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Mass walls are walls that provide energy efficiency through mass rather than insulative value. The mass allows them to store energy during the day and release it through the night. In the right climate they can be a better choice than walls that are lightly framed and heavily insulated. The misconception is that mass walls do not have any required R-Value.

However, the International Energy Code specifies that mass walls must still meet a set of R-value requirements. It defines mass walls as walls that are made of concrete block, concrete, insulated concrete form, masonry cavity, brick, earth, adobe and solid timber or logs. The insulation must be at least 50% on the exterior or integral to the wall to count. Otherwise you're back in the wood frame wall insulation requirements. In other words, brick veneer or log siding don't count.

If you do have at least 50% of the insulative value on the outside or integral  then your mass wall R-Values are:

• Climate Zone 1: 3
• Climate Zone 2: 4
• Climate Zone 3: 5
• Climate Zone 4 (except Marine): 5
• Climate Zone 5 and Marine 4: 13
• Climate Zone 6: 15
• Climate Zone 7 & 8: 19

As you get into the colder zones the mass wall R-Value more closely approximates the wood frame wall R-Value.

If you happen to be in Climate zones 1-3 there is an exception for insulation placement that doesn't meet the criteria. You can up your R-Values slightly to:

• Climate Zone 1: 4
• Climate Zone 2: 6
• Climate Zone 3: 8

Originally posted 2010-10-11 23:42:02.

1. Climate Zones in Colorado and the International Energy Conservation Code – Insulation R Values
2. Understanding Thermal Mass Walls in a Passive Solar Design
3. The Skinny on Thermal Mass
4. Temperature Control in Buildings – What is the Minimum Heat Level Required in the Building Code?
5. Engineered Retaining Walls for Harker Heights, Texas
6. Jefferson County Colorado Residential Energy Code Submittal Requirements
7. Home Energy Audits From Lightly Treading and Xcel Energy
8. CODE UPDATE: Significant Code Changes to the 2009 International Building Code – Fasteners