Can I simply add 1 inch of foam to go from R-19 to R-20?

Adding 1 inch of polyiso or XPS provides roughly R-4 to R-5 depending on the product, which more than covers the difference between R-19 and R-20 at the whole-wall level because it reduces thermal bridging. However, the effect depends on the existing assembly, cladding sequence, and vapor control. If you add foam to the interior or exterior, tape and seal seams and account for how the changed assembly will dry. Use product LTTR values and consult the manufacturer for exact R/inch.

Is R-20 worth the extra cost for my climate?

That depends on climate zone, fuel costs, and project priorities. In cold climates (IECC zones 5–8) incremental R is more valuable than in mild zones. Studies and Energy Star guidance show diminishing returns at higher R—so often money spent on air-sealing and continuous insulation pays off faster than small R increases in cavity-only installs. Use local energy calculators or contractor estimates to compare payback for your project.

Will changing from R-19 to R-20 reduce heating bills significantly?

Moving from R-19 to an effective R-20 assembly can reduce heat loss slightly, but real savings depend on whole-wall U-factor, airtightness, and climate. In practice, sealing gaps and adding continuous insulation often yields larger savings than a small cavity R increase. For precise estimates, model the assembly with a simple energy calculator or request a performance quote from a local contractor.

Can I use R-20 in a 2x6 wall without changing studs?

Yes—most commonly by pairing existing R-19 batts with 1/2"–1" of continuous rigid foam (polyiso or XPS) or by using dense-pack cellulose to increase effective cavity R. Closed-cell spray foam can also reach R-20 within the same depth. Each option has trade-offs in cost, moisture control, and installation complexity.

Which materials give the best R per inch for tight builds?

Polyiso and closed-cell spray foam offer the highest R per inch (roughly R-6 and up). XPS is about R-5 per inch. Dense natural options like cork are lower R/inch but can be useful for ecological builds. We compare these materials and their embodied impacts in our spray foam vs cellulose comparison and related guides.

R-19 vs R-20 Insulation: Which Do You Need?

R-Value Comparisons

Compare R-19 and R-20 insulation: differences, when each makes sense, installation tips, and practical recommendations for DIY eco builders.

By Graham Mann | Published: 5/21/2026

R-19 vs R-20 Insulation: Which Do You Need? Choosing between R-19 and R-20 insulation is a common practical question for budget-conscious DIY builders: does that extra R-value justify the cost, the extra thickness, or the retrofit work? This guide compares r19 vs r20 insulation, explains what the numbers mean, shows how different materials reach those R-values, and gives scenario-based recommendations for new builds and retrofits so you can decide with confidence. TL;DR: - For most 2x6 wall assemblies in temperate zones, R-19 batt plus 1/2"–1" continuous foam is a cost-effective path to roughly R-20 whole-wall performance. - In cold climates or tight builds, choose higher R/inch materials (closed-cell spray foam or polyiso) or increase cavity depth—these deliver measurable comfort gains. - Prioritize air-sealing and continuous insulation strategy before chasing small R increments; use the Department of Energy(https://www.energy.ca.gov/sites/default/files/2020-09/2019%20Insulation%20and...

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