2015 Challenge Participant:
Revival Homes - Katzin Residence
Applicants: David Jones, James Katzin
Project Address: 62 Perkins Road, Litchfield, CT 06759
Bdrms./Sq. Footage: 3 BD - 1,379 sq ft
Builder Website: firstname.lastname@example.org
General Project Overview:
There is a perception that “green” or high performance homes are something that only the wealthy can afford. We wanted to design a house that would shatter that perception both when considering the initial cost of construction, and even more importantly when considering the Total Cost of Ownership (TCO defined as initial construction costs, energy costs, maintenance/operational costs).
The focus on minimizing Total Cost of Ownership required the design to consider not only energy savings, but also the initial cost, durability and life cycle costs. The goal for the initial cost of construction would be less than the HVAC system or window package in many high performance homes. This pointed toward using factory built components whenever possible and simple/durable systems and materials.
Additionally in order to meet the very ambitious budget goals, we had to reconsider preconceptions about what a house in Connecticut looks like and how it is built. This required departing from the traditional style of stick building. The budget goal required us to accept change in order maximize performance and minimize cost.
A Different Approach
Whenever possible all building systems/ components had to serve multiple functions in order to meet the target budget. There was no room in the budget for complex systems such as ground source heat pumps, complicated wall assemblies, or resource intensive foundations/basements.
This house has no basement, and in fact no traditional foundation. The first floor walls are concrete panels with an integral stucco siding system. The roof and 2nd floor are Structural Insulated Panels. There is no central heating/cooling system. A single ductless mini –split system provides heating/cooling.
A basement is typically a low value space that requires a lot of resources to keep warm and dry, so we decided to eliminate it. The basement had little value since most of the traditional mechanical equipment that typically occupies a basement, such as a boiler, air handler and duct work had been eliminated.
Then the “foundation” was eliminated to reduce costs, embodied energy, and improves drainage in a wet site. The above grade concrete wall panels are built on crushed stone filled trenches extending below the frost line. The stone trench “foundation” supports the building, is less expensive to build, has less embodied energy and eliminates the need for a curtain drain on a wet sloped site.
We utilized the concrete slab as both the floor structure and the finished floor. The concrete slab is extremely durable, doesn’t require any additional resources, and adds thermal mass to the interior of the envelope.
Building Systems for the Shell
We set out to avoid complicated assemblies that require a great deal of labor and increase the chances for construction errors. We wanted to avoid the complexities of a stick framed wall, sheathed with wood panels, a WRB, exterior foam insulation to keep the sheathing warm, an air space to create a rain screen system, and a separate siding system.
We selected a precast concrete wall panel system (typically used as a foundation below grade) for our first floor walls. These panels have continuous foam insulation, serve as wall structure, siding, water barrier, and air barrier.
We used SIPs for the roof and 2nd floor walls. The prefabricated SIPs did not require any additional wood framing (no beams, posts, rafters, or studs). The SIPs provide continuous insulation with no thermal bridging. The solid foam core means there is no path for air leakage and condensation issues which are common with traditional porous forms of insulation.
Both SIPs and the concrete wall panels are prefabricated in factory controlled conditions and assembled on site. They decrease dry in time and the associated costs and mold risks. They minimize construction waste. Most importantly panelized construction simplifies air sealing.
Air sealing took priority above R-value in the envelope. The building envelope is composed of large factory built components with few joints, and the air sealing challenges are minimized compared with Stick Built construction. It is far easier to seal a wall made of 3 components rather than a wall made of 100 various components. The elimination of the foundation/floor joist intersection also eliminated an area typically difficult to air seal. Given the simplicity of air sealing such a house we were able to meet our goal reaching the Passive House Standard of .6 ACH @50 Pa. with far less effort than is required with other forms of construction.
Budget: Achieving a very high level of performance on a modest budget is the most significant feature of this house. Initial cost of construction and Total Cost of Operation were primary drivers of this design. Building a high performance house with an extremely low cost of operation and an “entry level” price point was a significant challenge. This project should help raise awareness of how much is possible at all price points and this goal is shared by the entire team.
Standards: This project is designed to comply with DOE Zero Energy Ready, Energy Star Version 3, Water sense, Indoor Air Plus standards.
Accessibility: The house is designed to allow living entirely on the first floor if needed. Unlike typical houses in the region, this house is built on a slab at grade with only a single step into the house at all exterior doors. The house has a first floor master bed/bath/laundry. There is a curbless shower on the first floor. The exterior has landscaped patio spaces at grade rather than an elevated wood deck.
Passive Survivability: This house contains significant thermal mass in the first floor slab, the concrete exterior walls, and the ¾ inch heavy weight plasterboard and veneer coat plaster on interior walls and ceiling. The house can maintain a reasonably comfortable temperature in the coldest periods for many days even without a heat source. Even with extended periods with no heat source its unlikely the house would ever get below 32 protecting it from freezing under the worst conditions.
Storm Resistance: The roof and 2nd floor walls are made of SIPs. SIPs homes have consistently performed better than stick built homes in severe storms, tornadoes, and earthquakes. The first floor walls are 2 inches of 6,000 psi concrete that is capable of withstanding severe impacts without damage and are extremely fire resistant. The concrete first floor walls are tied directly to the concrete slab without a wood connection to help the building resist uplift. The entire roof is covered with self-adhering membrane which would keep water out of the house even in a case of wind speeds severe enough to remove the shingles.
Moisture Resistance: The first floor walls are unusually tolerant of moisture. The concrete skin cannot rot and because of its density does not require any form of chemical sealer. The concrete wall system replaces the typical moisture sensitive stick framed wall, the WRB, the rain screen wall system, and a secondary siding material. The ridged foam insulation inside the wall prevents condensation in the stud cavity, does not absorb moisture or support mold if water was present. The thermally broken steel stud does not absorb moisture, rot, or support mold. The rock wool insulation repels water better than fiberglass, and does not support mold or absorb moisture like cellulose. The SIPs used for 2nd floor walls and the roof have solid foam insulation with no path for air leakage and the resulting danger of condensation associated with porous forms of insulation. The 2nd floor walls are protected with a rain screen system created with drainable house wrap.
Fire Resistance: All interior walls and ceilings are made with 5/8” “firecode” plaster board, a base coat and finish coat of plaster, for fire resistance well beyond the industry standard ½” drywall. The first floor wall cavities are filled with rock wool insulation which does not burn and eliminates the need for fire stopping at the top of the walls. The concrete exterior resists fire as well.
Heat Pump Dryer: A standard clothes dryer consumes a great deal of energy both to operate the dryer and to condition 150-200 cfm of air exhausted from the house when operating the dryer. Using a heat pump dryer reduced the direct energy requirements for dryer operation, but also eliminated the need to condition the “make up” air. The unvented heat pump dryer also eliminates the challenges of depressurization in an extremely air tight house.
Open Built: We expect this home to last hundreds of years. To remain viable in the future homes must adapt to the needs of various owners over time. Interior floor plan and mechanical systems are the most likely items to change over time. Planning for future changes in the building is known as open building. This house can accommodate future changes by having the first floor slab finished prior to building the interior walls. This makes future floor plan changes simpler since the finished fl