How Much R-Value Do I Need? Try Our R-Value Calculator

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Find out exactly how much insulation your home needs—without the guesswork.

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Let’s get one thing straight: when it comes to keeping your home warm in the winter and cool in the summer, R-value matters. A lot. But most homeowners (and even a few contractors) don’t really know what R-value they need, where, or why.

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That’s why we built a free, easy-to-use R-Value Calculator—to give you clear, code-backed recommendations based on where you live and what part of your home you’re insulating.

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But before you jump in and start punching in numbers, let’s cover the basics so you actually know what you’re looking at. Here's what we'll cover in this article:

• What is R-value
• Why does R-value matter
• Climate zones
• R-value calculator

What Is R-Value, Anyway?

R-value is how we measure insulation’s resistance to heat flow. Think of it like SPF for your house—higher R-value = more protection. The better the R-value, the slower your heated (or cooled) air escapes through your walls, ceilings, and floors.

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So when someone says “You’ve got R-13 in your walls,” they’re talking about how well that insulation holds the line between inside and outside temperatures.

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Different insulation types have different R-values per inch:

• Fiberglass batts: ~R-3.2 per inch
• Cellulose: ~R-3.5–3.8 per inch
• Spray foam (closed-cell): ~R-6.5 per inch

Why Does R-Value Matter?

Simple: it’s the difference between a home that stays comfy for cheap... and one that bleeds money every time the heat kicks on. Insufficient R-value leads to:

• Drafty rooms
• Sky-high utility bills
• HVAC systems working overtime
• Unhappy homeowners (maybe you?)

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The Department of Energy and local building codes require specific R-values depending on where you live. But unless you’ve memorized the DOE’s climate zone map (we have, but we’re weird like that), figuring it out on your own is a pain.

A Quick Note on Climate Zones

The U.S. is divided into climate zones (Connecticut is mostly Zone 5), and those zones determine how much insulation your home needs.

For example:

• Zone 3 (warmer southern states) might only need R-30 in the attic.
• Zone 5 (Connecticut) usually calls for R-49 to R-60 in the attic.
• Zone 7 (northern tier)? You’re looking at R-60+ and tight air sealing.

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You also need different R-values depending on whether you're insulating an attic, basement or wall. Garage's don't have unique R-Values. That's where things get tricky.

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Enter: the R-value calculator.

R-Value Calculator

We built this tool to take the confusion out of calculating R-value. Just plug in:

• Your state and county
• The part of your home you want to insulate

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...and boom—you’ll get the recommended minimum and maximum R-values based on your local code and climate.

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✅ No digging through PDFs
✅ No guessing
✅ No wrong answers

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Whether you’re upgrading attic insulation, finishing a basement, or insulating a new addition, this calculator gives you a clear starting point. From there, we can help you figure out the right material and get the job done.

Try Our R-Value Calculator

Use this R-value calculator to find out what your home really needs—and let’s make sure you’re not under-insulated, overpaying, or leaving comfort on the table.

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Common FAQ's About R-Value

What happens if I go too high with R-value?

If you go too high with R-value, the insulation delivers diminishing returns after meeting your climate zone’s recommendation. Extra insulation raises material and labor costs without major energy savings. Overstuffing can also compress insulation, reducing its effective R-value and undermining performance.

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Does R-value change if insulation gets wet?

Yes, R-value drops when insulation gets wet. Fiberglass and cellulose can lose up to 50% of their insulating power when soaked, with cellulose also clumping and settling. Closed-cell spray foam resists moisture and maintains its R-value even in damp or humid environments.

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Why does attic insulation need a higher R-value than walls?

Attic insulation needs a higher R-value than walls because heat rises and escapes most easily through the roof. Energy loss is greater in attics, so building codes and DOE guidelines specify higher R-values there. The attic acts like a head in winter—extra insulation provides essential protection.

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Does insulation’s R-value decrease over time?

Yes, insulation’s R-value can decrease over time depending on the material. Fiberglass and cellulose may settle or shift, creating gaps that reduce effectiveness. Spray foam maintains its R-value longer but can degrade with UV exposure. Regular inspections ensure performance and protect comfort and efficiency.

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Do all R-13 insulations perform the same?

No, not all R-13 insulations perform the same. While R-value measures resistance to heat flow, air leakage and installation quality change real-world performance. Poorly installed fiberglass batts with gaps can underperform compared to properly installed cellulose of the same R-value. Air sealing and craftsmanship matter as much as the number.

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