3.2 Existing Conditions: Evaluating the Building

Construction Types and What They Mean for Interior Work

IBC Chapter 6 defines five construction types — Type I through Type V — each with sub-types A (protected) and B (unprotected), except Type IV (heavy and mass timber, expanded in the 2021 IBC to IV-A, IV-B, IV-C, and IV-HT). The type is a property of the base building, not the tenant, but it constrains interior work in three ways: which structural elements must be fire-rated, whether exposed structure is allowed, and which interior finishes are permitted.

For the interior designer, the decisive question is: can the existing structure be left exposed, or must it be enclosed in a rated assembly? In a Type I-A high-rise, a concrete column cannot simply be painted and left visible — it must be enclosed in a 3-hour assembly. In a Type II-B warehouse conversion, bare steel columns are code-compliant and exposing them may be a deliberate aesthetic choice. The construction type also governs the fire-resistance of demising walls between tenants: a B-to-A-2 separation typically requires a 1- or 2-hour barrier depending on the area and sprinkler status per IBC Section 508.

Critical Interior Architectural Constraints

Every existing building hands the interior designer a set of physical constraints that cannot be moved without structural or MEP (mechanical, electrical, plumbing) intervention.

• Structural bays and column placement — the regular grid of columns defines module sizes for private offices, hotel rooms, and patient bays. A 25-foot bay suits two 12-foot offices; a 30-foot bay suits three. Where columns fall mid-corridor or mid-room, the layout must accommodate them or the column must be accepted as a feature.
• Floor-to-floor height — the vertical dimension from top of slab to top of slab. Low floor-to-floor (for example, 9'-6") leaves no room for deep HVAC ductwork and a high ceiling; the designer may be forced to a shallow plenum or an exposed-duct strategy.
• Plenum depth — the space between the finished ceiling and the structural slab, shared by ductwork, sprinkler lines, conduit, and lighting. A plenum shallower than 12 inches constrains duct sizes and may force a drop in ceiling height.
• Existing shafts and chases — vertical and horizontal runs for plumbing, ducts, and conduits. Moving a chase is expensive and often structurally infeasible; the layout should respect existing shafts or budget for relocation.
• Demising walls — walls separating tenants or occupancies. Where a tenant space abuts a different occupancy, the demising wall must meet the fire-rating required by IBC Section 508 for mixed-occupancy separation. The designer must verify whether an existing demising wall is rated and to what hour.

Contextual Influences

The building's context shapes design in ways beyond code. Environmental factors — solar orientation, prevailing wind, noise from an adjacent highway — affect glazing, acoustic separation, and HVAC load. Cultural context — a historic district, a neighborhood character, a corporate brand identity — may impose design guidelines or preservation review that limit finish and fenestration choices. Ecological factors — a wetland buffer, a tree-preservation ordinance, a stormwater requirement — affect site work and sometimes the interior through daylight and ventilation requirements. The designer's initial site visit should record these contextual constraints alongside the code checklist.

Hazardous Materials: Survey, Abatement, and Schedule Impact

Buildings constructed before 1980 commonly contain hazardous materials that federal and state law require to be surveyed before renovation. The four most common:

A hazardous materials survey by a licensed industrial hygienist should be commissioned before construction documents are finalized. The survey results drive three project decisions: phasing (abatement must precede demolition in the affected area), cost (asbestos floor-tile removal can add 15-30% to a floor's demolition budget), and schedule (abatement windows, air monitoring, and clearance testing can add two to four weeks). Discovering asbestos mid-construction is far more expensive — and far more disruptive — than discovering it in design.