damper: a valve or plate for controlling draft or flow of gases, including air, in a vent or ductwork; a manually-operated plate for controlling draft in a flue.

dampers: Controls that vary airflow through an air outlet, inlet, or duct. A damper position may be immovable, manually adjustable, or part of an automated control system.

dead-level roof: A roof with no slope; a flat roof.

dead load: Static load imposed by gravitational forces acting upon the structure and permanently installed building materials, such as a roof, wall, floor, and ceiling-covering materials.

deck: exterior floor system supported on at least two opposing sides by an adjoining structure and/or post, piers, or other independent supports.

decorative: ornamental; not required for the operation of essential systems and components of a building.

defensible space: an area around a building designed to slow the rate of an advancing wildfire

deferred-maintenance items: deficient items that cannot be remedied with routine maintenance, generally caused by neglect.

deflection: The amount of bending movement of any part of a structural member perpendicular to the axis of the member under an applied load; also referred to as sag.

delamination: A term used to describe the separation of laminated layers, either membrane plies or insulation.

describe: to report, in writing, a system or component by its type or other observed characteristics to distinguish it from other components used for the same purpose.

destructive: an act of demolishing, damaging or probing any system, structure or component, or to dismantle any system or component that would not be taken apart by an ordinary person in the course of normal maintenance.

detectable warning: raised bumps or domes that signal via cane or underfoot an approach to a traffic lane or change in surface level.

determine: to arrive at an opinion or conclusion pursuant to examination.

diaphragm: A horizontal structural element designed to transmit lateral loads to the shear wall and is built in as part of the roof and floor structures.

diffusers and grilles: Components of the ventilation system that distribute and diffuse air to promote air circulation in the occupied space. Diffusers supply air and grilles return air.

dimensional lumber: Yard lumber from 2 to 5 inches thick and 2 or more inches wide, and includes joists, rafters, studs, planks, and small timbers.

disability: a condition related to a person’s mobility, hearing, vision, speech, or cognition that impairs their ability.

disconnected: shut down.

Disinfectants: One of three groups of antimicrobials registered by EPA for public health uses. EPA considers an antimicrobial to be a disinfectant when it destroys or irreversibly inactivates infectious or other undesirable organisms, but not necessarily their spores. EPA registers three types of disinfectant products based upon submitted efficacy data: limited, general or broad spectrum, and hospital disinfectant.

dismantle: to open, take apart or remove any component, device or piece that would not typically be opened, taken apart, or removed by an ordinary occupant.

door closer: a mechanical device that controls the closing of a door.

downspout: Also called a leader, the pipe that carries water down from the gutter or scupper.

duct: a passageway, tube or conduit utilized for the transmission of air and vapors.

due diligence: a level of care in the inspection process that varies, depending upon the scope of work agreed upon by the inspector and his/her client.

dwelling unit: a single unit providing complete, independent living facilities, including permanent provisions for living, sleeping, eating, cooking and sanitation.