Radiant barrier

A material (typically an aluminum foil) that is good at blocking the transfer of radiant heat across a space because it has a low emissivity. In a hot climate it is often installed in attics under the roof decking to keep the attic cooler.

Radiant energy

Energy in the form of electromagnetic waves that travels outward in all directions from its source.

Radiant heat

A technology consisting of energy emitted from a heat source penetrating all objects in its path, including people. Objects are heated, as opposed to the air surrounding them (convection). The internal air temperature for radiant heated buildings may be lower than conventionally heated buildings to achieve the same level of body comfort (the perceived temperature is actually the same).

Radiant surface temperature

One of the four variables for human comfort. The other three are air temperature, relative humidity, and air movement.

Radiation

Transfer of heat by means of the straight-line passage of electromagnetic waves through space (including vacuums) from a warmer object to a cooler one. Sunlight is a form of radiation.

Radon gas

A radioactive, colorless, odorless gas that occurs naturally in soil in many areas. When trapped in buildings, concentrations build up, and can cause health hazards.

Rain barrel

A barrel used as a cistern to hold rainwater typically filled by a downspout. The water can then be used for garden irrigation, or piped inside a home as non-potable water. Rain barrels can be linked together in a chain. Food-grade barrels should be used to guard against water contamination.

Rain garden

A planted depression that is designed to absorb rainwater runoff from roofs, driveways, walkways, and compacted lawn areas. This reduces rain runoff by allowing stormwater to soak into the ground (as opposed to flowing into storm drains and surface waters which causes erosion, water pollution, flooding, and diminished groundwater). Rain gardens are often planted with native plants.

Rainscreen

A method of constructing walls in which the cladding is separated from a membrane by an airspace that allows pressure equalization to prevent rain from being forced in. Often used for high-rise buildings or for buildings in windy locations.

Rainwater harvesting

On-site rainwater harvest and storage systems used to offset potable water needs for a building and/or landscape. Systems can take a variety of forms, but usually consist of a surface for collecting precipitation (roof or other impervious surface) and a storage system. Depending on the end use, a variety of filtration and purification systems may also be employed. Also known as rainwater catchment.

Raised-heel truss

Roof truss constructed so the top member (rafter) is raised above the top of the wall instead of resting on it. Constructed this way to allow space for both attic insulation and an air path from the soffit vent into the attic.

Rammed earth

A wall-building technique, by which a certain mixture of earth, water, and usually a small amount of cement, is very forcibly tamped inside formwork. The resulting wall has high mass, so it works well in hot climates. It often needs no exterior or interior covering, thus saving materials.

REC

Renewable Energy Certificate: (see Green tag).

Reclamation

The process of improving or restoring the condition of land or other material to a better or more useful state.

Recycled content

The content in a material or product derived from recycled materials versus virgin materials. Recycled content can be materials from recycling programs ("post-consumer") or waste materials from the production process or an industrial/agricultural source (see Pre-consumer).

Recycled material

Material that would otherwise be destined for disposal but is diverted or separated from the waste stream, reintroduced as material feed-stock, and processed into marketed end-products.

Recycling

Process by which materials that would otherwise become solid waste are collected, separated or processed and returned to the economic mainstream to be reused in the form of raw materials or finished goods.

Recycling Area

Space dedicated to recycling activities is essential to a successful recycling program, both on the construction site and in the building after occupation.

Recycling Bin

Containers to temporarily hold recyclable materials until transferred to a larger holding facility of pick-up by a recycling service. Conveniently located bins increase recycling rates by allowing occupants to recycle more easily. Designing space for recycling bins is a physical reminder of a commitment to recycling.

Refrigerant

A volatile substance that can be used as a working (cooling) fluid in a cooling system.

Refurbished

Products that have been upgraded to be returned to active use in their original form. Refurbishing is considered a form of reuse, and is preferable to recycling as it requires less processing and inputs to return a product to useful service.

Relite

Windows or translucent panels above doors or high in a partition wall intended to allow natural light to penetrate deeper into a building.

Renewable energy

Energy produced from regenerative or virtually inexhaustible resources such as biomass, solar radiation, the wind, water, or heat from the Earth's interior.

Renewable resources

Resources that are created or produced at least as fast as they are consumed, so that nothing is depleted. If properly managed, renewable energy resources (i.e. solar, hydro, wind power, biomass, and geothermal) should last as long as the sun shines, rivers flow, wind blows, and plants grow.

Renovation

The process of upgrading an existing building. Usually there is an attempt to keep the same general appearance of the building with new materials or to return the building to its original appearance.

Resistance

The ability of all conductors of electricity to resist the flow of current, turning some of it into heat. Resistance depends on the cross section of the conductor (the smaller the cross section, the greater the resistance) and its temperature (the hotter the cross section, the greater the resistance).

Resource conservation

Practices that protect preserve or renew natural resources in a manner that will ensure their highest economic or social benefits.

Respirable particles

Very small air-borne particles that can be breathed into the lungs. These can be naturally occurring as with forest fires, and volcanoes, or man-made as in the burning of fossil fuels.

Restoration

The process of bringing back a structure or landscape to its original state.

Retained components

Portions of the finished ceilings, finished floors, full height walls and demountable partitions, interior doors and built-in case goods that existed in the prior condition and remained in the completed design.

Retrofit

The replacement, upgrade, or improvement of a piece of equipment or structure in an existing building or facility.

Reuse

A sustainable building strategy in that it reduces the strain on both renewable and nonrenewable resources, and when materials are reused on or near the site of salvage, they reduce transportation-related environmental impacts.

Revitalize

To give new life or vigor to, for example, to revitalize inner-city neighborhoods.

RGGI

Regional Greenhouse Gas Initiative or ReGGIe: a cooperative effort by nine NE and Mid-Atlantic states to discuss the design of a regional cap-and-trade program initially covering carbon dioxide emissions from power plants in the region.

RH

Relative humidity: the percentage of water vapor in the air in relation to the amount of water vapor the air could hold at that given temperature before condensing to liquid form.

Ridge

The peak of a pitched/sloped roof.

Risk assessment

Qualitative and quantitative evaluation of the risk posed to human health and/or the environment by the actual or potential presence and/or use of specific pollutants.

Rocky Mountain Institute

RMI is a not-for-profit “think and do tank” that works with individuals and organizations of every imaginable kind to help them use energy and resources efficiently while being ever-better stewards of the environment.

Roof washer

In rainwater harvesting, this is attached to the top of a cistern to divert the first few gallons of water off the roof to a drain (or other catchment) so that the water in the cistern stays as clean as possible. A length of dead end PVC pipe with a spill over point somewhere above the top of the tank is the simplest form of roof washer. This drained water can be directed to a plant bed or swale so it is not wasted.

Root barrier

Any material that restricts unwanted and invasive root growth from trees and shrubs particularly in streetscapes, retaining walls and near building foundations. The materials commonly used are plastic sheeting, landscape fabric, concrete, fiber cement sheeting and sheet metal.

Rubble

Waste material consisting of asphalt or concrete. These materials can often be recycled into new material, or reused as compacted base material for roads.

Run-off

Water from rainfall or irrigation that flows off of land, instead of soaking in. It effectively becomes a lost resource, and contributes to non-point source pollution.

R-value

A unit of thermal resistance used for comparing insulating values of different materials; the higher the R-value of a material, the greater it’s insulating properties. It is inversely proportional to the U-value. R = 1/U.