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Existing Conditions Modeling Standards – LoD and LoA for RFP Specifications

Why Existing Conditions Modeling Matters

A high-fidelity existing-conditions model is more than just a design convenience—it’s the cornerstone of a coordinated, data-driven project delivery strategy. When developed to rigorous standards of geometric accuracy and detail, this model becomes a single source of truth that anchors every phase of the capital project: from permitting and design, through construction, commissioning, and long-term facilities management.

Unlike paper as-builts or ad hoc site documentation, a standards-compliant BIM model ensures that every consultant, vendor, and contractor works from the same verified spatial information, reducing duplication of effort and minimizing clashes. It can save hundreds of hours of coordination meetings by making conflicts visible before they happen—and provides a shared digital reference for the building’s entire lifecycle.

By specifying clear expectations for Level of Detail (LoD) and Level of Accuracy (LoA) in the RFP, owners can ensure:

  • Precise coordination between disciplines and trades

  • Faster approvals and fewer RFIs

  • Seamless model handoffs from design to construction to operations

  • Long-term asset management value through spatially intelligent record models

This document provides plug-in paragraphs for each modeling discipline, along with recommended accuracy standards, so that owners can easily define what level of BIM documentation is required for their specific project needs—whether it's a feasibility study, renovation, adaptive reuse, or full restoration.

Level of Detail (LoD) as a BIM Language

In BIM practice, LoD serves as a three‑letter “language” to specify the maturity and granularity of a model—from broad massing to manufacturing‑grade detail—so all stakeholders share a clear, unambiguous expectation for deliverables. Rather than prescribing tools or file types, LoD speaks to what is in the model and why.

• LoD 200 (Approximate Geometry / Schematic Level): Used in permitting, feasibility studies, schematic design and early cost estimating, this level provides generic but dimensionally correct geometry—ideal for concept validation and high‑level coordination.
• LoD 300 (Accurate Geometry / Construction‑Ready): Applied to renovation, addition, and most interior fit‑out projects, LoD 300 delivers precise as‑built geometry and reliable quantities, supporting clash‑detection and construction documentation.
• LoD 350 (Precise Geometry / Specialized Detail): Reserved for historic preservation, cultural‑heritage projects, adaptive‑reuse schemes or any scenario demanding finish‑and‑interface fidelity, this level adds custom profiles, hardware, and surface articulations to create fabrication‑grade models.

 

Project Type

Feasibility, Concept Design, Permits

Renovations, Interior Fit-Outs

Historic Preservation, Adaptive Reuse

Recommended LoD

LoD 200

LoD 300

LoD 350

Purpose

Diagrammatic geometry, spatial validation

Accurate geometry for coordination + take-offs

Detail-rich model for clash detection + fabrication-level planning

 

Plug in RFP Language:

01 31 00 – EXISTING CONDITIONS MODELING – OVERVIEW

Accurate modeling of existing conditions is essential to project success. When executed to defined standards of detail and accuracy, the resulting Building Information Model (BIM) serves as the foundational digital record for all phases of project delivery.

The intent of this requirement is to ensure the model provides a verified, shared reference point for design, construction, and operations teams. By establishing a single source of truth early in the project, the Owner can reduce coordination errors, minimize rework, and streamline communication across trades and consultants.

This model is not solely for design coordination. It is a persistent asset that:

  • Enables early clash detection and spatial validation

  • Reduces the need for repeated site visits and field verification

  • Facilitates smoother handoff to contractors and fabricators

  • Supports turnover to facilities management and lifecycle planning

To meet these objectives, all models must conform to the specified Level of Detail (LoD) and Level of Accuracy (LoA) definitions outlined herein. These standards define both the content and fidelity of modeled elements and shall be applied consistently across all modeling disciplines.

Level of Accuracy (LoA) Requirements 

A high Level of Accuracy (LoA) is required for all existing conditions data. This encompasses both measured accuracy (the fidelity of field-collected data) and modeled accuracy (the fidelity of the BIM model to the real conditions). All measurements shall be obtained with instrumentation capable of sub-¼ inch point accuracy, ensuring that the raw spatial data closely reflects actual building geometry. The modeling process shall then maintain all key dimensions and locations within approximately ½ inch of true size or position, so the digital model reliably represents on-site conditions. This approach is technology-agnostic, focusing on performance outcomes rather than specific tools—any measurement method that achieves the stated tolerances is acceptable. By clearly defining these accuracy tolerances (often corresponding to LoA 40 for measured data and LoA 30 for modeled data), the RFP ensures that the delivered model will be both precise and trustworthy for downstream use. 

  • Measured Accuracy: ≤ 1/4 in. point variance (USIBD LoA 40)

  • Represented (Modeled) Accuracy: ≤ 1/2 in. variance from field truth (USIBD LoA 30) 

  • Validation: Method B (double‑check using overlapping data*). Each scan pass must overlap an adjacent pass and be cross‑registered until residual mis‑closure falls within the above tolerances.

  • Instrumentation: Any system capable of sub‑¼ in. single‑point precision is acceptable; vendor must document calibration and environmental logs.

*USIBD defines Method B as “check by overlapping data sets,” offering a statistically valid redundancy without the added cost of independent survey ties.

BIM Scope Options

(The following paragraphs provide ready-to-use descriptions for scope scenarios. They can be inserted into the RFP if a different Level of Detail is desired for a particular discipline. Each option defines the expected modeling scope at the specified LoD)

Architectural Modeling Options

Architectural Model LoD 200

 The model shall depict the building’s architectural envelope in its essential geometric form. Exterior and interior walls use standard wall profiles at accurate thickness and height, while floors, roofs, and ceilings are placed at true elevations; roof and ceiling planes that are intentionally sloped are modeled at their measured pitch. Door and window families are inserted at correct sizes with their default frames, handles, and muntins; openings alone are not acceptable. Storefront assemblies include default mullions; curtain‑wall panels appear without mullions at this level. Generic Revit fixtures for plumbing (lavatories, WCs, etc.) and fixed casework are positioned as approximate blocks to reserve space. Floor slabs are flat, with no ramps, slab edges, or depressions shown. Stairs appear as uniform flights with default stringers; railings use a default profile with balusters placed approximately. A simple chimney opening is included where present. No decorative trims, surface sweeps, custom rail profiles, or in‑situ wall/ceiling carvings are modeled.

Architectural Model LoD 300

The model shall depict all major architectural components are modeled to their exact as‑built dimensions and precise locations for dependable coordination. Walls retain default profiles but now accommodate stack‑wall steps or size changes; inclined floor slabs, ramps, and intentionally sloped ceilings are included. Doors and windows remain default families yet are placed with correct frames, panes, louvers, and vision panels. Storefronts and curtain walls both display default mullion grids with true spacing. Floors show slab edges, ramps, and other intentional slopes; ceilings remain plain but accurate. Stairs include material‑specific stringers; railings have the correct type with balusters located exactly along the run. Fixed casework appears as specific generic blocks sized to fit measured conditions. Chimneys are modeled as massed shafts matching observed dimensions. No ornamental profiles, custom joinery, or surface articulations are represented at this stage.

Architectural Model LoD 350

The model shall depict high‑detail and interface elements needed for construction‑level coordination. This highest pre‑HBIM level adds refined assembly and finish information needed for construction‑level coordination. Walls carry full surface articulation: baseboards, crown / cove moldings, sweeps, stack‑wall offsets, and any carved or recessed features present in‑situ. Door and window assemblies include custom frame profiles, detailed hardware clearances, and specialty vision or louver components. Storefronts and curtain walls receive custom mullion profiles; curtain‑wall anchors or offsets that affect space are shown. Ceilings depict coffers, soffits, bulkheads, and detailed sweeps; roofs add parapets, fascia, gutters, and drain locations. Floors incorporate slab edges, recesses, ramps, and depressions. Stairs feature custom stringer and tread profiles; railings include custom baluster and rail shapes spaced exactly. Built‑in millwork and casework are modeled with custom profiles; chimney masses add visible detailing. All elements occupying physical space—or intersecting with structural and MEPF systems—are captured so that clash detection and fabrication planning can proceed with confidence. 




Structural Modeling Options

Structural Model LoD 200

The structural existing-conditions model will be delivered at LoD 200. The model will capture the building’s primary load‑bearing framework in outline form. Columns, beams, trusses, and major floor or roof slabs are shown at correct locations and approximate cross‑section sizes, allowing users to understand spans, bays, and general member hierarchy. Roof structural objects are represented as flat framing without intentional slopes. Braces, secondary framing, and any connection hardware are omitted. Member profiles may use standard shapes rather than custom as‑built sections, and foundations are indicated only by their basic footprint or pad. This schematic‑grade structural model supports conceptual studies, massing alignment, and early discipline coordination without implying fabrication‑level precision. LoD 200 provides a lower-detail structural model option focused on broad structural geometry, suitable when detailed connections or precise member dimensions are not needed in the deliverable.

Structural Model LoD 300

The structural existing-conditions model will be delivered at LoD 300. At this level, every principal structural member—columns, beams, joists, trusses, and floor/roof framing—appears at its measured size, shape, and elevation so that clearances and quantities can be taken directly from the model. Roof structure aligns with observed slopes, including rafters or joists that follow the roof pitch, but purlins, webs, and braces remain excluded. Members end cleanly at supports with no discrete plates, bolts, or weld objects. Foundations are depicted with accurate plan size and top‑of‑concrete elevations. The resulting model provides a trustworthy as‑built frame for clash detection with architectural or MEPF systems, while deferring the minutiae of connections and secondary bracing to later detail stages. The LoD 300 structural model alternate is effectively a precise as-built structural frame, enabling design and analysis integration while omitting the minutiae of connections which can be assumed or detailed separately if needed.

Structural Model LoD 350

The structural existing-conditions model will be delivered at LoD 350, incorporating a high level of detail including connection features. This highest structural level rebuilds the framing system with full secondary members and connection detail. In addition to the accurately sized columns, beams, joists, trusses, and sloped roof framing of LoD 300, the model now includes braces, purlins, webs, knee braces, and other secondary elements wherever they appear. Critical connections are explicitly shown—beam‑to‑column seats, clip angles, base plates, gusset plates, anchor bolts, bearing pads, shelf angles, and similar hardware—sized to reflect their field‑verified footprint. Where connections are concealed yet spatially significant (e.g., oversized end plates), they are modeled as simplified solids occupying true extents. Foundation details such as grade‑beams or pier caps are included when visible or documented. With both member geometry and connection footprints present, this LoD 350 structural model allows exhaustive clash checking, fabrication planning, and sequencing, serving as a construction‑ready reference for the existing structure, capturing how members join and interact.

MEPF Modeling Options

MEPF Model LoD 200

The MEPF (Mechanical, Electrical, Plumbing, and Fire Protection) model of existing conditions will be provided at LoD 200. The model will include the major distribution lines and system components in a diagrammatic and approximate manner. The model captures primary building‑services infrastructure in an intentionally schematic form. Main supply and return HVAC ducts are shown with generic cross‑sections and slopes, including any flex connectors larger than eight inches but omitting branch take‑offs or accessories. Plumbing, hydronic, and fire‑protection piping appear only where nominal diameters exceed two inches, and electrical conduits over three inches are routed as single lines or extrusions; smaller lines and secondary branches are not modeled. Cable trays are depicted as horizontal default trays without inclination, and major equipment—air‑handling units, chillers, boilers, main switchboards, generators, pumps—is represented by simple volumetric blocks in approximate locations. Default ceiling grilles, diffusers, exhaust fans, sprinkler heads, and wall devices (switches, receptacles, hydrants) are placed generically to flag service zones, but no valves, dampers, coils, hangers, or seismic supports are included. The result is a high‑level services map that conveys spatial reservation and system presence while minimizing modeling effort. It is intended for contexts where a basic record of existing building systems is needed without the expense of detailed modeling; it is not suitable for fine clash detection or precise quantity calculations, but provides a foundation that can be further detailed in future phases if required.

MEPF Model LoD 300

The MEPF (Mechanical, Electrical, Plumbing, and Fire Protection) model of existing conditions will be provided at LoD 300, providing a detailed and accurate representation of major building services. Building‑services geometry becomes dimensionally dependable for coordination. All principal and secondary distribution elements are modeled to their true diameters or cross‑sections down to 1½ inches for piping and conduit; branch routing reflects actual slopes where present. Ductwork carries generic accessories such as elbows, tees, dampers, and simple transition pieces, and flex‑duct connectors are included at main connections but not extended to every terminal. Cable trays follow their observed paths—including inclines or drops—and display correct widths and side‑rail depths, though splice plates and splice‑bolts are omitted. Mechanical equipment (air‑handling units, rooftop units, pumps, VAV boxes, etc.) is shown with accurate overall dimensions and inlet/outlet stubs. Electrical panels, transformers, and generators are modeled to correct footprint and height. Plumbing and fire‑protection systems include shut‑off valves, meters, and representative sprinkler risers; pipe and duct hangers or seismic braces are still excluded. This LoD 300 model supports reliable clash detection, space validation, and preliminary quantity take‑offs without the granularity of every support or specialty fitting. It delivers an accurate depiction of existing building systems suitable for most design and renovation planning activities, without going into the ultra-fine granularity of every support or minor fitting.

MEPF Model LoD 350

The MEPF (Mechanical, Electrical, Plumbing, and Fire Protection) model of existing conditions will be provided at LoD 350, which entails a fully detailed modeling of all significant building services for existing conditions. The services model is elevated to full coordination detail. Ducts and pipes of all sizes are modeled with their complete suite of fittings and specialties: reducers, flex connectors, dampers, strainers, coils, expansion joints, test ports, and cleanouts. Flex‑duct networks extend to every terminal, and pipe and duct hangers, trapezes, seismic braces, and cable‑tray supports are represented where they occupy space. Cable trays are custom‑profiled, with true side‑rail geometry, all inclination changes, horizontal bends, tees, and dropouts. Conduits are shown individually—including small diameter—and include junction boxes and stub‑ups at equipment or device terminations. Mechanical equipment is modeled with connection flanges, maintenance clearances, and curb or inertia‑block details; electrical gear shows conduit entries and working‑space envelopes. Plumbing and fire systems depict every valve, backflow preventer, drain, and sprinkler head at exact coordinates. With both geometry and support hardware present, the LoD 350 MEPF model delivers zero‑tolerance coordination and enables fabrication drawings, installation sequencing, and comprehensive interference checking across all trades. This is suited for projects requiring zero-tolerance coordination (e.g., complex retrofits or dense mechanical spaces), as it delivers the highest confidence that the model contains every crucial MEPF element present in the facility.


Landscape Modeling Options

Landscape Model LoD 200

The site/landscape model of existing conditions will be provided at LoD 200. The deliverable will illustrate the site’s general features and topography in a simplified form. The site model presents a basic topographic surface showing major grade changes—hills, slopes, and flat zones—generated with broad contours or a coarse mesh suitable for orientation and massing studies. Default‑family site components are placed where observed: simple fence or railing runs, and bollards marking entries or walk zones. Building footprints, property boundaries, roads, driveways, primary sidewalks, and large paved plazas are outlined to scale but without curb profiles, drainage features, or surface patterns. No custom site furniture, light poles, signage, or minor landscape elements are included. This schematic landscape model offers a contextual snapshot that supports conceptual planning without prescribing precise earthwork or utility tie‑ins. The LoD 200 landscape model thus provides a contextual site overview that is useful for conceptual planning or orientation, ensuring the project team understands the setting of the building. It is not intended for tasks requiring precision (like tying into existing utilities or grading), as the emphasis is on overall form rather than accuracy of each site component.

Landscape Model LoD 300

The site/landscape model of existing conditions will be provided at LoD 300, offering a detailed and accurate depiction of the existing site conditions. The model refines terrain to basic topography enhanced with ground‑surface patterns and principal grade breaks—capturing berms, swales, and edge slopes that influence drainage or site access. Curbs and gutter lines are modeled where they bound roadways and parking areas; retaining walls and exterior steps are extruded at true height and length. Custom site components are added for all fences/railings, light poles, bollards, road‑way signage, and parking elements (stalls, wheel stops, accessible‑space markings) using measured footprints and heights. Walkways, plazas, and ramps display their actual extents and surface elevations, but small furnishings, textured finishes, and landscape planting beds remain generalized. The LoD 300 landscape model integrates spatially with the building model for grade coordination and layout validation while stopping short of full finish detail. ​​The focus is on all functional and spatial elements needed for design coordination, providing a reliable existing site model for architectural and engineering reference.

Landscape Model LoD 350

The site/landscape model of existing conditions will be provided at LoD 350, meaning an extremely detailed and precise capture of existing site conditions. The model depicts detailed topography built from dense points or break‑lines, reproducing minor undulations, swales, and finished grading critical to drainage design. All civil and landscape features are modeled with full geometric fidelity: curbs carry true cross‑sections (including curb‑and‑gutter pans), pavements are segmented by material or joint pattern, and retaining walls show thicknesses, step‑backs, and attached guardrails or handrails. Stormwater components—catch‑basin grates, culverts, open channels—are located with rim and invert elevations when available. Every site furnishing and fixture is represented individually: benches, trash receptacles, bike racks, signage posts, bollards, tree grates, planter boxes, and parking‑lot equipment appear at accurate size and position. Rooftop equipment visible from grade (e.g., rooftop condensers) is modeled volumetrically for view‑shed and crane‑planning assessments. The LoD 350 landscape model serves projects requiring exhaustive pre‑construction coordination—historic sites, dense urban parcels, or infrastructure‑heavy campuses—by virtually reconstructing every material surface and fixed exterior element present. The LoD 350 landscape model alternate is intended for projects where site complexity or sensitivity is high (for example, historical landscapes, tight urban sites, or infrastructure-heavy campuses), providing the utmost confidence that the existing outdoor conditions are fully documented in 3D form.

V Owen Bush