Vacuum Breaker: An anti-siphon device that prevents waste water from being drawn back into supply lines, potentially contaminating the water supply. A type of backflow preventer.

Valley: The internal angle formed by the junction of two sloping sides of a roof.

Valley Rafter: A rafter that forms the intersection of an internal roof angle. The valley rafter is normally made of double 2-inch-thick members.

Valley Shield: A quality underlayment for added protection in the heavy water flow areas of a roof. This self adhering product has a waterproof asphalt coating which offers excellent elongation and recovery properties for accommodating roof expansion and contraction and structural movement.

Valuation: An inspection carried out for the benefit of the mortgage lender to ascertain if a property is a good security for a loan.

Valuation Fee: The fee paid by the prospective borrower for the lender's inspection of the property. Normally paid upon loan application.

Valve: A device to stop, start or regulate the flow of liquid or gas through or from piping.

Vapor: The gaseous form of any substance.

Vapor Barrier: A membrane which is placed between the insulation and the roof deck to retard water vapor in the building from entering the insulation and condensing into liquid water.

Vapor Retarder: Any substance that prevents the transmission of water vapor.

Variable Rate: An interest rate that will vary over the term of the loan.

Varnish: A thickened preparation of drying oil, or drying oil and resin suitable for spreading on surfaces to form continuous, transparent coatings, or for mixing with pigments to make enamels.

Vehicle: The liquid portion of a finishing material; it consists of the binder (non-volatile) and volatile thinners.

Veining: In roofing, the characteristic lines or "stretch marks" which develop during the aging process of soft bitumens.

Veneer: Thin sheets of wood made by rotary cutting or slicing a log.

Vent: A pipe or duct which allows flow of air as an inlet or outlet.

Vent Pipe: A vertical pipe of relatively small dimensions which protrudes through a roof to provide for the ventilation of gasses.

Vent Stack: A vertical vent pipe installed for the purpose of providing circulation of air to and from any part of a drainage system.

Vent System: In plumbing, a system to provide a flow of air to or from a drainage system or to provide circulation of air within such system to protect traps seals from siphonage and back pressure.

Ventilation: The natural or mechanical process of supplying and removing air from any space.

Ventilator: Device installed on the roof for the purpose of ventilating the interior of the building.

Venting: The process of installing roof vents in a roof assembly to relieve vapor pressure. The process of water in the insulation course of the roof assembly evaporating and exiting via the roof vents.

Verify: To confirm or substantiate.

Vermiculite: An aggregate somewhat similar to perlite that is used as an aggregate in lightweight roof decks and deck fills. It is formed from mica, a hydrous silicate with the ability of expanding on heating to form lightweight material with insulation quality. Used as bulk insulation and also as aggregate in insulating and acoustical plaster and in insulating concrete.

Vertical: Being or situated at right angles to the horizon; upright.

Veterans Administration (VA): A federal agency that insures mortgage loans with very liberal down payment requirements for honorably discharged veterans and their surviving spouses.

Viscosity: The internal frictional resistance offered by a fluid to change of shape or to the relative motion or flow of its parts.

Visible: That which may be easily observed during the walk-through survey portion of the inspection.

Visible Light Transmittance: The percentage of visible light (390 to 770 nanometers) within the solar spectrum that is transmitted through glass.

Visqueen: A 4 mil or 6 mil plastic sheeting.

Visual Mock-Up: Small scale demonstration of a finished construction product.

Vitreous China: A non-porous ceramic that is coated with a ceramic glaze to form toilets and lavatories.

Void: A cardboard rectangular box that is installed between the earth (between caissons) and the concrete foundation wall. Used when expansive soils are present.

Volatile Thinner: A liquid that evaporates readily and is used to thin or reduce the consistency of finishes without altering the relative volumes of pigment and non-volatile vehicles.

Voltage: The driving force behind the flow of electricity somewhat like pressure is in a water pipe. Most homes are wired with '110' and '220' volt lines. The '110' volt power is used for lighting and most of the other circuits. The '220' volt power is usually used for the kitchen stove, water heater and dryer. (The terms '110' and '220' volts are a short hand, e.g. a '110' volt line is usually rated at 117 volts plus or minus 10%).

Voltmeter: Measures the voltage flowing through a circuit.