Your attic
How it works
How does this calculator work?
The range comes from ENERGY STAR's recommended insulation levels for Climate Zone 5, which Longmont sits in: R-49 to R-60 in the attic. That is a recommendation, not a code requirement. Longmont's own adopted code is the 2024 International Codes together with the Metro Cohort Model Code, effective July 1, 2026, and this site does not publish an attic R-value figure for that adoption — the Metro Cohort code is an alternative-compliance framework whose Climate Zone 5 ceiling table has not been read here. Confirm the number your permit is reviewed against with the city's building department.
The gap calculation is simple subtraction against your selected current-level bucket. Because the Building America Solution Center reports loose-fill cellulose settling 10-20% over its lifetime, a number you remember from years ago is often lower today — a measured depth check during the free in-home estimate gives you the real figure, not an estimate from memory.
According to ENERGY STAR, recommended insulation levels for retrofitting existing wood-framed buildings in Zones 6, 5, and 4C are R-60 added to the attic if the attic is uninsulated, or R-49 if it already has 3-4 inches of insulation.
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 the City of Longmont Building Services, “The City of Longmont has adopted the 2024 International Codes, along with the Metro Cohort Model Code and Colorado Wildfire Resiliency Code as of July 1st, 2026.”
According to the City of Longmont Building Inspection, Longmont's own roofing code guidance cites IRC Table R806.5 and IBC Table 1203.3 for climate zone 5 compliance.
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 — ask what R-value your contractor is quoting to, in writing, and confirm the figure your permit is reviewed against with the City of Longmont's building department. (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
Frequently asked about r-value target finder
Why does this calculator only cover attics, not walls or crawl spaces?
Because that's what this site has a sourced Climate Zone 5 figure for. ENERGY STAR states the attic recommendation directly (R-49 to R-60); a wall, crawl space, or floor figure would need its own source, which this property doesn't have verified yet. Rather than guess, we're leaving those out until we do.
Is R-49 or R-60 the real target for my Longmont home?
Both are ENERGY STAR recommendations for Climate Zone 5, not code minimums, and neither is a substitute for what your permit is reviewed against. R-60 leaves headroom because loose-fill insulation settles over its lifetime, which is why many contractors quote to it — start higher and you're still near R-49 years later. For the code figure, ask the City of Longmont's building department.
Does the calculator account for insulation settling?
Not automatically — it works from the current-level bucket you select. If you're estimating from what was installed years ago rather than a fresh measurement, keep in mind that the Building America Solution Center reports loose-fill cellulose settling 10-20% over time, so your actual current level may be lower than what was originally installed.
What if I don't know my current attic R-value at all?
Select "not sure" — the calculator will show you the range without guessing at a gap. A measured depth check during the free in-home estimate gives you the real number.
Does hitting R-49 or R-60 guarantee a rebate?
No — this calculator only addresses ENERGY STAR's recommended range, not rebate eligibility. Xcel's and Efficiency Works' rebates have their own separate requirements (a blower door test, a participating contractor, and more) beyond hitting a target R-value. See the attic insulation service page for the rebate details.
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