Orness Plaza

Mankato, MN
Completed May 2012

The Orness Plaza is a 7-story, 101-unit apartment building located in Mankato, Minnesota. Originally constructed in 1971, it is home to primarily an elderly and disabled population. The 100 one-bedroom and 1 two-bedroom units are arranged around an open atrium. A substantial renovation of the building began planning in 2009, with a focus on goals to improve occupant health, building durability and energy and water efficiency. Construction was completed in late spring of 2012. The project is received a LEED Silver certification under the new construction (v2009) from the US Green Building Council and fulfilled the Enterprise Green Communities Criteria with Minnesota Overlay.

The scope of work included the stabilization and restoration of the primary concrete structure, replacement of windows, installation of new insulation and exterior cladding systems, replacement of mechanical systems, introduction of mechanical fresh-air ventilation into each unit, asbestos tile abatement, mold abatement, and a complete unit-by-unit gut retrofit including full kitchen and bath.

A green charrette was held to kick-off the Orness project in December of 2009. An integrated design and construction team consisting of architects, engineers, commissioning agents, researchers in building science and public health, and the ownership development team worked together to set goals, and explore strategies to achieve project objectives. Primary goals for were to extend the useful life of the building; focus on health living environments for the residents; improve indoor environmental quality (IEQ); and reducing energy and water consumption. A holistic approach was utilized to understand and integrate solutions in the project.

The combined energy, health and IEQ targets emphasized an improved envelope focused on durability and thermal comfort. Other strategies used to meet the objectives were the introduction of fresh-air ventilation into units, revamped exhaust air systems, material selection to avoid contaminants, and elimination of future mold potential in the design and detailing of the envelope and window penetrations.


The energy conservation goal was to meet the energy target set by Architecture 2030 and reduce the total energy consumption in the building by 50% over the existing condition. The project team took a two-pronged approach to meet this goal. First, reduce the overall need for energy through envelope improvements. Second, meet the remaining needs of the building using energy efficient systems and appliances.

The condition of the 1971 building prior to renovation was poor. The primary structure and enclosure is a site poured concrete frame with exposed concrete aggregate panels. Hairline cracks developed in the panels over the last several years resulting in staining and spalling on the exterior. The original windows (aluminum single-pane sliders) failed almost immediately after construction. They were repaired over the years, but not previously replaced. Remediation, maintenance, and abatement of water infiltration resulting from pervasive window failures were on going. In several units mold had been remediated, also. The walls were insulated with ¾" polystyrene insulation on the interior face. The roof failed several years ago and was replaced. It was not be part of the scope of work for this project.

The project team considered several options for both repair and replacement of the existing envelope. They included the following: remove and replace the existing concrete panels with a new concrete or metal panel system; repair and stabilize the existing panels and insulate from the interior; and repair and stabilize the existing panels and insulate for the exterior.

The existing heating and cooling system was a hydronic system fed by a central natural gas fired boiler, and individual through-wall air conditioners. The building had an exhaust-only ventilation strategy and no mechanical fresh-air ventilation in the units. (The building has operable windows in the living-rooms and bedrooms). Replacement mechanical system options considered were a geothermal heat pump system, a hybrid geothermal heat pump (minimizing the well field by supplementing with a boiler to handle peak demand which is needed less than 10% of the year), and a four-pipe fan coil system.

The new heating and cooling system is a central geothermal ground source heat pump, which feeds a water loop connected to individual heat pumps located within each apartment unit. The new fresh air ventilation is de-coupled from heating and cooling to provide more reliable distribution throughout the building. Post-renovation fresh-air supply is ducted to each unit supplied by roof top units, and air is continuously exhausted via the bathroom fan from one of 12 powered roof ventilators (PRVs). A thirteenth PRV draws air out of the laundry and trash areas. A wall switch activated bathroom fan can increase intermediate exhaust air volume. The exhaust systems utilize existing ductwork.

A solar domestic hot water system was considered for the project. It was not included in the final scope of work of the project. Hot water is supplied by gas fired commercial grade hot water heaters.

Prior to renovation Onress Plaza had an energy intensity of 127 kBtu/sf-yr. Following the national Architecture 2030 criteria which mandates a 50% reduction for renovation projects the energy target is 64 kBtu/sf-yr. Post construction energy use is 70 kBtu/sf-yr. Given the major improvements in the building including the addition of fresh-air to units, improved exhaust air, and improved resident comfort the accomplishment is substantial.


The water saving strategies for the Orness Plaza apartments consisted primarily of the specification of efficient flow and flush fixtures. As there is minimal outdoor landscaping the majority of the water consumption is attributable to interior uses. The fixtures selected for the apartments are 1.5 gallon per minute (gpm) showerheads, 1.5 gpm kitchen faucets, 0.5 gpm bathroom faucets and 1.6 gallon per flush (gpf) toilets. The contemporary Green Communities Guidelines maximums for the project were 2.0 gpm showerheads, 1.5 gpm kitchen faucets, 2.0 gpm bathroom faucets and 1.6 gpf toilets. The fixtures specified satisfy the Green Communities Criteria requirements.


A primary focus of the renovation at Orness Plaza was resident health and indoor air quality. As noted above, Orness is the site of a health study funded by HUD. An extensive analysis of indoor air and environmental quality is part of the study. An update to this case study will be posted at the conclusion of the study in 2014.