linear foot, or fixture. Multiplying by quantities gives an estimate, though accuracy depends on good quantity takeoff and current pricing.