Short answer: wood has an R-value of roughly R-0.85 to R-1.5 per inch for softwoods and R-0.69 to R-1.4 per inch for hardwoods at 12% moisture content, according to the USDA Wood Handbook. Light woods such as cedar and white pine insulate best; dense hardwoods such as oak and hickory least. This page lists the Handbook values for 68 species, works out the R-value of common board, stud and timber thicknesses, and shows how moisture content changes the figure.
R-value is resistance to heat flow: higher is better insulation. In US units it is measured in h·ft²·°F/Btu; the “per inch” figure, which the Handbook calls thermal resistivity, is the reciprocal of thermal conductivity k. Multiply it by the thickness in inches to get the R-value of a piece of wood.
R-value of wood by species (Wood Handbook Table 4-7)
| Species | Type | Specific gravity | k at 12% MC | R per inch, 12% MC | R per inch, ovendry | R of 3/4 in | R of 1-1/2 in | R of 3-1/2 in | R of 5-1/2 in |
|---|---|---|---|---|---|---|---|---|---|
| Ash (black) | hardwood | 0.53 | 1.00 | 0.98 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Ash (white) | hardwood | 0.63 | 1.20 | 0.84 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Aspen (big tooth) | hardwood | 0.41 | 0.82 | 1.20 | 1.5 | 0.91 | 1.83 | 4.3 | 6.7 |
| Aspen (quaking) | hardwood | 0.40 | 0.80 | 1.20 | 1.5 | 0.94 | 1.88 | 4.4 | 6.9 |
| Basswood, American | hardwood | 0.38 | 0.77 | 1.30 | 1.6 | 0.97 | 1.95 | 4.5 | 7.1 |
| Beech, American | hardwood | 0.68 | 1.30 | 0.78 | 1.0 | 0.58 | 1.15 | 2.7 | 4.2 |
| Birch (sweet) | hardwood | 0.71 | 1.30 | 0.76 | 0.9 | 0.58 | 1.15 | 2.7 | 4.2 |
| Birch (yellow) | hardwood | 0.66 | 1.20 | 0.81 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Cherry, black | hardwood | 0.53 | 1.00 | 0.98 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Chestnut, American | hardwood | 0.45 | 0.89 | 1.10 | 1.4 | 0.84 | 1.69 | 3.9 | 6.2 |
| Cottonwood (black) | hardwood | 0.35 | 0.72 | 1.40 | 1.7 | 1.04 | 2.08 | 4.9 | 7.6 |
| Cottonwood (eastern) | hardwood | 0.43 | 0.85 | 1.20 | 1.4 | 0.88 | 1.76 | 4.1 | 6.5 |
| Elm (american) | hardwood | 0.54 | 1.00 | 0.96 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Elm (rock) | hardwood | 0.67 | 1.30 | 0.80 | 1.0 | 0.58 | 1.15 | 2.7 | 4.2 |
| Elm (slippery) | hardwood | 0.56 | 1.10 | 0.93 | 1.1 | 0.68 | 1.36 | 3.2 | 5.0 |
| Hackberry | hardwood | 0.57 | 1.10 | 0.92 | 1.1 | 0.68 | 1.36 | 3.2 | 5.0 |
| Hickory, pecan | hardwood | 0.69 | 1.30 | 0.77 | 0.9 | 0.58 | 1.15 | 2.7 | 4.2 |
| Hickory, true (mockernut) | hardwood | 0.78 | 1.40 | 0.69 | 0.8 | 0.54 | 1.07 | 2.5 | 3.9 |
| Hickory, true (shagbark) | hardwood | 0.77 | 1.40 | 0.70 | 0.9 | 0.54 | 1.07 | 2.5 | 3.9 |
| Magnolia, southern | hardwood | 0.52 | 1.00 | 1.00 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Maple (black) | hardwood | 0.60 | 1.10 | 0.88 | 1.1 | 0.68 | 1.36 | 3.2 | 5.0 |
| Maple (red) | hardwood | 0.56 | 1.10 | 0.93 | 1.1 | 0.68 | 1.36 | 3.2 | 5.0 |
| Maple (silver) | hardwood | 0.50 | 0.97 | 1.00 | 1.2 | 0.77 | 1.55 | 3.6 | 5.7 |
| Maple (sugar) | hardwood | 0.66 | 1.20 | 0.81 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Oak, red (black) | hardwood | 0.66 | 1.20 | 0.81 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Oak, red (northern red) | hardwood | 0.65 | 1.20 | 0.82 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Oak, red (southern red) | hardwood | 0.62 | 1.20 | 0.85 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Oak, white (bur) | hardwood | 0.66 | 1.20 | 0.81 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Oak, white (white) | hardwood | 0.72 | 1.30 | 0.75 | 0.9 | 0.58 | 1.15 | 2.7 | 4.2 |
| Sweetgum | hardwood | 0.55 | 1.10 | 0.95 | 1.2 | 0.68 | 1.36 | 3.2 | 5.0 |
| Sycamore, American | hardwood | 0.54 | 1.00 | 0.96 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Tupelo (black) | hardwood | 0.54 | 1.00 | 0.96 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Tupelo (water) | hardwood | 0.53 | 1.00 | 0.98 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Yellow-poplar | hardwood | 0.46 | 0.90 | 1.10 | 1.3 | 0.83 | 1.67 | 3.9 | 6.1 |
| Baldcypress | softwood | 0.47 | 0.92 | 1.10 | 1.3 | 0.82 | 1.63 | 3.8 | 6.0 |
| Cedar (atlantic white) | softwood | 0.34 | 0.70 | 1.40 | 1.7 | 1.07 | 2.14 | 5.0 | 7.9 |
| Cedar (eastern red) | softwood | 0.48 | 0.94 | 1.10 | 1.3 | 0.80 | 1.60 | 3.7 | 5.9 |
| Cedar (northern white) | softwood | 0.31 | 0.65 | 1.50 | 1.8 | 1.15 | 2.31 | 5.4 | 8.5 |
| Cedar (port-orford) | softwood | 0.43 | 0.85 | 1.20 | 1.4 | 0.88 | 1.76 | 4.1 | 6.5 |
| Cedar (western red) | softwood | 0.33 | 0.68 | 1.50 | 1.7 | 1.10 | 2.21 | 5.1 | 8.1 |
| Cedar (yellow) | softwood | 0.46 | 0.90 | 1.10 | 1.3 | 0.83 | 1.67 | 3.9 | 6.1 |
| Douglas-fir (coast) | softwood | 0.51 | 0.99 | 1.00 | 1.2 | 0.76 | 1.52 | 3.5 | 5.6 |
| Douglas-fir (interior north) | softwood | 0.50 | 0.97 | 1.00 | 1.2 | 0.77 | 1.55 | 3.6 | 5.7 |
| Douglas-fir (interior west) | softwood | 0.52 | 1.00 | 1.00 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Fir (balsam) | softwood | 0.37 | 0.75 | 1.30 | 1.6 | 1.00 | 2.00 | 4.7 | 7.3 |
| Fir (white) | softwood | 0.41 | 0.82 | 1.20 | 1.5 | 0.91 | 1.83 | 4.3 | 6.7 |
| Hemlock (eastern) | softwood | 0.42 | 0.84 | 1.20 | 1.4 | 0.89 | 1.79 | 4.2 | 6.5 |
| Hemlock (western) | softwood | 0.48 | 0.94 | 1.10 | 1.3 | 0.80 | 1.60 | 3.7 | 5.9 |
| Larch, western | softwood | 0.56 | 1.10 | 0.93 | 1.1 | 0.68 | 1.36 | 3.2 | 5.0 |
| Pine (eastern white) | softwood | 0.37 | 0.75 | 1.30 | 1.6 | 1.00 | 2.00 | 4.7 | 7.3 |
| Pine (jack) | softwood | 0.45 | 0.89 | 1.10 | 1.4 | 0.84 | 1.69 | 3.9 | 6.2 |
| Pine (loblolly) | softwood | 0.54 | 1.00 | 0.96 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Pine (lodgepole) | softwood | 0.43 | 0.85 | 1.20 | 1.4 | 0.88 | 1.76 | 4.1 | 6.5 |
| Pine (longleaf) | softwood | 0.62 | 1.20 | 0.85 | 1.0 | 0.62 | 1.25 | 2.9 | 4.6 |
| Pine (pitch) | softwood | 0.53 | 1.00 | 0.98 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Pine (ponderosa) | softwood | 0.42 | 0.84 | 1.20 | 1.4 | 0.89 | 1.79 | 4.2 | 6.5 |
| Pine (red) | softwood | 0.46 | 0.90 | 1.10 | 1.3 | 0.83 | 1.67 | 3.9 | 6.1 |
| Pine (shortleaf) | softwood | 0.54 | 1.00 | 0.96 | 1.2 | 0.75 | 1.50 | 3.5 | 5.5 |
| Pine (slash) | softwood | 0.61 | 1.20 | 0.86 | 1.1 | 0.62 | 1.25 | 2.9 | 4.6 |
| Pine (sugar) | softwood | 0.37 | 0.75 | 1.30 | 1.6 | 1.00 | 2.00 | 4.7 | 7.3 |
| Pine (western white) | softwood | 0.40 | 0.80 | 1.20 | 1.5 | 0.94 | 1.88 | 4.4 | 6.9 |
| Redwood (old growth) | softwood | 0.41 | 0.82 | 1.20 | 1.5 | 0.91 | 1.83 | 4.3 | 6.7 |
| Redwood (young growth) | softwood | 0.37 | 0.75 | 1.30 | 1.6 | 1.00 | 2.00 | 4.7 | 7.3 |
| Spruce (black) | softwood | 0.43 | 0.85 | 1.20 | 1.4 | 0.88 | 1.76 | 4.1 | 6.5 |
| Spruce (engelmann) | softwood | 0.37 | 0.75 | 1.30 | 1.6 | 1.00 | 2.00 | 4.7 | 7.3 |
| Spruce (red) | softwood | 0.42 | 0.84 | 1.20 | 1.4 | 0.89 | 1.79 | 4.2 | 6.5 |
| Spruce (sitka) | softwood | 0.42 | 0.84 | 1.20 | 1.4 | 0.89 | 1.79 | 4.2 | 6.5 |
| Spruce (white) | softwood | 0.37 | 0.75 | 1.30 | 1.6 | 1.00 | 2.00 | 4.7 | 7.3 |
Why density and moisture matter
The Handbook gives one equation for the thermal conductivity of wood across the grain at moisture contents below 25%: k = Gx(B + C·x) + A, where Gx is specific gravity at moisture content x (%), and A = 0.129, B = 1.34 and C = 0.028 in US units (Eq. 4-15, valid for specific gravity above 0.3 near room temperature). Two things follow. Denser woods conduct more heat, so they have lower R-values. And water conducts heat better than wood substance, so R-value falls as the wood gets wetter. Conductivity along the grain is higher again, on average about 1.8 times the across-grain value, so end grain insulates worst.
The table shows the effect of moisture for three woods, computed with Eq. 4-15 at the Table 4-7 specific gravities. Indoor wood is usually between 6% and 12% moisture content; outdoor wood in a humid climate is often 12% to 16% (see the EMC calculator).
| Moisture content | Engelmann spruce, R per inch | Douglas-fir (coast), R per inch | Northern red oak, R per inch |
|---|---|---|---|
| 0% | 1.60 | 1.23 | 1.00 |
| 6% | 1.46 | 1.11 | 0.90 |
| 12% | 1.33 | 1.02 | 0.82 |
| 16% | 1.26 | 0.96 | 0.77 |
| 20% | 1.20 | 0.91 | 0.73 |
| 24% | 1.14 | 0.87 | 0.70 |
Studs and framing: the thermal bridge
In a wood-framed wall the studs, plates and headers bridge the insulation. A 2×4 (3-1/2 in deep) in spruce, the main species in SPF framing lumber, is about R-4.7 through its depth; a 2×6 (5-1/2 in) about R-7.3. Southern pine, which is denser, gives about R-3.5 for a 2×4. The insulation in the cavities beside them is typically R-13 to R-15 in a 2×4 wall and R-19 to R-21 in a 2×6 wall.
Worked example, using the parallel-path method (heat flow through framing and cavity added by area): if framing makes up a quarter of the wall area, a figure we use only as an example, a 2×4 wall with R-13 batts has an effective R-value through the framing layer of 1 ÷ (0.25 ÷ 4.7 + 0.75 ÷ 13) = R-9.0, and a 2×6 wall with R-20 batts about R-14.0, before sheathing, drywall and air films are added. This is why energy codes and ENERGY STAR also recognise continuous insulation over the studs. For the recommended insulation levels where you live, see insulation R-values by climate zone, and to estimate quantities use the insulation calculator.
Floors, siding, paneling and log walls
- Hardwood floor: 3/4 in solid red oak is about R-0.62. Thin engineered floors have even less; the insulation below the subfloor does the work.
- Wood siding and paneling: 3/4 in western redcedar is about R-1.10 and 1/2 in about R-0.74. Thinner, overlapped bevel siding adds little; its value is weather protection, not insulation.
- Log walls: an 8 in thick solid wall of eastern white pine is about R-10.7, and of western redcedar about R-11.8, for the wood alone. Round logs are thinner at the joints, and gaps and chinking matter as much as the wood, so real log walls usually perform below these figures; log homes also benefit from the heat stored in the mass of the wood, which an R-value does not capture.
- Plywood and OSB: the Handbook does not tabulate panels. As an estimate only, 1/2 in Douglas-fir plywood using the Douglas-fir solid-wood value would be about R-0.51; glue lines and the density of a particular panel change the figure, so use the maker’s value where one is published.
Imported and other woods (computed with Eq. 4-15)
Table 4-7 covers only US species. For these imported woods with pages on this site we applied the same equation at 12% moisture content to the specific gravities in our database. Treat them as approximate in the same way.
| Species | Specific gravity at 12% | k at 12% MC | R per inch, 12% MC |
|---|---|---|---|
| Teak | 0.57* | 1.09 | 0.92 |
| Ipe | 0.92† | 1.66 | 0.60 |
| Genuine mahogany (Honduran / big-leaf) | 0.47* | 0.92 | 1.09 |
| African mahogany (khaya) | 0.44* | 0.87 | 1.15 |
| Sapele | 0.60* | 1.13 | 0.88 |
| Courbaril (jatoba) | 0.77* | 1.42 | 0.71 |
| Purpleheart | 0.71* | 1.32 | 0.76 |
| Iroko | 0.57* | 1.08 | 0.92 |
| Okoume | 0.35* | 0.72 | 1.38 |
| Light red meranti | 0.37* | 0.75 | 1.33 |
| Balsa | 0.17* | — | outside the equation range (G below 0.3) |
| Black walnut | 0.55 | 1.05 | 0.95 |
Frequently asked questions
What is the R-value of wood per inch?
About R-0.85 to R-1.5 per inch for softwoods and R-0.69 to R-1.4 for hardwoods at 12% moisture content, from Wood Handbook Table 4-7. Lighter woods insulate better: western redcedar is about R-1.5 per inch, red oak about R-0.82.
What is the R-value of a 2×4 stud?
A 2×4 is 3-1/2 in deep, so a spruce stud is about R-4.7 and a southern pine stud about R-3.5 through its depth, against R-13 to R-15 for the insulation between studs. That is why studs act as thermal bridges.
Is wood a good insulator?
Compared with other structural materials, yes: it conducts heat far less than steel, aluminium or concrete. Compared with insulation it is poor; fibreglass or cellulose insulation typically gives two to three times the R per inch of softwood lumber.
What is the R-value of a hardwood floor?
A 3/4 in solid red oak floor is about R-0.62, from the Handbook value. Most of a floor’s insulation has to come from the insulation below it.
Does wet wood insulate less?
Yes. The Handbook’s Eq. 4-15 shows conductivity rising with moisture content, so R-value falls; the table above shows the change from ovendry to 24% moisture content.
Sources
- USDA Forest Products Laboratory, Wood Handbook FPL-GTR-190 (2010): chapter 4, Thermal Properties (Eq. 4-15) and Table 4-7 (thermal conductivity of selected hardwoods and softwoods).
Last reviewed: 24 October 2026. Related: wood species database, lumber weight chart, lumber dimensions chart, insulation R-values by climate zone. Spotted an error? Please let us know.