Insulating Concrete Masonry Unit (CMU) Walls

Jun 7, 2024

Insulating Concrete Masonry Unit (CMU) Walls

Key Challenges

  • Older CMU walls can be difficult to insulate
  • Concrete blocks are lighter and can be grouted or filled with concrete
  • Ungrouted cells can accumulate water if unprotected
  • Insulating CMU walls can create moisture problems due to reduced drying capability

Strategies for Proper Insulation

Taped Dimple Mat Approach

  1. Dimple Mat Installation
    • Provides a drainage space and capillary break
    • Prevents moisture from reaching the framed interior
    • Allows use of various insulation methods
  2. Thermal and Moisture Barriers
  • Use taped extruded polystyrene (XPS) for thermal break
  • Prevents air leakage and vapor diffusion
  • Essential in cold and temperate climates
  1. Framed Wall Insulation
  • Use air and vapor permeable insulation
  • Options: Mineral wool, fiberglass, wood fiber, cellulose
  • Ensures stud cavities can dry out freely to the interior
  • Avoid moisture traps
  1. Uncoupling Wet Walls and Wood Framing
  • Prevent mold and rot

Exterior Protection if Dimple Mat is Infeasible

  1. Exterior Stucco/Parge Coat and Mineral Silicate Paint
    • Fills cracks or gaps, provides smooth surface
    • Easier drainage, reduces water absorption
    • Mineral silicate paint: vapor permeable, hydrophobic
    • Superior durability, aesthetic appeal
  2. Interior Fluid Applied Negative Side Waterproofing
  • Applied directly to CMU wall as final line of defense
  • Functions as air and vapor barrier
  • Prevents moisture from reaching framed wall cavity

Base of Wall Drainage Solutions

  1. Interior Perimeter Drainage Tile
    • Collects and directs water away
  2. Capillary Break and Uncoupling from Slab
    • Dimple mat at the base of walls
    • Prevents moisture wicking into the interior floor
  3. Concrete Excavation
    • Install drainage tile in crushed stone bed
    • Patch concrete after installation
    • Seal joint between drainage channel and slab

Additional Resources

  • Moisture Management Guides available at A-D designs.com/shop
  • Over 150 free building science articles

Conclusion

  • Proper insulation and moisture management are critical
  • Choose the right strategy based on specific wall conditions
  • Always ensure materials and techniques are appropriate for climate and wall type