Cellulose or fiberglass — which one belongs in your attic?
Cellulose is recycled paper treated with borates for fire and pest resistance. It is denser, delivers more R per inch, and packs around obstructions well. Its known trade-off is settling: it loses 15 to 20 percent of its depth over its service life, which means the R-value you were quoted and the R-value you have in year fifteen are not the same number unless the installer accounted for it.
Loose-fill fiberglass is lighter and does not settle meaningfully, but it delivers roughly 2.5 R per inch against cellulose's 3.5, so it needs noticeably more depth to reach the same target. Weight is the argument that usually decides it: on engineered trusses with a limited load allowance, the lighter material is the safer choice regardless of the R-per-inch comparison.
The question worth asking a contractor is not which material they prefer. It is what installed depth they are quoting, what R-value that depth produces in that specific material, and whether the settling allowance is already in the number. A quote that names an R-value without naming a depth has skipped the step where that gets verified.
Scope here is retrofit work on homes that are already built and lived in: assessment, removal where the existing material has to come out, air sealing, and installation. New construction runs on a different process and is normally handled through the builder — and it is worth knowing that Atmos excludes residential new construction from these rebates outright, so a new build does not have this money available to it in the first place.
Why does a top-up so often disappoint, and how do you avoid it?
Because insulation slows conduction and does almost nothing about air movement, and in a leaky ceiling plane air movement is the larger loss. Blowing fresh material over an unsealed ceiling produces a measurably better attic and a barely-different heating bill, which is the single most common way this work underdelivers.
The sequence that avoids it is unglamorous: seal the ceiling plane first — top plates, wire and pipe penetrations, the bath fan housings, recessed light cans, the attic hatch perimeter — then insulate over sealed work. Air sealing also carries its own separate Atmos rebate, a flat $575 where a blower door documents at least a 20% reduction in leakage, so the step that makes the insulation work is funded on its own terms rather than competing with it for budget.
The second avoidable disappointment is burying the diagnosis. Once fresh material is down, finding the leak you did not seal means moving it again. Anything that needs inspecting in the attic — wiring, a suspected roof leak, disconnected ductwork, a bath fan venting into the attic instead of outside — gets inspected before the hose comes out, not after.
What does blown-in work cost around Greeley?
No primary source publishes a Greeley-specific installed price per square foot, so this page will not print one as though it were measured. Front Range regional ranges from trade sources put blown attic work in the low single dollars per square foot installed, with cellulose and loose-fill fiberglass close enough to each other that material choice is rarely what decides the total.
What decides the total is scope. Square footage and target depth set the baseline. Removal of existing material, if it is needed, is usually the largest single adder. Air sealing before the install adds labour and is worth it. Access — a pull-down hatch in a hallway against a scuttle in the back of a closet — quietly changes the hours on the job.
The published side is the rebate. Atmos pays 75% of project cost up to $1,550 on attic insulation where existing insulation starts below R-20, and a separate flat $575 on air sealing that documents a 20% leakage reduction. Both are percentage or flat figures set by the program rather than estimates, which makes them the firmest numbers on this page.
Atmos rebate amounts verified August 5, 2026 against Atmos Energy's Colorado residential rebate page. Atmos states amounts are subject to change and that rebates are available until funding is fully allocated — confirm current amounts before scoping work.
Sources
What the data says
According to the Department of Energy, “loose-fill cellulose insulation typically settles 15-20% over its lifetime, reducing effective R-value at the same nominal depth.”
According to the ENERGY STAR, “air sealing alone — before insulation upgrades — can reduce energy bills by up to 15% in older homes.”
According to the Atmos Energy, “the Atmos Energy residential air sealing rebate pays a flat $575 and requires a blower door test documenting a minimum 20% CFM(50) leakage reduction.”
Take the next step
Want the depth and material identified first?
The assessment identifies what is in the attic, measures its depth, and converts the two into an actual R-value — the number the Atmos rebate turns on and the one a quote should be built from. If it is already near target, you will be told that rather than sold a top-up.
Get a quote
Tell Us About Your Home
30 seconds to fill out. Free quote, no high-pressure follow-up.
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-49 to R-60; anything less is under-spec. (2) Air sealing scope — insulation alone does nothing if air leaks aren't sealed first, and Atmos requires a blower door test to rebate it. (3) Rebate handling — ask who files the Atmos paperwork and confirm it goes in within 60 days of the install. (The federal IRA Section 25C tax credit ended December 31, 2025, and Colorado's HEAR program is closed. Atmos Energy's residential rebates are the primary insulation rebate stack for Greeley-area projects in 2026, and 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 blown-in insulation
Is cellulose or fiberglass better for a Greeley attic?
Neither is better outright. Cellulose gives more R per inch and packs around obstructions; fiberglass is lighter and does not settle. If your trusses have a limited load allowance, fiberglass is the safer choice. If depth is limited and you need R-value in the space available, cellulose gets you there in fewer inches.
How much does blown-in insulation settle?
Loose-fill cellulose typically settles 15 to 20 percent over its lifetime, which reduces effective R-value at the same nominal depth. A competent installer allows for it by blowing to a greater initial depth. Ask what settled depth the quote is designed to reach, not just what goes in on the day.
Can blown-in go over my existing insulation?
Usually, when what is there is dry, intact, and not vermiculite. That is the common case in Greeley's 1970s and 1980s stock. It has to come out first when it is wet, heavily compacted, rodent-damaged, or possibly vermiculite — in which case the material gets tested before anyone disturbs it.
Does blown-in insulation qualify for the Atmos rebate?
Yes, on the same terms as any attic insulation: 75% of project cost up to $1,550 where existing insulation starts below R-20. The rebate is written around the measure and the starting R-value, not the material, so cellulose and fiberglass are treated the same. The receipt has to state the R-value and amount installed.
How deep does it need to be?
Deep enough to hit R-49 to R-60, which is what Greeley's adopted 2021 IECC puts attics at. In cellulose that is roughly fourteen to seventeen inches settled; in loose-fill fiberglass, meaningfully more. This is why depth and material have to be quoted together — a depth figure on its own does not tell you the R-value.
Will it make a mess in the house?
Some dust is normal around the hatch and the crew should be masking and cleaning it. The machine itself stays outside with the hose run in through a window or vent, so the bulk of the material never travels through living space. Removal jobs are dustier than top-ups and should be scoped with containment.
When is blown-in insulation not the right call?
When the attic is already near target, when the ceiling plane has not been sealed and there is no plan to seal it, or when the real problem is somewhere else entirely — a duct disconnected in the attic, a bath fan discharging into it, or a roof leak. Blowing insulation over any of those buries the fault under a foot of material and makes the eventual repair worse.
How long does an install take?
A typical Greeley attic top-up is a single day and often less. Removal beforehand, vermiculite testing, or a full air-sealing pass will extend it, and any of those is worth the extra day rather than being skipped to keep the job inside one.
Related guides