SUMMARY REPORT ON COMPARISON OF THE LIFE CYCLE ASSESSMENTS
OF AN INSULATING CONCRETE FORM HOUSE AND A WOOD FRAME HOUSE
(PORTLAND CEMENT ASSOCIATION)
Introduction
This report compares the environmental impacts of a wood framed house to those of an insulating
concrete form (ICF) house. A Life Cycle Assessment (LCA) was used to conduct the comparison by
modeling houses with exterior walls made of either wood or ICF. The house size, layout and interior
walls for both the wood and ICF house remained identical.
The report, in general, concluded that the life cycle of a wood house has a greater impact on the
environment than for an ICF house.
Life Cycle Assessment
An LCA is an in-depth analytical method used to assess how the life cycle of a building product from raw
material acquisition through production, use and disposal, effects the environment. The report breaks
the LCA into 3 phases:
1. Life cycle inventory phase – a detailed collection of data associated with the energy inputs and
emissions to air, land and water, during the life cycle of a building product. Relevant inventory
data for this report was obtained from published reports and commercially available databases.
2. Life cycle impact phase – assesses potential social, economic and environment impacts based on
the energy inputs and emissions from the life cycle inventory phase. Three available impact
assessment methods were used and showed consistent results.
3. Life cycle interpretation – interprets the results of the life cycle inventory and impact phases
based on the objectives of the study. For example, an LCA can be used to decide which
competing building product should be used based on having the lowest overall impact on the
environment.
The LCA was conducted according to the International Standard ISO 14044, Environmental Management
– Life Cycle Assessment – Requirements and Guidelines.
Description of Houses Modeled for the LCA
The LCA was conducted on house designs where both the wood and ICF house are identical in size and
layout. Except the exterior walls were either a wood framed or an ICF wall, accordingly. The designs are
based on typical houses currently built in the US. Each house is a two-story single-family building with
four bedrooms, 2.7-m (9-ft) ceilings, a two-story foyer and family room, and an attached two-car garage.
Each house has 228 square meters (2450 square feet) of living space, which is similar to the 2005 U.S.
average of 226 square meters (2434 square feet) (NAHB 2007).
The homes were modeled in five cities to represent a range of climate conditions. The cities included
were Miami, Phoenix, Seattle, Washington (DC), and Chicago. These cities are often used by other
energy analysts when estimating energy use in buildings. Household use of energy in each location was
identical and simulation software was used to model the energy use.
Results of the LCA
Other than concluding that wood homes have a greater negative impact on the environment than ICF
homes, the results of the LCA also notes the following:
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In each of the five climates, the ICF houses have lower household energy use than the wood
frame houses.
The system capacity required for heating, ventilating, and air-conditioning is less for the ICF
house than for the wood frame house.
The insulation of ICF walls exceeds the International Energy Conservation Code (IECC)
requirements by as much as 40 to 500%, depending on climate. Whereas, wood framed walls
just meet the IECC requirements. (The IECC is the most widely used residential energy code in
the US).
The thermal mass of the ICF house moderates temperature swings and peak loads, resulting in
lower HVAC system requirements compared to a wood framed house.
The ICF house performs better than the wood frame house because of the additional added Rvalue of the insulation and the thermal mass of the concrete.
On average, the environmental impact is greater (worse) for the wood house than the ICF
house.
Largest source of environmental impact on a house is from household use of energy.
Approximately 95% of the negative environmental impacts are associated with household use of
electricity and natural gas. Similarly, approximately 95% of the life cycle energy use is from
household use of electricity and natural gas.
Cement manufacturing or concrete production has little effect on the life cycle energy use of a
house - less than 0.5% of the life cycle energy use is embodied in the concrete portion of the
house.
After climate, occupant behavior is the single most important factor contributing to energy
consumption in houses. As a result, the house life cycle energy use is a function of climate and
occupant behavior, not concrete content.
The most significant environmental impacts are not from construction materials but from the
production of electricity and natural gas, and the use of electricity and natural gas in the houses
by the occupants.
For a copy of the report click here.