A lot of homeowners have been mentioning recently that they recently had their home quoted for new siding. More often these days, along with this new siding will come either a new house wrap or a thin layer of foam board installed behind the siding. Combining siding with a new moisture barrier like house wrap or foam board is always a good idea, but it is not the same thing as having your walls insulated. The insulation value added to the outside is usually only a quarter inch to 1 inch, or about R1-R3.5 insulation value added. The difference here is adding insulation to the exterior of the home, vs adding insulation to the wall cavities closer to the interior of the home.
Most walls built from the 1900s onward will have somewhat consistent framing at 4” give or take. When doing a Mass Save energy assessment, the inspector will likely look to probe the walls to get the existing frame depth if the home is older than the 1900s. A minimum of 3 inches of wall cavity space is needed in order to get a blown-in cellulose insulation job done with good returns on your investment. It never hurts to have a no-cost Home Energy Assessment with Green Energy Gains to verify existing wall insulation and have a conversation about improvements that can be made and paid for in part by utility companies.
Existing wall insulation that is thicker than 1” causes issues when trying to insulate with blown cellulose. You tend to find a 1” insulation batt in homes built in the 1940s-late 60’s that have not been gutted/retrofitted with blown-in insulation in the past. Often in ranches, capes, bungalows, and even your standard colonial built in the 1950s or 60s, the only insulation existing in walls is a thin foil sheet, similar to heavy-duty aluminum foil everyone keeps in their kitchen. Insulation was not a required/often utilized addition to a home during a time when fuel prices were low and homes were being built at record speed to meet a growing post-war population. According to those old standards, these “insulated” walls have lots of improvements that can be made by opting to have insulation blow into the wall cavities.
Rather than applying a layer of foam board to the home’s exterior, wall cavity insulation requires drilling into a wall from the exterior. Insulation is inserted to fill the roughly 4” wall cavity before a weather-proof plug is used to close the hole. Most common sidings like vinyl, wood shingles, and clapboards can be removed and reattached easily. Ideally, if you are coinciding with new siding, make sure you have an energy assessment to ensure your wall cavities are already insulated. If they aren’t, it is wise to insulate before new siding is installed, to limit how many times siding pieces snap on and off. Insulating before siding also means the new foam going with the new siding isn’t going to be drilled through.
In short, no new siding even with foam board installed is not the same as insulating your walls. If your home was built in the 1970s or before, it’s always best to verify existing insulation levels before spending money on new siding. Ensuring your wall cavities between the studs are as insulated as possible is one of the easiest ways to make a home more energy efficient. All homes receive at least a 75% discount on qualified insulation work when qualified for a Mass Save Assessment. Be sure to take advantage of this program before making any major siding upgrades!