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: Maintenance and repairs that were not performed when scheduled or needed, and have been postponed to a future date. This often leads to a decline in the condition or performance of building systems, components, equipment, or building envelope, and may require corrective action to restore function or prevent further decline.

Deferred-Maintenance Items: Deficient items that cannot be remedied with routine maintenance, generally caused by neglect, and requiring attention before escalating into failures or causing a significantly adverse impact.

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.

Detention Basin: A basin that temporarily holds runoff during heavy rains and releases it slowly to prevent flooding and erosion

Determine: To arrive at an opinion or conclusion pursuant to examination.

Diagonal Crack: A crack typically found at the corner of walls and oriented at some angle; can indicate structural movement.

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.

Diffuser: A component of the ventilation system that supplies conditioned air into a space and can manage air output.

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.

Dilution Air: The combination of air and flue gases that lower emission concentration.

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.

Double-Hung Windows: Windows consisting of two sashes that slide vertically within the frame; allow for both top and bottom portions to be opened independently.

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

Drip Edge Flashing: A metal “L”-shaped flashing strip installed along the edges of a roof to guide water away from the fascia and help protect underlying roofing components.

Drip Leg: A vertical pipe at the low point in a fuel piping system that prevents sediment, debris, and moisture from entering a gas appliance.

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.