If you’re planning an addition in Montgomery County, you’re going to need more insulation in your walls, maybe.
Montgomery County Department of Permitting Services have adopted the 2021 version of the International Code Council codes as of December 10th, 2024. Building permit applications for additions, renovations and new construction submitted prior to March 31st, 2025 can continue to use the 2018 version of the codes. You can read the DPS press release.
If you’re looking for a plan review, check out my permitting support page. Even better, contact me to set up a consult for designing your dream home!
QUICK SUMMARY OF 2021 ENERGY EFFICIENCY CODE CHANGE
The super short version is that the amount of insulation you will need in your walls and roofs has increased. Walls will go from R20 to R30 and roofs from R49 to R60.
Note that there are way too many variables to summarize this in one sentence like I just did. More details below, and I have a second post about actual wall assemblies you can use to meet the new insulation requirements in Montgomery County, MD.
This code change will affect all homeowners doing additions or new construction projects in Montgomery County. I’ll get into the specifics in a minute, but, and I can’t believe I’m saying this, there really is “one simple trick” to continue using the 2018 insulation values, thus reducing the amount of insulation you need to install.
HOW BUILDING CODES WORK
Quick lesson in building codes.
The International Code Council writes building codes, such as the International Building Code, International Residential Code (IRC), International Energy Efficiency Code (IECC), International Swimming Pool and Spa Code, International Mechanical Code, etc. Local jurisdictions that oversee building construction and permitting, like Montgomery County, will adopt the ICC codes into law, usually with a few amendments to alter the code for specific local goals/requirements.
HOW TO STILL USE THE 2018 INSULATION REQUIREMENTS
In the adoption of the 2021 codes, Montgomery County added a local amendment that allows use of the “Maryland Alternative R-Value”. The Maryland Alternative R-Value is itself an amendment to the 2021 IECC written into the adoption of the I-Code to be used as a Maryland Building Performance Standards.
The Maryland Alternative R-Value is really just the 2018 insulation standards. You are allowed to use that if you choose one or more “Additional Energy Features” totaling a score of 6% or more. See the chart with 23 possible Additional Energy Features and their corresponding score.
I think the one MOST people will probably do is item 23, which requires homeowners to install at least three Energy Star rated appliances, such as a fridge, washer and dryer. That will get you 7% and allow you to use the 2018 insulation standards.
NEW MONTGOMERY COUNTY ENERGY EFFICIENCY REQUIREMENTS
Finally, the more detailed answer!
The 2018 code required wall insulation to be R20 or R13+5ci. To meet this standard you need either
- R20 insulation in your wall between your studs -OR-
- R13 between your studs with an R5 layer of continuous insulation
The building science behind the standard is this: If you have a wall with studs spaced at 16″ or even 24″ the insulation within the wall is interrupted every 16″ or so. Without other detailing or insulation, this creates a likely thermal bridge…a direct path for hot or cold to traverse the wall. The net result is that the effective R-Value of that wall is something lower than 20. Usually in the 16-17 range.
A layer of continuous insulation outside the studs (or sometimes even inside the studs) helps prevent thermal bridging and provides more even coverage. The wall will perform better, and in turn reduce the amount of insulation you need between the studs. This is the R13+5 option.
Although the R13+5 is more energy efficient, the easiest, most inexpensive, way to meet this standard is usually to install R20 within the wall, which means you need 2X6 studs with a 5.5” layer of pink fiberglass batts. I always prefer Rockwool insulation for a bunch of different reasons, but it’s the same general wall assembly.
Note that in my own house I used R20 + 6ci, so I believe in this stuff!
The 2021 codes increase the insulation requirements to R30 or R20+5ci or R13+10ci or 0 + 20ci
That means to meet the new code we could do
- R30 between the studs
- R20 between the studs with R5 continuous
- R13 between the studs with R10 continuous
- Nothing between the studs with R20 continuous
Whichever way you slice it, you're gonna need a bigger boat.
My guess is that the new default is going to be R20+5 because this keeps walls framed with 2X6 and the R5 can be easily met with a Huber Zip R6 panel which integrates the sheathing and insulation in one product. The R30 could be cool because you can do that with 2X8 stud and get nice thick walls, though most people probably won't want to give up those extra inches everywhere. The R13+10 seems like an expensive purgatory and the 0 + 20 would be super cool because you could do something like this and if that's what you want, call me maybe?
