Still Have Single-Pane Windows? Your Upgrade Options

According to the U.S. Department of Energy, about 12% of U.S. homes still have single-pane windows. If that's you, you have the most to gain from upgrading—and several options to consider.

The Problem with Single-Pane

According to Lawrence Berkeley National Laboratory, single-pane windows:

• Have U-factors around 1.0 (vs. 0.27 for modern double-pane)
• Allow cold glass surfaces that rob comfort
• Create condensation and frost problems
• Waste 50-70% more energy than modern windows

Option 1: Storm Windows

According to DOE and the National Park Service:

What it is: Secondary window installed inside or outside existing window

Performance gain: Reduces heat loss by 25-50%

Cost: $50-150 per window (interior) or $150-300 (exterior)

Best for:

• Historic homes where original windows must be preserved
• Budget-constrained projects
• Renters who can't replace windows

Limitations:

• Still underperforms modern double-pane
• Adds complexity to window operation
• Interior storms affect appearance

Option 2: Glass-Only Replacement

According to FGIA:

What it is: Replace single-pane glass with IGU in existing frame

Performance gain: Similar to new double-pane (U-factor ~0.30)

Cost: $150-300 per window

Best for:

• Sound frames with cosmetic value
• Historic homes with original wood windows
• Budget constraints

Limitations:

• Frame efficiency unchanged
• Not always possible (requires adequate glass pocket)
• Frame may need repair anyway

Option 3: Full Replacement

According to DOE:

What it is: Replace entire window—frame, sash, and glass

Performance gain: Full modern efficiency (U-factor 0.27 or better)

Cost: $400-800 per window installed

Best for:

• Frames in poor condition
• Maximum efficiency improvement
• Situations where frame technology matters (vinyl, fiberglass)

Comparing the Options

| Option | Cost | U-Factor Achieved | Best Scenario |
|--------|------|-------------------|---------------|
| Storm windows | $75-300 | ~0.50 | Historic/budget |
| Glass-only | $150-300 | ~0.30 | Sound original frames |
| Full replacement | $400-800 | 0.20-0.27 | Maximum efficiency |

The Bottom Line

Single-pane to modern double-pane is the biggest efficiency jump possible. According to DOE, full replacement provides the best performance, but storm windows or glass-only replacement can be practical alternatives when budget or historic preservation matters.

*For complete pane comparison, see: [Single, Double, and Triple-Pane Windows](/guides/single-double-triple-pane-windows)*