How Much Insulation Do Attic Walls Need?

Types of Insulation Suitable for Attic Walls

The type of insulation you choose impacts not only how much you’ll need but also how effectively it performs.

• Fiberglass Batts: Easy to install and affordable, ideal for standard wall cavities.
• Spray Foam: Provides both insulation and air sealing, suitable for irregular spaces.
• Blown-In Cellulose Insulation: Excellent for filling gaps, offering even coverage in tricky areas.
• Rigid Foam Board: Rigid Foam insulation has high R-value per inches of insulation, great for limited spaces or adding layers.
• Mineral Wool: Wool outperforms synthetic fibers in every category, including in moisture management, sound attenuation, longevity and resistance to flame.

Each type has pros and cons. For example, fiberglass insulation is cost-effective but less airtight, while spray foam insulation is highly efficient but more expensive.

Insulating Attic Knee Walls

First of all, what are they? Knee walls are short, vertical partitions that separate a finished attic space from the unconditioned space behind them. With improper insulation, these walls become a significant source of heat loss, making it hard to maintain comfortable temperatures in the finished space. Insulating knee walls effectively creates a thermal barrier, improving energy efficiency and indoor comfort year-round.

How to Insulate Knee Walls

• Use fiberglass batts cut to fit snugly between studs.
• Add rigid foam boards on the backside of the wall to boost R-value and prevent air leaks.
• Install a radiant barrier if the attic is prone to overheating in warmer climates.
• Air seal gaps around plumbing, wiring, or other penetrations to reduce air movement.

FAQ

What Happens if You Over-Insulate Your Attic Walls?

Adding too much insulation can trap moisture and hinder ventilation, potentially leading to mold growth or structural damage. Balancing sufficient insulation with proper ventilation is important for a healthy attic space.

Should Insulation Levels Be the Same for Attic Walls and Floors?

Not necessarily. While attic floors often require higher R-values to prevent heat loss from the living space below, walls may have slightly lower requirements, depending on their exposure and construction.

Can You Add New Insulation on Top of Old Insulation?

Yes, you can layer additional insulation over your current insulation as long as the old insulation material is in good condition and not compressed. Mixing types, like adding fiberglass batts over loose-fill insulation or blown-in cellulose, is also fine.