The best insulation for an attic floor depends on your joist spacing, the R-value you need, and whether a faced or unfaced batt makes sense for your home. The options below are fiberglass batts in several widths and thicknesses. Match the batt to your framing and local insulation guidance, and avoid compressing it to make it fit—compressed insulation may not deliver its labeled performance.
Table of Contents
Quick Comparison
| Product | Type | Size | Coverage | Best suited for |
|---|---|---|---|---|
| Owens Corning R-30 Unfaced, 19 × 48 in. | Unfaced fiberglass | 19 in. wide, 10 in. thick | 513.36 sq. ft. | Joist bays with room for a 10-inch batt |
| CertainTeed R-30 Kraft Faced, 23 × 48 in. | Kraft-faced fiberglass | 23 in. wide, 8 in. thick | 613.36 sq. ft. | Wider bays where a faced batt is appropriate |
| Owens Corning R-30 Unfaced, 16 × 48 in. | Unfaced fiberglass | 16 in. wide, 10 in. thick | 426.64 sq. ft. | Narrower joist bays needing R-30 batts |
| Knauf R-30 Kraft Faced, 15 × 48 in. | Kraft-faced fiberglass | 15 in. wide, 8 in. thick | 440 sq. ft. | Narrow bays where a faced batt is suitable |
| Owens Corning R-19 Faced, 23 × 48 in. | Kraft-faced fiberglass | 23 in. wide, 6.25 in. thick | 1,280 sq. ft. | Shallower bays or projects prioritizing coverage |
Coverage and dimensions are listed as supplied for each product. Confirm the package details and measure your framing before ordering, since the listed widths are not a substitute for checking your actual joist spacing.
Our Picks: Best Insulation For Attic Floor reviews
1. Owens Corning R-30 Unfaced 19-Inch Fiberglass Batt
This Owens Corning option is an unfaced fiberglass batt rated R-30, listed as 19 inches wide by 48 inches long and 10 inches thick. The package description specifies eight bags and 513.36 square feet of coverage. Its 19-inch width makes it a candidate for joist bays that measure appropriately, but measure the clear space between framing members rather than relying on nominal framing labels.
Because it has no moisture barrier, this batt may be useful when you do not need another facing layer or when adding insulation above an existing layer. Unfaced batts can also avoid creating an extra vapor-retarder layer in assemblies where one is not appropriate. The right vapor-control approach depends on your climate and attic assembly, so check local guidance before combining insulation layers.
The main practical question is depth: at 10 inches thick, it needs enough space to sit without being squeezed. It is a straightforward choice when you want R-30 insulation in a compatible bay and prefer an unfaced batt. It is not the right match for shallow framing that cannot accommodate its thickness.
Pros:
- R-30 rating in a 10-inch-thick batt
- Unfaced construction has no attached moisture barrier
- 19-inch width suits appropriately sized bays
- Package listing specifies 513.36 square feet of coverage
Cons:
- Requires enough depth to avoid compression
- Unfaced insulation does not provide an attached facing layer
Verdict: Choose this Owens Corning batt if your measured bays can accommodate a 19-inch-wide, 10-inch-thick unfaced R-30 product.
2. CertainTeed R-30 Kraft-Faced 23-Inch Fiberglass Batt
This CertainTeed batt is listed as R-30 high-density fiberglass, 23 inches wide by 48 inches long and 8 inches thick. Its kraft facing acts as a moisture-control layer, and the package description lists eight bags covering 613.36 square feet. The wider format may suit wider framing bays, provided the actual cavity dimensions match.
Facing is not a universal advantage. In many assemblies, the facing belongs on the warm-in-winter side, but the correct placement depends on climate, construction, and local code. Before installing this product over or beside existing insulation, make sure the added facing will not create an unsuitable second vapor retarder.
At 8 inches thick, this product may work where a 10-inch batt will not fit, while still carrying an R-30 label in the supplied description. Check the product packaging and the depth of your joists before buying. The 23-inch width is also a key constraint: do not force it into a narrower bay.
Pros:
- R-30 high-density fiberglass in an 8-inch thickness
- Kraft facing provides an attached moisture-control layer
- 23-inch width can suit wider bays
- Listed package coverage is 613.36 square feet
Cons:
- Facing direction and vapor control need to suit the assembly
- The wider batt may not fit narrower joist bays
Verdict: This is a good candidate when you need an 8-inch R-30 batt, have suitable 23-inch bays, and have confirmed that kraft facing is appropriate for your attic.
3. Owens Corning R-30 Unfaced 16-Inch Fiberglass Batt
This Owens Corning batt shares the R-30 rating and unfaced design of the 19-inch version, but its listed width is 16 inches. It is 10 inches thick and 48 inches long. The description gives a total coverage figure of 426.64 square feet for eight bags.
The narrower width is the key reason to consider it: it may fit framing bays that are too narrow for a 19- or 23-inch batt. Still, nominal bay spacing can differ from the clear opening, so measure each area and trim only as appropriate for the product. A loose fit can leave gaps, while forcing a batt into a tight space can compress it.
Like the other unfaced option, this one has no attached moisture barrier. That can be useful when facing is not wanted, but it means you should not select it expecting an integrated vapor retarder. Its 10-inch depth also rules it out for shallow cavities unless the insulation is installed in a suitable configuration without compression.
Pros:
- R-30 rating with a 16-inch listed width
- Unfaced construction avoids an attached vapor-retarder facing
- 10-inch thickness suits bays with enough depth
- Listed coverage is 426.64 square feet
Cons:
- Coverage is lower than the other listed R-30 packages
- Needs a full 10 inches of space to avoid compression
Verdict: Pick this model over the wider Owens Corning batt when your measured joist bays call for a 16-inch width and can accommodate 10 inches of insulation.
4. Knauf R-30 Kraft-Faced 15-Inch Fiberglass Batt
Knauf’s product is listed as R-30 high-density fiberglass with kraft facing. Each batt is 15 inches wide by 48 inches long and 8 inches thick, and the package description lists eight bags covering 440 square feet. Its narrower width distinguishes it from the 23-inch CertainTeed faced option.
The 8-inch thickness may fit some shallower spaces better than a 10-inch batt, but the required cavity depth and R-value should still guide your choice. The kraft facing is a moisture-control layer, not a reason to skip air sealing or moisture checks. Confirm its correct orientation for your climate and attic assembly before installation.
This model may be a practical option when you want a faced R-30 batt for narrower bays and have verified that the facing is suitable. Compared with the unfaced Owens Corning 16-inch batt, it is listed as 8 inches thick rather than 10 and includes facing. That difference can matter for both fit and vapor control.
Pros:
- R-30 high-density fiberglass rating
- 15-inch width for appropriately narrow bays
- 8-inch thickness may suit a shallower cavity than a 10-inch batt
- Listed package coverage is 440 square feet
Cons:
- Kraft facing may not suit every climate or layered assembly
- Measure carefully to avoid gaps or compression
Verdict: Consider the Knauf batt if you need a faced R-30 product in a 15-inch width and have confirmed that both its dimensions and facing work for your attic.
5. Owens Corning R-19 Kraft-Faced 23-Inch Fiberglass Batt
This Owens Corning batt is rated R-19 and is listed as 23 inches wide by 48 inches long and 6.25 inches thick. It has kraft facing and is described for 2-by-6 framing. The package listing specifies 10 bags and 1,280 square feet of coverage, making it the highest-coverage option in this group.
That larger coverage does not make it the strongest choice for every attic floor. R-19 is lower than the R-30 options here, so check the insulation level recommended for your home before choosing it as a stand-alone layer. Its thinner profile may be more suitable for shallow cavities, or for a project where the specified R-value and framing depth fit.
As with the other faced products, consider the facing’s placement and whether your attic already has a vapor-control layer. This batt can be an option for compatible 23-inch bays, but its lower R-value is an important trade-off compared with the R-30 choices.
Pros:
- Listed coverage of 1,280 square feet
- 6.25-inch thickness may suit shallower spaces
- Kraft facing is attached
- 23-inch width is intended for compatible framing bays
Cons:
- R-19 is lower than the R-30 alternatives in this list
- Facing may not be appropriate for every attic assembly
Verdict: Choose this batt when its R-19 rating and 6.25-inch depth match your project—not simply because its package covers the most area.
How to Choose Insulation for an Attic Floor
Start with the R-value your home needs
R-value measures resistance to heat flow; a higher value generally means greater insulating ability at the stated thickness. The right target depends on your climate, existing insulation, and home design. Check local energy guidance or consult a qualified insulation professional before buying. The R-19 product may be suitable for some projects, but it provides a lower labeled R-value than the R-30 options in this roundup.
Measure the joist bays and available depth
Measure the clear width between joists and the space available above the ceiling. Compare those measurements with the batt’s listed width and thickness. Do not assume the nominal framing size tells you the exact opening. Batts that are too wide or thick may be compressed, while undersized batts can leave gaps that reduce coverage.
Choose faced or unfaced based on the assembly
Kraft facing is a moisture-control layer. Its placement and suitability depend on your climate, local code, and the other materials in the ceiling assembly. Unfaced batts do not have that attached layer and may be a better fit when you are adding insulation over existing material, depending on the conditions. Avoid creating an unintended second vapor retarder; ask a local building professional if you are unsure.
Plan for the existing attic insulation
Before adding batts, check the existing insulation for wet areas, damage, or signs of pests, and address the cause of any moisture problem first. If you plan to add a new layer over old insulation, confirm that the new product’s facing and direction are suitable. Keep the insulation from blocking required attic ventilation paths.
Estimate coverage with a little room for layout
Measure the floor area you intend to insulate and compare it with the package coverage. The listed totals vary widely across these products, from 426.64 square feet to 1,280 square feet. Joists, odd-shaped spaces, and cuts can affect how much material you use, so calculate the area and allow for the layout rather than relying only on the number of bags.
Use safe installation practices
Fiberglass can irritate skin, eyes, and breathing passages during handling. Follow the product label and use suitable protective clothing, gloves, eye protection, and a dust mask or respirator as directed. Keep batts away from heat-producing equipment and electrical fixtures unless the fixtures are rated for insulation contact, and follow applicable safety and building requirements.
Frequently Asked Questions
What is the best R-value for an attic floor?
There is no single R-value that fits every home. The recommended level depends on your climate, current insulation, and local requirements. Compare the product’s labeled R-value with local guidance before choosing, rather than assuming that the highest available option is automatically suitable.
Is faced or unfaced insulation better for an attic floor?
Neither is always better. Faced insulation includes a moisture-control layer, and its correct placement depends on your climate and assembly. Unfaced insulation may be appropriate where an added facing is not needed or when adding a layer over existing insulation. Check local guidance before combining layers.
Can I compress fiberglass batts to make them fit?
Avoid compressing a batt to force it into a cavity. Choose a width and thickness that fit the measured space. Compression can reduce the insulation’s effectiveness, and a batt that is too large may also leave gaps around the edges.
Can I install new insulation over existing attic insulation?
In some cases, yes, but first check that the existing material is dry and in good condition. Make sure the new layer will not block ventilation or create an unsuitable second vapor retarder. The right approach depends on the existing insulation and your attic assembly.
How do I know which batt width to buy?
Measure the open space between the joists at several points. Compare the actual opening with the product’s listed width, since framing and spacing can vary. Select a batt that fits without being squeezed and fills the bay without leaving large gaps.
Is R-19 enough for an attic floor?
It may be enough for some projects, but it is lower than the R-30 options in this article. Whether it meets your needs depends on your climate, existing insulation, and the recommended total R-value for your home. Use local guidance to decide.
Should I block attic vents with insulation?
No. Keep required ventilation paths open so air can move as intended. If the insulation layout could cover an eave or other vent opening, use an appropriate ventilation baffle or ask a qualified professional how to preserve airflow.
Final Recommendation
For a general R-30 option without attached facing, the Owens Corning 19-inch batt is a strong place to start if your joist bays can accommodate its width and 10-inch thickness. Choose the 16-inch Owens Corning version for narrower bays, or consider the faced CertainTeed or Knauf options only after confirming that their dimensions and facing suit your attic. The R-19 Owens Corning batt offers broad listed coverage, but its lower rating makes it a more specialized choice. Measure first, check local insulation guidance, and select the batt that fits your framing and assembly without compression.
