Interior vs Exterior Storm Windows: Which Is Better for Seattle’s Moisture?

Seattle’s damp climate makes window performance a year-round concern for homeowners — especially in older or historic houses where original wood windows add charm but often lack insulation. Storm windows are one of the most effective upgrades for improving comfort, reducing drafts, and preventing moisture-related damage. However, a debate we often see is interior storm windows vs exterior storm windows. The answer depends on condensation behavior, home age, maintenance needs, and your long-term goals for energy efficiency.

Below, we break down Interiors vs Exterior Storm Windows and explain how each type performs in wet Pacific Northwest weather so you can choose the best fit for your home.

Understanding How Moisture Affects Storm Windows

Seattle’s climate brings extended periods of cool temperatures and high humidity. When warm indoor air meets cold window glass, condensation forms. Too much condensation on your windows leads to:

• Mold and mildew around sills
• Paint deterioration
• Wood rot in original window frames
• Fogging and visibility issues
  

The right storm windows Seattle helps regulate temperature differences and create a moisture barrier — but each style handles this differently.

Interior Storm Windows: Excellent for Condensation Control

Interior storm windows mount inside the home, creating an insulating air pocket between the original window and the storm panel. This configuration is highly effective in Seattle’s moisture-heavy climate.

How They Perform With Condensation

Because interior storm windows stay warmer than exterior ones, they significantly reduce interior glass condensation.

Key benefits include:

• Minimal moisture buildup on the storm panel
• Reduced risk of mold on sills and trim
• Better temperature stability along window edges
  

Interior storms maintain the warm side of the window system, preventing the cold draft-heavy interface that triggers condensation.

Best for Historic Homes

Interior storm windows shine in historic or landmark homes because:

• They don’t change the exterior appearance, preserving architectural character
• Installation is fully reversible
• They allow original wood windows to be maintained rather than replaced
  

For homes in neighborhoods like Capitol Hill, Queen Anne, or Ballard — where preservation is a priority — interior storms are often the preferred option.

Energy Savings

Quality interior storm windows can reduce heat loss by up to 50%, making them one of the most cost-effective historic home window upgrades in Seattle. They also help block drafts and dampen noise from busy streets.

Potential Drawbacks

• Interior panels may need to be removed seasonally for ventilation
• Not ideal for windows that require frequent opening
• They rely on the condition of the existing window; major rot must be repaired first
  

Exterior Storm Windows: Effective but Higher-Maintenance in Seattle

Exterior storm windows mount on the outside of the window frame, shielding the original window from wind, rain, and debris. These offer strong weather protection but require careful moisture management.

How They Perform With Condensation

In a rainy climate, exterior storms can accidentally trap moisture between the storm panel and original window if not vented properly.

You may see:

• Condensation on the underside of the storm glass
• Water collecting at the sill
• Accelerated wood deterioration

Proper weep holes and regular maintenance are essential.

Best for Air Sealing and Weather Protection

Exterior storms excel at creating a strong physical barrier against drafts and driving rain — important for homes in exposed locations or older structures with slightly irregular window frames.

Energy Savings

Exterior storm windows improve insulation and air sealing, though their performance is more dependent on conditions outside the home. They offer measurable energy savings but often less condensation control compared to interior storms.

Potential Drawbacks

• Higher maintenance due to dirt, algae, and constant rain exposure
• Visible from the exterior, which may conflict with historic restrictions
• More difficult to access and clean
  

Historic Home Considerations: Preservation Matters

Many of Seattle’s older neighborhoods include homes built between the 1890s and 1940s. These windows were often handcrafted, contributing significantly to the architectural character.

Interior storm windows are typically the most compatible because they:

• Protect original wood windows without altering their look
• Provide high energy efficiency while preserving authenticity
• Are often approved for historic landmark districts
  

Exterior storms may be restricted in certain preservation zones.

Which Option Controls Moisture Better?

For Seattle’s climate, interior storm windows generally outperform exterior systems in moisture control because they:

• Keep the window assembly warmer
• Prevent humid indoor air from contacting cold glass
• Reduce opportunities for condensation to collect in hidden places
  

If your primary goal is moisture control windows, interior storm panels are usually the superior choice.

Cost & Installation: What Seattle Homeowners Should Expect

• Interior storms tend to cost slightly less and offer easier installation, especially for uneven historic frames.
• Exterior storms may require more customization and ongoing maintenance but offer strong exterior weather protection.

So, Which Storm Window Is Best for Seattle? Interior vs Exterior Storm Windows

Both options, however, are more affordable and less invasive than full window replacement.

When comparing interior and exterior storm windows for Seattle homes, interior storm windows tend to come out ahead for most situations. They offer excellent condensation control, making them especially effective in Seattle’s damp, moisture-heavy climate. Interior storms are also the best option for historic or older homes since they preserve original windows and remain invisible from the exterior. Both interior and exterior storm windows provide strong energy efficiency benefits, but interior options require significantly less maintenance over time. While exterior storm windows do offer stronger direct weather protection, they are more visible, often restricted on historic homes, and require careful venting and installation to prevent trapped moisture. Overall, interior storm windows are the recommended choice for Seattle homeowners—particularly those with older homes or moisture-sensitive frames—while exterior storms remain a viable option for homes that need added weather shielding and are properly designed to manage moisture.

Thinking About Upgrading Your Storm Windows in Seattle?

Whether you live in a 1905 Craftsman or a mid-century home, choosing the right storm window system can dramatically improve comfort, reduce condensation, and preserve your home’s character.

If you need help comparing options, exploring storm windows Seattle solutions, or planning historic home window upgrades, I can help craft content or refine this blog for a contractor’s website.