Terms Starting with O and P

OC (on-center) - The distance from the center of one regularly spaced framing member to the next. Studs and joists are commonly 16 or 24 inches OC.

Off-peak - Periods other than peak electrical demand periods.

On-peak - Periods when energy consumption is highest and the most expensive energy-supply systems are operated; generally peak period refers to period of greatest demand on an electric utility.

Oriented Strand Board or OSB or Chip Board or Wafer Board - A manufactured wood panel made out of 1"- 2" wood chips and glue. Often used as a substitute for plywood in the exterior wall and roof sheathing.

Outside corner - The point at which two walls form an external angle, one you usually can walk around.

Overhang - Outward projecting eave-soffit area of a roof; the part of the roof that hangs out or over the outside wall.

Panel - Wood, glass, plastic, or other material set into a frame, such as in a door. Also, a large, flat, rectangular building material such as plywood, hardboard, or drywall.

Partition - An interior dividing wall. Partitions may or may not be bearing.

Passive solar - A system that uses natural heat transfer processes to move captured solar energy (in the collector) to the storage or living space.

Paving - Materials—commonly masonry—laid down to make a firm, even surface.

Payback - The length of time before the money you save with new equipment, insulation, etc. will equal your original investment. Commonly used in evaluating energy-related items.

Payment schedule - A pre agreed upon schedule of payments to a contractor usually based upon the amount of work completed. Such a schedule may include a deposit prior to the start of work. Payments are often scheduled for the beginning of the month and allow the contractor to subcontractors and suppliers by the 10th of the month. There may also be a temporary 'holdout' at the end of the contract for any small items which have not been completed.

Peak demand - The greatest amount of electricity or natural gas used by utility customers during the day or year.

Percolation or perc. test - A test to determine of the soil on a proposed building lot is capable of absorbing the liquid affluent from a septic system.

Permeability - A measure of the ease with which water vapor penetrates a material.

Permit - A governmental authorization to perform a building process as in:

Phase change - The change of a material from liquid to solid, or liquid to gas, or vice versa.

Phase-change material (PCM) - A material that melts at or near room temperature and that can therefore be used for heat storage purposes.

Pier - A masonry post. Piers often serve as footings for wood or steel posts.

Pilot hole - A small-diameter hole that guides a nail or screw.

Pilot light - A small, continuous flame that ignites gas or oil burners when needed.

Pitch (roof) - The slope of a roof expressed in feet rise per foot of run.

Plenum - The main hot-air supply duct leading from a furnace.

Plumb - True vertical. Also see level.

Plumb bob - A lead weight attached to a string. It is the tool used in determining plumb.

Plywood - A building panel made by gluing together thin layers of wood. Alternating grain directions from one layer to the next adds strength.

Polyisocyanurate foam - A rigid foam board insulation often used in location where there is not enough room for standard batt insulation. A nice word which can be used to impress or confuse someone. Programmed to various temperature settings One of the least expensive ways to reduce energy consumption.

Post - A vertical framing member usually designed to carry a beam. Often a 4" x 4", a 6" x 6", or a metal pipe with a flat plate on top and bottom (see diagram).

Post-and-beam - A basic building method that uses just a few hefty posts and beams to support an entire structure. Contrasts with stud framing.

Pressure Relief Valve - A device mounted on a hot water heater or boiler which is designed to release any high steam pressure in the tank and thus prevent tank explosions.

Pressure-treated wood - Lumber that has been saturated with a preservative.

Primer - A first coating formulated to seal raw surfaces and hold succeeding finish coats.

Process heat - Heat, usually steam at high temperature and pressure, used in industrial processes.

PVC or CPVC - A type of white plastic pipe sometimes used for water supply lines.