Architecture and Engineering Firm Entity Structure: The Professional Entity, the S Election, and the QBI Deduction the Profession Kept

Design firms decide their entity with the state board's ownership rule, a decade of liability, and a deduction the statute let them keep. The ownership rule: state architecture and engineering practice acts govern who may own a design firm — some states require a majority (or all) of the owners to be licensed in the profession and require the firm to hold a certificate of authorization; some permit non-licensee ownership with a licensed responsible charge; a few restrict the entity type to a professional corporation or PLLC — and a firm practicing in several states (design firms are multistate by nature — a project's state licenses the firm and its principals) meets each state's rule for its firm registration (the consulting multistate guide's framework, with the firm-registration layer on top); the entity is chosen within those rules, and its ownership changes (a new principal, a retiring one) are registration events in every state where the firm holds a certificate. The liability floor: professional liability follows a building — a design defect claim arises when the defect manifests, which may be years after completion (the statutes of repose set the outer limit — six to twelve years by state), so a firm's exposure at any moment is every building it designed in the past decade; the professional entity separates the firm's liabilities (and a partner's design error) from the principals' personal assets — the responsible professional remains liable for their own sealed work — with the errors-and-omissions policy (claims-made — the architecture deductions guide) and its tail, general liability, cyber, and the umbrella as the first line, and the contract's limitation-of-liability clause as the second. The tax structures (the LLC cost guide): a sole practitioner's PLLC or professional corporation disregarded (Schedule C) or with the S election; a multi-principal firm as an S corporation (the common form — salaries by role and production, distributions by ownership) or a partnership-taxed PLLC (guaranteed payments and flexible allocations — the law firm entity guide's compensation mechanics); and the C corporation — historically common in design firms (the professional corporation's origins) and still used by some for the retained earnings that fund an ownership transition (below), with the double tax on distributions as the cost. The payroll exists: a design firm beyond the sole practitioner has designers, drafters, and staff on payroll — the S election's incremental cost is the 1120-S and basis tracking; the sole practitioner creates the payroll for one. The reasonable salary for a principal: an employed senior architect's or engineer's compensation (the profession's compensation surveys are detailed by role, firm size, and region — a project manager, a senior project architect, a principal-level employee at a larger firm; US$110,000 to US$200,000 for a principal-level employee in most markets) plus the owner's business development and management component; documented against the surveys and revisited. The saving: payroll tax avoided on the distribution portion — a principal netting US$360,000 with a US$170,000 salary saves the 2.9 percent Medicare tax on the distribution plus the Social Security tax on the slice of the wage base the salary leaves unused (about US$6,500); a sole practitioner netting US$140,000 with a US$105,000 salary saves payroll tax on US$35,000 (about US$3,700 — against a new payroll for one). The QBI deduction — the profession kept it, and the entity must count it: architecture and engineering are excluded from the specified service trades by name (the statute's exception — the SSTB guide), so the 20 percent deduction applies at every income level, subject above the threshold to the wage-and-property limitation (50 percent of W-2 wages, or 25 percent of wages plus 2.5 percent of qualified property) — which changes the S election's arithmetic in two ways the health and law professions don't face: the salary's exclusion from qualified business income is a real cost (a US$170,000 salary removes US$34,000 of deduction at the 20 percent rate — worth US$12,000 at a 35 percent bracket, more than the payroll-tax saving), and above the threshold the firm's W-2 wages (the staff's and the principals') are what support the deduction at all — a sole practitioner above the threshold with no payroll has a limitation near zero and needs the S election's salary as wages (the coaching entity guide's mechanics), while a firm with a US$1.7 million payroll has a limitation that covers any principal's deduction; the worksheet therefore runs the payroll-tax saving against the QBI cost of the salary, with the limitation computed under each structure — and for a multi-principal firm with staff, the S election wins only where the payroll-tax saving outruns the salary's QBI cost — often not for principals in the top brackets, which is why the partnership-taxed PLLC gets the same worksheet — and where the election is made, the salary sits at the bottom of the defensible range (the QBI cost pulls it down; the reasonable-compensation requirement holds the floor). The 179D deduction and the entity: the section 179D deduction allocated to a designer (the deductions guide) passes through to the owners under any pass-through structure — a large allocation year is a low-tax year, and the estimated-tax recompute and the salary decision both see it. The ownership transition — the design profession's succession problem: design firms are sold internally more than externally — a founder transfers ownership to younger principals over a decade, typically by selling shares at a formula value (book value plus a multiple of revenue, or an appraisal) financed by the buyers' bonuses and the firm's distributions — and the entity shapes the mechanics: in an S corporation, the founder's sale of stock is capital gain (single-taxed; the buyers get no step-up in the firm's assets, which matters little for a service firm whose assets are people), the firm's distributions to the buyers fund the payments (taxed to the buyers as pass-through income first), and the single-class-of-stock rule means the buyers' shares carry the same economics as the founder's; in a partnership, the transition runs through the partnership agreement's capital account and profits-interest provisions (a younger principal can receive a profits interest — a share of future profits with no capital account — as compensation that isn't taxed at grant, the mechanism partnerships have and corporations lack); in a C corporation, the firm's retained earnings can redeem the founder's shares (a redemption taxed as capital gain to the founder if it qualifies) — the historical reason design firms stayed C corporations, with the double tax on the earnings that funded the redemption as the price; an ESOP (employee stock ownership plan) is the alternative for a larger firm (the founder's sale to the ESOP with the gain deferred under section 1042 if the firm is a C corporation, or the ESOP-owned S corporation's exemption from income tax on its share — a structure with its own costs and a fiduciary layer). The models. The sole practitioner: the PLLC on Schedule C below about US$120,000 of net (a new payroll for one, the QBI cost of a salary, a full QBI deduction below the threshold); the S election above it — and necessary above the threshold for the wage limitation. The two-principal firm with staff: the S corporation with salaries from the surveys at the bottom of the defensible range, distributions by ownership, the staff's wages supporting the QBI limitation, and a buy-sell agreement (the chiropractic entity guide) funded by insurance; or the partnership for unequal principals who want profits interests for the next generation. The firm planning a transition: the entity chosen for the mechanics — the S corporation's stock sales financed by distributions, the partnership's profits interests, or the C corporation's or ESOP's redemption structure — with the state boards' ownership rules checked at every step (a new owner must be licensed where the state requires it, and the certificate of authorization updated). The annual re-run: profit, the payroll, the principals' salaries against the surveys and the QBI cost, the limitation, the 179D allocations expected, the transition plan's next step, and the multistate registrations — revisited each January.

Key takeaways

• The state practice acts govern ownership — licensed majorities, certificates of authorization, entity types — in every state where the firm is registered; ownership changes are registration events.
• Professional liability follows a building for a decade (the statutes of repose) — the professional entity, the E&O policy with its tail, and the contract's limitation clause are the three layers.
• Architecture and engineering kept the QBI deduction, so the S election's salary has a real QBI cost (worth more than the payroll-tax saving at a principal's bracket) — set the salary at the bottom of the defensible survey range, and above the threshold count the firm's W-2 wages as the limitation's support.
• The payroll exists for any firm beyond a sole practitioner; the sole practitioner above the threshold needs the S election's salary as wages.
• The ownership transition shapes the entity: S corporation stock sales financed by distributions, partnership profits interests for the next generation, or a C corporation's or ESOP's redemption — each with the boards' ownership rules checked.
• A 179D allocation year (for projects begun by June 30, 2026) is a low-tax year under any pass-through — seen by the salary decision and the estimates.

The design firm's entity worksheet

State ownership rules and certificates of authorization (every registered state). Coverage (E&O by project type with tail planning, GL, cyber, umbrella); contract limitation clauses. Payroll in place (or created for one). Principals' salaries from the compensation surveys — bottom of the defensible range. Distribution portion; payroll tax saved (Medicare, and Social Security up to the wage base). QBI: deduction under each structure; salary's exclusion cost; W-2 wage limitation above the threshold. 179D allocations expected. Transition plan: mechanic (stock sales / profits interests / redemption / ESOP); buy-sell funding. Multistate registrations. Net result. Fifteen minutes each January, with the surveys and the boards' rules open.

Worked example

Three firms. One: a sole practitioner architect netting US$310,000 with no staff, single, taxable income above the top of the QBI phase-in range — on Schedule C her QBI deduction would be limited to near zero (no W-2 wages; US$40,000 of equipment supports US$1,000); the S election with a US$115,000 salary (a senior project architect's survey compensation plus management) creates the W-2 wages that support a full deduction on the remaining qualified income (about US$37,000), on top of about US$13,600 of payroll-tax saving on the US$195,000 distribution — she elects, and the new payroll for one is the price. Two: a two-principal engineering firm with twelve staff netting US$720,000 — an S corporation: salaries of US$180,000 each (a principal-level survey figure set low in the defensible range — the QBI cost pulls them down; the reasonable-compensation floor holds), US$360,000 of distributions (the worksheet shows each principal's payroll-tax saving, about US$5,000, running below the salary's QBI cost; the firm keeps the election for its corporate certificates of authorization and its buy-sell structure and reruns the comparison each year), the staff's US$1.3 million payroll supporting the QBI limitation many times over, a buy-sell agreement funded by insurance, certificates of authorization in five states, and a US$280,000 179D allocation on a municipal project (construction begun before the June 30, 2026 construction-start cutoff) making this a low-tax year the estimates recomputed for in October. Three: a founder, 63, transitioning a 22-person architecture firm to three younger principals over eight years — the firm's C corporation converted to an S corporation five years ago (the five-year built-in gains recognition period now past), the founder's shares sold in annual tranches at a formula value financed by the buyers' bonuses and the firm's distributions (capital gain to the founder; the buyers licensed in every state where the board requires it; the certificates updated each tranche), and the partnership alternative — profits interests for the three — modeled and rejected because the firm's lenders and the state boards preferred the corporate form. Three firms, one profession, and the QBI deduction the statute let them keep decided the first one's entity while the transition decided the third's.

Official sources

The IRS states: “S corporations are corporations that elect to pass corporate income, losses, deductions, and credits through to their shareholders for federal tax purposes. Shareholders of S corporations report the flow-through of income and losses on their personal tax returns and are assessed tax at their individual income tax rates.” — Internal Revenue Service, S corporations, https://www.irs.gov/businesses/small-businesses-self-employed/s-corporations

The IRS states: “This component of the deduction equals 20 percent of QBI from a domestic business operated as a sole proprietorship or through a partnership, S corporation, trust, or estate.” — Internal Revenue Service, Qualified business income deduction, https://www.irs.gov/newsroom/qualified-business-income-deduction

Practitioner note

A design firm's entity decision has an item the health and law professions never see: the QBI deduction survives, so the S election's salary has a real cost — a US$170,000 salary removes US$34,000 of deduction, worth more at a principal's bracket than the payroll-tax saving — which is why our design firm worksheets set salaries at the bottom of the defensible survey range and count the firm's W-2 wages as the limitation's support above the threshold. We check the state boards' ownership rules in every registered state, plan the professional liability tail against a decade of buildings, and choose the entity for the internal transition the profession relies on — because the founder's shares are sold to the next principals, not to a consolidator.

See also: For related guidance, see the dental practice entity guide; and browse every small business tax guide, by situation.

Next step

Fairlight Accounting is a cross-border accounting and tax practice with a U.S. Tax Desk and a Canadian Tax Desk. Our U.S. Tax Desk handles architecture and engineering firm entity planning — state practice act ownership compliance and certificates of authorization, professional liability structuring, the S election worksheet with survey-based compensation and QBI cost analysis, wage limitation planning, 179D allocation years, and internal ownership transition design. See pricing or book a call.