The New Orleans Passive House
- Limehouse Architects & Hines Design Associates -
Traditional New Orleans houses perform well as passive houses. The generations of learning about how to live in a hot, humid climate have left a rich variety of tools and designs for living here.
We can apply the current learning about climate control, the new materials now available, and some insights learned by research and testing to the wealth of vernacular wisdom about building in this climate and improve the performance, resilience, and sustainability of New Orleans houses. We hope that some approaches shown here will be equally valid in retrofitting many of the existing damaged and abandoned houses which already have the old vernacular “bones”, which are sitting in the old familiar neighborhoods, awaiting the green solution of repair, retrofit, improvement and preservation. We know that retrofitting an existing houses is a far greener exercise than building from scratch and New Orleans is full of possible reclaimed passive homes.
Low Energy Building– The Current Approach
Much of low-energy use engineering presumes a required environmental standard of controlled temperature and humidity, with high levels of insulation delivered in a tightly sealed envelope. The Passive House Institute challenges this approach and looks to applying a strict limit on energy regardless on whether the energy is used for climate control, appliances, or user energy. Passive House claims that we in the U.S. rely too heavily on photovoltaic arrays to counter poor design and detailing. We note that much of Passive House design originated in northern Europe and that both Passive House and Energy Star based technologies are not yet fully understanding the bigger picture of human habitation in relationship to climate.
The result of the sealed and idealized temperature and humidity world of a low-energy house are several:
1. Isolation from the actual habitat where we live. When windows are designed to be most efficient when always closed, we are cut off from the sounds of rain, birds singing, the breeze in the trees, sounds and smells of the neighborhood.
2. Lack of adaption to climate which results in difficult thermal transitions when we go outside in a hot climate. We feel less inclined to sit on a porch, work in a garden, go for a walk, ride a bike, participate in a neighborhood community. The thermal shock intimidates.
And yet, human beings are remarkably able to adapt to all sorts of environments, even extreme ones. The original New Orleans houses were remarkably good at providing enough comfort without cutting off all relationship to the environment. People who still live in these houses become familiar with how to operate these houses. Opening the house up, or closing it to hold cool air, using the functional shutters to shield the windows from direct sun or heat, using prevailing winds to cool are all techniques that used to be quite familiar for living in these houses. The occasional fan to move the air around was one of the few electric powered tools that accomplished this.
Combining High-Tech with Vernacular Passive Wisdom
In our submission we felt it was necessary to provide adequate heating, cooling, and dehumidification as well as air sealing so that the house could be operated as a fully performing high-tech house, but we the goal for this house is to be used whenever feasible as a traditional New Orleans passive house.
We knew that a tightly sealed house removes the temperature gradient between floor and ceiling as convection currents are nullified when there is little air leakage. The tradition of high ceilings came about before air sealing and made survival possible in the New Orleans climate. Since, we wanted to create a house that would make use of open windows for much of the year, we designed for a 12' ceiling as well as traditional triple-hung floor-to-ceiling windows that induce air flow. We then specified these windows to selectively reflect infra-red light, with good U values and shading coefficients. We then went further and provided shading by porches and added functional shutters to give residents several ways to manage their home.
We understand that people have traditionally interacted with their houses, opening an closing windows, ventilating the house at night, customizing their use of the house. Most energy design software today does not allow for that interaction, but we feel it is both reasonable and important for a real-world experience.
Our design offers several ways to use a house. It can be used in the current standard as a tightly sealed and highly insulated house with a highly–energy efficient air-to-air heat pump that combines heating with cooling and dehumidification. The Heat Pump would include fresh air ventilation to current air change standards.
The house would also have a de-humidification only option that could be used to achieve comfort levels without using the heat pump. This would still clearly require closed windows, but could come closer to providing a local climate connection to temperature. The dehumidification system would operate as a fresh air ventilation system as well.
We intend that the house can also be successfully operated for many months as a naturally ventilated house with open windows, and resident control of passive systems. We feel that this offers the most energy efficient and connects the resident best with the environment of both climate and place. We have added a south-facing gallery porch and a west facing porch to enhance the use of the house. We have considered using trellises on vines to mitigate sun on exposed walls, but feel that in traditional New Orleans neighborhoods some side wall shading can occur from neighboring houses so the climatic effect of the urban design plays a part in a passive house as well.
Heating will reflect the typical closed windows and ventilation via the heat-pump system.
Problems we have encountered are that most software programs do not model the impact of de-humid-ification only systems, and resident operated shading or venting systems are simply not considered. Current software considers a house as an isolated tightly sealed unit on a treeless plain, with no context other than orientation, isolated from place and un-affected by human usage.
Using Passive Techniques to Increase Resiliency
One clear issue with housing in New Orleans is water, whether experienced as high humidity, wind driven rains, or flooding, water threatens houses with rot, termites, mold, and mildew. For this reason, we have chosen closed-cell foam insulation with an external water and air barrier. This will keep structural members dryer as well as increase the seal against infiltration in the walls, floors and ceiling. Interior walls will be finished with paperless drywall to avoid mold growth. In the case of future floods, water can pass under and even through the building. Closed cell foam and paperless drywall will not support mold growth and opening walls to repair electric systems will not involve accessing through sodden batt or cellulose insulation.
Many approaches to building in New
Orleans have sealed the attic space into the conditioned envelope as well, but here we decided to seal the envelope at the attic line. With the 12' ceiling we could easily accommodate the HVAC system within the conditioned space and it allowed use to use the attic/roof as a shaded roof with full passive ventilation of the attic space. The attic is not envisioned for occupancy and therefore did not require additional fire-proofing.
Foundations will be either grade beam with concrete block piers, or borate treated wood piers depending on local soil conditions. The floor will be sealed and insulated with closed cell foam.
Wall framing will be with 2x6 studs @ 24" o.c. and structural insulated sheathing to yield an R-28 wall. Walls, foundation and roof will comply with current hurricane building load requirements with attachments and detailing.
We feel that the future of the New Orleans Passive House design must accommodate retrofit, preservation and repair as well as new construction. It needs to consider the best of traditional knowledge about forms, current energy technology, urban design, and landscape solutions and must always consider the human experience and quality of life as essential to its creation.