TechPractices: Long and Gordon, Dove Street, Boston, MA

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Summary

Most developers would think at least twice before taking on this project. In an area noted for its crime, a builder teamed up with the City of Boston to tear down a crack house and replace it with durable, energy efficient, two-story homes, strategically placed to tie together and revitalize the neighborhood. Using hybrid modular/panelized housing, the builder realized these goals at a tidy profit.

Details

The City of Boston improves its depressed areas through target projects as part of a comprehensive urban strategy. Because of the often small scale of renewal efforts, lot choice and construction scheduling are critical to maximize the impact of the initiative. In the case of Dove Street, Boston's Department of Neighborhood Development wanted to target the worst part of the neighborhood. The ideal site, highly visible and well-trafficked, also happened to be home to a narcotics outlet and stolen car chop shop-a benefit just to tear down. Since there was no reason to believe crime would disappear immediately with demolition, the construction method had to take security into account-vandalism and construction-site theft can make affordable housing less so.

This is where modular construction shines, because it minimizes material storage on site and the duration of on-site construction. Within a few hours, a project can go from bare foundation to enclosed house with windows installed and doors locked. To create a psychological feeling of security and to fit in with the townhouses on the street, the architect designed tall front facades and high-peaked roofs. The homes' resulting prominence demanded the scale be broken up like a large custom home. So the architect added a covered porch, projected the kitchen, and created a volume that adds depth to the facade. These elements are prefabricated panels shipped with, but distinct from, the modular boxes. The result looks just like a site-built home.

The houses are designed to conserve energy, featuring high-performance windows and tight exterior envelopes to limit heat loss. Exterior walls have R-19 fiberglass batts, exceeding that required by code. Instead of insulating the basement, R-19 batts were applied under the first floor--a more economical approach than foundation wall insulation that decreases the conditioned volume of the house. Insulated steel bulkhead doors provide basement access and further reduce heat exchange between the house and outside. Long-lasting compact fluorescent lamps (CFLs) are used throughout the houses to save electricity and reduced maintenance. The integrally-ballasted fixtures allow lamp replacement with economical, non-ballasted CFLs.

Installation/Construction

Dove Street may not have been possible as a strictly site-built project, due to the substantial preparatory work the lot needed. First, the existing house and garage needed to be torn down and carted off. The garage had been used to disassemble stolen cars for parts, and many gallons of used automotive oil had seeped into the soil below. The builder hired a specialty contractor to alternately core drill the ground for testing and remove sections of the soil.

While this painstaking process occurred, the factory built the modules, which could be delivered almost 90% complete. Once foundations and utilities were in, each house was delivered in four 12' x 31' modules, leaving the porch, roof tie-in, and some finish work to be done on site. The builder could deliver the larger components only between 9:30AM and 3:30PM to avoid rush hour traffic, so it took two days to set the houses. In most suburban areas both houses could be set in one day.

Tilt-up roofs are folded down to fit beneath overpasses during transport and hinged up on site. This allows for steeper roof pitches. A small section of the roof, where it jogs at the front, was delivered as a separate unit riding on the "tongue" of the trailer in front of the box, to save space. The exterior of a projecting kitchen volume was slid out of the kitchen area at delivery. These panels were then laid in by crane and sealed the same day the modules were placed. The company now uses engineered wood wall framing at selected areas within the structure to prevent factory-installed vanities and cabinets from bowing partitions. Small diameter, new-growth trees provide wood strips that are glued together to make laminated studs--a stronger, more environmentally benign lumber product priced 10% to 15% more than standard studs.

To withstand shipping stresses, each module sits in a double 2 x 12 rim band supporting 2 x 12 floor joists. Other procedures to stiffen the structure for transportation result in energy benefits. Sheathing and drywall is glued and screwed to studs, reducing air movement within the exterior wall cavities. Electrical receptacles are caulked from the backside. To prevent energy-robbing cracks from opening up during transport, joints along the exterior walls are glued and caulked. The architect notes an additional advantage of two-story modular construction: Since the first floor ceiling and second floor are independently framed for rigidity during transport, the increased mass and volume of the cavity reduces sound transmission between the first and second stories.

Benefits/Costs

The modules for each house cost $60,000, less than $43/sf, delivered and set on the foundations. However, total construction costs for each house were close to $130,000, or $92.86/sf, due to approximately $100,000 of unique site conditions. Since each home sold for $105,000, the city subsidy amounted to about $25,000 per house. Land acquisition ($24,000), Demolition ($24,000), environmental testing and remediation, and lot subdivision ($6,000) were significant cost and schedule items-the soil clean-up alone cost almost $50,000. Still, the City claims the investment is well worth it, as the houses are a key part of a plan to help stabilize this formerly crime-ridden area; the cost of law enforcement and court time would quickly have exceeded the construction investment.

Although modular is not always less expensive than site building, going modular enabled substantial savings here, making an otherwise economically prohibitive project possible. The city estimates approximately 10% savings compared to onsite building. In addition, building the houses conventionally would have taken at least six weeks, opening up plenty of time for break-ins, material theft, and illegal dumping. Although a suburban venture could have carried these costs, this market could not support it, and required the combination of subsidy and fast modular construction to make it happen.

Code/Regulatory

The existing house was only 800 sf. Since the city cannot develop real estate on its own, the city brought in a private builder/developer to buy the tiny lot and the adjacent garage lot. The city then sold two more adjacent vacant lots to the builder (for one dollar) to provide plenty of area for the two houses. The builder could then proceed with zoning subdivision. Once the site was cleared and cleaned, the Massachusetts Department of Environmental Conservation required an independent engineer to file a 21E report certifying that the site is clean of contaminated soil.

Feedback

The City of Boston had worked with the modular manufacturer before. Based on previous experience, the city's marketing unit and architects worked with the manufacturer to refine the interior layout as a prototype for Boston's infill housing. The architect estimates that, compared to site building, this approach will save the City $5,000 to $7,000 per house in detail design/shop drawing review alone, placing the responsibility on the manufacturer.

Contact(s)

Do you have a specific question? Try the contacts listed below:

Builder/Developer
Long and Gordon
617-266-2100

Customized Structures, Inc.
P.O. Box 884 - Plains Rd.
Claremont, NH 03743-0884
800-523-2033

City of Boston, Dept. Of Neighborhood Development
617-635-0472