A HABITAT FOR HUMANITY HOUSE USING
INSULATED CONCRETE FORMS
The design, construction, and maintenance of buildings have a tremendous impact on our environment and our natural resources. There are more than 76 million residential buildings and nearly 5 million commercial buildings in the U.S. today. These buildings together use one-third of all energy consumed in the U.S., and two-thirds of all electricity. By the year 2010, another 38 million buildings are expected to be constructed. The challenge will be to build them smart, so they use a minimum of nonrenewable energy, produce a minimum of pollution, and cost a minimum of energy dollars, while increasing the comfort, health, and safety of the people who live and work in them.
Our built environment is also a major source of the pollution that causes urban air quality problems, and the pollutants that impact climate change. They account for 49 percent of sulfur dioxide emissions, 25 percent of nitrous oxide emissions, and 10 percent of particle emissions, all of which damage urban air quality. 35 percent of our carbon dioxide emissions, the chief pollutant blamed for climate change is attributed to building consumption.
Traditional building practices often overlook the interrelationships between a building, it’s component parts, it’s surroundings, and it’s occupants. "Typical" buildings consume more of our resources than necessary, negatively impact the environment, and generate a large amount of waste. According to Laurence Doxsey, former Coordinator of the City of Austin Green Building Program, "a standard wood-framed home consumes over one acre of forest and the waste created during construction averages from 3 to 7 tons." Often, these buildings are costly to operate in terms of energy and water consumption. And they can result in poor indoor air quality, which can lead to health problems.
There are many opportunities to make buildings cleaner. For example, if only 10 percent of homes in the U.S. used solar water-heating systems, we would avoid 8.4 million metric tons of carbon emissions each year.
Sustainable building practices offer an opportunity to create environmentally sound and resource-efficient buildings by using an integrated approach to design. Sustainable buildings promote resource conservation, including energy efficiency, renewable energy, and water conservation features; consider environmental impacts and waste minimization; create a healthy and comfortable environment; reduce operation and maintenance cost; and address issues such as historical preservation, access to public transportation and other community infrastructure systems. The entire life cycle of the building and its components is considered, as well as economic and environmental impact and performance.
These ideas became important when designing and constructing Habitat for Humanity homes. Habitat homes must be affordable to construct, using techniques that are manageable by a largely volunteer workforce, but more importantly, the homes must be simple to maintain and efficient and inexpensive to operate. Operational costs are extremely important when working affordable housing. So it is just as important to keep future operating costs to a minimum, as it is to keep first costs (of construction) within an affordable range.
Toward these sustainability, efficiency, and affordability goals, a class was set up at the University of Illinois School of Architecture to examine these ideas within the context of a Habitat for Humanity home. The central ideas are to embrace holistic, sustainable design ideas in an affordable, easy to construct residence and participate in it’s construction.
One of the unique characteristics, and the focal point of this house are the insulated concrete forms, (ICF’s). ICF’s are walls constructed of concrete but the forms are left in place to serve as a continuous insulation and sound barrier to reduce energy loss and infiltration. The major advantages or this construction type are:
With the use of ICF’s, there is a 25% to 50% energy savings as compared with that of wood or steel framed homes. The paybacks in energy savings are estimated to be within five years.
DESIGN DETAILS
This house was designed to affordable, sustainable, and accessible. By using a split-level design, the footprint of the building was reduced to 900 square feet, thus allowing the plan to become more interchangeable in it’s orientation on the lot. Depending on the location, site orientation, and other environmental conditions, the house can vary to become as efficient as possible. This plan consists of a split-level, four bedroom and one and a half bath. The total livable area is 1276 square feet. The entry, living room and kitchen all sit above the crawl space while the bedrooms are part of the split level. The house is visitable, which means it has an accessible entrance, living room, kitchen and bathroom.
MAIN FLOOR PLAN
LOWER LEVEL PLAN
Floor construction
The floors of the house are constructed of two different materials because of the fact that one sits at grade level, for the entrance, one sits above grade and one is below grade. The floors that are at grade and above grade are constructed of ¾" plywood on 9 ½" wood I-Joists. The joists are 16" on center. The plywood is then finished with carpet and laminate flooring in the living areas. The floor that is below grade is poured concrete. The livable area below grade will be finished with a carpet covering while the unlivable crawl space will be a rough concrete finish.
Wall construction
The exterior walls are constructed of insulated concrete forms, (ICF’s). Expanded-polystyrene forms, with a hollow center cavity, are erected like a set of Lego blocks and then the core is poured concrete. The forms stay in place as permanent parts of the wall. The forms provide a continuous insulation and sound barrier that reduced the infiltration rate to one-half that of a typical stick frame home. The inside form then serves as a backing for dry-wall while the outside form serves as backing for siding, brick or any other type of finish. In this situation, stucco will be the exterior finish. The walls are solid concrete so they offer a greater protection from storms. 4" of foam insulation and 6" of concrete provide an R-value of 17. Plus, the ICF’s extend well below grade so the infiltration is almost half that of standard stick frame homes and there is a high thermal mass that contribute to energy savings. The paybacks in energy savings are estimated to be within five years.
Roof and Ceiling Construction
The roof and ceiling construction is designed with the bottom of the overhang, the soffit, at the same level as the ceiling of the house. This simple modification of the usual roof-ceiling framing provides space to extend the ceiling insulation over the outside walls and still maintain adequate ventilation. Asphalt shingles will cover the #15 felt and 7/16" inch O.S.B. sheathing that rests on the 2" x 4" wood prefabricated trusses. R- 38 insulation is used and the ceiling is ½" gypsum board with a paint finish.
Shading
While the south-facing windows provide solar heat for the house from October to April, the windows should be properly shaded to cut down the heat gain for the rest of the year. Deciduous trees are useful because they are full of leaves during the summer months to help cut down heat gain, but during the winter months when solar gain is needed, the leaves are gone and they do not interfere with the solar gain. Roof overhangs play another big role by providing shade because of the angle of the sun. During summer months when the sun is high, the overhangs will block the unnecessary heat gain, but during the winter when the sun is low, the overhangs to not interfere. This shows how the entire site must be incorporated in the design to provide the most efficient home possible.
Energy savings
Because there are no seams in the wall system, conduction losses through foundation and above ground walls are cut in half. The loss through infiltration is also cut in half. Not only does the concrete cut down energy loss, it provides the house with a higher thermal mass, which smoothes out the large swings in temperature. This keeps the house a little warmer on the coldest days and a little cooler on the warmest days.
According to data from Energy10, an energy simulation program, this home would require 44% less energy to heat and 32% less energy to cool as compared to stick framed homes. A typical 2000 square foot home can save $200 is heating costs each year and $65 in cooling costs. The bigger the home, the larger the savings will be. With the energy savings that will occur due to the insulated concrete forms, less mechanical equipment is required and the savings there can be from $500 to $2000.
SO WHY USE INSULATED CONCRETE FORMS?
Building with insulated concrete forms offer the opportunity to build a home that is environmentally sound and resource efficient. Sustainability can be defined as meeting the needs of the present without compromising the ability of future generations to meet their own needs. By building with insulated concrete forms, with respect to affordability, energy efficiency, human comfort, ease of construction and accessibility, sustainability can be achieved. Insulated concrete forms create a solid wall with continuous insulation and noise barriers so the living spaces remain in a smaller range of temperatures. The temperature peaks that are present in typical stick frame homes are not present in this type of home, therefore, occupants feel much more comfortable. And now that the temperature peaks are not present, money is saved because heating the home in the winter and cooling the home in the summer takes less energy and smaller mechanical systems are needed. Insulated concrete forms do not contain any CFC’s, HCFC’s or formaldehydes, so the health of the occupants are not in any danger. The walls have a two-hour fire rating and can withstand the harsh conditions of hurricanes and tornadoes. The ease of construction allows insulated concrete homes to be constructed by non-skilled workers and the flexibility allows for a wide range of design ideas. Insulated concrete forms are a sustainable solution that are environmentally friendly, builder friendly and most important of all, home owner friendly.