Comparison of Carbon Emissions of Modular and Site Built Houses

Abstract

The construction industry has significant environmental impacts by consuming natural resources, generating waste, and emitting greenhouse gases (GHG) that lead to global warming and climate change. Globally, in 2018 the building sector accounted for 39% of energy and process related CO2 emissions. The residential sector contributes to a significant share of energy consumption and GHG emissions. The controlled factory environment and rapid assembly process of modular construction is increasing its use as a solution to housing shortage and affordable housing. This research is investigating potential of the modular construction in reduction of the environmental impacts of residential construction.
The goal is to compare the cradle to site GHG emissions of modular and site-built houses, and recommend measures, methods, and strategies to reduce the GHG emissions of modular houses. In addition, the study will determine the life cycle cost of the recommended measures and suggest methods and strategies to reach carbon neutrality in modular houses. This study also will conduct life cycle assessment analysis for a modular house and an equivalent site-built house within the scope of cradle to site (figure 1) to measure GHG emissions (CO2, N2O, and CH4). The process based LCA approach will be used to estimate the GHG emissions of both cases. Data will be collected from several sources such as Ecoinvent, United States Life Cycle Data bases, GREET, a Modular House Factory, and a Construction site.
The preliminary findings of this research based on literature review, interview with experts, and data collection result indicate that modular houses have lower environmental impacts compared to their comparable site-built houses; initial embodied emissions of materials have the highest percentage of total emissions of buildings; and traditional construction materials used in each region can significantly affect the building’s environmental impact. For example, use of concrete or masonry construction materials has a negative environmental impact compared to steel or wood. The reviewed literature showed that the most common sources of embodied emissions are making and transporting buildings materials, construction waste disposal, transportation of prefabricated components to site, and resource and energy consumption during construction. Few studies included transportation of construction crew to the factory and to the construction site. In addition, bill of materials and interview results show that for modular homes, the construction cost is 10 percent lower in material and 40 percent lower in labor cost. The contributions of this research are as follows:
• Development of a set of recommendations to reduce GHG emissions of modular houses.
• Articulation of the technical complexities in implementing energy efficient and carbon-neutral measures in current manufacturing facilities.
• Identification of measures that could lower environmental impacts of a house in an affordable manner.
This study would benefit construction builders and researchers.

Full text

Comparison of Carbon Emissions of Modular and Site Built Houses
Maryam Kouhirostami1* and Abdol R. Chini, Ph.D.1 and Robert J. Ries Ph.D.1
1 M.E. Rinker, Sr. School of Construction Management, University of Florida
*m.kouhirostami@ufl.edu
Problem Statement
Aim
Modular Homes: LCA stages/Activities
Site-built Homes: LCA stages/ Activities
REQUIRED DATA
Modular vs Site-built
INTRODUCTION
PRELIMINARY RESULT
METHODOLOGY
Type of
equipment, type
of fuel, utility bill
from site/factory,
productivity rate
Type of vehicle, module unit travel
distance, number of laborers,
distance from material suppliers to
site/factory, daily travel distance
for labor
Quantity of
materials, GHG
emission factors
of materials,
waste factors
Contribution
LCA Modeling Process
1. Define goal and
scope
2. Collect inventory
3. Perform impact
assessment
4. Interpret
results
5. Report
results
Defining all the activities and impact assessment
methods included in the model and how each
activity is modeled.
Data collection process from different sources:
Ecoinvent, United States Life Cycle Data bases,
GREET, a Modular and site-built House Builders.
Evaluate potential environmental impacts.
Productivity
Rate
Bill of
Materials
Type of vehicle, emission
factor for vehicle and fuel,
distance from site/factory
to landfill, quantity of
disposal
Material Transportation Construction Disposal
Scope: cradle to site (initial embodied emissions)
Activities: extraction of raw materials,
transportation (material/module unit/crew),
construction (factory/site), installation of unit,
disposal (factory/site)
Methodological approach: process-based LCA
Impact assessment: global warming (GHG)
Literature review shows that modular houses
have a lower environmental impacts compared
to site-built houses.
Selection of construction materials, location of
the house, and construction techniques have
major environmental impacts.
Few studies included transportation of
construction crew to the factory and to the
construction site.
Collected data and bill of materials show that
modular houses have lower waste and higher
material usage than site-built houses.
Construction of a modular house is 10% lower in
materials cost and 40% lower in labor cost
than its comparable site-built house.
Site-built Modular
Data/Sources
Building components: undercarriage, floor,
walls, roof, doors, and windows
Source: a modular house builder
Building components: floor, walls, roof,
frame, doors/windows
Source: a site-built house builder
Average number of laborers:190 per day
Productivity: 4 houses per day (exclude
installation and foundation)
Source: a modular house builder
Average number of laborers: 6 per week
Time to complete: 25 to 30 weeks
Source: a site-built house builder
Data Collection
Boundary and Scope
Collected data from communication with modular and site-built housing builders: Bill of materials,
productivity rate, crew travel distances, drawings, and utility bill.
The interpretation phase looks at
the results of the study, puts
them into perspective, and
recommend improvement.
10
percent
reduction
40
percent
reduction
Modular
Site-built
Material
Labor
1/3
Reduction
based on
labor cost
The energy and process-related GHG
emissions share of the building sector in
the USA is almost 40%.
Studies show that the inefficiency of
current construction methods is one of
the important causes of its environmental
impacts.
Modular construction has potential to
address the current housing crisis due to
its advantages: lower cost, lower waste,
higher productivity, faster
construction time and lower
environmental impacts.
The goal is to compare the cradle to site
GHG emissions of modular and site-
built houses, and recommend
measures, methods, and strategies to
reduce the GHG emissions of modular
homes.
Development of a set of
recommendations to reduce GHG
emissions of modular houses.
Articulation of the technical complexities
in implementing energy efficient and
carbon reducing measures in current
manufacturing facilities.