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What R-11 Insulation Is For

R-11 fiberglass insulation shares the same physical cavity fit as R-13 — both are dimensioned for 2x4 framing — but delivers slightly lower thermal performance at a slightly lower cost. The 3.5-inch nominal thickness fills 2x4 wall cavities exactly without compression, the same as R-13. The difference between the two R-values is fiber density: R-13 packs more glass fiber per cubic foot of cavity, producing higher thermal resistance at higher material cost.

R-11 is the right pick when the building does not require code-compliant wall insulation but you still want the thermal benefit and sound-control properties of a properly-fitted 2x4 wall batt. Interior partition walls, unconditioned outbuildings, retrofit projects in older buildings, and accessory structures all use R-11 frequently. New construction in conditioned spaces typically goes with R-13 or higher to meet IECC requirements.

At Insulation Overstock, R-11 is available with every NAIMA-certified facing in the catalog. VR-R Plus is the cheapest at $0.55 per square foot. WMP-10, WMP-30, and WMP-50 run $0.61 per square foot. The savings versus R-13 is about 15 percent.

R-11 Thickness and Composition

R-11 Nominal Thickness

R-11 fiberglass insulation has a nominal installed thickness of 3.5 inches. This matches the actual cavity depth of standard 2x4 wall framing exactly without compression. R-13 has the same thickness but with higher fiber density.

R-11 Roll Dimensions

R-11 rolls ship in 4-foot, 5-foot, and 6-foot widths. Roll lengths typically run 40-60 feet depending on width, giving 200-360 sq ft of coverage per roll.

Available Facings for R-11

All four NAIMA-certified facings (VR-R Plus, WMP-10, WMP-30, WMP-50) plus black-faced variants are available in R-11. Facing selection follows project moisture requirements and aesthetic preferences as detailed on the facing comparison page.

Where R-11 Insulation Works Best

Interior partition walls. The most common R-11 application. Interior walls between rooms provide sound dampening and partial thermal separation, but do not need to meet exterior wall code minimums. R-11 delivers the cavity fit without the R-13 price premium.
Unconditioned outbuilding walls. Detached garages, sheds, and outbuildings that will not be heated regularly use R-11 in 2x4 walls for partial thermal moderation and rodent/dust control without the cost of full code-compliant insulation.
Retrofit projects in older buildings. Older buildings being upgraded with insulation often use R-11 in walls because the existing wall assemblies were not designed around current energy code — the marginal benefit of stepping to R-13 in a building with single-pane windows and no air sealing is small.
Accessory structures and small shops. Small backyard shops, studio buildings, and accessory dwelling units in mild climates frequently use R-11 walls because building code may exempt structures under a certain size from full IECC compliance.
Sound-control interior walls. R-11 provides meaningful sound dampening at lower cost than R-13. Common in home offices, bedrooms adjacent to common areas, and any interior partition where acoustic separation matters more than thermal performance.

R-11 Insulation Cost

R-11 wholesale pricing slots between R-10 and R-13:

R-11 Wholesale Pricing by Facing
  • VR-R Plus: $0.55 / sq ft (10 cents below R-13)
  • WMP-10 / WMP-30 / WMP-50: $0.61 / sq ft
  • Black-faced variants: $0.59 to $0.65 / sq ft

On a 1,500 sq ft interior partition wall project, R-11 VR-R Plus saves $150 vs equivalent R-13 ($825 vs $975 material cost). On larger projects (2,500+ sq ft), the savings exceed $250.

R-11 vs R-13: When Each Makes Sense

R-11 and R-13 both fit 2x4 walls. The decision between them is about whether the application needs code-compliant thermal performance or whether the budget savings justify the modest performance reduction.

Application Recommended R-Value
New construction exterior walls (any climate)R-13
Interior partition wallsR-11
Unconditioned outbuildingsR-11
Retrofit in non-code-compliant buildingsR-11
Sound-control interior wallsR-11
Conditioned space exterior walls (Zone 1-2)R-13 (code minimum)

R-11 Insulation FAQ

What is R-11 insulation used for?

R-11 fiberglass insulation is dimensioned for 2x4 wall cavities, similar to R-13 but with slightly less thermal resistance and a lower per-square-foot cost. It is commonly used in interior partition walls, light-duty exterior walls, and unconditioned outbuilding wall applications where R-13 is not strictly required.

How thick is R-11 insulation?

R-11 fiberglass insulation is 3.5 inches thick at nominal installed depth. This matches the actual cavity depth of standard 2x4 wall framing exactly without compression.

How much does R-11 insulation cost per square foot?

Wholesale R-11 fiberglass insulation costs $0.55 per square foot for VR-R Plus and $0.61 per square foot for WMP-10, WMP-30, or WMP-50. It is about 10 cents per square foot cheaper than R-13.

R-11 vs R-13: which should I choose?

R-13 is the IECC code minimum for walls in Climate Zones 1-2 and the default choice for new construction in 2x4 walls. R-11 is the budget alternative for interior partitions, unconditioned outbuildings, and retrofit projects where code compliance is not required. The performance difference is about 15 percent; the price difference is also about 15 percent.

Does R-11 fit 2x4 walls?

Yes. R-11 fiberglass at 3.5 inches matches 2x4 wall cavity depth exactly. The fit is identical to R-13; the difference is in fiber density rather than thickness.

Is R-11 code-compliant for walls?

No. R-11 does not meet IECC wall minimums in any climate zone for conditioned buildings. R-11 is appropriate for interior partition walls, unconditioned outbuildings, and applications where code minimums do not apply. For code-compliant 2x4 wall insulation, choose R-13 or higher.

Order R-11 Fiberglass Insulation

Wholesale R-11 with every facing available. The cost-effective 2x4 wall pick for interior partitions and non-code-driven wall applications.

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