Insulation planning starts with a rough target and a material takeoff, but the final answer depends on adopted local code, product labels, installation quality, air sealing, moisture control, fire or ignition barrier requirements, and the selected compliance path.
This guide frames the calculator as a source-aware planning screen. It can help organize early quantities for walls, attics, basements, crawls, and rim joists, but it does not replace the IECC/IRC as adopted locally, manufacturer fact sheets, product coverage charts, rebate rules, AHJ review, or qualified building-science review.
R-Value Target Pointers by Climate Zone
The International Energy Conservation Code includes residential prescriptive insulation tables, but the adopted local edition, amendments, exceptions, and compliance path control the real requirement. The values below are planning context only, not a pass/fail code determination. Note that this table blends values from different IECC editions (the 2021 edition raised several targets — for example, ceilings in Zones 2–3 to R-49 and Zones 4–8 to R-60) — always check the edition your jurisdiction has adopted:
| Zone | Example Cities | Ceiling | Wood Frame Wall | Floor | Basement Wall |
|---|---|---|---|---|---|
| 1 | Miami, Key West | R-30 | R-13 | R-13 | R-0 |
| 2 | Houston, Phoenix, Jacksonville | R-38 | R-13 | R-13 | R-0 |
| 3 | Atlanta, Dallas, Las Vegas | R-49 | R-20 or 13+5ci | R-19 | R-5ci |
| 4 | Seattle, DC, Memphis | R-60 | R-20 or 13+5ci | R-19 | R-10ci |
| 5 | Chicago, Denver, Boston | R-60 | R-20 or 13+5ci | R-30 | R-15ci |
| 6 | Minneapolis, Burlington | R-60 | R-20+5ci or 13+10ci | R-30 | R-15ci |
| 7 | Duluth, International Falls | R-60 | R-20+5ci or 13+10ci | R-38 | R-15ci |
| 8 | Fairbanks, Barrow | R-60 | R-20+5ci or 13+10ci | R-38 | R-15ci |
ci = continuous insulation means insulation outside or otherwise continuous across framing. Verify the actual code path, attachment, water control, fire details, and cladding requirements before selecting a continuous-insulation assembly.
Do not treat the table as a local code answer. Many jurisdictions use a different edition or amendments, and many projects use a UA tradeoff or performance path instead of a simple component table.
Insulation Calculator
Calculate insulation quantity by type for walls, attic, crawl space, and basement. Climate zone R-value targeting per IECC, cavity depth checks, settling factors, and vapor barrier recommendations.
Insulation Types Compared for Early Takeoff
Each insulation type has different nominal R-value, packaging, installation constraints, cost, and code/fire/moisture details. Product labels and manufacturer fact sheets control the exact R-value, coverage, facing, and limitations:
Fiberglass Batts
R-3.0 to R-3.8 per inch. The most common residential insulation. Pre-cut widths for 16" and 24" OC framing. Easy to install (friction-fit between studs). Common sizes: R-13 (3.5" for 2×4 walls), R-19 (6.25" for 2×6 walls), R-30 (9.5" for ceilings), R-38 (12" for ceilings). Cost: $0.50–$1.00 per sq ft installed. Disadvantage: performance depends heavily on installation quality. Gaps, compression, and missing sections destroy effectiveness.
Blown Cellulose
R-3.2 to R-3.8 per inch. Made from recycled newspaper treated with borate fire retardant. Blown into attic floors or dense-packed into wall cavities. Fills gaps and irregular spaces better than batts. Cost: $0.60–$1.20 per sq ft installed. Disadvantage: settles 15–20% in attic applications (loose fill), so you must install 15–20% more than target depth. Dense-pack wall applications do not settle.
Mineral Wool (Rockwool/Roxul)
R-3.7 to R-4.2 per inch. Higher R-value per inch than fiberglass. Fire-resistant (melting point over 2,000°F), moisture-resistant, and sound-absorbing. Semi-rigid batts are easier to cut precisely and hold shape in wall cavities. Cost: $1.00–$1.60 per sq ft. Best for fire-rated assemblies, sound isolation walls, and exterior continuous insulation (rigid boards).
Spray Foam — Open Cell
R-3.5 to R-3.7 per inch. Expands to fill cavities completely, sealing air leaks. Vapor permeable (allows drying). Good for walls and rooflines. Cost: $1.00–$1.75 per sq ft installed. Requires professional installation. Not recommended in cold climates without an interior vapor retarder because moisture can condense in the foam.
Spray Foam — Closed Cell
Often around R-6.0 to R-7.0 per inch depending on product and test basis. Closed-cell foam can be low-perm at sufficient thickness, but do not assume it satisfies every vapor, air, fire, ignition-barrier, or thermal-barrier requirement. Cost, blowing agent, installer, exposure, and code requirements vary by product and jurisdiction.
Rigid Foam Board
EPS: R-3.8–R-4.4 per inch. XPS: R-5.0 per inch. Polyisocyanurate (polyiso): R-5.7–R-6.5 per inch. Used for continuous exterior insulation over wall sheathing, under slabs, and on basement walls. Cut-to-fit with a utility knife. Cost varies by type and thickness.
For most residential planning, compare material cost, R per inch, installation quality, air sealing, moisture drying path, fire requirements, and product availability together. The calculator only covers the quantity screen.
Calculating Rough Quantities: Batts and Loose-Fill
Quantity calculation differs by insulation type, and product packaging matters. Use calculator output as a rough takeoff and then check the selected product label or fact sheet before ordering:
Batt Insulation
Batts are sold in bags that cover a specific square footage at a specific R-value. Read the bag label — it tells you exactly how many square feet the bag covers. For a gross calculation: total wall cavity area (height × width minus framing) ÷ bag coverage = bags needed.
A practical shortcut: one bag of R-13 fiberglass batts (15-inch width for 16" OC) covers about 40 sq ft. One bag of R-19 (15-inch) covers about 48 sq ft. Count the total cavity area and divide by the bag coverage.
Do not deduct framing area from the insulation calculation. Batts are cut to friction-fit between studs — you need batts for every stud bay. Deducting would leave you short.
Blown Cellulose (Attic)
Cellulose is sold in bags with a coverage chart on the label. Coverage depends on the settled R-value you want to achieve. For R-38 settled cellulose (common attic target), you typically need about 10.5 inches of settled depth, which requires 12.5 inches of initial installed depth (the settling factor).
Coverage per bag varies by manufacturer, product density, target R-value, and installed depth. The product label or coverage chart is the source to use for purchase quantity.
Dense-Pack Cellulose (Walls)
Dense-pack is blown at higher pressure (3.5 lbs per cubic foot density) into enclosed wall cavities through small holes. It does not settle because the density prevents it. Coverage per bag is lower than loose-fill because you are packing more material into the same space. Typically requires professional installation.
Loose-fill bags = area and target R-value checked against the selected product coverage chart.
The app keeps a local weight-based planning row for quick screening, but the manufacturer chart controls final bags, installed depth, and settled R-value.
Settling and Coverage Labels for Loose-Fill Insulation
Loose-fill insulation coverage depends on product density, installed depth, settled depth, and target R-value. Product labels and FTC-required fact sheets are the source for final coverage:
Cellulose
Settles 15–20% in loose-fill attic applications. Install 15–20% deeper than the settled target. If you need R-38 (10.5" settled), install to 12–12.5 inches. The bag label provides both installed and settled depths for each R-value — follow it.
Fiberglass Loose-Fill
Settles 1–4% — significantly less than cellulose. The light, fluffy texture compresses slightly under its own weight but maintains depth well over time. Install at the label-recommended depth for the target R-value.
Mineral Wool Loose-Fill
Settles 1–3%. Dense, heavy fibers resist settling. Comparable settling behavior to fiberglass loose-fill.
Dense-Pack (Any Material)
Does not settle. The installation method compresses the material to 3.5 lbs/cu ft (cellulose) or equivalent density for fiberglass, which prevents any settling over time. This is one of the primary advantages of dense-pack over loose-fill for wall cavities.
For attic insulation, depth markers and follow-up inspection are useful, but the selected product coverage chart, installer instructions, and local program requirements control the acceptable installed and settled depth.
Use the bag label or manufacturer fact sheet for installed thickness, settled thickness, coverage, and R-value. The calculator local settling factor is only a planning screen.
Vapor-Retarder Boundaries by Climate
Vapor barriers and vapor retarders affect drying potential, condensation risk, and durability. Climate matters, but so do exterior insulation ratio, cladding, rain control, air sealing, existing layers, basement or crawlspace moisture, and local code. Treat the notes below as planning cautions, not final assembly design:
Cold Climates (Zones 5-8): Review Warm-Side Vapor Control
Heating-dominated assemblies often need warm-side vapor-control review, but the correct class and location depend on the selected assembly, exterior insulation, air sealing, drying path, and local code. Do not add polyethylene or faced products without checking the complete wall or roof assembly.
Mixed Climates: Review Both Drying Directions
Mixed climates can see seasonal moisture drives in both directions. Class III or variable-permeance approaches may be appropriate in some assemblies, but cladding reservoir, exterior foam, air leakage, and interior humidity change the risk.
Hot-Humid Climates (Zones 1-3): Avoid Interior Poly Assumptions
Cooling-dominated assemblies often need inward drying potential. Interior polyethylene can be risky, but the final answer still depends on the assembly and local code.
No Single Rule Covers Every Assembly
Use the calculator output as a prompt to ask the right vapor and drying questions. Final vapor-retarder selection should come from adopted code, product instructions, and qualified building-science review.
Do not use the calculator as vapor-retarder approval. Check assembly layers, air sealing, exterior insulation ratio, rain control, existing vapor layers, local code, and product instructions before installing faced batts, polyethylene, spray foam, or smart membranes.
Common Mistakes That Waste Energy
Insulation performance depends more on installation quality than R-value. A perfectly installed R-13 wall outperforms a poorly installed R-19 wall. The most common mistakes:
1. Gaps and Voids
A gap covering just 5% of the wall area can reduce the wall's effective insulation value by 25% or more. Air flows through the gap, bypassing the insulation entirely. The most common gap locations: around electrical boxes, at the top and bottom of stud bays, where plumbing penetrates the wall, and at irregular framing (corners, headers, soffits).
2. Compressed Batts
Fiberglass batts get their R-value from trapped air between fibers. Compressing a batt reduces the air space and reduces the R-value. An R-19 batt compressed into a 2×4 cavity (3.5 inches instead of 6.25 inches) only delivers about R-13. Worse, the compressed batt may not fully fill the cavity width, creating air gaps on the sides.
3. Missing Air Sealing
Insulation slows conductive heat transfer. Air sealing stops convective heat transfer (moving air carrying heat). If warm air can flow through or around the insulation — through can light openings, top plates, plumbing chases, or duct penetrations — the insulation is much less effective. Air seal all penetrations before (not after) installing insulation.
4. Ignoring the Attic Hatch
An uninsulated attic hatch or pull-down stair is a 10–15 sq ft hole in your building envelope. Insulate and weatherstrip the attic access point to match the surrounding ceiling insulation. Rigid foam glued to the back of the hatch plus weatherstripping costs $20 and takes 30 minutes.
5. Stuffing Batts Behind Wires and Pipes
Batts should be split around wires and pipes, not stuffed behind them. Stuffing creates a compressed area (reduced R-value) and an air gap between the batt and drywall. Split the batt into two layers and place one behind and one in front of the obstruction.
Air sealing is often critical before adding insulation, but the right sealant, fire blocking, ventilation, electrical clearance, combustion-air, and moisture details depend on the house. Handle those details before relying on a material quantity takeoff.
Frequently Asked Questions
Use climate-zone tables only as a starting point. The actual requirement depends on adopted local code, amendments, compliance path, assembly type, and AHJ interpretation.
Spray foam can be useful where air sealing or high R per inch matters, but value depends on product data, installer quality, fire or ignition barrier requirements, vapor behavior, and project goals. The calculator does not make that investment decision.
Use the selected product label or fact sheet for installed depth, settled depth, coverage, and R-value. The calculator loose-fill factors are local planning rows only.
Maybe. Climate zone is only one factor. Assembly layers, exterior foam ratio, air sealing, rain control, existing vapor layers, basement or crawlspace moisture, and local code control the final vapor-retarder choice.
Sometimes, but existing material must be checked for moisture, compression, gaps, pests, mold, vermiculite/asbestos risk, electrical clearances, and air-sealing defects before adding material.
That depends on the assembly. Insulation can help, but sound performance also depends on framing, drywall layers, resilient channels, sealing, penetrations, and tested STC data.
Check the manufacturer coverage chart for the selected product, target R-value, installed thickness, settled thickness, and bag weight. The app bag count is a rough local screen.