White Paper: Multifamily Manufactured and Modular Construction
- Feb 26, 2013
By Robert Koch, AIA, Fugleberg Koch Architects
Prefabrication in construction has been available for decades. It has traditionally been provided in three major forms:
- Panelization—The use of interlocking or interconnecting wall, floor and roof assemblies fabricated on tables (on or off site) and assembled on building pads. Its greatest efficiencies come from repetitive component members used in fabricating highly repetitive plan solutions.
- Core modules—Wet or infrastructural modules that concentrate utility assemblies into compact transportable packages to be field joined with conventional or panelized construction components.
- Manufactured or modular structures—Modular structural boxes factory fabricated and field joined either horizontally or vertically to form larger interior environments and often involving selective field fabrication.
Reasons for considering manufactured multifamily housing approaches
Not to be confused with mobile homes, manufactured or modular construction is not intended for continuous portability, although they may envision occasion relocation. They therefore are not categorized as vehicles such as RVs, mobile homes and 3rd wheels. The manufactured or modular approach, however, is often employed to fabricate smaller buildings intended to house activities in which room sizes and shapes are seldom subject to change and are appropriate to the modular dimensional limitations of the assembly.
Many are familiar with storage, office and classroom applications of this approach. Housing in most of its forms is an excellent application opportunity for the methodology when the appropriate conditions to support its consideration are in place.
Conventional field erection (including panelized methodologies) in many instances will remain both competitive and preferred when compared with modular manufactured approaches. The modular option comes into fair consideration when one or more key parameters invite its eligibility:
- Weather limitations—Weather in many locations offers seasonal or even continuous impact on the building process. Excessively wet, cold, or hot environments often have limited construction seasons that must rely upon fabrication time management techniques to assure maximum construction effectiveness in limited seasonal windows. The ability to effect weather-enclosed environments quickly can either shorten the overall construction period or allow interior activities to occur when exterior conditions are substandard.
- Labor cost or availability—In many urban areas labor costs are high due to the protective nature of trade organizations or to the limited supply of adequate workforce. Modular manufacturing can offer the opportunity to conduct a meaningful portion of the construction in more competitive labor markets using sheltered, assembly line techniques, thus allowing task-skilled fabricators to conduct much of the building process without formal construction-trade training and apprenticeship.
- Speed of erection—Independent of the seasonal consideration, modular fabrication can also shorten the “on-site” fabrication time by transferring much of it to the factory environment (where often it can be implemented in quicker, less weather-dependent, and even “round-the-clock” fabrication processes.
- Area of work—Sites with infrastructure limitations, hostile environments, an absence of mobilization room, or rough topographic conditions are all candidate sites for modular fabrication. While transport access to the site will remain critical (generally by overland but occasionally by barge or helicopter), the modular assembly process on site can often be effected in compact areas with limited debris challenges and quick physical outcomes.
- Portability/permanence—Occasionally housing applications require the ability to move the inventory from time to time. Housing used as a land warehousing activity and field construction housing for major remote construction housing would be examples of such applications. Modular fabrication would allow the units to be employed for their purpose and then resold and relocated in the future with reclaimed value otherwise disposed of.
- Quality—Factory fabrications usually rely upon superior material and construction processes less commonly found in the field. Dimensional precision, connection and adhesive redundancies and even transit resistance often contribute measurably to the quality of the overall product.
Manufactured buildings can frequently be permitted as prototype buildings for multiple applications throughout any given state. With this prototype permitting process, local code agencies only review the site related activity of site work, foundations, connections and field construction that may also be included.
In addition to the ability to source more competitive labor resources, other pricing advantages can sometimes come into play. Construction occurring in different jurisdictions is sometimes effected by different tax or currency rates as well. By example, fabrications in Canada, shipped to the United States can frequently benefit by both favorable tax and currency factors.
What are the obstacles?
Labor unions in some parts of the country control the ability to outsource non-union workforce. Most manufactured settings live outside the construction labor union influence and thus represent competitive interests to the unions and their employees. Local construction regulations intended to protect union interests and local labor forces can sometimes deny the ability to use manufactured units through governance over the labor force. Lending standards that may mandate “Davis Bacon” employment considerations can also potentially affect the same result.
Most local codes are intended to administer to conventional fabrications. Each area of their governance can be challenged by manufactured approaches. Jurisdictional authority, compliance capability, permitting, inspections and also transportation must be considered. Manufactured approaches depend upon the ability of the product to be moved from the point of fabrication to the development destination. This consideration introduces opportunity for cost and complications. Their key determinations are: distance, dynamics and dimensional limitations.
Another potential obstacle is market prejudice. Manufactured housing has long been associated with cheap housing and in turn has carried an expectation of a lower standard of fabrication. While this is not true, it can require a market education mission to advance awareness of the construction qualities of the product to assure consumers of the equal or better fabrication quality it can offer.
In addition, there are site construction demands. The installation of manufactured units on site will depend at varying measure upon field fabrications that precede and follow their site assembly. The integration of these separate forces requires a construction oversight or trade involvement that could compromise the efficiencies of the systems employed. Consider the following:
- Limited scope/limited interest—small field sub contracts may be hard to source
- Field trade experience—the familiarity of the product may be uncertain
- Remedial corrections—damage due to transit could involve special skills or equipment
- Garages, foundations and common area needs—major parts of a development could demand substantial field fabrication
There may also be structural demands. Moving a house or any part of one produces forces upon the structure that could challenge conventional design criteria. While manufactured fabrications are designed for movement the dynamic of transit and erection can induce stresses that produce some damage that would need to be field repaired.
Finally, don’t ignore details related to the ownership of design, documentation, copy write and patent rights. The effort to design, quality control, value engineer and perfect a workable solution in manufactured housing requires multiple applications to optimize the investment. The collection of considerations engineered into any product should thus be protected with greater vigor than conventional construction approaches. Every aspect of the product should be viewed as “invention” and controlled by the team members who contribute to the outcome to avoid loss of control and competitive dilution of the market.
Bob Koch, AIA, is managing member and president of Fugleberg Koch, a design firm located in Winter Park, Fla. (Metropolitan Orlando), specializing in architecture, planning, urban design and development consulting.
Case Study/Slide Show: Brookside Meadows Project, Pleasant Valley, N.Y.
The following photos illustrate the pad ready to occupancy sequence for an eight unit building containing stacked flats. Please note: The precast foundation work and building fabrication is occurring during freezing temperatures with little negative impact on process.
- The garage slab on grade and limited support walls are erected prior to box arrival and placement.
- The boxes arrive unfinished on the exterior with vapor barrier envelopes removed after placement.
- Roof lines are erected as tilt up panels or truss assemblies to reside upon the tops of upper modules.
Exterior siding and shingles together with building appointments and accessory appendages are added in the field.