Library · Structures, greenhouse & energy
Insulation R-Value.
Insulation R-Value Calculator
Stack up insulation layers; calculate combined R-value and U-value. For greenhouses, livestock barns, root cellars, walk-in coolers.
R-value reference
| Material | R-value per inch | Notes |
|---|---|---|
| Closed-cell spray foam | R-6 to R-7 | Best per inch; vapor barrier built-in; expensive |
| Polyiso (foil-faced rigid) | R-6 to R-6.5 | Top R-value; good for above-grade |
| XPS (extruded polystyrene, "blueboard") | R-5 per inch | Below-grade rated; foundation insulation |
| EPS (expanded polystyrene) | R-3.6 to R-4 per inch | Cheaper than XPS; lower R; lower water resistance |
| Open-cell spray foam | R-3.5 per inch | Air seal benefit; cheaper than closed-cell |
| Fiberglass batt | R-3 to R-4 per inch | Standard; needs vapor barrier; degrades when wet |
| Cellulose (loose-fill) | R-3.5 per inch | Recycled paper; fire-retardant treated; excellent for retrofits |
| Mineral wool | R-3.7 to R-4.2 per inch | Fire + water resistant; good for damp environments |
| Straw bales | R-1.5 per inch | R-30 per bale (~ 18" thick); natural building |
| Hemp / hempcrete | R-2 to R-2.5 per inch | Natural building; some thermal mass |
| Wood (lumber, log) | R-1.25 per inch | Some R; mostly structural |
| Concrete | R-0.08 per inch | Negligible R; thermal mass instead |
| Earth (compacted) | R-0.25 per inch | Thermal mass benefit when bermed |
| Air gap (1" or more, sealed) | R-1 to R-2 | Bubble-wrap technique; modest gain |
| Single glass | R-1 | Baseline window |
| Double-pane glass | R-2 to R-3 | Standard window; argon-filled higher |
| Single poly (greenhouse) | R-0.85 | Standard greenhouse glazing |
| Double poly inflated | R-1.5 | 40% reduction in heat loss vs single |
| Twin-wall polycarbonate 8mm | R-1.6 | Permanent; long-life |
| Twin-wall polycarb 16mm | R-2.5 | Better insulation; less light transmission |
Recommended R-values by use
| Application | Walls (R-value) | Roof / ceiling | Foundation |
|---|---|---|---|
| Greenhouse (cold zone 4-6) | R-10 to R-20 (north wall) | (glazing, not insulated) | R-10 perimeter foam |
| Livestock barn (heated) | R-19 to R-30 | R-30 to R-40 | R-10 |
| Livestock barn (unheated) | Minimal — depends on species | Vapor barrier critical | — |
| Root cellar | R-10 to R-20 | R-20+ | Earth-bermed often sufficient |
| Walk-in cooler / freezer | R-30 to R-40 | R-40 to R-60 | R-20+ |
| Workshop / heated outbuilding | R-19 to R-25 | R-30 to R-40 | R-10 to R-15 |
| Smokehouse / curing | R-19 (heat retention) | R-30 | — |
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