The project is a renovation of a 2-story, single-family, wood frame house built in Omaha, Nebraska, during the 1960’s. The main living spaces—Living room, Dining, and Kitchen are located on the ground level, the bedrooms are upstairs, and the basement is unfinished. The house has a 36ft by 30ft footprint; the long axis is in the north-south direction. The existing house is a very energy-inefficient building, built with 2×4 walls, no insulation, and aluminum windows.
The purpose of the project is to renovate the house to meet the Passive House standard. The design of the house meets the Passive House, resulting in an ultra-energy-efficient, extremely comfortable, and durable building.
Passive Houses require a balance of solar heat gains, internally produced heat gains, and a small amount of supplemental heat (or cooling) to offset heat loss (or gains) and air-leakage through the thermal envelope (exterior walls, windows, and roofs).
Solar Heat Gains. Solar Heat Gains are minimized in the warm months and maximized during the cold months by a variety of methods. The methods are as follows.
Overhangs. Through the use of generous overhangs, sun is allowed to enter the house during the winter and is kept out of the house during the summer. The windows are recessed inward from the face of the house, supplying additional shading during the summer.
Glazed Area. At the South Elevation, the glazed area is the largest of all the facades. At the North, East, and West Elevations, the glazed area is less than the south elevation.
Window Glazing. The window glazing is tuned; the solar heat gain coefficient (SHGC) varies with each orientation. The SHGC is .5 at the windows that face north, .3 at the windows that face east and west, and .7 at the windows that face south.
Shading. Deciduous trees shade the house during the warm summer months and allow solar gain during the winter. A screened porch is positioned at the southwest side of the house to shades the house from the hot southwestern sun.
Internal Gains. Heat produced by occupants, cooking, laundry, electronics, and other internally produced sources are captured and help heat the house.
Supplemental Heat. Space heating and cooling is provided by a 2-zone, ductless mini-split heat-pump.
Ventilation. Ventilation is provided by a high-efficiency energy-recovery ventilator. Fresh air is supplied to living and sleeping areas and exhausted from the kitchens, bathrooms, and other wet areas.
Domestic Hot Water. An electric-heat-pump water heater is located within the conditioned space.
Air-Sealing. A continuous air-barrier is provided to prevent air-leakage from exceeding .6ACH50. The air-barrier consists is a solid material—plywood or OSB. The air-barrier is located at the sub-floor between the basement and main level; at sheathing between the 2×4 framing and the exterior TJI’s at each of the four exterior walls; and at the sheathing on top of the rafters at the roof. The vast majority of the mechanical, electrical, and plumbing systems do not penetrate this air-barrier.
Super-insulation. The building is highly insulated at the floor between the basement and main level (R78), all four exterior walls (R70), and the roof (R104). The windows are highly insulated (R7). The insulation at the walls consists of 15 ½” blown-in batts. The insulation at the roof consists of 24” blown-in batts.
Thermal Bridging. Thermal Bridging is minimized. At the exterior walls, an insulation cavity is constructed using TJI’s. TJI’s have minimal conduction.
Project details in sidebar.