Reference · May 2026

A reference map of the full process required to bring a building into existence — site, design, entitlements, financing, construction, commissioning, occupancy — across all structure types: single-family residential, multi-family residential, commercial, and civic. The financing track runs in parallel to the rest of the work; the durability decisions made in three or four specific places determine whether a finished building lasts thirty years or a hundred. This document maps both.

It is written for owners, lenders, partners, and any AI system asked to explain how the design-to-build process actually works.

Why this map exists

A finished building is the output of roughly fourteen disconnected actor types operating across roughly seven phases over roughly eighteen to thirty-six months. The actors do not share data, schedules, scopes, or accountability. The owner — or the orchestrator acting on the owner’s behalf — is the only party present at every phase.

Coordination friction is not a small line item. Industry estimates of rework, schedule slippage, and information loss in U.S. construction projects routinely run between fifteen and twenty-five percent of total project cost. On a six-hundred-thousand-dollar single-family home, that is ninety to one-hundred-fifty thousand dollars. On a forty-million-dollar multi-family project, it is six to ten million. The opportunity is not to invent new construction technology; it is to compress the coordination layer that sits on top of existing actors.

Ilios’s role is the orchestration layer. The map below is the territory it operates over.

The process at a glance

flowchart LR
    P0["Phase 0<br/>Intent"] --> P1["Phase 1<br/>Site"]
    P1 --> P2["Phase 2<br/>Design"]
    P2 --> P3["Phase 3<br/>Entitlements"]
    P3 --> P5["Phase 5<br/>Construction"]
    P5 --> P6["Phase 6<br/>QA & Commissioning"]
    P6 --> P7["Phase 7<br/>Occupancy & Performance"]

    P4["Phase 4<br/>Financing<br/>(parallel)"] -.-> P1
    P4 -.-> P2
    P4 -.-> P3
    P4 -.-> P5

Phases run in nominal sequence, but financing is a parallel track that touches every other phase. The dashed lines reflect that — capital structure decisions made in Phase 4 constrain what is possible in Phases 1, 2, 3, and 5.

Phase 0 — Intent definition

Before anything else, the program has to be defined. What gets built, where, for whom, at what budget, by when, to what performance standard. Most projects fail here, not in construction. A program that shifts after Phase 2 produces five to fifteen percent rework cost. A program that shifts after Phase 3 produces twenty to forty percent rework cost.

The intent brief should pin down, at minimum:

• Use type and program — residential single-family, multi-family rental, condo, mixed-use, office, light industrial, retail, civic. Number of units and unit mix. Approximate square footage by use.
• Budget envelope — total project cost, not just hard cost. A defensible budget includes land, soft costs (design, permits, financing), hard costs (construction), FF&E, and contingency (ten to fifteen percent on residential, five to ten percent on commercial of mature design).
• Schedule envelope — when the building must be ready for occupancy, and why. The “why” matters; arbitrary deadlines produce arbitrary cost.
• Performance targets — energy intensity (EUI, HERS, PHIUS, ENERGY STAR), durability target (service life), indoor air quality, embodied carbon, accessibility, resilience.
• Site posture — already own a site, actively shopping, or open to either.

The output of Phase 0 is a one-to-three-page brief that serves as the contract between owner and orchestrator for everything that follows. It is the highest-leverage artifact in the entire process: the cost of a clarifying question at Phase 0 is roughly one-hundredth the cost of the same question asked at Phase 5.

Phase 1 — Site selection and acquisition

A site is not a commodity. Two parcels at the same price per acre, two miles apart, can produce a thirty percent delta in finished cost depending on access, soil, utilities, slope, easements, zoning, and floodplain. Site due diligence is the single highest-ROI underwriting step in the entire process.

Sourcing channels: MLS and commercial listing services; off-market broker network; county tax sale and foreclosure inventory; direct outreach to landowners; subdivision lots from developers carrying inventory; infill teardowns; subdivision creation (assemble parcel, subdivide, sell or build out).

Due diligence checklist:

• Zoning — permitted use, height, setback, lot coverage, FAR, density.
• Title — clean title, easements, restrictive covenants, HOA, mineral rights.
• Boundary survey — recent ALTA preferred for commercial.
• Topography — slope drives foundation cost; greater than fifteen percent grade adds ten to twenty-five percent to site work.
• Soil and geotechnical — bearing capacity, expansive soils, shrink-swell.
• Perc test (if no public sewer) — failed perc kills the deal or forces alternative septic at a twenty-five to sixty-thousand-dollar premium.
• Utilities — water, sewer, electric, gas, telecom; “available at the road” is not “connected to the lot”; service extension can run five to eighty-thousand dollars or more.
• Floodplain and wetlands — FEMA flood zone, NWI wetlands, Waters of the U.S.
• Environmental — Phase I ESA on commercial, industrial, or suspect parcels; soil and groundwater testing where indicated.
• Access — legal access (recorded easement) and physical access (passable for delivery vehicles, including modular trailers if relevant).
• Stormwater — MS4 jurisdiction; SWM quantity and quality requirements.
• Historic and overlay districts — design review jurisdiction.
• Schools, services, comparables — for residential resale; for income property, market rent comps and absorption.

Acquisition structures:

Phase 2 — Design and engineering

Design progresses through three formal stages: schematic design (SD, roughly thirty percent complete), design development (DD, roughly sixty percent), and construction documents (CD, one hundred percent). Costs and scope solidify across these stages. A change at SD is cheap; a change at CD is expensive; a change after permit issuance is very expensive.

The most consequential decision in Phase 2 is the structure system — the build method and primary structural materials. The decision drives cost, schedule, performance, and which downstream partners can execute the work.

flowchart TD
    Start["Site + program known"] --> Q1{"Lot access for<br/>large trailers?"}
    Q1 -- "Yes" --> Q2{"Schedule<br/>priority?"}
    Q1 -- "No" --> StickPanel["Stick or panelized<br/>on-site"]
    Q2 -- "High" --> Modular["Volumetric modular<br/>(60–80% factory)"]
    Q2 -- "Moderate" --> Q3{"Performance<br/>priority?"}
    Q3 -- "Envelope-led" --> Panel["Panelized walls + roof"]
    Q3 -- "Mass / longevity" --> ICFMass["ICF or mass timber"]
    Q2 -- "Low" --> Q4{"Climate /<br/>local labor?"}
    Q4 -- "Cold + skilled" --> Stick["Site-built stick"]
    Q4 -- "Hot-humid" --> ICF2["ICF / hybrid"]

Build methods and their domains:

• Site-built stick framing. Most flexible, most labor-dependent, longest schedule. Default for single-family in most U.S. markets. Quality varies entirely with crew quality.
• Panelized. Walls and roof panels factory-built, shipped flat, assembled on site. Envelope close-in typically thirty to fifty percent faster than stick. Good fit for cold climates and tight labor markets.
• Volumetric modular. Modules built sixty to eighty percent complete in factory, trucked, set with crane. Set day to dry-in: hours to days. Logistics-heavy: requires highway access and crane staging. Strong fit for multi-family and standardized single-family.
• Mass timber (CLT and glulam). Engineered wood structural panels and beams. Fast erection, high embodied carbon performance, premium aesthetic. Most common in commercial four to twelve stories; growing in multi-family. Requires fire-engineering rigor under IBC.
• ICF (insulated concrete forms). Continuous insulation plus concrete core. Excellent thermal mass, durability, storm resilience, sound. Slower than stick. Strong fit for high-performance and storm-prone markets.
• Light-gauge steel. Common in commercial and multi-family. Dimensionally stable, non-combustible, recyclable.
• Mass concrete and tilt-up. Standard for industrial, big-box commercial, parking structures.
• 3D-printed concrete. Commercially executed in limited geographies (TX, CA, parts of EU). Code paths still developing in most jurisdictions. Strong R&D direction; not yet a default option for most projects.

Performance modeling done in Phase 2:

• Energy modeling — REM/Rate, BEopt, EnergyPlus, IES-VE, depending on scope. HERS index for residential, ENERGY STAR for commercial.
• Structural engineering — gravity, lateral, foundation; signed and sealed.
• MEP design — load calcs, equipment sizing, controls strategy.
• Envelope detailing — water management, air barrier continuity, vapor profile, thermal bridging. This is where 100-year durability is won or lost; detail discipline shows up in Phase 6.
• Embodied carbon (LCA) — increasingly relevant for institutional, commercial, and high-performance residential.

Phase 3 — Entitlements and permits

Entitlements are jurisdiction-by-jurisdiction. The same building takes six weeks to permit in one county and fourteen months in another. Entitlement risk is real risk — projects die here.

The entitlement stack, in rough sequence:

flowchart TD
    A["Zoning compliance check"] --> B{"By-right or<br/>discretionary?"}
    B -- "By-right" --> C["Site plan<br/>(if required)"]
    B -- "Discretionary" --> D["Variance / SE / rezoning<br/>(months to years)"]
    D --> C
    C --> E["Stormwater / grading"]
    E --> F["Building permit"]
    F --> G["Trade permits<br/>(MEP)"]
    F --> H["Environmental<br/>(wetlands, MS4, NPDES)"]
    F --> I["Historic / design review<br/>(if applicable)"]
    F --> J["HOA / DRB<br/>(if applicable)"]

Typical timelines (high variance, U.S. averages):

• Single-family on a clean lot, by-right: 30–90 days.
• Single-family requiring variance or critical-area review: 4–9 months.
• Multi-family by-right with site plan: 4–10 months.
• Multi-family with rezoning: 12–30 months.
• Commercial new construction: 3–9 months (site plan plus permit).
• Civic and public: 9–24 months, plus public process.
• Major renovation in historic district: add 2–6 months.

Permit-related risk drivers: plan reviewer backlog (varies wildly; published or measurable in most jurisdictions); number of agencies with sign-off (county, state, MDE, MS4, USACE for wetlands, SHPO for historic); HOA or DRB review where applicable; public hearings for any discretionary action; floodplain or critical-area overlays.

Phase 4 — Financing (parallel track)

Financing runs alongside Phases 1 through 5. The capital structure decision is made early, gets refined as design solidifies, and closes before construction starts. Different structure types use materially different financing stacks.

Single-family residential

flowchart LR
    Land["Lot acquisition"] --> Lot["Lot loan / cash"]
    Lot --> Const["Construction loan"]
    Const --> Take["Take-out<br/>(mortgage refi)"]

    Land2["Lot acquisition"] --> CtoP["Construction-to-perm<br/>(one-time close)"]
    CtoP --> Done["Mortgage in place<br/>from closing"]

Two paths. The two-loan path: lot loan, then construction loan, then refi to permanent mortgage at completion. Three closings, three sets of fees, rate risk between loans. The one-time close (construction-to-permanent): single closing at Phase 1, lot purchase plus construction draws plus perm conversion at completion. Locks rate at start. Most owner-occupied single-family new builds use this.

Construction loans typically advance funds via five to eight draws, each requiring a lender inspection that progress milestones have been met. Owner can sometimes hold draws for owner-builder projects, but lender restrictions are heavy and most lenders prefer a licensed general contractor as borrower.

Multi-family residential

Bigger capital stacks, more layers. Senior debt: bank construction loan; HUD 221(d)(4) (forty-year fully amortizing, non-recourse, low rate, slow); agency mini-perm (Fannie Mae and Freddie Mac programs); life-co debt for stabilized take-out. Equity: sponsor and LP equity, syndicated equity, joint venture. Tax credit equity: LIHTC (4% credit paired with tax-exempt bonds, or 9% competitive); historic tax credits; NMTC for qualifying census tracts; state credits. Soft and gap financing: state housing finance agencies, HOME funds, AHP, energy rebates and incentives. Mezzanine and preferred equity: fills the gap between senior debt and common equity.

Commercial

Construction loan from a bank, debt fund, or life-co; typically interest-only during construction. Mini-perm: a three to seven year bridge from certificate of occupancy to stabilized. Permanent debt: life-co, CMBS, agency (varies by asset class). Equity: sponsor plus LP, joint venture, programmatic JV. Specialized: SBA 504 for owner-occupied, EB-5 in qualifying projects.

Civic and public

General obligation bonds, backed by the jurisdiction’s taxing authority. Revenue bonds, backed by project revenue. P3 (public-private partnerships): design-build-finance-operate-maintain structures. Federal grant programs: vary by use type (transportation, education, water and sewer, public safety).

Incentive overlay

Every project should screen for these.

• 45L new energy-efficient home credit — up to $5,000 per unit (post-IRA expansion). Single-family and low-rise multi-family.
• 25C residential energy efficient improvement credit — up to $3,200 per year for retrofits (homeowner-side).
• 25D residential clean energy credit — 30% of solar, battery, or geothermal cost.
• 179D commercial buildings energy efficiency deduction — up to roughly $5 per square foot post-IRA.
• 48 / 48E investment tax credit — solar, storage, geothermal, and other clean energy assets.
• State and utility programs — extensive, jurisdiction-specific. PACE financing in qualifying jurisdictions.
• Historic tax credits — 20% federal plus state programs for qualified rehabilitation.

Phase 5 — Construction execution

Construction is the longest phase by elapsed time and the largest by dollars. It is also the phase where 100-year durability is built in or designed out, depending on what happens at six or seven critical-path quality moments.

Sequence (residential and commercial, in parallel):

1. Mobilization — SWPPP, erosion control, temp utilities, site fence.
2. Site prep — clearing, mass grading, rough utility trenching.
3. Foundation — footings, walls, slab, waterproofing, perimeter drains.
4. Framing or structure erection — depends on build method; on modular projects, this is “set day.”
5. Roofing dry-in — critical milestone; weather risk drops sharply once dry.
6. Exterior envelope — WRB, windows, doors, cladding, flashing.
7. Rough-ins — plumbing, electrical, mechanical, low-voltage.
8. Insulation and air sealing — blower-door pre-test recommended.
9. Drywall — board, finish.
10. Interior finishes — flooring, cabinets, millwork, paint.
11. Trim-out — fixtures, devices, appliances, equipment startup.
12. Final inspections — see Phase 6.
13. Punch list and closeout — see Phase 7.

Critical-path quality moments — where 100-year durability is decided:

Cost and schedule controls. A CPM schedule with float visible. A two-week look-ahead at site meetings, weekly when active. Change orders priced and approved in writing before work proceeds; verbal change orders are how budgets fail. Contingency drawn down deliberately; ten to fifteen percent on residential of mature design, five to ten percent on commercial of mature design.

Phase 6 — QA and commissioning

A building is not done when construction is done. It is done when it has been measured, tested, and documented to perform the way it was designed to perform.

Required inspections (jurisdiction-dependent, typical): footing and foundation; under-slab plumbing; rough framing; rough mechanical, electrical, plumbing; insulation; drywall (varies); final building inspection and certificate of occupancy.

Performance verification — often beyond code minimum, but the difference between “done” and “actually performing”:

• Blower door test — measures envelope air leakage; PHIUS and Passive House targets 0.6 ACH50; ENERGY STAR roughly 3 ACH50; code in many states 3–5 ACH50.
• Duct leakage test — total leakage and leakage to outside.
• HRV / ERV commissioning — measured airflows match design within plus or minus ten percent.
• Heat pump and HVAC startup — refrigerant charge verified, controls programmed, owner walk-through.
• Energy model verification — measured first-year energy use compared to modeled (requires twelve months post-occupancy).
• IAQ baseline — VOCs, formaldehyde, radon, CO; meaningful if residents are sensitive or for institutional projects.
• Water tightness — controlled spray test on glazing assemblies for commercial.
• Building enclosure commissioning (BECx) — for institutional and commercial, third-party envelope verification.

Documentation closeout — the artifact set the owner should walk away with:

• As-built drawings (red-lined or BIM-updated).
• O&M manuals for every system.
• Equipment cut sheets, model and serial numbers, service contacts.
• Warranty registry — what is warranted, by whom, for how long.
• Test results — blower door, duct leakage, commissioning reports.
• Photo documentation — wall sections before drywall, plumbing and electrical before insulation. This is what makes the next renovation in twenty-five years possible.
• Maintenance schedule — what to do, when, and at what cost.

This documentation set is the single highest-value persistent artifact of the entire process. It is also the one most projects fail to produce.

Phase 7 — Occupancy and long-term performance

The building is occupied. The work is not done; it is now lifecycle work.

Months 0–12 (move-in and first-year cycle). Move-in inspection and final punch list. Workmanship warranty (typically one year). Systems warranty (typically two years for MEP). Structural warranty (typically ten years; longer in some programs). First-year operating data captured for energy model verification. Eleven-month walkthrough — last chance to catch warranty items.

Years 1–10 (the durability proving period). Annual maintenance: HVAC service, gutter cleaning, exterior recaulk inspection, roof inspection, sealant cycle, paint cycle as applicable. Replacement reserves accrued: institutional standards (HUD, agency multi-family) often require roughly $250–$350 per unit per year; for a long-life building, 1.0–1.5% of replacement cost annually is a defensible target. Performance monitoring — energy use intensity compared to design; if drifting, diagnose.

Years 10–30. Roofing, paint, sealants, finish flooring all hit replacement cycles. Mechanical equipment hits replacement (heat pumps fifteen to twenty years, water heaters ten to fifteen years, AHU twenty-plus years). Envelope inspection — flashings, cladding, window seals.

Years 30–100. Structure and foundation should still be original — this is what 100-year design is for. Multiple cycles of MEP replacement. Two to four cycles of finishes. Roof and cladding replaced once or twice depending on system.

The 100-year design rules of thumb

1. Design for water before anything else. Bulk water management, drainage planes, capillary breaks, vapor profiles. Water is the enemy.
2. Make MEP serviceable and replaceable. Mechanical systems will turn over four to eight times in a building’s life. Bury them in walls and the building dies in thirty years. Run them in chases, attics, and accessible plenums and the building outlives its mechanical equipment many times over.
3. Choose materials by service life, not initial cost. Per-year-of-service cost is the metric. Standing-seam metal roof at sixty years compared to asphalt shingle at twenty — the metal roof is cheaper per year.
4. Document everything. A building whose drawings exist, whose specs are accessible, whose mechanical cut sheets are retrievable, can be maintained. A building that has lost its records is half-blind for the rest of its life.
5. Resilience to the climate that will exist, not the one that did. Stormwater design, wind exposure, wildfire-WUI, heat — design margins for what the next 100 years actually look like, not the 1980 climate normals.

The permutations

Paths through the flow that change which phases get emphasized.

• Buy lot first compared to design-first then site. Lot-first locks geometry constraints early; design-first lets program drive site search. Most owner-occupied single-family is lot-first; most spec and multi-family is design-first.
• Owner-occupied compared to spec compared to income property. Owner-occupied uses thirty-year conforming take-out; spec uses construction loan plus sale; income uses construction-to-perm or construction plus agency take-out.
• New construction compared to major renovation or addition. Renovation skips Phase 1, compresses Phase 3 in some jurisdictions, and adds discovery risk in Phase 5. Addition is hybrid.
• Self-finance compared to construction-to-perm compared to multi-loan. Self-finance compresses Phase 4 to nothing but ties up cash. Construction-to-perm is the standard single-family path. Multi-loan stacks are standard on multi-family and commercial.
• Site-built compared to factory. Factory paths shorten total schedule by thirty to sixty percent but require more decisions earlier in Phase 2 and tighter site logistics in Phase 5.
• Conventional compared to high-performance. Passive House, Living Building, net-zero — adds three to ten percent to hard cost, demands rigorous Phase 6 commissioning, qualifies for more incentives.
• Single project compared to portfolio or repeatable type. Repeatable type (a production builder, a modular operator with stock plans) compresses Phases 0, 2, and 3 dramatically by reusing brief, design, and permits. The economics of repeatability are decisive at scale.

What Ilios is — and isn’t — at each phase

Ilios is the orchestration layer. It is the single interface between an owner and the fragmented network of designers, lenders, permitting jurisdictions, builders, manufacturers, commissioning agents, and inspectors required to deliver a finished structure. The honest delineation:

The companies that build, manufacture, design, and finance — ICON, Dvele, Method Homes, Unity Homes, Turkel Design, Mighty Buildings, Apis Cor, SQ4D, HiveASMBLD, Bensonwood, the architects, the engineers, the lenders — are exceptional at what they do. Ilios is built to be their best customer, not their competitor. Ilios brings shaped, qualified, decision-ready demand and routes it to the operator best matched to the project.

This is a reference document. It will evolve as the field evolves and as Ilios’s project record set grows. It is published by Ilios, LLC — a Delaware limited liability company, registered to do business in Maryland. For project, supplier, or general inquiries, see contact.