How do I measure the depth of my attic insulation?

Push a ruler or a marked stick straight down through the insulation until it touches the ceiling drywall below, then read the depth at the top surface. Do it in three or four places away from the hatch and away from the eaves, because insulation settles unevenly and the area near the hatch is usually the most disturbed. Use the typical reading, not the deepest one. If the joists are visible above the insulation, you almost certainly have less than the recommended level, because a standard joist is 2x6 to 2x10 and that is only 5.5 to 9.25 inches.

Is 6 inches of attic insulation enough?

Almost certainly not, anywhere in the United States. Six inches of blown fibreglass is roughly R-13 to R-16, and six inches of cellulose about R-19 to R-23. The lowest ENERGY STAR recommendation for any climate zone is R-30, which applies only to zone 1 at the southern tip of Florida and Hawaii. Most of the country is recommended R-49 to R-60. Six inches is typical of houses built before the 1980s that have never been topped up.

Can I just add new insulation over the old?

Usually yes, and it is the normal way to do this. Old insulation that is dry, clean and free of rodent or mould damage does not need to come out. New loose-fill goes straight over the top, and unfaced batts can be laid across the joists at right angles. The exception is a vapour barrier: never lay faced batts on top of existing insulation with the facing down toward the old material, because that traps moisture between the layers. Remove the facing or use unfaced material.

Does my R-value drop as the insulation gets older?

Loose-fill settles, which reduces depth and therefore total R-value, and most of that settling happens in the first few years. Beyond settling, insulation that stays dry and undisturbed does not meaningfully lose R-value with age. What does destroy performance is water, compression from stored boxes or a walked-on floor, and displacement from anyone working in the attic. Insulation that has been wet and dried is usually still degraded, because the fibres mat and the loft does not come back.

Why does this tool give me a range instead of one number?

Because R-value per inch genuinely varies. Blown fibreglass runs about R-2.2 to R-2.7 an inch depending on the product and its installed density, and cellulose about R-3.2 to R-3.8. A tool that reports a single number is reporting a precision that does not exist. The range brackets the honest answer, and where the decision is the same at both ends of the range, which it usually is, the range is all you need.

Does a radiant barrier count toward my R-value?

No. A radiant barrier reflects radiant heat rather than resisting conduction, so it has no useful R-value per inch and cannot be added to an R-value target the way bulk insulation can. The two are measured differently and do not add together. A radiant barrier can reduce summer heat gain in a hot, sunny climate, but it is not a substitute for depth and it should never be counted as one.

How much insulation do I have?

By Insulation Report Editorial. Last reviewed August 2026. How we research this.

Measure the depth of the insulation on your attic floor in inches, then multiply by the R-value per inch of the material. Blown fibreglass gives about R-2.2 to R-2.7 an inch, cellulose about R-3.2 to R-3.8, and fibreglass batts about R-2.9 to R-3.8. Ten inches of blown fibreglass is therefore roughly R-22 to R-27. Compare that against the level recommended for your climate zone, which ENERGY STAR puts at R-30 in the far south and R-49 to R-60 across most of the country. If the joists are still visible above the insulation you have under about 10 inches, which is short nearly everywhere. Adding over the top is the normal fix, and the old material only has to come out first if it is wet, mouldy, rodent contaminated or might be vermiculite. Treat any depth reading as an estimate rather than a measurement, because loose-fill settles over time and its R-value does not rise strictly in proportion to depth.

Check your own attic

Enter what you measured. The result is a range rather than a single number, because R-value per inch genuinely varies with product and installed density, and a single number would be false precision. The ZIP is optional and is used only to look up your climate zone.

Depth to R-value, by material

The same arithmetic in table form. Read down to your measured depth and across to your material. Ranges are given because R per inch varies by product and by how densely the material was installed.

Measured depth	Blown-in fibreglass	Blown-in cellulose	Loose-fill mineral wool	Fibreglass batts	Mineral wool batts
3 inches	R-7 to R-8	R-10 to R-11	R-8 to R-11	R-9 to R-11	R-10 to R-13
4 inches	R-9 to R-11	R-13 to R-15	R-11 to R-15	R-12 to R-15	R-13 to R-17
5 inches	R-11 to R-14	R-16 to R-19	R-14 to R-19	R-15 to R-19	R-17 to R-21
6 inches	R-13 to R-16	R-19 to R-23	R-17 to R-22	R-17 to R-23	R-20 to R-25
7 inches	R-15 to R-19	R-22 to R-27	R-20 to R-26	R-20 to R-27	R-23 to R-29
8 inches	R-18 to R-22	R-26 to R-30	R-22 to R-30	R-23 to R-30	R-26 to R-34
10 inches	R-22 to R-27	R-32 to R-38	R-28 to R-37	R-29 to R-38	R-33 to R-42
12 inches	R-26 to R-32	R-38 to R-46	R-34 to R-44	R-35 to R-46	R-40 to R-50
14 inches	R-31 to R-38	R-45 to R-53	R-39 to R-52	R-41 to R-53	R-46 to R-59
16 inches	R-35 to R-43	R-51 to R-61	R-45 to R-59	R-46 to R-61	R-53 to R-67
18 inches	R-40 to R-49	R-58 to R-68	R-50 to R-67	R-52 to R-68	R-59 to R-76
20 inches	R-44 to R-54	R-64 to R-76	R-56 to R-74	R-58 to R-76	R-66 to R-84

R-value per inch from published material data, carried as ranges in src/data/r-values.ts with sources recorded in this site's reference data notes. Spray foams are not in the table because they are installed by a contractor to a specified thickness rather than measured after the fact by a homeowner, and closed-cell foam at R-6 to R-7 an inch is a different calculation entirely.

What the number should be

ENERGY STAR publishes recommended attic levels by climate zone, and states that its guidance is based on the 2021 International Energy Conservation Code. The recommendation for an attic that already has three to four inches is one step below the recommendation for a bare attic, which is why the table below carries both.

Climate zone	Uninsulated attic	Already has 3 to 4 inches	Roughly where
Zone 1	R-30	R-25	Southern tip of Florida, Hawaii
Zones 2 and 3	R-49	R-38	The Gulf coast, the south, southern California
Zones 4 to 8	R-60	R-49	Most of the country, from the mid-Atlantic north

The joist trick, if you have no ruler

Look across the attic floor. If you can see the tops of the ceiling joists standing proud of the insulation, you have less than the depth of a joist. A standard ceiling joist is 2x6, 2x8 or 2x10 nominal, which is 5.5, 7.25 or 9.25 inches actual. So visible joists mean under about 9 inches in the deepest common case, which is roughly R-20 to R-24 in fibreglass and short of the recommendation in every climate zone in the country.

If the insulation is level with the joist tops you are at joist depth. If it is well above them and you cannot see them at all, you are likely at 12 inches or more and worth measuring properly before spending anything.

You may not need to do anything

This is the section most pages on this subject leave out, and it is the honest answer for a real share of people who measure their attic.

You are within about R-10 of the recommendation. The savings from closing a small gap are real but slow, and the payback on the last few inches is much longer than on the first few. Insulation has strongly diminishing returns: going from R-11 to R-30 saves far more than going from R-38 to R-49.
You have air leaks you have not dealt with. Air sealing the ceiling plane first is almost always the better spend, because insulation slows conduction but does nothing about air moving through gaps around light fittings, plumbing stacks, the attic hatch and top plates. Insulation laid over an unsealed ceiling underperforms its label, sometimes badly.
You are about to reroof, rewire or add ventilation. Doing insulation before work that will disturb it wastes the money twice.
Your attic is a conditioned space or has spray foam at the roofline. Then the floor depth is not the relevant measurement and this tool does not apply.

We do not sell insulation and we do not install it, which is why we can say that. If your measurement comes out close to the recommendation, the useful next step is usually an air sealing check, not more depth.

When the answer is to hire someone

Adding loose-fill over an accessible, floored, walkable attic is a genuine do-it-yourself job, and blowing machines are rentable. Hiring is the realistic answer when any of the following is true: the existing material is wet, mouldy or rodent contaminated and has to come out first; the material is or might be vermiculite, which is a separate licensed trade; clearance is low or the attic is a knee wall, cathedral ceiling or bonus room; the wiring is old; the soffit vents need baffles before any material goes near the eaves; or the ceiling needs proper air sealing first.

For a gap of more than about 20 R-values across a whole attic, the material volume alone usually makes a contractor competitive with renting, because they buy material below shelf price and the machine time is included.

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Common questions

How do I measure the depth of my attic insulation?: Push a ruler or a marked stick straight down through the insulation until it touches the ceiling drywall below, then read the depth at the top surface. Do it in three or four places away from the hatch and away from the eaves, because insulation settles unevenly and the area near the hatch is usually the most disturbed. Use the typical reading, not the deepest one. If the joists are visible above the insulation, you almost certainly have less than the recommended level, because a standard joist is 2x6 to 2x10 and that is only 5.5 to 9.25 inches.
Is 6 inches of attic insulation enough?: Almost certainly not, anywhere in the United States. Six inches of blown fibreglass is roughly R-13 to R-16, and six inches of cellulose about R-19 to R-23. The lowest ENERGY STAR recommendation for any climate zone is R-30, which applies only to zone 1 at the southern tip of Florida and Hawaii. Most of the country is recommended R-49 to R-60. Six inches is typical of houses built before the 1980s that have never been topped up.
Can I just add new insulation over the old?: Usually yes, and it is the normal way to do this. Old insulation that is dry, clean and free of rodent or mould damage does not need to come out. New loose-fill goes straight over the top, and unfaced batts can be laid across the joists at right angles. The exception is a vapour barrier: never lay faced batts on top of existing insulation with the facing down toward the old material, because that traps moisture between the layers. Remove the facing or use unfaced material.
Does my R-value drop as the insulation gets older?: Loose-fill settles, which reduces depth and therefore total R-value, and most of that settling happens in the first few years. Beyond settling, insulation that stays dry and undisturbed does not meaningfully lose R-value with age. What does destroy performance is water, compression from stored boxes or a walked-on floor, and displacement from anyone working in the attic. Insulation that has been wet and dried is usually still degraded, because the fibres mat and the loft does not come back.
Why does this tool give me a range instead of one number?: Because R-value per inch genuinely varies. Blown fibreglass runs about R-2.2 to R-2.7 an inch depending on the product and its installed density, and cellulose about R-3.2 to R-3.8. A tool that reports a single number is reporting a precision that does not exist. The range brackets the honest answer, and where the decision is the same at both ends of the range, which it usually is, the range is all you need.
Does a radiant barrier count toward my R-value?: No. A radiant barrier reflects radiant heat rather than resisting conduction, so it has no useful R-value per inch and cannot be added to an R-value target the way bulk insulation can. The two are measured differently and do not add together. A radiant barrier can reduce summer heat gain in a hot, sunny climate, but it is not a substitute for depth and it should never be counted as one.

Sources: Recommended attic levels from ENERGY STAR, "Recommended Home Insulation R-Values", which states its guidance is based on 2021 IECC Residential Provisions Table R402.1.3. R-value per inch from published material data, carried as ranges rather than point values. Climate zone lookup from the Pacific Northwest National Laboratory and Department of Energy county climate zone dataset for the 2021 IECC, joined to the US Census Bureau 2020 ZCTA to county relationship file. A radiant barrier reflects radiant heat rather than resisting conduction, so it has no useful R-value per inch and cannot be counted toward an R-value target. It is measured differently from bulk insulation and the two do not add together. Limits: loose-fill settles and its R-value does not scale strictly proportionally with depth, so a depth reading is an estimate rather than a measurement of installed R-value; about 3 percent of ZIPs straddle a climate zone boundary and are reported as such; Puerto Rico has no published IECC zone. Page reviewed August 2026. Corrections: [email protected].