A shell space is commercial space with little or no interior finish. The landlord delivers the structure, the roof, the exterior walls and a bare floor, and the tenant builds the interior it needs.
NAIOP, the Commercial Real Estate Development Association, publishes the industry's glossary of terms. It defines shell space as "space within a property without any, or a minimal level of, interior improvement and finish" (NAIOP, Terms and Definitions). The term "frequently refers to space in a newly constructed building awaiting a tenant to customize interior demising walls, electrical or other space design needs".
A demising wall separates one tenant's premises from a neighbour's or from the common corridor. The base building is what the landlord builds for every tenant: the structure, the roof, the lobby, the elevators and the main utility lines.
Listings and leases describe the condition of a space with a ladder of labels, from the least finished to the most:
- Cold shell, also called a cold dark shell, gray shell or raw shell: the bare enclosure.
- Warm shell: a shell with heating, cooling and utility connections.
- Vanilla shell, also called a vanilla box or white box: walls, basic systems and often a ceiling, ready for the tenant's finishes.
- Full build-out or turnkey: a finished space, ready to occupy.
The labels carry no fixed meaning. A lawyer writing in Probate & Property, the American Bar Association's real estate journal, observes that "in leases (and probably in most loan situations), the meaning of Vanilla Box is not that certain" (American Bar Association, Probate & Property). The lease's description of the work decides what the tenant receives.
A cold shell is the least finished condition a landlord offers. The same article describes a cold dark shell as space that probably lacks heating, cooling and lighting, and may lack even connections for electricity or plumbing. The tenant of a cold shell builds nearly everything inside:
- demising walls, interior walls, doors and ceilings
- lighting, wiring and outlets
- heating and air-conditioning
- restrooms, plumbing and finishes
A vanilla shell is a partly finished space. Two definitions quoted in the article show the range. A commercial finance glossary calls a vanilla box a "shell interior of rentable space, with landlord-installed utilities, subfloor, and finished but unpainted drywall". The International Council of Shopping Centers (ICSC) calls it "a space partially completed by the landlord based on negotiations between tenant and landlord". Its dictionary adds that "every landlord's definition is different", and lists the usual contents: heating and air-conditioning, walls, floors, a stockroom wall, basic electrical and plumbing work, a rear door and a storefront.
Bank examiners use the retail version of the term. The Office of the Comptroller of the Currency (OCC) supervises US national banks, and its handbook says retail landlords usually deliver a "white box", which it describes as "primed drywall and a concrete floor" (OCC, Commercial Real Estate Lending).
A warm shell has the building's systems connected to the space. The article describes a warm vanilla shell as one that includes heating and cooling plus electrical and plumbing connections. A tenant in a warm shell extends systems that already run. A tenant in a cold shell pays to bring them in, which adds design and permit work before the finishes start.
A full build-out is a space finished for a tenant's use, with interior walls, ceilings, lighting, systems and finishes in place. The tenant moves in its furniture and equipment and starts work.
The phrase also names the work that takes a shell to that state. A space that a previous tenant built out and left is second-generation space. NAIOP defines relet space, "sometimes called 'second-generation space'", as "existing space that was previously occupied by a tenant". A new tenant can keep its walls and wiring and change the rest.
| Condition | What the landlord delivers | What the tenant still builds |
|---|---|---|
| Cold or gray shell | Structure, roof, exterior walls and a bare slab | Nearly the whole interior, systems included |
| Warm shell | The shell, with heating, cooling and utility connections | Walls, ceilings, lighting and finishes |
| Vanilla shell or white box | Walls ready for paint, basic systems, often a ceiling | Paint, flooring, fixtures and the layout |
| Second-generation space | A previous tenant's build-out | Changes for the new layout |
| Full build-out or turnkey | A finished space | Furniture, equipment and cabling |
| Build-to-suit | A building designed for one tenant | Little or nothing |
Turnkey means the landlord builds and pays for the tenant's improvements. NAIOP defines turnkey as "a landlord's agreement to provide and pay for improvements to a tenant's premises" (NAIOP, turnkey). The landlord delivers the premises "in a condition ready for the tenant's stipulated use". A landlord that pays for a turnkey build-out recovers the cost through the rent and the length of the lease.
Build to suit means a developer designs and builds a whole building for one tenant. NAIOP defines a build-to-suit as "a building that is designed and tailored for a specific tenant" (NAIOP, build-to-suit). The tenant or occupant usually contracts for the project. The opposite is a speculative building, which a developer builds "without any preleasing in place". NAIOP calls speculative development "generally considered to be higher risk than build-to-suit development". A speculative building often reaches the market as shell space, waiting for tenants to choose their interiors.
A special purpose property is a building designed for one use, which would cost a great deal to convert to another. A heavily customized build-to-suit can become one. If the occupant leaves, few other businesses can use the building, and lenders price that risk when they underwrite a commercial real estate loan.
The US Small Business Administration (SBA) sets a higher contribution for these buildings. Under its 504 loan program, a borrower contributes at least 15% of the project cost when the project involves "a limited or single purpose building or structure", against 10% in the base case (13 CFR 120.910). On a $2,000,000 project, the borrower puts in $300,000 instead of $200,000.
The lease decides who pays. The landlord pays for the work its work letter lists, and the tenant pays for the rest, often with an allowance from the landlord.
NAIOP defines a work letter as "a legal document that outlines the obligations of the landlord relative to the improvements necessary to prepare leased premises for a tenant's occupancy". Its glossary names what a work letter typically includes:
- a description of the improvements
- their cost
- the portion of the cost the landlord pays
- the completion date
- the contractors' insurance
On a shell, the landlord's work usually covers the base building and the utility lines to the premises. The tenant's work covers the rest, often funded in part by an allowance: see tenant improvements and the TI allowance.
The delivery condition belongs in the first document of the deal, the letter of intent: see what goes in an LOI for a commercial lease. The ABA article recommends "a work letter containing a definite description" of the condition of the premises at delivery (American Bar Association, construction terms).
Rent starts on the rent commencement date the lease sets. On a shell, the tenant often takes possession first and builds out before that date, so it pays no rent on space it cannot use yet. The gap depends on the job and on the city's permits and inspections. Tie the date to the landlord's delivery of the shell and to the permit, so a late delivery moves the rent date with it.
A lender looks at the building as it stands and as it will stand. The OCC's handbook names three values in a construction appraisal: the current market value, "often referred to as the 'as is' value", a prospective value "upon completion" and a prospective value "upon stabilization" (OCC handbook). It adds that market values for "partially leased or vacant buildings" must include "analysis for appropriate deductions and discounts". An empty shell still has its build-out, its leasing costs and its months of lease-up ahead, which is why a property can carry more than one value.
US contractors charged 36% to 67% more for nonresidential building work in August 2026 than in December 2019, depending on the trade. The figures come from the producer price indexes of the Bureau of Labor Statistics (BLS).
The delivery condition decides who pays for the work, so the price of the work sets what a label is worth. A producer price index tracks what contractors charge for the same work over time, and the chart follows four trades. Roofing and concrete contractors build the shell. Electrical contractors, and plumbing, heating and air-conditioning contractors, install the systems that turn a shell into a vanilla shell and then a full build-out.
Source: U.S. Bureau of Labor Statistics, Producer Price Index by industry, contractors' nonresidential building work, monthly, via FRED (series PCU23816X23816X, PCU23811X23811X, PCU23821X23821X, PCU23822X23822X), December 2019 to August 2026; rebased to December 2019 = 100 by Sphera Credit.
From December 2019 to August 2026, roofing rose 67.3% (FRED, roofing) and concrete 44.1% (FRED, concrete). Electrical rose 39.7% since December 2019 (FRED, electrical), and plumbing, heating and air-conditioning 36.1% (FRED, plumbing and heating). The steepest climb came in 2021 and 2022. Electrical and concrete prices eased in 2023, then rose again.
Take $120,000 of electrical work and $80,000 of plumbing, heating and air-conditioning work at December 2019 prices. The same work costs 38% more at August 2026 prices.
| Trade | Price in December 2019 | Same work in August 2026 |
|---|---|---|
| Electrical | $120,000 | $167,700 |
| Plumbing, heating and air-conditioning | $80,000 | $108,900 |
| Total | $200,000 | $276,600 |
An index gives no cost per square foot, which depends on the space, the city and the finishes. Ask a contractor to price the tenant's work before you sign: an allowance is a fixed sum, and the tenant pays any overrun.
In Canada, Statistics Canada publishes building construction price indexes. It reports that non-residential building construction costs rose 3.5% in the year to the second quarter of 2026 (Statistics Canada, The Daily).