Achieving Passive House Standards: Insights from H.R. Crawford Gardens

​For real estate developers and builders considering incorporating Passive House standards into a future multifamily residential project, Soto Architecture’s design of H.R. Crawford Gardens provides several lessons on elevating (affordable) multifamily design cost-effectively. 

This article delves into five key steps Soto Architecture employed in the design of H.R. Crawford Gardens to attain Passive House (PHIUS) certification along with Enterprise Green Community Plus 2020, Energy Star Multi-Family New Construction, DOE Zero Energy Ready Homes, and EPA Indoor airPLUS. 
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If that sounds like a lot, you’re right, it is! But many of these programs are designed into the Passive House standards. In the end, it all comes together in a symphony of systems and decisions working together to provide a beautiful, safe and healthy building for residents of the building. 


5 Principles

1. Air-Tight Construction / Blueprint Robotics
2. Superior Thermal Insulation
3. Great Windows and Doors that Don’t Break the Bank
4. Mechanical Ventilation with Energy Recovery
5. Building Electrification and Renewable Energy Integration

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1. Air-Tight Construction and Panelized Construction

Achieving a high level of airtight construction is critical to meeting the Passive House standard. Without air tightness, the potential for energy leakage or unwanted air infiltration can lead to serious moisture and durability issues. A high-quality air barrier, typically self-adhered or fluid-applied, is used in conjunction with robust interior air sealing details. 
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The H.R. Crawford Gardens framing package is fabricated by a panelized builder offsite in Baltimore, M.D. The framing, sheathing and water-resistive air barrier (WRB) are fabricated in a warehouse under controlled conditions and assisted with high-tech manufacturing procedures instead of out in the elements. This allows the majority of exterior WRB joints, fenestration openings, and penetrations to be properly taped and quality control reviewed at eye level rather than high up on scaffolding in the elements. Greater consistency is achieved and the finished product is of higher quality. Panel joints will still need to be sealed in the field, but with proper preparation, this will be similar to the standard manufacturer transition.

Walls are ready to be delivered on site and assembled.

2. Superior Thermal Insulation

 H.R. Crawford Gardens prioritizes superior thermal insulation. The walls, floors and roof assemblies all work to limit heat transfer from inside to out or vice versa, depending on the season. Exterior walls have a layer of continuous exterior mineral wool insulation paired with standard batt insulation between studs. This continuous exterior insulation along with thermally broken cladding attachments eliminates thermal bridging at the exterior wall studs found on typical code-level projects. Rigid insulation is used at foundation walls and below the slab to reduce heat transfer through the ground. 
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Lastly, the roof assembly uses a combination of rigid insulation on top of the structural roof sheathing paired with spray foam insulation below the sheathing. The key to success for floors, walls and roofs is that the insulation is installed on the outside of the building where it can be used to its fullest uninterrupted extent to create a thermal blanket for the building. There are no exotic materials here either. All of these are commonly used products within the building industry and are installed in well-known assemblies to allow for cost-effective and high-performance construction.

Thermally broken girts, such as the Smart CI Greengirt, are a cost effective way to improve your insulation effectiveness.

3. Great Windows and Doors, Without Breaking the Bank

The Passive House standard emphasizes the installation of high-performance windows and doors with exceptional airtightness and thermal properties. Doors and windows typically become the weak points of a well-insulated wall. Accounting for this in Northern climates often means utilizing triple pane windows with robustly engineered frames.

In the Washington, D.C. region, and as used at HR Crawford, high-performance double pane windows can still achieve the required U-values and Solar Heat Gain Coefficients without adding an additional layer of glass. Casement-style or other compression-style windows provide tighter air seals reducing air infiltration. While this is an upgrade over a standard code-compliant vinyl single-hung window, it falls below the higher costs of triple-pane windows. The improved air tightness and thermal performance enhance occupant comfort by reducing drafts, providing a quieter interior space, and providing long-term operational efficiency.

Intus Windows makes a great double pane window that meets Passive House standards in the DC region.

4. Balanced Mechanical Ventilation with Energy Recovery
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To maintain optimal indoor air quality while conserving energy, H.R. Crawford Gardens incorporates a dedicated Energy Recovery Ventilator (ERV) for each floor. The ERV provides a continuous supply of fresh air to every living space and common area while simultaneously removing stale air through exhaust ductwork. The ERV is then capable of recovering heating or cooling energy from exhaust air to temper the incoming fresh air. This process retains energy compared to constantly exhausting air directly to the exterior and limiting the conditioning of the incoming air required. For localized heating and cooling within the apartments, a high SEER mini split heat pump is provided at every unit to keep spaces comfortable. Occupants will benefit from a healthier living environment while the property owner will benefit from lower energy costs and lower tenant turnover. 

​Diagram of how an ERV works - credit to South Central Services​

5. Building Electrification and Renewable Energy Integration
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Sustainability and energy codes are driving towards building electrification and site-generated renewables. Multifamily buildings tend to have a few key areas that still employ fossil fuels. These include gas cooktops, gas-fired mechanical systems, gas water heaters and emergency power backup systems. 

At HR Crawford, we moved to all electric appliances, a relatively simple switch and the ERV enabled us to replace the typical gas-fired Dedicated Outdoor Air System (DOAS) with a more efficient system. We are still employing a backup generator that utilizes natural gas. This is a limited use case that doesn’t impact the daily operation of the building while providing building safety and security in the event of power losses. 

The last big hurdle is the water heating system. Electric heat pump water heaters can be employed on an individual unit basis or building-wide. Note that standard electric water heaters don’t tend to meet the energy efficiency requirements for high-performance buildings. While heat pump water heater technologies are rapidly improving, the jump to this type of system did not result in a favorable cost-benefit analysis. For this building, a traditional, but highly efficient building-wide gas-fired water heating system with recirculation loops was chosen to provide hot water for residents. The building has been electrically wired for future transition to an electric system once the costs fall in line with current systems. 

​Using these steps to design high-performance multifamily residential projects like H.R. Crawford Gardens offers enduring benefits for both market-rate and affordable housing developers and owners. The energy-efficient design provides a more comfortable, cost-effective, and healthier space for tenants, contributing to increased affordability. Additionally, the durability and minimal maintenance requirements of air-tight and factory-built exterior and interior wall panels ensure reduced long-term operational costs, while higher performance also provides enhanced long-term positioning for developers.

Hr Crawford Gardens project page