Overinsulation

Overinsulation is the practice of installing insulation beyond what a building climate, design, and ventilation require, often at the point of diminishing returns and sometimes causing adverse effects. It can result from aggressive energy retrofits, misinterpretation of building codes, or the use of very high R-values without corresponding ventilation.

Potential problems include moisture-related issues such as interstitial condensation and mold growth when vapor control is not aligned with climate and construction; reduced indoor air quality and occupant comfort due to overly tight envelopes without adequate mechanical ventilation; overheating in summer or in passive-solar designs if heat gains are not managed; and practical issues such as damage from trapped moisture, rot, or insulation compression at joists and studs, which can degrade performance.

Overinsulation is more likely to occur in retrofits that seal buildings too tightly without ventilation, or in renovations that add insulation in walls or roofs without considering air leakage paths, drainage planes, and vapor diffusion. It can also extend payback periods when insulation costs are not offset by energy savings.

Mitigation includes conducting a building energy audit; modeling or monitoring humidity and temperature; ensuring appropriate ventilation, such as continuous mechanical ventilation with heat recovery where suitable; coordinating insulation with vapor barriers and drainage planes; avoiding unnecessary double vapor barriers; and maintaining adequate moisture management and thermal comfort.

In summary, while insulation is essential for energy efficiency, excessive insulation without proper ventilation and moisture control can harm indoor air quality, durability, and comfort.