Can you get the same performance as R-20 with R-13 plus continuous insulation?

Yes, in many cases R-13 plus about R-5 of continuous exterior insulation can produce a whole-wall U-factor similar to an R-20 cavity because the continuous layer interrupts stud thermal bridging. The exact equivalence depends on stud fraction, the CI material's installed R per inch, and airtightness. For code compliance or precise energy modeling, convert the assembly to a whole-wall U-factor using ASHRAE or local compliance tools. That said, locating the CI outside the sheathing usually improves moisture resilience in cold climates because it keeps the sheathing warmer; interior foam adds complexity to the vapor profile.

Is it worth reframing 2x4 walls to 2x6 for R-20?

Reframing to 2x6 provides permanent space for deeper cavity insulation and simplifies service routing and window jamb detailing. Whether it is worth the cost depends on project timing and budget: reframing is most sensible during major renovations or when replacing cladding. For many retrofits, exterior rigid foam or dense-pack cellulose gives similar thermal improvements with less disruption and lower cost.

Will thicker insulation cause moisture problems?

Thicker insulation itself doesn't automatically cause moisture problems, but changing the wall's thermal profile can alter where and when condensation forms. Adding exterior insulation tends to keep sheathing warmer and reduces condensation risk. Interior foam or adding impermeable layers can create vapor traps if not detailed correctly. Consult local code, follow hygrothermal design guidance (ASHRAE or building-science resources), and ensure proper flashing and ventilation where needed.

How much energy will I actually save by moving from R-13 to R-20?

The actual energy savings vary with climate, airtightness, heating fuel, and occupant behavior. In cold climates the incremental savings from R-20 versus R-13 are larger; in mild climates they are smaller. Use tools like the insulation savings calculator to model local conditions. Also consider that improving airtightness or upgrading windows may yield comparable or larger savings than increasing cavity R alone.

Which insulation types match R-20 with the lowest carbon footprint?

Dense-packed cellulose combined with selective continuous insulation (for example a thin layer of low-carbon foam or a natural product like cork) often yields a lower embodied carbon solution compared with thick foam or closed-cell spray foam. Mineral wool is another moderate-carbon option with good fire and moisture performance. Evaluate embodied carbon alongside lifecycle energy with a simple lifecycle check and prioritize materials with recycled content and low-GWP blowing agents when possible.

R-13 vs R-20 Insulation: Which Do You Need?

R-Value Comparisons

Compare R-13 and R-20 insulation for walls, cost, space, and retrofit options to decide which is right for your DIY eco home.

By Graham Mann | Published: 6/2/2026

R-13 vs R-20 Insulation: Which Do You Need? Deciding between R-13 vs R-20 insulation often comes down to wall depth, climate, and how much disruption you can tolerate during a retrofit. This article compares the two common wall R-values for DIY eco homes, explains how cavity R-values translate to whole-wall performance, and gives practical retrofit routes — from dense-packed cellulose to adding continuous rigid foam — so you can choose the most cost-effective, low-carbon option for your project. The primary goal: help budget-conscious DIY builders decide whether to accept a 2x4/R-13 assembly or pursue R-20-level performance with modest extra effort. TL;DR: - R-13 fills a standard 2x4 cavity (~3.5 in); it's low-cost and space-efficient but whole-wall performance falls short in cold climates. - R-20 requires a 2x6 cavity (~5.5 in) or R-13 plus ~R-5 continuous foam; it reduces thermal bridging and improves whole-wall U-factor. - For retrofits, dense-pack cellulose or exterior rigid foam o...

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