Developed length of the longest run in feet, including the equivalent length of fittingsIn: Water supply pipe sizing guide
LAANC / airspace authorization
The Low Altitude Authorization and Notification Capability, the automated system that grants near real-time approval to fly below the set ceiling in controlled airspace.In: Drone inspection field guide
Lab pressurization
Holding the lab negative to the corridor by exhausting more air than is supplied, so fumes stay in the labIn: Lab fume hood exhaust guide
Tile with any edge over 15 in; lippage is the height step between adjacent tile edges, commonly held to about 1/32 in on tight joints.In: Ceramic and porcelain tile installation
Laser screed
Self-propelled machine that strikes off to a rotating laser plane with auger, vibrator, and screed plateIn: Laser screed and screeding methods
Last furnishing
The final date you supplied labor or materials to the project; the recording clock usually runs from it, and punch work may count while warranty work often does not.In: Mechanics lien and preliminary notice
Last Planner System
The Lean Construction Institute planning method that pushes the work commitment down to the foremen who do the workIn: Daily huddle field guide
Last Planner System (LPS)
The lean planning method of cascading levels: master schedule, phase pull plan, look-ahead, weekly work plan, and PPC learningIn: Lean construction field guide
Time for a packet to cross the fabric; the tail (99th or 99.9th percentile) sets job completion time because the collective waits on the worst pathIn: Network observability for the AI fabric
Latent / evaporation load
The moisture leaving the pool and deck, in pounds of water per hour, that the HVAC must remove; the design driverIn: Natatorium HVAC field guide
Tension ties from the deck framing into the house framing that resist the deck pulling away from the wall, separate from the ledger gravity boltsIn: Deck construction field guide
Stacking measures so each covers the gap in the one before it, making the site the harder target rather than a fortressIn: Jobsite security and theft prevention
Layout point / as-built
A designed point staked in the field, and the survey of what was actually built compared back to the modelIn: Construction layout
Layout robot
A machine that prints or marks the building layout from the coordinated model directly onto the slab or deck, positioned against survey controlIn: Construction robotics
Layup
Protecting an idle boiler from corrosion, wet with treated water or dry with desiccant or nitrogenIn: Boiler water treatment field guide
LB / LL / LR
90-degree elbow bodies named by the direction the cover or side opening faces: back, left, or rightIn: Conduit bodies and fittings
Pound-inches and pound-feet are the common torque units; 12 lb-in equal 1 lb-ft; newton-meters are the metric unit, with 1 lb-ft about 1.356 N-mIn: Termination torque QA field guide
lb/sq ft (psf)
Pounds per square foot, the unit for uniform distributed load; kilopascals in metricIn: Raised floor load rating test
lbf (pounds-force)
The unit for concentrated, rolling, ultimate, and pedestal loads in US data sheets; newtons in metricIn: Raised floor load rating test
Leakage-current detection and interruption power cord, the protection expected on plug-connected PTACsIn: PTAC and PTHP field guide
LCR / LCRR / LCRI
EPA Lead and Copper Rule, its Revisions, and its Improvements; the federal rules for lead in drinking waterIn: Lead service line guide
LDD
Luminaire dirt depreciation, light lost to dirt on the fixture between cleaningsIn: Commercial lighting design
Lead inductance
Voltage developed across the SPD leads during the fast surge, adding to the let-through; the reason for short leadsIn: SPD installation field guide
Lead RRP
EPA Renovation, Repair, and Painting rule requiring a certified firm and lead-safe practices when work disturbs pre-1978 paint in covered buildings.In: Interior demolition strip-out
Lead source
How a customer first found you; tracked on every record so you know which marketing paysIn: Customer database and CRM
Lead-based paint
Paint with lead at or above the regulatory level, common before the 1978 residential ban; assume it in pre-1978 buildings unless tested otherwiseIn: Lead-safe renovation (RRP)
Running the project as a production system aimed at reliable workflow by removing waste, the waiting and rework, rather than blaming the workerIn: Lean construction field guide
LED power supply (class 2)
A listed low-voltage supply, commonly class 2, converting 120 V to the 12 or 24 V DC the LED modules useIn: Electric sign installation
LEF
Load equivalency factor: how many standard axles' worth of damage one axle does, rising with about the fourth power of loadIn: Asphalt pavement thickness design
Legal outlet
A point the site is allowed to discharge to, a storm system, easement, watercourse, or its own ground, not the neighbor's lotIn: Drainage, grading, and slope
Legally required standby (NEC 701)
Backup for code-required loads that are not immediate life safety, with a longer transfer expectation and its own coordination requirementIn: Emergency and standby power systems
LEL / explosive atmosphere
Lower explosive limit; ventilation holds tank vapor below 10 percent of itIn: Tank coating and lining
LEL / percent LEL
Lower explosive limit, the concentration at which a flammable gas can ignite, read on the meter as a percentage of itIn: Confined space entry field guide
120 V AC; 208 to 240 V AC; and DC fast charging fed three-phase, delivering DC to the batteryIn: EVSE install and commissioning
Level 2
AC charging at roughly 208 V to 240 V, the common commercial and home charger rangeIn: EV feeder sizing walkthrough
Level 5
The top commissioning level, the integrated systems test, run after Levels 1 through 4 are signed offIn: Integrated systems test (IST)
Level of accuracy (LOA)
The spec'd accuracy of the scan and model, per the USIBD specification; LOA says how correct, LOD says how completeIn: Reality capture and scan-to-BIM
Leveling / scratch / wedge course
A thin, variable-thickness lift that fills ruts and lows before the wearing courseIn: Asphalt mill and overlay
Leveling pad
The compacted crushed-stone base, commonly about 6 in, that the buried first course is set level onIn: Segmental retaining wall build
Levels of finish 0 to 5
The GA-214 scale of how much taping and coating a wall gets; Level 4 is the standard painted finish, Level 5 adds a full skim coat for critical light and glossIn: Drywall and gypsum board finishing
Lithium iron phosphate (LiFePO4): lower energy density, more thermally stable, trending in data center backupIn: Rack BBU and ride-through
LFP / NMC
Lithium iron phosphate, higher onset and less violent; nickel manganese cobalt, higher energy and lower onsetIn: Lithium-ion thermal runaway safety
LFP vs NMC
Lithium iron phosphate, more thermally stable and now dominant in stationary storage, versus nickel manganese cobalt, denser but with a lower thermal-runaway onsetIn: Battery energy storage (BESS)
LGR vs desiccant dehumidifier
Refrigerant unit that condenses moisture to low grains, versus a desiccant wheel for lower humidity and cold or bound-water dryingIn: Water mitigation and drying guide
An active instrument that fires laser pulses and times the return to measure precise distances and build a point cloudIn: Reality capture and scan-to-BIM
The pressure difference the compressor must develop between evaporator and condenser; high lift is the primary surge driverIn: Centrifugal chiller surge control
Lift insert
Cast-in hardware the crane rigging hooks to, located and embedded per the engineered lift drawingIn: Tilt-up bracing and erection
Lift station
A pump system that collects wastewater in a wet well and pumps it through a force main to a gravity sewer when it cannot get there by gravityIn: Sewage lift station field guide
Return loss, VSWR, and distance-to-fault on the line, and passive intermodulation, the interference from non-linear junctionsIn: Cell tower and antenna install
A worker trained and qualified to perform tree work near energized conductors under OSHA 1910.269In: Tree removal and stump grinding
Line-interactive / VI
Regulates voltage with an AVR, still transfers to battery on a true outageIn: UPS types and technologies
Linear-drive optics (LPO)
A pluggable optic with the DSP removed, driven directly by the switch silicon, for lower power while keeping the hot-swappable form factorIn: Optical circuit switch and photonics
Linear-foot items
Materials bought by length off the edges and lines: drip edge, starter, cap, valley metalIn: Roof measurement and squares
Lined-clear opening
The inside duct dimension after the liner, the dimension that carries the air for sizingIn: Duct insulation field guide
The accounting of optical loss against the optic's power budget, and the optical signal-to-noise ratio the coherent receiver needs to recover the signalIn: Data center interconnect (DCI)
Lion-tailing
Over-thinning that strips interior branches and leaves weight on the tips, weakening limbs and exposing barkIn: Tree pruning and maintenance
Liquefaction
Loose, saturated sand losing strength under earthquake shaking as pore pressure spikes and the grains float apartIn: Ground improvement and grouting
A fixed daily amount the contractor owes for late completion under the contractIn: Project scheduling
Listed / UL assembly
A tested design, such as a UL design number, fixing the material, thickness, steel, and conditions that earn the ratingIn: Structural fireproofing
Listed vs recognized
A listed component is complete in itself; a recognized component goes into a larger assembly under stated conditionsIn: UL 508A control panel and SCCR
Lithium-ion (LFP / NMC)
Lithium iron phosphate, favored in data centers for thermal stability, versus the denser but less stable nickel manganese cobaltIn: Data center battery and storage types
Lithium-ion (LFP)
Lithium iron phosphate, the lithium chemistry common in UPS service for its thermal stability, managed by a BMSIn: UPS battery maintenance and testing
Live data feed
The real-time stream from the BAS and sensors, status, alarms, conditions, and energyIn: Digital twin for operations
Live load
The movable design load from equipment, people, and service, in psf, that the structure is engineered to carryIn: Structural design for AI racks
A living wall has plants rooted in a medium on the wall; a green facade has climbing plants rooted in the ground that grow up a trellis or cable.In: Living wall and green wall systems
Light loss factor, derates initial output to maintained, commonly 0.7 to 0.9In: Commercial lighting design
LOA / CFA
Letter of Authorization and Connecting Facility Assignment, the authorization plus the exact cabinet, panel, and port a cross-connect lands on; expires if not built in its windowIn: Cross-connect patch records
Load (watts / amps)
Power a display draws; sum the watts, divide by the supply voltage for amps to size against the circuitIn: Commercial holiday lighting install
Load and span class
NEMA VE-1 rating pairing a working load (lb per linear ft) with a support span (ft)In: Cable tray field guide
A wall in the load path carrying weight from above; shoring is the temporary support that holds the load while it is removed and a permanent header goes in.In: Interior demolition strip-out
Load-demand dispatch
Running only the sets the load needs, starting and stopping sets on load with priority rotation for even run hoursIn: Generator paralleling
Loadbreak elbow
A 200 A separable connector with an arc-interrupting tip that can be operated energized with a hot stick; a deadbreak elbow is 600 A and must be deadIn: MV termination and splicing
Loaded crew rate
The crew's hourly cost including wage plus the labor burden of taxes, insurance, and benefitsIn: Landscape estimating and bidding
The grid coordinate, equipment tag, room, or lineup section that ties each photo, test, and signoff to the exact place the work isIn: Proof packet assembly
The moment the wedges seat and hold; the small strand draw-in is the seating loss, about 1/4 in to 3/8 inIn: PT slab stressing
Locked-rotor / inrush current
The high current at the instant of starting, commonly six to eight times running current, which the branch device must passIn: Motor circuit sizing, NEC 430
Lockout / restart / runback
Isolating energy before service; restart is automatic re-energizing, runback is a loaded incline rolling backward when the drive releasesIn: Conveyor system installation
Level of development: how detailed and reliable an element is, on a common scale of 100 concept, 200 generic, 300 accurate, 350 with connections, 400 fabrication, 500 as-builtIn: BIM VDC coordinationAs-built record drawings
Log-Tchebycheff
The traverse point spacing (from ISO 3966, used in ASHRAE 111) that makes the simple average of readings the true average velocityIn: Air balancing report field guide
The roughly 6-week window where upcoming tasks are screened and their constraints removed so the work is readyIn: Lean construction field guide
Loop / circuit
One continuous run of tube from the manifold supply, through the floor, and back to the manifold returnIn: Radiant floor heating design
Loop resistance
The round-trip resistance of the conductors carrying current, the source of both the drop and the heatIn: PoE voltage drop and heat
Loose-fill vs unitary
Loose-fill is granular material at a set depth (engineered wood fiber, rubber mulch, sand); unitary is a bonded system (poured-in-place rubber, tiles)In: Playground safety surfacing
Loose-laid
A membrane laid relaxed over the substrate with no field fasteners or adhesive, held only by ballastIn: Ballasted roof systems
Loose-shipped
Items shipped separately from the assembly, such as bus links, racking tools, keys, and sparesIn: Switchgear receiving inspection
Loose-tube / ribbon cable
Fibers floating in buffer tubes, or bonded into ribbons for high count and mass fusion splicingIn: OSP fiber and FTTH construction
LoRaWAN / private LTE
LoRaWAN is a long-range, low-power network for small sensor packets; private LTE or 5G is a high-capacity network you control on siteIn: Connected jobsite and RTLS
Isolating and locking a machine to a zero-energy state before anyone enters the danger zoneIn: Struck-by and caught-in hazards
Louvered / motorized pergola
An aluminum pergola with adjustable blades that tilt for sun and close to a watertight roof, often on a motor with a sensorIn: Pergola and shade structure guide
Gas heater with a steel tube emitter at a moderate surface temperature, commonly near 1100°F, over a long areaIn: Infrared radiant heater field guide
Low-lift vs high-lift grouting
Grouting the wall in short increments as it rises, versus laying it tall and grouting from the bottom in lifts with cleanoutsIn: CMU block wall construction
Low-slope
A roof too flat to shed reliably, commonly under roughly 2:12, waterproofed with a continuous membraneIn: Roofing system types
Low-slope roof
A roof at a shallow pitch, commonly 1/4 in. per ft or less, where drainage and membrane integrity drive performanceIn: Roof maintenance program
Low-suction cutoff
A required control that shuts a booster down before it pulls a vacuum or negative pressure on the suction mainIn: Booster and PRV system guide
Low-voltage vector mapping (EFVM)
A wetted-surface, perimeter-loop, two-probe method that maps the current vector to a breach; works under overburdenIn: Electronic leak detection
Lightweight aggregate, the porous aggregate that cuts the density of the concreteIn: Lightweight concrete
LWCO
Low-water cutoff, the control that shuts the burner when water level drops too low, preventing dry-firing of the vesselIn: Boiler startup commissioning
LWIC
Lightweight insulating concrete, a poured deck over form deck that gives slope and holds waterIn: Roof deck substrate types