Namesort ascending Definition
Rainscreen

A building enclosure rain control strategy that accepts that some water will penetrate the outer surface (the cladding, which “screens” rain) and removes this water back to the exterior by gravity drainage over a drainage plane, through a drainage gap, and exiting via flashing and weep holes. It is another term for a Drained system, however, some use the term only for systems that have larger drainage gaps (e.g., 1/2") or just for systems that are also ventilated (a ventilated drained approach) or just for systems that attempt to pressure-equalize (a Pressure-Equalized Rainscreen).

Rain Penetration Control Layer

See Water Control Layer.

Rain Control Layer

See Water Control Layer.

Radiation

The movement of energy by electromagnetic waves; can occur through a gas or a vacuum.  One of the three modes of heat transfer (in addition to convection and conduction). At normal temperatures, radiation is in the infra-red region of the spectrum, whereas solar radiation is at visible wavelengths. Controlling radiation is important to both heat transfer through porous insulations and through windows, as well as playing a significant role in daylighting and solar heating.

R.A.P.

abbr. return-air pathway

A commercial product that serves the same function as a transfer grille or jump duct, but also adds some light and sound transmission resistance.

R-value

Quantitative measure of an assembly or material resistance to heat flow for a unit temperature difference and a unit area. It is the reciprocal of the U-factor. The units for R-value are m2 K/W. As R-value increases, conduction through an assembly or material decreases for the same temperature difference. As an example of the context in which R-value should be placed, 25% to 40% of a typical building's energy use can often be attributed to air infiltration, and air conditioning loads are often dominated by solar heat gain.

The effect of thermal bridging and different framing details requires a metric more complex than just a single R-value to allow for meaningful comparisons. Five R-values have been and are used in the building industry. Oak Ridge National Labs (ORNL) proposed a number of definitions (Christian and Kosny 1995). We have found it useful to add some and extend their definitions.

  1. Installed Insulation R-value. This R-value is commonly referenced in building codes and used by industry. This is simply the R-value labeled on the product installed in the assembly.
  2. Center-of-Cavity R-value. The R-value at a line through an assembly that contains the most insulation, and the least framing, typically, the middle of a stud-bay in framed construction.
  3. Clear-wall R-value. R-value of an assembly containing only insulation and minimum necessary framing materials at a clear section with no windows, corners, columns, architectural details, or interfaces with roofs, foundations or other walls.
  4. Whole-wall R-value. R-value for the whole opaque assembly including all additional structural elements (such as double studs), and typical enclosure interface details, including wall/wall (corners), wall /roof, and wall/floor connections.
  5. True R-value. The R-value of an enclosure assembly that includes all thermal bridging, air leakage, wind washing, convective loops, radiation enhancements, thermal and hygric mass, and installation defects.

Each of these measures is progressively more realistic. The True R-value is very difficult to measure without field samples.
 

Quick Set

See Flash Set.

PV

abbr. photovoltaic

Punched Window

A window installed as a “punched” opening surrounded by cladding, as opposed to being arranged in vertical or horizontal strips.

Puffer Stick

See Smoke Pencil.

Psychrometrics

The study of air and its energy and water vapor contents.

PSC

abbr. permanent split-capacitor (motor)

Primer

A coating intended to prepare the surface of the substrate for the subsequent application of a paint, adhesive or adhered membrane.

Pressure-Equalized Rainscreen

A specific type of drained wall system that uses spatial compartmentalization, careful venting to air leakage ratios, and stiff components to encourage short-term equalization of drained cavity (also the air chamber) pressures with exterior wind pressures to reduce the pressure across the screen (or cladding). Such systems rely on effective drained to control rain, and if functional, merely reduce the rainwater that the drained system must accommodate.

Pressure Boundary

The primary air enclosure boundary separating conditioned air and unconditioned air. Typically defined by the air control layer system.

Pot Life

The duration of time that the wet state material remains workable after it has been mixed.

Ponding

A condition where water stands on a roof, slab, or any other nominally horizontal surface for prolonged periods due to poor drainage and/or deflection of the surface.

Polyisocyanurate

See PIC.

Plywood

A wood product made of three or more layers of veneer joined with glue, and usually laid with the grain of adjoining plies at right angles.

Plenum

An air compartment or chamber to which one or more ducts are connected, forming part of either the supply air, return air or exhaust air system. Plenums can include areas above ceilings, below floors, or in wall cavities. The practice of using unsealed building cavities to circulate air may result in indoor air quality issues.

Plate

Sill plate or “mud sill”: a horizontal member anchored to a masonry wall.

Sole plate: bottom horizontal member of a frame wall.

Top plate: top horizontal member of a frame wall supporting ceiling joists, rafters, or other members.

PITI

abbr. principal, interest, tax, and insurance

PIC

abbr. polyisocyanurate

A closed-cell foam insulation material typically sold in rigid boards (but also available as a liquid, sprayed foam). R-value can range from R-5.6 to R-9, depending on the manufacturer, the age of the foam, and the presence or absence of foil facings. Foil-faced PIC has a greater R-value and is also vapor impermeable (less than 0.1 perm). The use of ozone-depleting substances as blowing agents is being phased out. Most U.S. PIC manufacturers now use pentane.

PEX

abbr. cross-linked polyethylene (PE) tubing

Permeance

The physical property that defines the ease with which water molecules diffuse through a material. It is to vapor diffusion what conductance is to heat transfer. The unit of measurement is typically the "perm."

Related Resources: Info-312: Vapor Permeance of Some Building Materials; Info-500: Building Materials Property Table

Penetration

A hole passing through the building envelope in which ducts, pipes, wires, structural elements, and windows are run between inside and outside.  Windows are also a penetration.

PATH

abbr. Partnership for Advancing Technology in Housing

Previously the Partnership for Advancing Technology in Housing, PATH is now an online resource for homeowners and homebuyers, the homebuilding industry and federal agencies.

Parapet Wall

A low wall around the perimeter that projects above the level of the top of the adjoining roof level.

Pa

abbr. Pascal

A metric unit of measurement of pressure, defined as a Newton per square meter. One inch of water column is equal to about 250 Pa.

Ozone

An oxygen chemical compound of the form 03 instead of 02 (common atmosphereic oxygen). This 3-atom molecule is an even more active oxidizing agent than its more common 2-atom relative. At ground level, ozone is a pollutant and in the upper atmosphere it is a UV shield. Ozone's highly reactive nature tends to accelerate the breakdown of synthetic materials such as paints, plastics, and volatile organic compounds.

Outdoor Air

Air outside the building.

OSB

abbr. oriented strand board

Open-Cell SPF

See ocSPF.

ocSPF

abbr. open-cell spray polyurethane foam

A type of spray foam insulation with a semi-rigid cellular structure and a density between 8 and 22 kg.m3 (0.4 and 1.4 lb/ft3). Provides a nominal thermal resistance of R-3.6 per inch (this will vary from manufacturer-to-manufacturer). Some spray foams use greenhouse gases, but others, such as water blown foams, do not.

 

Occupiable Space

Any enclosed space inside the pressure boundary and intended for human activities, including (but not limited to) all habitable spaces, toilets, halls, laundry areas, closets, and other storage and utility areas.

OASys

A type of indirect/direct evaporative cooler.

o.c.

abbr. on center

NZEH

abbr. net zero energy house (or home)

NHQ

abbr. National Housing Quality

The National Housing Quality Program was created by the NAHB Research Center as a focal point for the advancement of quality control practices in residential construction.

 

NATE

abbr. North American Technician Excellence

The leading non-profit certification program for technicians in the heating, ventilation, air-conditioning, and refrigeration (HVAC/R) industry and the only test supported by the entire industry.

Pages