Definition
What is cellulose insulation, and how does it work?
Cellulose is loose-fill insulation made primarily from recycled newsprint, shredded and treated with a fire retardant (typically borate-based). It's installed the same way as loose-fill fiberglass: a blower machine stays outside the home while a hose feeds material into the attic, where it's fanned across the joist plane, or into a wall cavity, where it's dense-packed through small drilled access holes.
The characteristic worth knowing about cellulose specifically is settling. Loose-fill cellulose will settle 10 to 20 percent over time due to gravity and vibration — a real, material-specific behavior that a contractor accounts for by installing to a greater initial depth (in an attic) or by dense-packing to a high enough density (in a wall) that settling doesn't leave a meaningful gap. This isn't a defect unique to bad installs; it's a known property of the material that good installation practice plans around.
Cellulose is not a fix for moisture, ventilation, or air-leakage problems on its own, and it's more sensitive to moisture exposure than fiberglass — wet cellulose can mat down and lose R-value. Any active leak or unaddressed moisture source in the target space should be resolved before cellulose goes in, not after.
Qualification signals
Who needs cellulose insulation in Longmont?
Cellulose is a reasonable choice anywhere loose-fill fiberglass would also work — open, accessible attic floors and existing wall cavities via dense-pack — and it's a common choice for homeowners specifically interested in a recycled-content material. The settling behavior above means a slightly deeper initial attic install (or a properly dense-packed wall) is worth confirming with your contractor rather than assuming a one-time depth measurement will hold indefinitely.
It's not the right call for a space with an active moisture problem — resolve leaks or excess humidity first. Beyond that, the same candidacy signals as blown-in fiberglass apply: pre-1990 Longmont homes with under-insulated attics or empty wall cavities are the most common fit.
Cost & the cost of waiting
How much does cellulose insulation cost in Longmont — and what does waiting cost?
Cellulose attic work in Longmont typically runs $1.50 to $3.50 per conditioned square foot installed, in the same range as blown-in fiberglass, putting most 1,500-2,500 sq ft homes between $1,500 and $5,500 before rebates. Dense-packed into a wall cavity, the same material runs closer to $2.00 to $4.00 per square foot of wall area. Where your project lands depends on current insulation level, access, and any required pre-work — not on cellulose specifically costing more or less than fiberglass in most cases.
Both this property's rebate programs reduce net cost, but they are NOT the same kind of number and this page will not add them for you. Xcel's rebate is a percentage of project cost, capped by location. Efficiency Works' rebate is a flat rate per square foot, available only to Longmont Power & Communications electric customers. Whether a single project can claim both is not settled by anything either program has published — ask your contractor to confirm for your specific address before assuming a combined figure.
Cost figures are conservative ranges. The free in-home estimate gives exact numbers based on your home and required pre-work — not a range.
Longmont context
What's different about cellulose insulation in Longmont?
Longmont sits at roughly 4,980 feet in IECC Climate Zone 5B, with a winter design temperature around −2°F (−10°F for boiler sizing). An under-filled or settled cellulose attic loses more heat in a Longmont winter than the same gap would in a milder climate, which is part of why accounting for the material's known 10-20% settling at install time matters here, not just as a general best practice.
The rebate landscape is genuinely two-utility here. Xcel Energy runs the gas-and-electric rebate available to every Longmont address, with dollar caps set by where the work happens (attic, wall) rather than what material is used. Longmont Power & Communications, the city's own municipal electric utility, doesn't cover the whole city — verified against Colorado's official utility-territory data, LPC serves roughly 61% of Longmont by area, with Xcel, Poudre Valley REA, and United Power splitting the rest. Only LPC electric customers can access the separate Efficiency Works rebate. Check your electric bill; that's the fastest way to know which side of the line your address is on.
According to the International Energy Conservation Code, “the 2021 IECC (R402.1.2) sets attic insulation minimums at R-49 to R-60 for Climate Zone 5.”
Process
How does the cellulose insulation process work?
Pre-work inspection
Crew inspects the target cavity — attic floor or wall — for existing insulation depth or fill, moisture or pest signs, and any obstructions before scoping material quantity, accounting for expected settling.
Air sealing first
Top plates, can lights, and other penetrations are sealed before material goes in — required for both the Xcel and Efficiency Works blower-door tests.
Baffle or access-hole setup
For an attic, soffit baffles go in to protect eave-vent airflow. For a wall, access holes are drilled per stud bay.
Blowing the cellulose
Cellulose is blown via a hose run from the machine outside — to a measured initial depth across the attic floor (deeper than the target R-value alone would suggest, to account for settling), or to high density inside each wall cavity.
Depth or density verification
Crew measures installed depth (attic) or checks fill density per bay (wall) to confirm coverage accounts for expected settling, and takes photos for rebate paperwork.
Rebate paperwork
Crew completes whichever program's forms apply to the address — Xcel's application, and a separate Efficiency Works application if the home is LPC electric. Each program's paperwork is filed separately; neither office handles the other's forms.
Rebates & credits
What rebates apply to cellulose insulation in Longmont?
Cellulose insulation doesn't carry a rebate line of its own — Xcel and Efficiency Works both key their dollar figures to where the material ends up, not what it's made of. Blown into an attic, the work falls under Xcel's 30%-of-cost, $500 attic cap (gas-heat customers, 1.5x multiplier) and Efficiency Works' $0.77 per square foot flat-ceiling-attic rate. Dense-packed into a wall, it falls under Xcel's $350 wall cap and Efficiency Works' $1.16 per square foot exterior-wall rate — the same figures a fiberglass or spray-foam job in the same location would draw on. Neither program's published figures adjust for cellulose's own settling behavior; that's a durability consideration for your contractor's install depth, not a rebate variable.
Cellulose doesn't have its own rebate line — both programs pay by location, not material:
- Xcel Energy — applies regardless of electric utility — 30% of project cost for gas-heat customers, up to $500 if the cellulose goes into an attic or $350 if it goes into a wall, with a 1.5x multiplier when the heating fuel is Xcel gas. Electric-only or non-Xcel-gas customers see reduced caps: $15 for attic, $25 for wall. Requires a participating contractor and a blower door test documenting at least a 20% reduction in CFM50.
- Efficiency Works — Longmont Power & Communications electric customers only — $0.77 per square foot for flat-ceiling attic work, or $1.16 per square foot if the cellulose goes into an exterior wall, cathedral ceiling, crawl space, basement wall, or cantilever floor. Requires an Efficiency Works assessment first.
These are separate programs from separate sources, and neither one prices by material. Nothing published by either states that a single project can combine both — confirm which applies to your address before assuming a combined figure.
According to the Building America Solution Center, “loose-fill cellulose will settle from 10 to 20 percent over time due to gravity and vibration.”
According to Efficiency Works (Platte River Power Authority program, for Longmont Power & Communications electric customers), “Efficiency Works pays $1.16 per square foot for most insulation measures (conditioned crawl space, basement wall, cantilever floor, exterior wall, cathedral ceiling, conditioned attic) and $0.77 per square foot for flat-ceiling attic insulation, available only to residential electric customers of Longmont Power & Communications.”
For Efficiency Works eligibility and current incentive values, see Efficiency Works home rebates. Eligibility may depend on which electric utility serves your address, program funding levels, and qualifying product specifications.
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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 — the model energy code for Climate Zone 5 calls for R-49 to R-60 attic insulation; ask what your contractor is quoting to. (2) Air sealing scope — insulation alone does nothing if air leaks aren't sealed first, and Xcel requires a blower door test to rebate it. (3) Rebate handling — ask which programs your specific address qualifies for. Xcel and Efficiency Works are separate programs with separate paperwork, and not every address qualifies for both. (The federal IRA Section 25C tax credit ended December 31, 2025 — no federal insulation credit applies to 2026 work. Xcel Energy's insulation and air-sealing rebate remains active for its gas and electric customers. Longmont Power & Communications electric customers may separately qualify for an Efficiency Works rebate — check your bill to see which utility serves your address. Boulder County EnergySmart pays a third, income-qualified-only rebate as of January 1, 2026.) (4) Removal scope — older homes often need old insulation removed before new install. If a quote skips all four, get another quote.
Frequently asked
What do Longmont homeowners ask about cellulose insulation?
Should I do cellulose insulation if my home was built after 2010?
Probably not yet. Post-2010 homes were built to recent code — most attics started well above the pre-1990 baseline. If your bills are normal and comfort is fine, hold the money. The 10-15 year mark is when settled batts and unsealed penetrations start showing up; that's when cellulose insulation pays back on a newer home.
Do you handle new construction insulation?
We focus on retrofit insulation for existing homes. New construction insulation typically goes through your general contractor or builder, and pricing, code compliance, and timing all work differently for new builds. If you're working on new construction and need an insulation contractor, note that in the message field below and we'll refer you to a partner with new-construction experience.
Does cellulose insulation qualify for a rebate?
Not as its own category — Xcel and Efficiency Works both key their dollar figures to where the cellulose is installed, not what it's made of. Cellulose in an attic falls under the same attic figures a fiberglass job would use; cellulose in a wall falls under the wall figures. See the rebate breakdown above for the actual numbers.
Does cellulose insulation settle over time?
Yes — loose-fill cellulose settles 10 to 20 percent over time due to gravity and vibration. A properly done install accounts for this by blowing to a greater initial depth in an attic, or dense-packing walls to a density that holds. Ask your contractor how they're accounting for settling in your specific install.
Is cellulose or fiberglass insulation better?
Both fall under the same rebate figures and price similarly. Cellulose is made from recycled paper and settles 10-20% over time; fiberglass doesn't settle the same way but has its own considerations, including different handling and coverage behavior. Your contractor can walk through which fits your specific project.
Is cellulose insulation safe if it gets wet?
Wet cellulose can mat down and lose R-value, and it's more moisture-sensitive than fiberglass. Any active leak or moisture source in the target attic or wall should be resolved before cellulose goes in — this page doesn't cover mold remediation, which is a separate scope if moisture has already caused a problem.
How much does cellulose insulation cost for a typical Longmont home?
Attic work typically runs $1.50 to $3.50 per square foot installed, and dense-packed into walls, $2.00 to $4.00 per square foot of wall area — the same general range as blown-in fiberglass. The free in-home estimate gives exact numbers, not a range.
Can cellulose be dense-packed into an existing wall?
Yes — through small drilled access holes, at high density, the same underlying technique described on this site's wall insulation page. It's one of the two common materials (with fiberglass) used for wall dense-pack.