Passive House Retrofit – Stable & Carriage House

Project Description

We live in a climate emergency. This client chose to act accordingly.

The Spencer Carriage House Deep Energy Retrofit/Restoration is the first Passive House level retrofit of a designated DC Landmark building.
Listed on the National Register of Historic Places, this 1905 structure is one of the last remaining stable/carriage houses built to serve the large mansions in the Dupont Circle area. Originally the horses and carriages were housed below, and servants above.  Over the last hundred years the building has been used as a garage, a car dealership, a fashionable restaurant, and in its last incarnation, a popular Dupont Circle nightclub. When this client acquired the building it lay empty and exposed to rain and weather. No original interior trim or features remained and the original layout had long been abandoned.

Client goals

  • To preserve a historic DC Landmark and create a home for aging in place in a vibrant part of the District.
  • To exceed the District of Columbia’s 50by32 goals, achieving as close to net zero energy use as possible without sacrifice to comfort or lifestyle.


  • Navigation between requirements for deep energy retrofitting and the Historic Preservation Review Board’s requirements for responsible historic preservation.
  • Air sealing and elimination of thermal bridging when working with an existing floor framing system.
  • Working on a site defined on three sides by alleys and zero lot lines.

Yoko Barsky, the interiors architect of Deco Design Studios, had a longstanding relationship with the client and brought us in to handle exterior restoration, structural work, and deep energy retrofitting. The project was a true collaboration in achieving energy goals without compromise to client design goals.

Energy Reduction Achievements
The project achieved every energy metric for Passive House Institute U.S. (PHIUS) certification: heating energy, cooling energy and total energy use. It narrowly missed the stringent PHIUS airtightness requirement.  Tested at 1.6ACH@50Pa, it is approximately two times as airtight as required for Energy Star certification.

With a total annual site energy demand of 16,386 kWh determined by PHIUS energy modeling, the house is zero energy ready, with space available on the south roof for the 16.3 kW photovoltaic array that would be required. Current DC Historic Preservation Review Board requirements do not allow visible solar arrays on Landmark buildings.

The first floor contains guest bedrooms, a small apartment, and utility spaces. A non-conforming shed addition at the east end was replaced to create adequate space for two cars. A large entry foyer contains an ornamental stair leading to the second floor living spaces. A small glass elevator is set just off the foyer.

The second floor comprises a large open living/dining/kitchen area at its west end and the master suite at its east end. A small separate catering kitchen serves large events.

At the attic level, a space was carved out of the north roof (invisible from the street) for a small entertaining deck and outdoor kitchen. The deck is accessed by the elevator and small spiral stair.

Exterior masonry was restored according to the Secretary of the Interior’s 1983 Standards. Non-complying openings were removed and original openings restored.  The roof was replaced to match the original. Deteriorated copper cupolas were rebuilt to match the originals. They now house the elevator hoistway and all air intake and exhaust vents. Original heart pine floor joists were repurposed into flooring,  cabinetry and furnishings. Exterior signage from older incarnations were preserved. The disco ball from the night club adorns the stairway ceiling.

Clients moved in in February 2019. Specifics on energy retrofitting strategies are provided further below.


Overall strategy: reduce overall energy demand to that which can be supplied by onsite PV

  • Reduce heating and cooling energy demand to the absolute minimum through air sealing an insulation
  • Provide the most efficient HVAC system possible, sized to the reduced loads
  • Reduce hot water energy demand and internal electrical loads to a minimum

Building envelope
First floor slab (R21):

  • Removed severely cracked and sloped slab
  • 4” rigid foam over 4” gravel
  • 20 mil vapor barrier completely taped and sealed over foam
  • New 4” reinforced floor slab

Exterior walls (R40):

  • Restored exterior face of masonry per standards of the Secretary of Interior
  • Cleaned and removed loose paint from interior face of exterior masonry walls
  • Liquid air/water barrier at interior face of masonry
  • Continuous 2” rigid EPS foam adhered to air/water barrier
  • New double stud (2×6 + 2×4) wall set 1” off rigid insulation
  • 9-1/4” densepack fiberglass in framing cavities
  • Fully taped “smart” vapor barrier at interior face of framing
  • New triple-glazed, custom meranti Passive House windows (R9) with simulated divided light
  • Upper sash fixed sash over lower operable inswing tilt/turn units to match dimensions and appearance of original double hung sash

Roof (R55)

  • Removed under-sized and deflecting roof framing
  • New roof framing and sheathing to code
  • 2.5” open faced EPS SIP panels above sheathing for added insulation and to prevent thermal bridging through rafter framing
  • 9-1/4” densepack fiberglass insulation in rafter framing cavities
  • 1” rigid EPS board against undersurface of rafters to break thermal bridging
  • Fully taped layer “smart” vapor barrier over furring strips below EPS board

MEP systems
A Mitsubishi City-Multi HVAC system serves the entire building. The selection was based upon the need to handle peak loads of very large gatherings (6 tons) in both summer and winter, and yet ramp down to handle much lower demands (1.5 tons) the rest of the year.

Fresh air is provided by a separately ducted Zehnder ComfoAir 550 energy recovery ventilator, with a 84% efficiency rating for energy and 50%  rating for humidity exchange. Fresh air is introduced to all living spaces, and exhaust taken from all baths and kitchens, creating essentially a one way trip for air through the home.

Hot water is provided by four solar thermal panels, with backup electrical resistance water heating.

All lighting is LED. All appliances are Energy Star. All motors are ECM.

Project team:
Interior architecture and design:     Yoko Barsky, ASID, Washington, VA
Project manager:                              Izumi Kitajima, CPHC
Structural enginer:                            Rossetti Engineering, Fairfax, VA

General contractor:             Federalist Builders Inc., Washington, DC
Masonry:                              Vaughan Masonry Restoration, Alexandria, VA
Ornamental Metals:             Fred Crist Metalwork. Exterior grille work.
`                                            AK Metals, Alexandria, VA. Stairs, counters
Cabinetry and millwork:       Dovetail Millwork, Rixey, VA
Roofing:                               Clerkin Roofing and Sheet Metal, Washington, DC
Plumbing:                            H D Johnson and Sons, Washington, DC
HVAC:                                  Michael Bonsby HVAC, Gaithersburg, MD
Electrical:                             W&W Electric, Silver Spring, MD
Solar Thermal:                    Solar Energy Services, Inc, Millersville, MD

Interior photos of completed work by Matt Brazier Photography.

Project Details

  • Date February 5, 2019
  • Tags Aging in Place, Deep-Energy Retrofits, Remodeling and Additions
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