Definition
What is attic insulation, and how does it work?
Attic insulation is the loose-fill or batted thermal layer installed across the floor of an unconditioned attic — directly above the ceiling drywall — to slow heat flow between the conditioned home below and the unconditioned attic above. Materials come in the same families used across the Front Range: loose-fill cellulose, loose-fill fiberglass, and batted fiberglass or mineral wool.
Loose-fill installations use a blower machine that stays outside the home; a flexible hose runs into the attic where the crew fans material evenly across the joist plane to a measured depth. Batted installations are hand-laid between joists.
Attic insulation is not a fix for moisture, ventilation, or air-leakage problems on its own. If bath fans vent into the attic, or top plates are unsealed, those need addressing first — adding insulation over an unsealed or wet attic plane can trap the underlying problem rather than solve it.
Qualification signals
Who needs attic insulation in Longmont?
Most Longmont homes built before 1990 are reasonable candidates for an attic top-up. The signals: visible existing insulation at six inches or less, rooms that run noticeably hotter or colder than the rest of the house, ice damming in winter, or a pre-1990 build date with no record of an insulation upgrade.
Newer Longmont homes (built 2010 or later) generally meet the code in effect at construction, but builder-grade batts settle and gap within ten to fifteen years — worth a look at that point, not before.
Cost & the cost of waiting
How much does attic insulation cost in Longmont — and what does waiting cost?
Attic insulation in Longmont typically runs $1.50 to $3.50 per conditioned square foot installed, putting most 1,500-2,500 sq ft homes between $1,500 and $5,500 before rebates. The spread depends on current insulation level, attic geometry, and any required pre-work.
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 per measure. 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 attic 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). Those figures drive real load calculations, not just a code checkbox — an attic running under-target loses more in a Longmont winter than the same gap would in a milder climate.
The rebate landscape is genuinely two-utility here in a way most Front Range markets aren't. Xcel Energy runs the gas-and-electric insulation rebate available to every Longmont address. 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 attic insulation process work?
Pre-work inspection
Crew inspects existing insulation depth, checks for moisture or pest signs, and assesses ventilation before scoping the job.
Air sealing the attic plane
Top plates, recessed light cans, bath fan housings, and attic-hatch perimeters are sealed with caulk, low-expansion foam, and gaskets — required for both the Xcel and Efficiency Works blower-door tests.
Baffle installation
Soffit baffles go in where needed to keep insulation from blocking eave-vent airflow, preserving the ventilation path that prevents roof-deck moisture.
Insulation install
Loose-fill is blown to a measured depth via a hose run from the blower machine outside; batts are hand-laid between joists where applicable.
Depth verification + cleanup
Crew measures installed depth across the attic to confirm R-value 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 attic insulation in Longmont?
Attic insulation in Longmont draws on two separate, non-combined programs. Xcel Energy's citywide rebate pays 30% of project cost for gas-heat customers, up to $500, with a 1.5x multiplier when the heating fuel is Xcel gas. Longmont Power & Communications electric customers may separately qualify for an Efficiency Works rebate of $0.77 per square foot for flat-ceiling attic insulation — available only on the LPC-served portion of the city, and not stated anywhere as combinable with the Xcel figure.
Xcel Energy — applies regardless of electric utility:
- Xcel Energy Insulation and Air Sealing Rebate — 30% of project cost for gas-heat customers, up to $500 for attic insulation, with a 1.5x multiplier when the heating fuel is Xcel gas. 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:
- Efficiency Works Retrofit Rebate — $0.77 per square foot for flat-ceiling attic insulation (most other insulation measures pay $1.16/SF). Requires an Efficiency Works assessment first and applies only to residential electric customers of Longmont Power & Communications.
These are separate programs from separate sources. 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 Xcel Energy, “Xcel's insulation and air sealing rebates require a documented reduction of at least 20% in CFM50 — cubic feet per minute at 50 pascals — verified by a blower door test before and after the work.”
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 current Xcel rebate amounts and program rules, see the Xcel Energy insulation and air-sealing rebates page. 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.
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 — 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 attic insulation?
Should I do attic 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 attic 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.
How much R-value should my Longmont attic have?
Longmont sits in Climate Zone 5B, where the model 2021 IECC ceiling-insulation table prescribes R-49 minimum. For retrofit upgrades, R-60 is the recommended target. This is the model code's own figure for the climate zone, not a claim about which specific code edition the City of Longmont currently enforces.
Does my Longmont home qualify for a rebate?
For attic insulation, likely yes for Xcel's rebate — it applies citywide to Xcel gas and electric customers. Whether you also qualify for the separate Efficiency Works rebate depends on your electric utility: only Longmont Power & Communications customers can access it, and that's roughly 61% of the city, not all of it. Check your electric bill, or ask your contractor to confirm before assuming either way.
Can I claim both the Xcel and Efficiency Works rebates on one project?
We don't know, and we're not going to tell you that you can. Neither program's published rules state whether a single project may claim both, and a side-by-side incentive table isn't the same as a combination rule. Ask your contractor or the programs directly for your specific project before counting on a combined number.
How much does attic insulation cost for a typical Longmont home?
Most 1,500-2,500 sq ft Longmont homes price between $1,500 and $5,500 before rebates, depending on current insulation level, attic geometry, and any required pre-work. The free in-home estimate gives exact numbers, not a range.
Should I insulate the attic floor or the rafters?
For the vast majority of Longmont homes, insulating the attic floor — the joist plane between the conditioned home and the unconditioned attic — is correct. Insulating the rafters is a different design, typically using spray foam, and is only justified when the attic holds HVAC equipment or finished living space.
Will adding attic insulation cause moisture problems?
Only if the install skips ventilation. Attic insulation needs to preserve soffit-to-ridge airflow via baffles at the eaves; otherwise trapped moisture can cause roof-deck rot. Ask your contractor to confirm ventilation will be preserved before the job starts.