What R-value do I need for exterior walls?

Depends on climate zone. R-13 minimum for 2x4 walls, R-20 for 2x6 walls. Check IRC Table N1102.1.2 for your zone.

Faced or unfaced batts?

Faced batts have a built-in vapor retarder. Use faced in new construction with the facing toward the heated side. Use unfaced when adding to existing insulation.

Does compressing batts reduce R-value?

Yes significantly. A compressed R-19 batt in a 3.5-inch cavity only delivers about R-13. Always use the right thickness for the cavity.

Fiberglass Batt InsulationGenerating image…

Insulation

Batt

$0.30-$1.00 per sq ft depending on R-value

Fiberglass Batt Insulation: The Most Popular Choice (2026)

Prepared by Lumberama's Building Materials Team

|Last updated May 15, 2026|Sources & methodology

Fiberglass batt insulation consists of flexible blankets of spun glass fibers sized to fit between standard stud and joist spacing. It is the most widely used residential insulation due to its affordability, ease of installation, and range of R-values. Available faced or unfaced for different vapor barrier needs.

Key Features

R-11 to R-38 values; Fits standard 16 and 24 in framing; Faced and unfaced options; Non-combustible; Easy DIY installation

Specifications

R-13: 3.5 in thick for 2x4 walls. R-19: 6.25 in for 2x6 walls. R-30: 9.5 in for attic floors. R-38: 12 in for attic floors. Width: 15 or 23 in.

Applications

Exterior walls; Attic floors; Cathedral ceilings; Floor joists; Basement walls

Installation Overview

Cut batts to fit snugly between framing without compressing. Place faced batts with vapor barrier toward heated space. Avoid gaps, voids, and compression. Cut around electrical boxes and pipes for full coverage.

Pros & Cons

Pros

✓ Most affordable insulation; Easy to install; Wide R-value range; Non-combustible; Readily available everywhere

Cons

✗ Loses effectiveness if compressed; Itchy to handle; Moisture absorbs and reduces performance; Gaps reduce effectiveness; Requires protective gear

Top Brands

Owens Corning

Johns Manville

CertainTeed

Knauf

Code Requirements

R-values per IRC Table N1102.1.2 for climate zone. Vapor retarder per IRC R702.7. Must fill cavity without compression. Air sealing required per IRC N1102.4.

Buying Tips

Measure cavity depth before buying to get proper R-value. Wear long sleeves, gloves, and a dust mask during installation. Unfaced batts are cheaper if you are installing a separate vapor barrier.