Analysis of Energy Savings and Incremental Construction Costs for New Single Family Homes in Houston, TX under the 2012 IECC

Environment Texas

EECC has conducted a preliminary analysis of the energy savings and incremental construction costs associated with the possible adoption of the 2012 IECC for new, 2,400 square foot single family homes in Houston, TX. This analysis specifically aims to calculate the impact of the latest energy code compared to the city’s current code, the 2006 IECC + 15 percent.

This analysis finds that incremental costs should be approximately $1,623 per new home, representing an estimated increase in the first-cost of a new home of less than one percent.  The energy cost savings achieved by the new code are estimated as $252 per year.  As a result, monthly utility bill savings to the home owner are more than three times as much as the additional mortgage payment needed to cover the added first-cost of energy saving features required by the 2012 code.  

This cash-flow difference is enough to pay back the buyer’s added down-payment in less than two years (or sooner if the loan allows a down payment below 20%).  After that date, the owner continues to save $177 annually in lower utility bills – and even more if energy prices increase.

Energy Savings and Construction Cost Methodology
 
To calculate energy savings and incremental construction costs, this analysis defined a “typical” single family house to represent new residential development in Houston. The home modeled is two stories in height, with exterior dimensions of 30 by 40 feet with wood-framed 2 x 4 walls and a slab on grade foundation. This size and foundation type is based on regional construction practices. In Texas (as nationally) the average new home is approximately 2,400 square feet—which is the size used in this analysis. 

For the purposes of this analysis we assume a baseline home that meets the requirements of the 2006 IECC + 15 percent, which is Houston’s current code.  While builders have a variety of options to meet the existing code’s required 15 percent efficiency improvement over the 2006 IECC, the inspections department in Houston indicated that most builders choose Compliance Method #2, which calls for builders (or their designee) to run RESCheck software and also perform duct and whole house pressure testing. Although some leading builders in Houston are already building to a higher standard or electing other methods to achieve a 15 percent improvement, the inspections department in Houston indicated that this is the most common, expedient, and low-cost method for achieving compliance with the code.

Using this model home as a baseline, we identified the building components that would have to be upgraded from the current 2006 IECC + 15 percent code, to meet the prescriptive requirements in the 2012 IECC. These changes included upgrades to attic insulation from R-30 to R-38 blown-in insulation, an upgrade of windows, an increase from zero to 75 percent compact florescent bulbs in hard-wired fixtures, R-3 insulation on hot water pipes from the hot water heater to kitchen, an upgrade of insulation and weather sealing for attic access hatches, and a programmable thermostat.

Energy savings were modeled by ICF International (ICFI), an international energy consulting firm with extensive experience in the use of hourly building energy simulation software to estimate energy performance and energy savings of alternative building codes and design concepts.  Although the numbers included in the analysis represent a careful, independent technical judgment by ICFI staff, it should be kept in mind that – like any such analysis – the results depend on a number of assumptions about the physical features of a typical new home, operating practices, energy prices, and other factors.

Both the existing 2006 IECC + 15 percent code and the new 2012 IECC code allow a builder to choose among a number of alternatives to comply with the code.  In this case, ICFI conservatively chose to compare the results from the prescriptive path of each version of the code. ICF uses BeaconTM, an hourly simulation model that utilizes DOE-2 or EnergyPlus, and summarizes building performance in terms of estimated annual energy costs, based on long-term average weather conditions in a given climate zone (city), DOE/EIA state level energy costs. ICF also estimates energy consumption by end-use, fuel type, electricity peak demand, and air conditioner size in each prototype home. More details of the modeling assumptions used in this analysis are available on request.

Incremental Costs

This analysis conservatively estimates incremental construction costs for the average new home in Houston to be roughly $1,623. These estimates are derived from a variety of sources, drawing on construction cost estimating software, experience in neighboring states, and local building suppliers. Costs are described below and summarized presented in table 1, below.

To estimate incremental costs for ceiling (or attic) insulation, we rely on estimated construction costs from the well-regarded 2011 RS Means Contractor’s Pricing Guide. To approximate actual costs of new home construction, the total incremental cost from RS Means includes material costs, labor, and contractor overhead and profit. The additional cost associated with an upgrade from R30 to R38 blown-in insulation is estimated as $302.40.

Builders will also need to make window upgrades to meet the 2012 IECC. To meet the improved u and SHGC factors for the 2012 IECC (.4 and .25, respectively) our analysis expects that window frame material must be upgraded from aluminum to vinyl with low-e gas between panes. This added cost is conservatively estimated by the Efficient Windows Collaborative (EWC) as $4.00 per square foot—making it the largest proposed incremental cost in a move to the 2012 IECC. It is important to note that some builders may already install windows that meet the 2012 IECC requirements, but in an effort to be conservative (and strictly compare the two codes) this analysis assumes that builders are currently using the least-cost window to meet existing code requirements. 

As well, to meet the 2012 IECC builders will have to install programmable thermostats in lieu of manually controlled units, a change estimated at $50. Also, high-efficiency lights are required in 75 percent of hard-wired fixtures, which is not required in the 2006 IECC. Usually, this requirement is met with compact florescent lights (CFLs). Our analysis estimates that the upgrade of 75 percent of light bulbs will cost no more than $50. An additional 2012 IECC code change will require builders to insulate hot water distribution lines to kitchens. We believe the cost impact of this change is small, as R-3 insulation costs less than 50 cents per linear foot and most insulation products can be “clipped” around supply pipes after the plumbing rough-in. As a result, this cost is estimated at $100 per new home. 

Finally, to meet the 2012 IECC we estimate an additional $100 to seal and insulate the attic hatch. This cost varies widely by home, and depends on whether or not attic access is achieved through a wall opening (such as a door) or via an overhead pull-down stair. For wall openings, cost is expected to be much lower, as builders can simply adhere surplus insulation to the unconditioned side of the door. For attic pull-down stairs, a variety of kits can be placed over the stairs by builders, but costs are higher. Prior analysis for pull-down stair insulation and sealing completed in conjunction with the Home Builders Association of South Carolina estimated this cost to be $100—an estimate which has also been used in this analysis in an effort to default to the most conservative option.

Construction Cost Savings

While complying with the 2012 IECC increases first-cost in some areas, the new code also presents opportunities to reduce costs for HVAC equipment as a result of an improved building envelope. Among other possible savings, builders will be able to reduce the size of costly mechanical equipment. For this prototype home, builders are able to reduce the cooling system capacity from 48,000 kBtuh to 42,000 kBtuh or from 4 to 3.5 tons. This reduction in air conditioner capacity can result in first-cost savings of approximately $408 for each new house.  

Energy Cost Savings

According to the model used in this analysis, upgrading to the 2012 IECC will result in energy cost savings for homeowners of $252 per year. These annual utility bill savings represent energy savings of 13.4% of the home’s total energy use that is regulated by the building code.  It is noteworthy that these savings assume constant energy prices; if energy prices continue to rise consistent with historical trends, savings will be greater in future years. 

Mortgage Payback for Homeowners

Homebuyers will be able to include in their mortgage the incremental first-costs of meeting the 2012 IECC, while benefiting from lower utility bills starting on day one.  With estimated energy cost savings of $252 per year, monthly utility bill savings are more than three times as much as the additional mortgage payment needed to cover the added first-cost of energy saving features required by the 2012 code.  

This cash-flow difference is enough to pay back the buyer’s added down-payment in only one year and ten months (or sooner if the loan allows a down payment below 20%).  After that date, the owner continues to save $177 annually in lower utility bills – and even more if energy prices increase. 

This payback analysis assumes that homebuyers purchase a new home with 20% down at the current nationwide interest rate of 4.01 percent. This scenario would result in an increased down payment of $325 with additional monthly mortgage cost of $6.21. Taking into account energy savings and lower utility bills, a cash flow analysis indicates that the homebuyer would break even within one year and ten months. After that break-even date, home owners would continue to save $177 in energy costs. Homebuyers with a lower down payment—such as 5 or 10 percent—will realize payback much more quickly. Mortgage payback to homeowners for 5 and 10 percent down payment scenarios are presented below in Table 2.

*For tables, see attached document.

About the EECC

The Energy Efficient Codes Coalition (EECC) is a coalition of energy efficiency advocates involved in the development of the national model energy codes. EECC draws supporters from government, regional energy efficiency alliances, academia, think tanks, utilities, environmental groups, utilities, low-income housing groups, energy consumers, and businesses. The EECC has been heavily involved in the most recent two cycles of IECC code development. Our partner organizations and supporters are also deeply involved in the processes of state and local adoption and implementation of the model codes.

Contact Information: 

2012 IECC Adoption and Energy Codes Policy

William D. Fay                        Jeffrey Harris
Executive Director                     Senior Vice President – Programs
Energy Efficient Codes Coalition                Alliance to Save Energy
(202) 530-2214                        (202) 530-2243
[email protected]                        [email protected]
                            
Technical Analysis 

John Miller
Senior Research Associate
Building Codes Assistance Project
 (202) 530-4340 (direct)
[email protected]