Definition
What is wall insulation, and how does it work?
Wall insulation, in the retrofit sense, almost always means dense-pack: a crew drills a small access hole per wall-cavity bay (from outside, under the siding, or from inside near the ceiling) and blows cellulose or fiberglass into the cavity at high density, then patches the holes. It's a different process from new-construction wall insulation, which installs batts or spray foam into open cavities before drywall goes up.
Dense-pack works because most pre-1990 Longmont walls were built with 2x4 framing and either no insulation or thin, settled batts that have compressed and left gaps at the top of the cavity. Filling the full cavity at high density closes those gaps and stops convective air movement inside the wall.
Wall insulation is not typically paired with exterior siding replacement unless siding is already being removed for other reasons — dense-pack access holes are small and patchable, so a full siding tear-off isn't required to insulate the walls underneath.
Qualification signals
Who needs wall insulation in Longmont?
The clearest signal is a wall that feels noticeably cold to the touch in winter, especially near exterior corners, or a home where the attic has already been upgraded but comfort complaints persist. Pre-1990 Longmont homes with original 2x4 wall framing are the most common candidates.
Homes with brick veneer or stucco exteriors can still be dense-packed in most cases — the access-hole method works through most common Longmont exterior finishes, though the specific approach varies by wall type. The free in-home estimate confirms what your walls can accept before any work starts.
Cost & the cost of waiting
How much does wall insulation cost in Longmont — and what does waiting cost?
Wall insulation in Longmont typically runs $2.00 to $4.00 per square foot of wall area installed, reflecting the labor-intensive drill-and-patch process compared to open-attic blowing. A typical 1,500-2,000 sq ft home's exterior wall area often prices between $2,500 and $6,000 before rebates, depending on wall height, number of stories, and exterior finish.
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 wall 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). A cold, uninsulated wall loses more heat per square foot in a Longmont winter than the same wall would in a milder climate — wall insulation compounds with a well-insulated attic rather than substituting for it.
The rebate landscape is genuinely two-utility here. 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 wall insulation process work?
Pre-work inspection
Crew identifies wall framing type, checks for existing insulation via a small test hole or borescope, and confirms the exterior finish's drill-and-patch approach before scoping the job.
Access hole layout
One access hole is typically drilled per stud bay, positioned to reach the full cavity height — from outside under siding where possible, or from inside near the ceiling where the exterior finish doesn't allow it.
Dense-pack installation
Cellulose or fiberglass is blown into each cavity at high density (typically 3.5+ lbs/cubic ft for cellulose) via a hose fed through the access hole, filling the bay from bottom to top.
Density verification
Crew checks fill density and coverage per bay, watching for common problem areas like fire blocking, wiring runs, and top-plate gaps that can leave a cavity partially filled.
Patch and cleanup
Access holes are patched to match the existing siding or interior finish, and the crew cleans up blown-material overspray.
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 wall insulation in Longmont?
Wall 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 $350 for wall insulation, 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 $1.16 per square foot for exterior wall 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 $350 for wall 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 — $1.16 per square foot for exterior wall insulation. 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.
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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 wall insulation?
Should I do wall 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 wall 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.
What R-value should my Longmont exterior wall have?
A dense-pack retrofit fills the existing cavity depth rather than rebuilding the wall to a new-construction target — a standard 2x4 cavity dense-packed with cellulose lands around R-13 to R-14, a major improvement over an empty or settled-batt cavity. This site's sourced code citation (the model 2021 IECC's Climate Zone 5 table) covers the attic target — R-49 to R-60 — directly; ask your contractor for the specific wall figure that applies to your project.
Does my Longmont home qualify for a wall insulation rebate?
Likely yes for Xcel's rebate — it applies citywide to Xcel gas and electric customers, up to $350 for wall insulation. Whether you also qualify for the separate Efficiency Works rebate depends on your electric utility: only Longmont Power & Communications customers can access it. Check your electric bill, or ask your contractor to confirm before assuming either way.
Will drilling access holes damage my siding or interior walls?
The holes are small — typically an inch or so in diameter, one per stud bay — and are patched to match the existing finish afterward. Vinyl and wood siding are usually patched invisibly; stucco and masonry patches may be visible on close inspection unless the exterior is repainted. Your contractor should show you the planned hole locations and patch approach before starting.
Can I insulate walls without removing drywall?
Yes — that's the point of dense-pack. It's specifically a retrofit method that avoids the cost and disruption of removing drywall or siding. Full removal is occasionally used when walls are already open for another reason (a remodel, for instance), but it isn't required for standard wall insulation.
How do I know if my walls already have insulation?
A borescope inspection through a small test hole is the reliable way to check — visual guessing from the outside doesn't tell you fill density or whether older batts have settled and left gaps. The free in-home estimate includes this check before any work is scoped or quoted.