Recommended R-value calculator
In IECC climate zone 5 the recommended targets are R-49 for the attic, R-15 for walls and R-30 for floors. Pick your zone from 1 to 8, mark Marine Zone 4 if it applies, and get all three targets for a wood-frame home. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Climate zone
- 5
- Zone label
- Cool
- Attic r
- 49
- Attic r min
- 38
- Attic r max
- 60
Choosing insulation levels without a climate context is how attics stay under-insulated in cold zones and walls get over-specified where cooling loads dominate. Homeowners, remodelers, energy auditors, and estimating apps need a single, shareable answer to a practical question: for this IECC climate zone, what attic, wall, and floor R-values make sense for an efficient wood-frame envelope. This recommended R-value calculator maps climate zones one through eight to deterministic attic, wall, and floor targets, including optional Marine Zone four floor upgrades, so takeoffs and education pages stay consistent across clients. Values follow a fixed DOE-style guidance table in inch-pound units; the engine does not call weather APIs or invent product thicknesses.
From climate zone to insulation targets
Choosing insulation without a climate context is how attics stay under-insulated in cold zones and walls get over-specified where cooling loads dominate. This calculator takes the IECC climate zone of the building, from 1 to 8, and returns three targets for an efficient wood-frame envelope: the attic, the wall cavity and the floor over unconditioned space. Zone 5, for example, gets R-49 in the attic, R-15 in the walls and R-30 in the floor. Homes in Marine Zone 4 can be marked as such, and then the floor target steps from R-19 to R-30 to match cool-zone practice while attic and wall stay on the Zone 4 band.
What the table does and does not cover
The values come from a fixed table in inch-pound units, so the same zone always gives the same answer and can be shared between a homeowner, an energy auditor and an estimator. They are a first-pass target before you choose products or bid an insulation depth, not a reprint of every continuous-insulation line in the latest energy code edition. Local amendments, multifamily corridors, mass walls and metric R-values are outside its scope, and it does not replace local code minimums or a full energy model.
Climate zone input, Marine Zone 4, and what the table represents
Start with the IECC climate zone for the building location. Zones one and two cover the hottest regions of the continental map; zones seven and eight cover the coldest. The table is guidance for an efficient envelope, not a reprint of every continuous-insulation line in the latest energy code edition.
Local amendments, multifamily corridors, mass walls, and SI (metric) R-values are outside this product.
What you can do with it
First-pass envelope targets
Homeowners and auditors map a parcel’s IECC climate zone to attic, wall, and floor R targets before choosing products or bidding depth.
Marine Zone 4 floor upgrades
Coastal mixed-zone projects set marine true so floor R steps to cool-zone practice while attic and wall recommendations stay on the Zone 4 band.
FAQ
What does the marine flag do?
For other zones marine is ignored and reported as false.
Is the recommended R-value calculator free?
The browser tool runs free on your device.
What range of attic R-values fits climate zone 5?
The table gives a band from R-38 to R-60 for the attic, with R-49 as the recommended target. Walls run from R-13 to R-21 around R-15, and the floor stays at R-30.
Is this the same as my local energy code minimum?
No. The targets are guidance for an efficient wood-frame envelope, not a substitute for local code minimums, continuous insulation tables or a full energy model. Local amendments, multifamily corridors and mass walls are outside its scope.
Are the R-values given in metric units?
No. They are inch-pound values, expressed in hour times square foot times degree Fahrenheit per Btu, and they come from a fixed guidance table. Metric R-values are outside its scope.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/home/recommended-r-value \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"climate_zone":5}'const res = await fetch("https://api.kit.forhosting.com/home/recommended-r-value", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"climate_zone": 5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/home/recommended-r-value",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"climate_zone": 5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/home/recommended-r-value", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"climate_zone":5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"climate_zone":5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/home/recommended-r-value", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"climate_zone": 5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "home.recommended_r_value",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Climate zone input, Marine Zone 4, and what the table represents
Enter climate_zone as an integer from one through eight, or as a short string such as five, CZ5, or zone 5. Optional aliases zone, cz, iecc_zone, climate, and climate_zone_id keep form bindings flexible. When the home sits in Marine Zone four, set marine to true (aliases is_marine, zone_4_marine, marine_4) or pass a zone string that includes the word marine with zone four: the floor recommendation steps from R-19 to R-30 to match cool-zone practice while attic and wall targets stay on the mixed-zone band.
Reading attic_r, wall_r, floor_r, bands, and envelope_score
Example: climate zone five returns attic R-49, wall R-15, floor R-30 with attic band thirty-eight to sixty. On success the response echoes climate_zone, a short zone_label such as Cool or Mixed marine, and marine true only when Marine Zone four rules actually applied. Primary planning fields are attic_r, wall_r, and floor_r—the recommended IP R-values for attic, wall cavity-class insulation, and floor over unconditioned space. Identical inputs always produce identical JSON because the path is a pure static map with no network, random seed, or wall clock. Pair this endpoint with home.attic_insulation_depth when you already know the attic target and need inches of blown fill, and with home.insulation when you sum multi-layer thickness times R-per-inch into assembly R and U for a full wall or roof stack.
API usage, pricing, retrofit workflows, and practical limits
Call the free in-browser recommended R-value calculator for homeowner education, classroom demos, and first-pass envelope targets without opening a spreadsheet of climate maps. The capacity does not download weather normals, rebate rules, or live product catalogs—those remain your application layer—while this tool stays a transparent, testable lookup that every client can reproduce offline. Send a JSON body with required climate_zone and optional marine. Use the prepaid API when a renovation app, utility rebate pre-screener, energy audit tool, contractor tablet form, or property-management pipeline needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Prefer the official IECC or DOE climate-zone map for the parcel when assigning climate_zone, and treat marine carefully only for true Marine Zone four locations rather than every coastal ZIP code. Authors shipping SDKs can map climate zone, three recommended R-values, optional bands, and envelope_score into a compact table for inspectors and homeowners reviewing an upgrade quote.
Integration use cases
Estimating apps and CI fixtures
Retrofit tools and automated tests pin deterministic attic_r, wall_r, and floor_r for each climate zone without re-coding DOE tables in every client.
Technical questions
How do I get recommended attic, wall, and floor R-values?
Send climate_zone as an IECC zone integer from 1 to 8 (or a string like CZ5). The response returns attic_r, wall_r, floor_r plus min/max bands for each surface.
What happens if climate_zone is 0 or 9?
The request fails with invalid_input. Only IECC climate zones 1 through 8 are supported.
How is this different from the insulation R-value and attic depth calculators?
home.insulation sums layer thickness × R-per-inch into assembly R and U. home.attic_insulation_depth converts a target R into inches of fill. This tool answers which attic, wall, and floor R targets to aim for from climate zone alone.