The core concept of base build, also known as shell and core construction, is that the construction is simply the basic structure of a building. Afterward, a range of build-out and interior construction work is completed before the building is occupied.
This building concept was developed in the U.S. and was mainly applied to office buildings developed to be rented out. Initially, developers would fit out complete offices by installing carpet tiles, lighting, access floors, and air conditioning in a notional layout that would be in a standard design for the building’s prospective tenants.
However, it soon became apparent that the tenants’ actual ideas for the space were very different from the standard layouts produced by developers. As a result, a lot of money would be wasted taking up the floors, removing ceilings, and altering electrical and mechanical fittings in order to accommodate office partitions.
This led to it becoming a normal practice for most commercial building developers to purchase materials meant for build-out of the tenants’ spaces. They would then leave them stacked on the floor of the open area to be installed to the clients’ specifications.
What Is A Shell In Construction?
The shell of a building is the component that separates the interior space of the structure from its exterior and surrounding areas. It can have a number of features, most commonly the foundation, roofing, doors, windows, and footers
Depending on the purpose of the building and the contractor, there are different types of construction materials that are used to build the shell, including metal, stone, concrete, and wood.
What Does Shell And Core Construction Involve?
Also known as “base build,” this construction consists of only the building core and its exterior elements (the shell). The build-out work is then left to tenants to carry out before they occupy the building. It is an approach that creates a blank slate on which the tenant can create a working space that is an exact fit for their own needs.
Base build construction is commonly used for the development of office buildings meant for occupation by multiple tenants, making it a popular choice. The two key features of core and shell construction are:
- Building owners can provide tenants with flexible spaces that they may modify.
- Tenants can customize their commercial spaces cost-effectively since they do not need to develop an entire building.
What Is Included In The Core And Shell Of A Building?
As explained above, shell and core construction focuses on creating the building’s main structure without including interior finishes such as furniture or flooring. The key elements of the shell and core build include:
- The structural skeleton and foundation
- Base plant
- Building cladding
- External work
- Complete common areas including staircases, lobbies, elevators, loading bays, reception areas, toilets, and parking lots
- The building envelope that includes external walls, roofs, glazing, and insulation
There are additional components that may optionally be included in a core and shell project, such as:
- Fire barriers
- Mechanical, fire detection, security, electrical and plumbing systems
- Pathways, boundary walls, pavement, and fencing
- Statutory requirements
It is important to note that no standard determines what elements are included in a core and shell construction project. They are determined according to the needs of the project specified by the building owners.
Vanilla Shell vs. Grey Shell
Vanilla shell, also known as a warm shell – or a white box – is commercial real estate that a contractor delivers to a landlord or tenant with basic finishings put in place.
Typical finishes for a warm shell include:
- Electrical panels and outlets
- Finished ceilings with lighting
- Finished bathrooms
- HVAC ducts and controls
- Finished floors or sealed concrete
- Functional sprinkler system
On the other hand, a grey shell construction – or cold shell – is a commercial space that is delivered to the tenant completely unfinished. A cold shell building will generally have no plumbing, no electrical work, unfinished floors, and bare walls.
However, they may have an allowance for electrical service and a connection point to the sewer. This space may also have an HVAC unit included without any controls or ductwork. Depending on building codes, a sprinkler may also be installed, but usually not dropped to the finished height of the ceiling until after occupancy.
The vanilla shell is a good choice for a tenant who requires a nearly-finished space to enable fast move-in. On the other hand, a grey shell requires more work to be done for completion but gives greater scope for the tenant to install custom finishes.
Build-out is the process of making the interior of a shell building ready for occupation. The build-out includes installation of features like interior walls, lighting, electrical fixtures, flooring, furnishings, and other mechanical installations. A completed build-out means that the structure is ready to be used by tenants.
There are two ways that most commercial build-outs are carried out. In the first instance, the landlord purchases materials and leaves them in the unfinished spaces for the tenant to install as they see fit. On the other hand, a landlord may not provide build-out materials but instead offer a rent-free fit-out period.
Depending on the needs of the tenant and the design of the building, there are two types of build-outs:
1. Type A Build-Out
A Type A build-out involves outfitting the structure with elements of finishing by the developer or a landlord. Although there is no standard definition of a Type A build-out as it varies from one developer to the next, it could include the following elements:
- Raised ceilings or floors
- Interior surface finishes
- Mechanical or electrical services
If a tenant’s build-out requirements are complex, they can ensure their needs are met by getting involved in the construction of the core and shell project. What’s more, getting involved early in the process saves money that may be needed to modify an existing build-out.
2. Type B Build-Out
The Type B build-out is what most commercial building tenants are familiar with. This type of build is carried out on a space where basic flooring and the external walls, mechanical and electrical services, lifts, shared toilets, and ceilings are already in place. It is similar to an individual moving into a new house and then installing their own choice of décor, flooring, and lighting, making it unique and personal.
In a Type B build-out, all of the elements added to the space are chosen by the tenant. A developer provides the tenant with a blank space that they may then complete by installing:
- Reception areas
- Décor and branding
- Multimedia and audiovisual equipment
- Meeting and conference rooms
In most cases, a developer will contribute to the cost of the tenant’s grommets, floor boxes, and carpets. These are then installed as a Type B build-out, instead of installation during the Type A works as they are susceptible to damage and may not fit in with the tenant’s preferred design or color scheme.
The practical completion of the build-out of a core and shell construction is defined within the tenant-landlord contract. The contract should include all requirements stipulated in local building codes for the occupation of a structure except the Type B build-out works that are carried out by tenants.
According to standard contracts for core and shell commercial properties, the landlord takes responsibility for the base structure construction costs, but not necessarily for the installation of finishes. This can include furniture, carpeting raised flooring, ceilings, air conditioning, or other indoor build-out elements.
Understanding the Building Envelope
There are two types of building shells – loose envelope and tight envelope buildings. The category of building envelope that a tenant chooses will have a major impact on the structure’s energy efficiency. A large number of ground-up building types make use of loose envelope construction, while most modern commercial buildings use tight protectors.
A building with a loose construction envelope has numerous openings that may allow wind, moisture, and pests to enter and exit easily. This type of construction envelope also lets more air enter the structure and escape. This could be an advantage if a tenant wishes to enjoy fresh air in their commercial space throughout. However, if there is air conditioning or a heating system in place, they will not work as efficiently as they should and will result in high energy bills.
Conversely, a tight envelope on a shell building will allow far less air to escape. This means that conditioned air stays within the structure for a longer time, resulting in lower utility bills. However, the fact that this type of construction restricts the flow of air in and out of the building means that the quality of the air in the interior of the shell is poor.
What Are the Advantages of a Shell Building Structure?
Everyone has their own idea of what an ideal layout for a workspace looks like, making it nearly impossible for a landlord to predict tenant needs. For this reason, it makes more sense to simply build a shell, leaving the finishing touches to the tenant once they move in.
The key advantages of this type of construction for commercial buildings include:
- The process of design and build is considerably faster, resulting in cost savings. The main structure of the shell and core, which has a longer lead time, can be built while tenants figure out the details of their interior décor and fittings.
- The occupants of the structure start with a more flexible blank canvas which does not impact on the overall design of the building.
- Since there is no need for tenants to strip out fittings, waste is reduced.
- The thermal mass of a typical concrete core enhances the building’s heat storage and results in more energy-efficient construction.
- Because of the underlying flexibility of shell construction, it is generally straightforward for the interior fit to be changed to suit subsequent occupants of the space.
Shell and Core Construction Wrap-Up
Shell builds are a beneficial option for offices and other commercial properties due to the flexibility in their design. With the option of Type A and Type B envelope build-outs, the possibilities of tenant construction are endless. In the long run, shell and core builds are better for cutting costs and improving energy efficiency due to better insulation and reduced waste from building materials. It’s important to also remember to go into construction planning with the tenant-landlord contract laid out, so both parties understand the specifications of the project. That way there is no confusion over the building design.