A builder framing an addition in Colorado and a homeowner opening up walls in an older Denver house often ask the same thing: is R-20 enough? It sounds like a safe number, since it is close to the R-21 batts sold for 2×6 walls. The answer depends less on the batt, and more on which energy code your town or county has adopted.
R-20 fiberglass batts are about 5.5 to 6 inches thick and are made for 2×6 walls. In Colorado, R-20 in the wall cavity met the older 2018 code for the Front Range climate zone on its own. Under current codes, R-20 in the cavity meets requirements only when it is paired with at least R-5 of continuous insulation, such as foam board, on the outside of the wall.
How Thick Is R-20 Insulation and Where Does It Fit?
R-20 batts are sized for 2×6 framing. Owens Corning sells R-20 kraft-faced batts at 5.5 inches thick, which fills a 2×6 cavity without compression, and some brands make R-20 at about 6 inches. Continuous insulation reaches R-20 at different depths. The table shows rough thickness for each common material.
Material
Thickness for about R-20
Where it goes
Fiberglass batt
5.5 to 6 inches
2×6 wall cavities
Mineral wool batt
About 5 inches
2×6 wall cavities
Closed-cell spray foam
About 3 inches
Cavities, rim joists
Polyiso board
About 4 inches in cold weather
Outside the sheathing
Extruded polystyrene board
About 4 inches
Outside, below grade
The thickness changes because each material holds a different R-value per inch, and what R-value means for insulation explains why the number on the label only holds at full thickness.
Where R-20 Insulation Meets Colorado Wall Requirements
Colorado has no statewide residential building code. Towns and counties adopt their own, and a 2022 state law sets the minimum energy code they must use when they update. That is why R-20 passes in some places and falls short in others.
Older Energy Codes That Accepted R-20 Alone
Under the 2018 energy code, a wood-framed wall in the Front Range climate zone could pass with R-20 in the cavity, or R-13 plus R-5 of continuous insulation. Many homes built in the last several years were insulated to that standard. A town or county that has not updated its codes since mid-2023 may still use it, so R-20 alone can still pass there.
Current Colorado Code: R-20 Plus Continuous Insulation
Under the 2022 state law, a local government that updates any building code after July 1, 2023 must adopt the 2021 energy code or better, according to the Department of Energy’s Colorado code status page. That code’s wall options pair R-20 in the cavity with R-5 of continuous insulation, or R-13 with R-10. Updates after July 1, 2026 move to a state model code with similar wall options.
Colorado Climate Zones and Local Amendments
The state spans four climate zones, from the warmer southeast to the high mountains. An Insulation Institute summary of the Colorado model code lists wood-frame wall options of R-30, R-20 plus R-5, R-13 plus R-10, or R-20 continuous. Some places go further, such as unincorporated Boulder County. Homeowners planning insulation in Boulder projects should confirm local amendments first.
How to Build a Colorado Wall That Passes With R-20 Insulation
If your jurisdiction uses the 2021 code or the newer state model, R-20 batts are only half of the wall.
R-20 Batts Plus Exterior Foam Board
The most common approach pairs R-20 or R-21 batts in a 2×6 wall with about an inch of foam board over the sheathing, adding at least R-5. Tape the foam seams so the layer also blocks air. The foam also covers the studs, which cuts heat loss through the framing that batts cannot touch. Window and door trim needs extensions to match the thicker wall, so plan those details early. Batts made for 2×4 walls follow theR-13 versus R-15 insulation path, paired with R-10 foam.
Spray Foam and Other Paths to Code
Closed-cell spray foam adds high R-value per inch and air seals as it goes, and what closed-cell spray foam insulation is explains why it stops drafts and moisture. Some builders use a performance path, trading more attic or window efficiency for less in the walls. Choosing the right foam insulation for a Denver home depends on the wall, the budget, and the code path. Closed-cell foam also works well in rim joists, where batts leave gaps.
R-20 Insulation in Existing Denver Homes
Existing walls do not have to meet new code values unless they are part of a permitted project. If you open a wall for a remodel, the new insulation should meet the code for that work. When walls stay closed, injection foam insulation installation can fill the cavities, and comparing injection foam versus spray foam insulation shows the trade-offs.
Older Denver bungalows and ranch homes often have 2×4 walls, which cannot hold an R-20 batt. In those homes, high-density R15 batts or dense blown insulation fill the cavity, and exterior foam can be added when the siding is replaced.
Better walls help all year. Denver winters bring cold nights and wide temperature swings, and well-insulated walls so insulation that keeps heat in during winter. Kraft-faced batts act as the room-side vapor retarder most walls here need, and the paper must sit behind drywall since it burns. Fuller walls also soften street noise and shorten furnace cycles.
Grizzly Insulation CO measures each space and installs batt insulation to current Colorado energy recommendations. Our team recommends fiberglass or mineral wool, cuts each batt to fit, and seats it against the framing with no gaps or compression. Every project starts with a free inspection and a clear quote.
R-20 batts are about 5.5 to 6 inches thick and made for 2×6 walls. In Colorado, R-20 alone met the older 2018 code for the Front Range, but current codes pair R-20 in the cavity with at least R-5 of continuous insulation. Because each town and county adopts its own code, check with your local building department before you buy. Existing walls only need to meet code when they are part of a permitted project.
It depends on your local code. Under the older 2018 code, R-20 in the cavity could pass on its own. Under the 2021 code and the newer state model, R-20 needs at least R-5 of continuous insulation outside the wall. Your permit documents will show which code edition applies to the project.
They are close. Both are made for 2×6 walls, and R-21 is a high-density batt at 5.5 inches. Either one meets the R-20 cavity value in current code options when paired with exterior foam. Mineral wool batts for 2×6 walls rate even higher, at about R-23.
Denver adopted the 2021 energy code in 2023. For new walls, that means R-20 in the cavity plus R-5 of continuous insulation, or R-13 plus R-10. Check with the city before you start, since codes change. Existing homes only need to meet it for permitted work.
No. A 2×4 wall is only 3.5 inches deep, and an R-20 batt would be crushed. Use R13 or high-density R15 in 2×4 walls, and add foam outside if the wall must meet current code. Older Denver bungalows with 2×4 walls usually take this route during remodels.
Call or check the website of your local building department. The state has no statewide residential code, so each town or county sets its own. Your permit documents will list the energy code edition that applies.
R-20 Insulation: Thickness & Where R-20 Meets Colorado Wall Requirements
A builder framing an addition in Colorado and a homeowner opening up walls in an older Denver house often ask the same thing: is R-20 enough? It sounds like a safe number, since it is close to the R-21 batts sold for 2×6 walls. The answer depends less on the batt, and more on which energy code your town or county has adopted.
R-20 fiberglass batts are about 5.5 to 6 inches thick and are made for 2×6 walls. In Colorado, R-20 in the wall cavity met the older 2018 code for the Front Range climate zone on its own. Under current codes, R-20 in the cavity meets requirements only when it is paired with at least R-5 of continuous insulation, such as foam board, on the outside of the wall.
How Thick Is R-20 Insulation and Where Does It Fit?
R-20 batts are sized for 2×6 framing. Owens Corning sells R-20 kraft-faced batts at 5.5 inches thick, which fills a 2×6 cavity without compression, and some brands make R-20 at about 6 inches. Continuous insulation reaches R-20 at different depths. The table shows rough thickness for each common material.
The thickness changes because each material holds a different R-value per inch, and what R-value means for insulation explains why the number on the label only holds at full thickness.
Where R-20 Insulation Meets Colorado Wall Requirements
Colorado has no statewide residential building code. Towns and counties adopt their own, and a 2022 state law sets the minimum energy code they must use when they update. That is why R-20 passes in some places and falls short in others.
Older Energy Codes That Accepted R-20 Alone
Under the 2018 energy code, a wood-framed wall in the Front Range climate zone could pass with R-20 in the cavity, or R-13 plus R-5 of continuous insulation. Many homes built in the last several years were insulated to that standard. A town or county that has not updated its codes since mid-2023 may still use it, so R-20 alone can still pass there.
Current Colorado Code: R-20 Plus Continuous Insulation
Under the 2022 state law, a local government that updates any building code after July 1, 2023 must adopt the 2021 energy code or better, according to the Department of Energy’s Colorado code status page. That code’s wall options pair R-20 in the cavity with R-5 of continuous insulation, or R-13 with R-10. Updates after July 1, 2026 move to a state model code with similar wall options.
Colorado Climate Zones and Local Amendments
The state spans four climate zones, from the warmer southeast to the high mountains. An Insulation Institute summary of the Colorado model code lists wood-frame wall options of R-30, R-20 plus R-5, R-13 plus R-10, or R-20 continuous. Some places go further, such as unincorporated Boulder County. Homeowners planning insulation in Boulder projects should confirm local amendments first.
How to Build a Colorado Wall That Passes With R-20 Insulation
If your jurisdiction uses the 2021 code or the newer state model, R-20 batts are only half of the wall.
R-20 Batts Plus Exterior Foam Board
The most common approach pairs R-20 or R-21 batts in a 2×6 wall with about an inch of foam board over the sheathing, adding at least R-5. Tape the foam seams so the layer also blocks air. The foam also covers the studs, which cuts heat loss through the framing that batts cannot touch. Window and door trim needs extensions to match the thicker wall, so plan those details early. Batts made for 2×4 walls follow the R-13 versus R-15 insulation path, paired with R-10 foam.
Spray Foam and Other Paths to Code
Closed-cell spray foam adds high R-value per inch and air seals as it goes, and what closed-cell spray foam insulation is explains why it stops drafts and moisture. Some builders use a performance path, trading more attic or window efficiency for less in the walls. Choosing the right foam insulation for a Denver home depends on the wall, the budget, and the code path. Closed-cell foam also works well in rim joists, where batts leave gaps.
R-20 Insulation in Existing Denver Homes
Existing walls do not have to meet new code values unless they are part of a permitted project. If you open a wall for a remodel, the new insulation should meet the code for that work. When walls stay closed, injection foam insulation installation can fill the cavities, and comparing injection foam versus spray foam insulation shows the trade-offs.
Older Denver bungalows and ranch homes often have 2×4 walls, which cannot hold an R-20 batt. In those homes, high-density R15 batts or dense blown insulation fill the cavity, and exterior foam can be added when the siding is replaced.
Better walls help all year. Denver winters bring cold nights and wide temperature swings, and well-insulated walls so insulation that keeps heat in during winter. Kraft-faced batts act as the room-side vapor retarder most walls here need, and the paper must sit behind drywall since it burns. Fuller walls also soften street noise and shorten furnace cycles.
Watch for the signs your home needs better insulation, such as cold walls, drafts, and high winter bills. Homeowners who upgrade during a remodel often notice the benefits of new wall insulation the first winter.
Grizzly Insulation CO measures each space and installs batt insulation to current Colorado energy recommendations. Our team recommends fiberglass or mineral wool, cuts each batt to fit, and seats it against the framing with no gaps or compression. Every project starts with a free inspection and a clear quote.
For additions and garages, we install closed-cell spray foam insulation as an air barrier, with the highest R-value per inch. Before you plan exterior wall insulation in an older home, our team can explain which code path fits.
Conclusion
R-20 batts are about 5.5 to 6 inches thick and made for 2×6 walls. In Colorado, R-20 alone met the older 2018 code for the Front Range, but current codes pair R-20 in the cavity with at least R-5 of continuous insulation. Because each town and county adopts its own code, check with your local building department before you buy. Existing walls only need to meet code when they are part of a permitted project.
Frequently Asked Questions
It depends on your local code. Under the older 2018 code, R-20 in the cavity could pass on its own. Under the 2021 code and the newer state model, R-20 needs at least R-5 of continuous insulation outside the wall. Your permit documents will show which code edition applies to the project.
They are close. Both are made for 2×6 walls, and R-21 is a high-density batt at 5.5 inches. Either one meets the R-20 cavity value in current code options when paired with exterior foam. Mineral wool batts for 2×6 walls rate even higher, at about R-23.
Denver adopted the 2021 energy code in 2023. For new walls, that means R-20 in the cavity plus R-5 of continuous insulation, or R-13 plus R-10. Check with the city before you start, since codes change. Existing homes only need to meet it for permitted work.
No. A 2×4 wall is only 3.5 inches deep, and an R-20 batt would be crushed. Use R13 or high-density R15 in 2×4 walls, and add foam outside if the wall must meet current code. Older Denver bungalows with 2×4 walls usually take this route during remodels.
Call or check the website of your local building department. The state has no statewide residential code, so each town or county sets its own. Your permit documents will list the energy code edition that applies.