How to Estimate Insulation Needs and Achieve R-Value Requirements

Insulating your home well means more than just filling the walls. All building materials — sheathing, drywall, siding, insulation, windows, even vapor barrier — contribute to the overall R-value of a structure. We’re building in International Energy Conservation Code (IECC) Climate Zone 6, so code requires us to achieve an overall R-value of 15. Here’s what all that means, and how we met the requirements.

R-Value Explained

Family Handyman

• R-value refers to the resistance (R) insulation has to temperature conduction. The higher the R-value number, the better a material prevents the flow of heat into (or out of) a structure.
• The higher R-value you achieve, the more money you can save on heating and cooling bills.

The “hot roof” option

Family Handyman

• Since our Getaway doesn’t have an attic, there is no ceiling space to lay down batts of insulation. Our only option was a hot roof, i.e. a roof that’s insulated and sealed.
• We chose spray foam for speed and consistency. A hot roof also may have rigid foam sandwiched between the roof sheathing and the roofing material.

Insulate the rim joist

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• The best way to insulate a rim joist is to use closed-cell spray foam. It’s fast, thoroughly seals the space and is actually fun to apply.
• We’re aiming for a thickness of two inches, which provides an R-11 rating.
  • Rigid insulation is another option for rim joists. Adding it requires no special equipment, but it’s a time-consuming process.

Batt insulation for the walls

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• Owens Corning has a new formulation for batt insulation. It’s made from the highest recycled content in the industry and a new sustainable manufacturing process.
• We love it because the new product eliminates the nasty itch that makes most insulation difficult to work with. We just might look forward to our next insulation project!

Seal with 6 mil vapor barrier

Family Handyman

• Instead of Kraaft-faced batts, choose to apply 6 mil vapor barrier instead.
  • PRO TIP: Apply gasket seal around windows and doors to complete the seal.