Definition
What is fiberglass batt insulation, and how does it work?
Fiberglass batts are pre-cut, pre-sized panels of spun-glass fiber insulation, sold in standard widths to fit between framing members spaced 16 or 24 inches on center. A crew hand-fits each batt between joists (attic floor), studs (wall), or rafters (cathedral ceiling), trimming as needed around obstructions.
It's the traditional cut-to-fit method, distinct from blown-in loose-fill (machine-blown to a measured depth) or spray foam (sprayed wet and cured in place). Batts come faced (with a paper or foil vapor retarder attached) or unfaced, and in standard or high-density versions offering more R-value per inch of thickness.
Batt installation is straightforward in open, accessible framing but loses effectiveness fast when compression, gaps, or obstructions come into play — a batt squeezed to fit a too-narrow space, or cut short around a wire run, delivers less than its rated R-value at that spot. Careful, consistent fitting matters more with batts than with loose-fill, which naturally flows around minor obstructions.
Qualification signals
Who needs fiberglass batt insulation in Longmont?
Batts are a strong fit for open, accessible attic floors with regular joist spacing and few obstructions, and for open wall or floor framing before drywall goes up — new construction and additions, or a remodel where walls are already open. They're also a reasonable retrofit choice for an easily accessible attic where a homeowner wants a visually verifiable install (batts are easy to see and measure, unlike loose-fill depth).
For an attic with irregular framing, low headroom, or a lot of obstructions, blown-in loose-fill typically installs faster and with fewer gaps than hand-fitted batts. For an existing, closed wall cavity, batts aren't an option at all — that's dense-pack blown-in territory, since there's no way to hand-fit a batt behind finished drywall.
Cost & the cost of waiting
How much does fiberglass batt insulation cost in Longmont — and what does waiting cost?
Batt insulation in Longmont typically falls within the same $1.50 to $3.50 per conditioned square foot range as blown-in attic work, putting most 1,500-2,500 sq ft homes between $1,500 and $5,500 before rebates — batts often price toward the lower end of that range in straightforward, open framing, though access and any required pre-work still move the number. In new-construction or open-framing wall work, per-square-foot batt pricing is quoted separately; see this site's new construction page for that scope.
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 fiberglass batt 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). Whichever material fills the cavity, an under-target attic or wall loses more heat in a Longmont winter than the same gap would in a milder climate — batts installed to the model code's R-49/R-60 attic reference figure perform the same as any other material installed to the same target.
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 fiberglass batt insulation process work?
Pre-work inspection
Crew inspects the target framing — attic joists, wall studs, or rafters — measuring bay spacing and noting obstructions like wiring, ductwork, or plumbing that will need trimming around.
Air sealing first
Top plates, can lights, and other penetrations are sealed before batts go in — required for both the Xcel and Efficiency Works blower-door tests, and something batts alone can't do.
Batt selection and cutting
Batts are selected for the framing width and target R-value, then cut to length for each bay, including partial-length pieces around obstructions.
Hand installation
Each batt is fitted snugly into its bay without compression or gaps — compressed or gapped batts lose R-value at exactly the spot where the gap is.
Fit verification
Crew checks for gaps, compression, and missed obstructions bay by bay, 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 fiberglass batt insulation in Longmont?
Fiberglass batt insulation doesn't carry a rebate line of its own — Xcel and Efficiency Works both key their dollar figures to where the batts are installed, not what they're made of. Installed in 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. Installed in an open wall cavity, it falls under Xcel's $350 wall cap and Efficiency Works' $1.16 per square foot exterior-wall rate — the same figures a blown-in or spray-foam job in the same location would draw on.
Fiberglass batts don't have their 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 batts go into an attic or $350 if they go 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 batts go 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 International Energy Conservation Code, “the 2021 IECC (R402.1.2) sets attic insulation minimums at R-49 to R-60 for Climate Zone 5.”
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.”
For current Xcel rebate amounts and program rules, see the Xcel Energy insulation and air-sealing rebates page. 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 fiberglass batt insulation?
Should I do fiberglass batt 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 fiberglass batt 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 fiberglass batt insulation qualify for a rebate?
Not as its own category — Xcel and Efficiency Works both key their dollar figures to where the batts are installed, not what they're made of. Batts in an attic fall under the same attic figures a blown-in job would use; batts in a wall fall under the wall figures. See the rebate breakdown above for the actual numbers.
Are batts better than blown-in insulation?
Neither is universally better. Batts work well in open, evenly-spaced, accessible framing and let you visually verify the install. Blown-in flows around obstructions and irregular spacing more easily. The better fit depends on your specific attic or wall's framing and accessibility, not a blanket rule.
Can batts be installed in an existing, finished wall?
No — batts require an open cavity to hand-fit into, which means removing drywall or working before it goes up. An existing, closed wall cavity is dense-pack blown-in territory instead; see this site's wall insulation page for that process.
What R-value should my Longmont attic or wall have?
For attics, Longmont sits in Climate Zone 5B, where the model 2021 IECC prescribes R-49 minimum, R-60 recommended. This site doesn't have a sourced wall R-value target the same way — ask your contractor for the specific figure that applies to your wall project. Batts are sold in standard and high-density versions to hit different R-values within the same framing depth.
How much does batt insulation cost for a typical Longmont home?
Attic batt work typically falls in the same $1.50 to $3.50 per square foot range as blown-in attic work, often toward the lower end in open, accessible framing. The free in-home estimate gives exact numbers, not a range.
What happens if a batt is compressed or doesn't fully fill its bay?
It loses R-value right where the gap or compression is — a batt squeezed into a too-narrow space, or cut short around an obstruction, doesn't perform at its rated value at that spot. Careful, consistent fitting matters more with batts than with loose-fill material.