a carbon negative Passivhaus in New Orleans

When the folks at design by many announced that they were holding a competition for a Passivhaus in New Orleans, we jumped at the chance to throw something together over the course of a(n extremely packed) week. We’re typically not fans of crowd-sourced competitions, but lately we’ve been really interested in pushing the boundaries of Passivhaus and felt this was a good opportunity to raise the bar a little. We really wanted to keep some of the traits of a shotgun – especially scale and spatial arrangement – and hopefully we were somewhat successful in that regard. In any case, we’re pretty confident in the numbers, so if anyone is interested in building a modern, affordable, Passivhaus in New Orleans…

NoLa[PH]
NoLaPH is intended to be a low-cost, low-tech and easily constructed CO2 reducing Passivhaus. NoLaPH achieves Passivhaus and moves beyond carbon neutrality without costly triple-pane windows and over insulated envelopes, ensuring a truly affordable, sustainable and comfortable home.

Design
NoLaPH is a play on the traditional shotgun typology, with a pivoted gable roof and a pushed-out bay. The rotation of the roof allows for a clean, modern take on a traditional ‘shotgun’ while also being efficient for rainwater harvesting, solar harvesting and effective shading of the house. The pivoted gable allows tall, naturally lit spaces. The hallway is re-purposed as a semi-public space, with a full-length study area.

The pushed out bay allows for more outdoor living area than a traditional shotgun. While this creates a higher surface area to floor area ratio, the optimized envelope and fenestration allows achievement of the Passivhaus standard with minimum effort. The additional decks effectively double the area of the house while allowing a multitude of variegated daylight and natural ventilation. They also make for legendary house parties.

Above-grade wall assembly, U-value=0,25 W/m²k (R-22.3)

  • GWB
  • uninsulated 2×4 wall
  • ½” plywood (air barrier)
  • 3″ foil faced polyiso
  • Rear ventilated rainscreen

Floor assembly, U-value=0,15 W/m²k (R-36.8)

  • Wood flooring
  • plywood
  • 9 1/2″ open web wood truss w/ 4″ cellulose
  • 1/2″ plywood (air barrier)
  • 3″ foil faced polyiso
  • 1/2” cement board

Roof assembly, U-value=0,25 W/m²k (R-22.7)

  • GWB
  • inverted wood truss
  • ½” plywood (air barrier)
  • 3″ foil-faced polyiso
  • battens/counter battens
  • corrugated metal roof

Environment
NoLaPH is a durable structure that has the ability of being completely deconstructed and recycled. Though intended to be stick-framed, NoLaPH is pre-fab friendly and could easily be adapted to prefabrication or panelization systems. Precast concrete piers require minimal site disturbance. Low/No-VOC finishes are selected for occupant health. The materials used are low-carbon products with minimal embodied energy and Global Warming Potential (GWP). The utilization of photovoltaics + Passivhaus allows for one of the first CO2 reducing homes in North America, meaning that not only is the house CO2 neutral/plusenergiehaus, but it is actually reducing the carbon footprint of its non-Passivhaus neighbors.

Energy
Achieving Passivhaus significantly reduces the heating and cooling demand of NoLaPH. With a peak cooling load of less than 4.26BTU/sf, a traditional mini-split is actually oversized for the house. Utilization of a hot water heat pump, which conditions the space as it heats water, further reduces the energy while assisting in active cooling. Compact fluorescent lighting, energy efficient appliances, adequate daylighting and reduced reliance on active heating and cooling push the specific primary energy demand to 27.4kBTU/ft2a. With the installation of a grid-tied 3kW photovoltaic system, more energy is produced than needed on an annual basis. Thus, not only is NoLaPH low-cost to construct, it is also low-cost to operate.

Water
NoLaPH’s monosloped roof allows for harvesting rainwater to a single or multiple points. A rainwater harvesting system is intended for nourishing “edible estates” on the lot, while reducing the demand on a decaying infrastructure. With incorporation of a properly sized tank, biodigester and city approval, NoLaPH could be net-zero for water as well.

Envelope
The reclaimed cypress and fiber cement rainscreen is durable and ensures water shedding. The polyisocyanurate insulation manages inward vapor drive and reduces thermal bridging. All wood is treated with non-toxic borate. Drywall is paper free to reduce mold buildup. Because the 2×4 wall is uninsulated and an interior air barrier is not utilized, all walls can serve as MEP chases, keeping the cost of construction low and reducing the likelihood of air barrier degradation. Utilization of shaded double-pane wood-clad windows with low-SHGC ensures comfort in a hot/humid climate without sacrificing aesthetic or environmental impact.

Air Barrier
The air barrier used is borate-treated plywood taped with Siga or 3M to ensure airtightness.

Ventilation
Utilization of an UltimateAir Recouperator Energy Recovery Ventilator (ERV) and MERV13 filters ensures superior indoor air quality. The inverted roof trusses allow duct runs within the thermal envelope/air barrier, as well as incorporation of down lights.

Airtightness: 0.60ACH50 (by design)
Heating Demand: 9,91 kWh/m²a (3.14 kBTU/ft²a)

Primary Energy Demand: 86,4 kWh/m²a (27.4 kBTU/ft²a)

Cooling Demand: 15 kWh/m²a (4.75 kBTU/ft²a)
Cooling Load: 13,44 W/m² (4.26 BTU/ft².hr)

Heating/Cooling
Though the house is incredibly diaphanous and can operate through most of the year without reliance on heating or cooling due to the optimization of the façade and windows, supplemental heating and cooling for extreme days is provided by a 1-ton mini-split system. The utilization of multiple decks allows for adequate passive ventilation during the day and night cooling in summer.

  • Location: New Orleans (LA)
  • TFA: 999.33 ft² (out of 1,000 ft² max)

additional links:

  • Geoff Briggs

    I’m a big Passive House proponent, but I’m writing today to ask about the software you used to prepare this presentation. Further, did you employ some type of automation to construct the 3D framing model shown in the last image? Thanks.

    Cheers,
    Geoff Briggs

  • http://bruteforcecollaborative.com mike eliason

    geoff,

    software was really basic due to uber-compressed timeframe – archicad + sketchup w/ a little illustrator/photoshop post-editing.

    the 3-d framing was just me messing around in sketchup over the course of an hour. i “built” an open web wood truss component in about 3 minutes and copied/manipulated. threw up some studs for OVE that were cut (intersected plane). the roof truss was just an inverted wood truss that was drawn once and then copied/manipulated.

    it’s not ideal, but it was only meant to serve as a diagram.

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