8 dwellings

145-151 Laurel St.

Northern Liberties, Philadelphia


The first LEED for Homes Platinum duplex residences

in the U.S.A.

This eight unit residential project explores the highly efficient and architecturally latent potentials hidden within the traditional form of the Philadelphia “Row” home. The vertical rhythm, regularity yet diversity of this most prevalent residential urban typology was the primary source of inspiration for this experiment. Thin faces fronting both Laurel and Pollard Streets mask and blur conventional lines of demarcation between all eight duplex dwellings both vertically and horizontally. In the process, a degree of density yet expansiveness uncommon to the thin space of the urban duplex emerges.  The Philadelphia “Row” is by nature a long, thin slice of dense, sustainable, urban space, typically ‘light-deficient’ and insular at its core. Thin Flats questions this traditional ‘deficiency’ by spatially reconfiguring the relationship between the interior and its skin such that its ‘core’ is flooded with light and air. This skin also affords each room on the ‘periphery’ of the dwelling the ability to step outside, and yet remain within the skin.








– Third Party verification that each unit is a minimum 50% more energy efficient in cooling, and domestic hot water energy usage than required by code

– Solar Thermal panels to provide domestic hot water needs

– Planted ‘green’ roofs to decrease thermal heat gain, prolong roof life, assist in storm water management, and provide planted and habitable rooftop gardens with views of center city

– Rainwater harvesting cisterns beneath parking area for irrigation of yards / gardens

– Each unit includes a detailed Home Owner’s Manual outlining the specific features and systems that are offered in the home that make it a LEED Platinum project

– Low flow faucets and fixtures reduce water consumption by 50%

– Concrete containing a minimum of 25% recycled fly ash content

– Double pane, low E, argon filled, thermally broken, aluminum clad wood windows and doors

– Home automation technology by Colorado vNet – centralized and programmable lighting, heating, cooling, security, and audio/video entertainment system to maximize convenience and minimize energy use

– Grade 1 insulation package including foam sealing of all joints to minimize air infiltration and closed cell spray-in foam insulation in exterior walls

– Maximum use of sustainable framing materials

– Maximum use of locally sourced / manufactured materials

– Hydronic radiant in-floor heating system

– HVAC system designed to ACCA Manual recommendations

– HRV(Heat Recovery Ventilation) system- Insulated hot water supply pipes

– Low or no VOC (volatile organic compounds) emitting paints, adhesives, and sealants

– Located within one block of public transportation

– Electric car charging port with fully electric car optional



The façade of Thin Flats is at once a surface and a void, blurring the limits of the units within. The façade of the lower units is pushed back from the sidewalk to accommodate circulation.  The separation also floods a ‘basement’ space with light, aids in solar shading and creates a veil from public view. Balconies on upper floors recess behind the surface of the veil to create opportunities for civic engagement within the thin space of the façade.



Mike McDonald is an award winning green builder and developer.  Prior to joining sustainable custom home builder and general contractor Ryan Associates, Mike was the first builder to complete three LEED® Platinum custom homes in Northern California with McDonald Construction & Development. Mike’s brothers, who operate as Onion Flats are the design and development team behind the Thin Flats project in Philadelphia.