What R-value is in your attic now?
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Why can’t you just measure the depth?
Because depth is half the equation. R-value is depth multiplied by the material's resistance per inch, and the two common loose-fill materials differ by about 40% on that figure. Eight inches of cellulose is roughly R-28. Eight inches of loose-fill fiberglass is roughly R-20. From the attic hatch those two look like the same attic.
That difference lands exactly on the number that decides the money. The Atmos attic rebate applies where existing insulation starts below R-20. The cellulose attic in that example does not qualify and the fiberglass one is right on the line — same depth, different answer. Identifying the material is not a technicality here.
The other reason to distrust a single depth reading is that insulation does not sit level. It settles, it gets displaced by anyone who has been up there, and it is almost always shallower near the eaves where the roof line closes down. One reading in the middle of the attic flatters the house. Several readings, using the lower ones, describes it.
What are you actually aiming for in Greeley?
R-60, and R-49 only where the insulation carries its full uncompressed depth over the wall top plate at the eaves. Both come from the 2021 International Energy Conservation Code, which the City of Greeley adopted by Ordinance No. 25, 2022, final reading August 2, 2022, effective January 1, 2023, replacing the 2018 edition. It is the city's own adopted standard rather than a regional rule of thumb.
Worth noting what this page deliberately does not say: it does not state a climate zone as a Greeley fact. Greeley publishes none. The federal county table that places Weld County in Zone 5B is dated August 2015 and predates the city's own 2021 adoption, so citing the zone as local policy would be quoting a stale federal classification back at you. The adopted code edition is the defensible number and it is the one used here.
Above R-60, added depth stops paying. The relationship between R-value and heat loss is not linear — going from R-11 to R-30 removes far more loss than going from R-49 to R-68 does, because each additional inch works against a smaller remaining loss. Money that would go into a third top-up is nearly always better spent on air sealing.
Sources
What the data says
According to ENERGY STAR's recommended R-value levels, recommended insulation levels for retrofitting existing wood-framed buildings in Zones 6, 5, and 4C are R60 added to the attic if your attic is uninsulated, or R49 if you already have 3-4 inches of insulation.
According to the International Energy Conservation Code, the 2021 IECC sets a minimum ceiling insulation R-value of R-60 in Climate Zone 5 under Table R402.1.3, and Section R402.2.1 allows R-49 to satisfy that requirement only where the full height of uncompressed R-49 insulation extends over the wall top plate at the eaves.
According to the Building America Solution Center, “loose-fill cellulose will settle from 10 to 20 percent over time due to gravity and vibration.”
Take the next step
Want this measured rather than estimated?
The free assessment measures depth across the attic, identifies the material, and gives you the R-value in writing — which is what the Atmos application needs anyway. If the number comes back at or above target, that is what you will be told.
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We've Got It. Here's What Happens Next.
We've got your info and are routing it to a local pro. When they call, here's what to look for in the quote you receive: (1) R-value target — Greeley builds to the 2021 IECC, which puts attics at R-60, and accepts R-49 only where the insulation carries its full uncompressed depth over the wall top plate at the eaves; anything less is under-spec. (2) Air sealing scope — insulation alone does nothing if air leaks aren't sealed first, so it belongs on the quote as its own line with its own scope, and a blower door test is what documents the before-and-after. (3) Rebate handling — ask who files the rebate paperwork with your gas utility, and confirm what that utility's filing deadline is and that the application will go in inside it. (The federal IRA Section 25C tax credit ended December 31, 2025, and Colorado's HEAR program is closed. Which utility to ask about an insulation rebate depends on your town: Atmos Energy's residential rebates are the primary insulation rebate programs in Greeley, Evans and Eaton, while the natural gas utility is Xcel Energy in Johnstown, for most of Milliken, and for most locations in Severance — Xcel sets out its own insulation and air sealing rebate terms on its rebate page. Income-qualified households can get insulation work done at no cost through the state Weatherization Assistance Program.) (4) Removal scope — older homes often need old insulation removed before new install. If a quote skips all four, get another quote.
Frequently asked
Questions about attic R-value
How do I measure attic insulation depth?
Push a ruler or tape straight down through the material until it touches the ceiling drywall, and read the depth at the top of the insulation. Do it in several places rather than one — material settles unevenly and is usually shallower near the eaves. Use the lower readings, because the thin spots are what actually govern performance.
Why does the material matter as much as the depth?
Because R-value per inch differs by roughly 40% between the two common loose-fill materials. Eight inches of cellulose is about R-28; eight inches of loose-fill fiberglass is about R-20. Those two attics look identical from the hatch and are on opposite sides of the Atmos rebate threshold.
What R-value does Greeley actually require?
R-60 for attics, and R-49 only where the insulation carries its full uncompressed depth over the wall top plate at the eaves — both from the 2021 IECC, which the City of Greeley adopted by Ordinance No. 25, 2022, effective January 1, 2023. That is the city's own adopted code rather than a regional generality, and it is what a Greeley attic is measured against.
Why is the rebate threshold different from the code target?
They answer different questions. R-60 is how much insulation the code says an attic should end up with, and R-49 only where the insulation carries its full uncompressed depth over the wall top plate at the eaves. Below R-20 is the condition Atmos sets for paying the attic rebate — it identifies homes with the most to gain. A home can be below code and above the rebate threshold at the same time, which is a common and confusing result.
What if I cannot tell what the material is?
The tool falls back to 3.0 R per inch, which sits between cellulose and loose-fill fiberglass, and flags the result as the widest estimate on offer. Cellulose looks like gray shredded paper; loose-fill fiberglass is white or yellow and fluffy. If it looks like small pebbly flakes, stop — that may be vermiculite and it should not be disturbed.
Does the number this gives me count for the rebate?
No, and it is not meant to. The Atmos application needs a documented value from the installation, and the receipt has to state the R-value and the amount installed. This is a planning estimate to tell you whether the conversation is worth having at all.
When does this tool tell me not to bother?
When you enter a depth and material that put you at R-49 or above. R-49 is the lower of the two figures Greeley's adopted code names — the 2021 IECC puts attics at R-60, and accepts R-49 only where the insulation carries its full uncompressed depth over the wall top plate at the eaves — and once you are past it more depth buys very little. The honest answer at that point is that your money is better spent elsewhere or not at all. That is a real output here, not a disclaimer.
My attic has two different materials layered. What then?
Measure each layer and add the R-values together — six inches of cellulose over four inches of old fiberglass batt is roughly R-21 plus R-13. Run the tool twice and add the results. Layering is normal in Greeley's older stock and does not cause a problem as long as the lower layer is dry.
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