Narrow Duplex

Overview

The development of Portland’s narrow lots is a contentious issue, and the demand for affordable rental housing is at an all-time high. With this project we wanted to explore the potential for narrow lots to provide a model for affordable housing — providing not just one, but two units — in a structure that matched the scale of adjacent development. The two units (a 2bd/1ba main house and a 1bd/1ba attached ADU) each include a loft with operable skylights, separate washer/dryers, and bathrooms with full tubs. To maximize fexibility and adaptability, the two units are designed so that an opening in the separation wall allows the structure to easily become a single 4bd, 2ba single family home.

Our construction partners on this job were Marsh Construction and A&R Solar. This project was undertaken as a 50/50 partnership with a private local investor.

Cost

Numerous cost-saving measures were employed in this project. The asymmetric gable roof was prefabricated offsite, delivered and installed for under $5,000. The trusses included the floor framing for the lofts as well as the finish ceiling for the first-floor bedrooms, saving on framing and finishes. The distinctive form of the gable was governed by the south-facing slope, which was optimized for solar panel installation and orientation. Framing, siding, and painting costs were kept to a minimum by creating second-floor lofts rather than full second stories. Both units feature sealed (but not stained) concrete floors and industrial-grade light fixtures. The bedroom lighting is provided via switch-controlled outlets and plug-in lamps rather than permanent overhead lighting.

Many of the cost-saving strategies reflected innovative Code research. Each of the lofts make use of different exemptions in the ORSC to not require stairs, the space for which often dominate narrow lot house plans. There is no finish sheet rock ceiling or overhead lighting in the bedrooms and hallways, which saved on cost, but required special attention be paid to fire-resistance requirements. The money saved was used to purchase extra insulation (the project is insulated 35% above Code requirements), LED lighting throughout, and a 6.9 kWh solar panel array shared equally between the two units. The loft railing in each unit was custom-designed and locally fabricated using the roof truss as a motif, while still satisfying life-safety and structural requirements.

Due to our agreement with our investment partner, detailed final costs are not available. A rough breakdown is as follows (FY 2017):

core and shell$139,800
solar panels$20,900
two kitchens (incl. appliances)$11,600
custom guardrails (approx. 38 linear feet)   $1,300
permits/inspections$8,800
total$182,400
total area1,526 sf (940 sf main unit + 586 sf ADU)
total cost per square foot$120/sf

According to the Portland Housing Bureau’s 2017 numbers the front house could rent at $1680/month and the ADU could rent for $1400/month and the units would still meet the 30% housing burden for the median family income ($74,700/yr). The rent for the larger unit was set at $1575, and between the solar panels and the water/sewer bill the unit hits the $1680 target. The rent on the ADU was set even lower – $1200/month. If we assume a 75% factor to account for maintenance and vacancy, the ROI would be: $24,975 (annual rent) / $182,400 (total cost) = 14% ROI

This is a significant ROI for two units of new construction, to say nothing of the sustainability and affordability aspects. We believe this represents a significant opportunity to reimagine narrow-lot development in a way that provides additional density in our existing communities (with all the accompanying benefits) and also fits in with existing development.