What if we added insulation on every re-siding job?
The “doing this while doing that” concept is one of the best incremental ways to advance sustainability in existing homes. For example, when replacing water fixtures, get low-flow WaterSense certified; when upgrading appliances, go quiet, select ENERGY STAR certified appliances and switch to all-electric; and when needing a new A/C, opt for a Heat Pump instead, which can be standalone or paired with an existing gas furnace.
Now, a new movement is well underway, led by the US Pacific Northwest National Laboratory (PNNL). Its acronym is AIRS, which stands for Adding Insulation While Residing. The idea is simple: every time a home or building needs to be resided, we should ensure that it is also getting continuous exterior insulation added. The insulation can be foam, mineral wool, or even wood fiber. Most re-siding companies need to start doing this, and most weatherization programs prefer to drill and fill the walls instead of adding continuous exterior insulation.
The GreenHome Institute is proud to be a PNNL funding recipient to administer this research project here in Michigan. Before taking on the program, we launched a 1-hour continuing education session on the topic. We are looking at researching this approach on at least nine homes and now have our first project completed to share some initial information.
The first thought might be energy efficiency, utility bill savings, and comfort for the owners or tenants of homes that get AIRS. However, additional important benefits of this work are the reduction of wall moisture issues and durability risk reduction. In fact, many siding jobs are not taking this opportunity, leaving in place moisture risks that are reducing the life of the walls and homes due to deficient construction and renovation practices. To illustrate this, you can see the Building Science Advisor (BSA) tool evaluation we did on the previous wall assembly versus the new one here. Here is a CEU webinar we did on the Building Science Advisor tool.
According to the BSA tool, adding 1 inch of Owens Corning EXTRUDED POLYSTYRENE (XPS) continuous exterior insulation to this first test home significantly reduced the risk of wall sheathing moisture content and mold.
We suggested that the siding contractors add two inches of insulation, but they were fairly resistant to that idea – which is what this research project is about. Trying to convince siding contractors that adding insulation is important is going to take a lot of work. Adding more insulation requires more effort from the installer. Design conversations will happen, and they will be different for each home.
However, let’s look at the wall’s durability. If we had added the additional one inch as advised in Climate Zone 5, you can see that scenario versus the two inches suggested below, which moves it from a potential sheathing risk to the light green zone of reduced risk. 
From an energy efficiency standpoint, each home we work with receives a GreenHome Inspection before and after work is completed. This process includes reviewing many components of the home. Still, the focus of this program is to give the home and overall US DOE Home Energy Score and determine the home’s air leakage and total energy usage before and after the retrofit. For this particular home, the overall score went from a 4 to a 6, which included over $100 in utility savings and nearly 15 members in total energy reduced both in heating and cooling, which was the result of the exterior rigid being added, three windows being replaced, and a 22% air leakage reduction. If you do the math, that is a 13% savings in energy usage, which gets us pretty close to the savings needed for the Inflation Reduction Act State HOMES rebates of 15% in measured savings needed to get $4-$8k in rebates. 
Not only are energy and money being saved, but the owner also said, “I’ll add that aesthetically, the house looks great. From a functional standpoint, my wife and I definitely have noticed that the two bedrooms that previously felt colder than the rest of the house feel much more comfortable.”
The other aspect of our GreenHome Inspection included reviewing ventilation systems. With a tighter home, we need to see if ventilation needs to be improved to optimize occupant health when these jobs are being completed.
Stay tuned as we report on the eight additional homes. Note that PNNL will be releasing case studies on these homes. Two GreenHome Institute members have already completed an AIRS study on their homes. One case study is forthcoming, and the other, which you can find here, was done by Tom at Builder World Builders.
