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Retrofit Decision Tool

We make recommendations to help homeowners reduce energy costs and help fight climate change.

In order to combat climate change, the U.S. is aiming to decarbonize its energy sector by 2050. Within this sector, the residential buildings market has one of the most diverse existing landscapes and generally requires the most individual attention by energy auditors and contractors per unit of energy saved. Existing residential buildings need a pathway towards a more streamlined approach to decarbonization.

RMI, the National Renewable Energy Laboratory (NREL), Lawrence Berkeley National Laboratory (LBNL), and Pacific Northwest National Laboratory (PNNL) are collaborating to develop a process for modeling the existing building stock, assigning certain existing building configurations with specific upgrade packages, and ultimately prioritizing certain segments of the country for building envelope upgrades. A detailed overview of the logic associated with this tool will be published soon.

A primary goal of this effort is to identify a simplified pathway for buildings to become zero carbon aligned (ZCA). To be considered CA, buildings should have a low energy load that can reasonably be offset with on- and/or off-site renewable energy generation and - until the grid becomes decarbonized - can draw on grid energy at the times when it is cleanest. For some building types, achieving ZCA status will require only a few upgrades (e.g., electrifying building equipment but without comprehensive envelope insulation upgrades). For other building types, especially those in colder climates, zero-carbon alignment might require higher-performance, whole-building upgrades that include additional insulation. Ultimately, the recommended retrofit packages are assigned based on consideration of solar photovoltaic generation potential, building heating, ventilation, and air conditioning (HVAC) system type and capacities, and the minimum envelope upgrade necessary to achieve CA status.

The Retrofit Decision Tool (RDT) quickly and easily navigates this analysis and provides a simple package upgrade recommendation to achieve ZCA status. The five possible recommendation outputs from this tool include:

  • No Upgrade Recommended: These homes are already ZCA. This may be true for newer homes that are well insulated and already electrified.
  • Equipment Electrification: These homes may already have enough insulation to be ZCA, however equipment may not currently be all-electric.
  • Basic Envelope + Equipment Electrification: These homes may just need a small amount of added insulation and light window improvements along with the equipment electrification to become ZCA.
  • Current Code Envelope + Equipment Electrification: These homes may need a relatively substantial envelope upgrade to become ZCA.
  • Beyond Code Envelope + Equipment Electrification: These homes are likely in a cold climate that requires even more substantial envelope upgrades to become ZCA.

Users of the RDT can enter basic characteristics of their residential building in the input screen below. The tool then identifies a recommended upgrade package based on buildings from a dataset with similar characteristics, links to installation instructions, and connects to a collaborator that can assist with purchasing the materials associated with each of the packages.

Retrofit Decision Analysis Form

1. Where is the building located?
Enter either the ZIP code or the state/county in which your building is located. You may start typing to filter the list.
If you have Central AC, your building has ducts. See images below for examples (click to zoom in and see more info).

Flex duct
Flex duct
Example vent
Example vent
Example vent
Example vent
Based on your response to a previous HVAC question, your building is expected to have ducts.
See images below for some examples (click to zoom in and see more info).

Fiberglass batt wall insulation
Fiberglass Insulation
Blown-in wall insulation. Image courtesy of Cellulose Insulation Manufacturers Association (CIMA).
Blown-in Insulation
Rigid foam wall insulation
Rigid Foam Insulation
See images below for some examples (click to zoom in and see more info).

Fiberglass batt ceiling insulation
Fiberglass Insulation
Blown-in ceiling insulation
Blown-in Insulation
Spray-in foam ceiling insulation
Spray-in foam insulation
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.