Accessory dwelling units, also known as granny units or backyard cottages, offer housing and climate solutions in one tiny package. Often, especially in California where new ADU State laws have been relaxed to encourage ADUs, these units are heralded as a great solution for creating affordable housing options for renters. The affordability comes from the limits on size for the ADUs which tends to be up to about 50% of the main houses size or smaller.  

It turns out that building small and within existing neighborhoods has climate benefits as well.

“The compact size of these homes makes them energy efficient which cuts lifetime CO2 emissions by as much as 40% as compared to median sized family homes,” according to a recent article by Margaret Morales entitled, The Forgotten Green Housing Option: Accessory Dwelling Units

In the article, Morales goes on to reference a 2010 Oregon Department of Environmental Quality report that found that “a typically sized new single-family homes (defined as about 2,300 SF) built to industry standards is responsible for 60 percent more emissions than a home approximately half its size over the course of an average 70-year home lifespan, from construction to demolition.”  Below is a graph from the after mentioned Oregon DEQ Study that demonstrates how size does reduce climate impacts.

graph shows that ADUs have about half the climate change impact of a standard size home
Estimated climate change impact of a median sized ADU compared to “medium-sized” (2262 sf) single family residence. The estimate for the ADU comes from a regression on the 4 data points, extrapolated from Oregon DEQ (2010) Figure 45 pg. 83.

Infill Development

Another sustainable benefit of ADUs is that they are considered infill development, meaning, they are created in places with existing infrastructure such as roads and utilities. By creating homes in existing neighborhoods, as compared to building out in new areas, less sprawl occurs and the chance of residents using existing transportation and trails systems increases, according to As density increases, vehicle and fuel use per household decreases.

In short, ADUs can offer homeowners, the community and our planet some great benefits. Learn more about ADUs and how to go about building one in Truckee here.

By: Seana Doherty, Housing Program Manager