So you want Flexible Lease Space?

One of the primary goals for the MEP design of each retail center, whether a large Life Style Center or a smaller Strip Center, is to have flexible lease space. The question always arises, “What if a restaurant wants this space?” or “What if a tenant takes three spaces?” While there is not a one size fits all solution for every center, there is a series of decisions each developer needs to make prior to beginning the MEP systems design phase of a new center. Following is a description of various options for Mechanical, Electrical, and Plumbing/Fire Protection along with the pros and cons of each to assist with the planning phase of future retail centers.


HVAC
Most municipalities use a model energy code which dictates the amount of lighting that can be utilized in a retail space and ASHRAE 62.1 is widely accepted as the standard for calculating the amount of outside air required for a space. Thus whether utilizing RTU’s, split systems, or a central system, sizing and installing units for a typical retail space under the shell package is not a huge risk. The advantages of doing this include having all the equipment from the same manufacturer and a shorter tenant fit up time. The drawbacks to this approach include the upfront cost of the units before tenants are in place as well as the potential that some other type of occupancy, a restaurant for example, might wants a particular space - thus the need to view design with a balance of cost and flexibility. The points of analysis should include the size of the development, utilities available, how long the developer plans to hold the property, and last but not least, the anticipated tenant mix. Below is a brief explanation of the various types of systems which can be utilized in retail design along with the flexibility pros and cons of each.

Roof Top Units (RTU’s) – By far, most owners will opt for the use of package roof top units. These units combine heating and air conditioning into one unit and as the name implies, they typically require a flat roof for mounting. These units can be specified based on the intended use of each space, or if not known at the time, loads can be calculated based on typical retail usage. When utilizing RTU’s there are three options for the shell package: install the units based on typical retail requirements, install curbs only based on intended usage, or install no units under the shell package.

If the developer decides to install the units under the base shell package, placement of the unit can increase flexibility. As long as there are no visibility issues, the units should be set to the front half of the building. This will allow flexibility if the space is leased to a restaurant as the additional units could be placed on the rear of the space where a kitchen would typically be located. This type of application is not only very flexible but increases the speed of future tenant build-outs.

The second option is to place the roof curbs in anticipation of future RTU placement. Since most manufacturers’ equipment utilizes the same roof curb for groups of unit sizes, this leaves the sizing of the equipment fairly flexible. The advantages of this approach is that the units are not purchased until tenants are identified while allowing the roof work to be done under the base building to ensure a good continuous roofing system by one contractor.

The final option is to put no curbs or units in under the shell. While the advantages are no cost upfront and maximum flexibility for unit placement as tenants are identified, the major disadvantage of this approach is cutting holes in a new roof each time a new tenant moves in.

Central Systems – Strictly from an efficiency and flexibility standpoint, the most flexible HVAC system for large retail and mixed-use applications is a central system consisting of either a chiller/boiler or large RTU’s with VAV boxes. These units provide a lot of flexibility; however, the initial cost of this type of system and the requirement for the landlord to prorate energy bills will keep the vast majority of malls, strip centers and stand alone buildings from using this type of system.


Electrical
There are two main considerations for shell retail Electrical Service design. The primary consideration is the capacity of the overall service. For larger centers, this may be accomplished through a package switchgear unit or for a variety of centers it might include a wireway with a series of disconnects and meters. As noted with other utilities, the main focus of this portion of the design should analyze the worst case usage. The equipment size is not always reflective of the worst case, but in order to maximize flexibility the secondary conduits from the transformer to the building should always be sized based on worst case analysis for the entire facility. The primary difference is that while the package switchgear cost considerably more, in larger applications the space requirements can be significantly less than the wireway option.

Once the main service is designed, consideration must be given to conduit, wire, and panel distribution for the future tenant spaces. The most flexible option is to install conduit only. These conduits can be run under the slab, or to maximize flexibility, they can be run overhead so as to allow conduits to easily be shortened or extended as tenants require. While not as flexible as the overhead conduits, the PVC conduits underslab can be increased in size to add flexibility while not adding the same costs to the project as overhead metal conduit will. These same alternatives need to be considered for telephone/data conduits to each tenant.

While less flexible, the quickest approach for future tenants, is to size the panels based on the intended use of the space and provide the meter, disconnect, and panel under the shell package. One disadvantage of this approach is that if a tenant takes more than one space, some municipalities require the services to be combined into one meter.


Plumbing
The design for plumbing in a retail shell building is typically straight forward; however there are several considerations which should be reviewed when designing the water, sanitary, fire protection and gas (where applicable) systems for the overall center.

Water - When considering domestic water service, it is important to bear in mind the type of tenants that will be served. Depending on the local pressure and water flow, a typical restaurant space could require a 2” line as opposed to a retail space which might only require a ¾” line. The most flexible design involves working with the developer to consider a worst case scenario as far as water usage is concerned. This worst case can be utilized to calculate the overhead pipe size along with a series of 1” and 2” taps/valves to allow for ease of future tenant connections.

Sanitary - Sanitary waste systems for most retail facilities are very basic with a 4-inch building sanitary main being typically sufficient.  One option is to run under-slab the entire length of the facility with the sanitary main providing cleanouts only at code required locations. This pipe can be run in either a 10ft “leave-out” (no concrete slab) in the rear of the space or it can have the slab poured completely over it. While the latter approach has an initial low cost, it is often more than offset by slab cut/patch and longer tenant construction timeframes.

A second approach to sanitary, if the landlord has a good idea of the types of tenants they will be attracting, is to run the entire length with the main sanitary and providing restroom stubs in a few key locations for possible tenants who need to get in their space quickly.

Once again, food service facilities will have additional requirements - specifically, the need for a grease interceptor and related grease-laden waste piping.  Unless a specific tenant is known, grease interceptors are not typically designed under the shell package. While there are many ways to handle the grease waste, the most flexible approach if a space has the potential to be a restaurant is to provide two stubs out of the facility in case the grease interceptor must be located outside of the space.

Fire Protection - Typically under the shell design a main riser will be installed and in some cases a line will be installed along the entire rear of the facility. The logical question is how big should the line be (both the incoming and the overhead). More than any other aspect of the design, this is dependent upon the available flow and pressure from the local utility. Once the information is acquired from the utility, the sizing of both the main entry and the main riser size can be calculated based on the size of the spaces and there intended use, or worst case usage if tenants are unknown.

Gas – When gas is available at a site there are two primary design decisions that must be made with regards to gas service for a retail shell building. The first is the overall requirements of the facility and the second is distribution of gas piping. As noted with water service above, based on the worst case anticipated needs of the developer, the main gas service can be sized for maximum flexibility. Ensuring that enough gas is brought to each building is critical as acquiring additional gas after pavement is down can be extremely expensive. The distribution of gas piping is dependent upon the selections made during the HVAC design phase. If gas is needed in the shell space, there are two options for gas piping. The gas pipe and associated metering can either be all sized for retail tenants, all for restaurant tenants, or a combination based on the developers expectations for each space.

As you can see, one set of design parameters will not fit the design requirements of all retail centers; however, a little planning ahead can increase the facility flexibility for both the developer and the future tenants.

Flexibility? So flexibility is dependent upon your perspective. Whether the design focuses on low cost or speed of tenant occupancy, there is no “one size fits every retail center” solution; however, a careful analysis of each of these components will lead to the most flexibility for your next center.

Trent Beighle, PE is the President of PE-Services. For further information contact Trent at trent@pe-services.com or Roger Butler, PE at roger@pe-services.com. For a more in-depth discussion on this topic check out www.pe-services.com/blog.shtml.

Originally published in Retail Construction Magazine, May/June 2008.