Why Hot Roofs Are a Problem in Alaska – What Homeowners Need to Know

Introduction

When you're building or remodeling in Alaska, your roof isn’t just a cap on your home—it’s your first line of defense against snow, wind, and moisture. One of the most common design mistakes we see is using a “hot roof” system in the wrong setting. While this design can work in certain climates, it often leads to serious issues in the Alaskan environment.

At 138 Construction, we want to break down what a hot roof is, why it’s risky here, and what works better.

What Is a Hot Roof?

A “hot roof,” also known as a warm roof or unvented roof assembly, places insulation directly against the underside of the roof sheathing—with no ventilation channel above it. The framing and roof deck are all within the heated, conditioned space of the building.

This design is often used for modern architecture, vaulted ceilings, or flat roof designs. In theory, it improves energy efficiency by keeping heat inside. But in cold climates like Alaska, this setup introduces several long-term problems.

Why Hot Roofs Fail in Alaska

1. Ice Dams and Roof Leaks

Alaska’s winters bring months of snow. In a hot roof system, heat from inside the house rises and melts the snow from underneath. The water runs to the eaves, refreezes, and forms ice dams. These dams trap water, which then leaks under shingles and into your home—leading to water damage, mold, and expensive repairs.

2. No Room to Vent Moisture

Ventilation is critical in cold climates to let any moisture in the roof cavity escape. Without vents, hot roofs trap humidity, which condenses on cold surfaces inside the roof system. Over time, this leads to:

• Rotting rafters or decking

• Mold in insulation

• Wet ceilings and drywall damage

3. Reduced Roof Lifespan

Improperly built hot roofs tend to degrade much faster. Moisture trapped inside can cause delamination of the plywood, sagging ceilings, or even structural failure over time. In snowy climates, hot roofs are simply less durable unless they’re built with extreme precision.

4. Difficult to Retrofit or Repair

Unlike cold roofs, hot roofs require all components (insulation, air barrier, vapor barrier) to be installed perfectly from day one. Any future fixes are expensive and often require ripping apart finished ceilings or re-roofing the entire structure.

When Is a Hot Roof Acceptable?

There are rare cases where hot roofs work well in Alaska, including:

• Flat or low-slope roofs where venting isn’t practical

• Homes in coastal or windy areas where snow doesn’t accumulate

• Projects that use spray foam or exterior rigid insulation, combined with a continuous, high-quality vapor barrier

In these situations, execution is everything. Even one bad seal can lead to failure.

Cold Roofs: A Better Choice for Alaska

A cold roof includes a ventilated attic or ventilation channels between the insulation and the roof sheathing. This allows airflow to remove moisture and keep the roof deck cold enough to prevent snowmelt.

Benefits of cold roofs:

• Prevents ice dams

• Extends roof lifespan

• Reduces risk of moisture damage

• Easier to inspect and maintain

• More forgiving if installation isn’t perfect

  
  

At 138 Construction, we design our cold roof systems with:

• Raised heel trusses for full insulation at the eaves

• Proper venting at soffits and ridges

• Air-sealed and taped vapor barriers

• Insulation rated for Alaskan winters (R-49 to R-60)

How to Spot a Hot Roof Problem

If your home has a hot roof, here are some warning signs to look out for:

• Icicles forming along the eaves

• Water stains on ceilings

• Moldy or musty smells in upper rooms

• Roof leaks during spring thaw

• Sagging or frost-filled insulation

If you see any of these, get your roof inspected before more damage occurs.

Ready for a Roof That Handles Alaska?

Whether you’re designing a new home or upgrading an existing one, let 138 Construction build a roof that lasts. We specialize in cold roof systems designed for Alaskan weather and know how to avoid the expensive traps that hot roofs can create.

Call us at 907-513-1378 or visit 138constructionllc.com to schedule a roof consultation.

Frequently Asked Questions (FAQ) – Hot Roofs in Alaska

1. What’s the difference between a hot roof and a cold roof?

A hot roof has no ventilation above the insulation—everything is packed tight against the roof deck. A cold roof includes a vented space between the insulation and the roof deck, allowing airflow to prevent moisture buildup and ice dams.

2. Why are hot roofs risky in Alaska?

Alaska’s long winters and heavy snow mean that hot roofs can trap heat and moisture, causing snow to melt and refreeze at the eaves. This leads to ice dams, leaks, rot, and mold. Cold roofs are better suited for these conditions.

3. Can I have vaulted ceilings without a hot roof?

Yes. Using raised-heel trusses or ventilated parallel chord trusses allows you to maintain an open ceiling aesthetic while still using a cold roof design with proper insulation and airflow.

4. What’s the best insulation for Alaskan roofs?

For cold roofs, blown-in cellulose or fiberglass batts rated R-49 to R-60 are common. In hot roof designs (if used), closed-cell spray foam or rigid foam boards are needed—but they must be installed perfectly with a continuous vapor barrier.

5. Can you fix a hot roof that’s causing issues?

Yes, but it depends on the severity. In some cases, ventilation channels can be added during a reroof. Other times, full tear-offs and rebuilds are required to switch to a cold roof system. We can inspect and advise the best solution.

6. How do I know if I have a hot roof?

If your home has no attic or ventilation along the roof edges or ridge, it may be a hot roof. Signs include icicles, roof leaks in spring, or unusually warm roof surfaces in winter.

7. Is a hot roof ever the better option?

In certain areas—like parts of western Alaska with frequent high winds and little snow accumulation—a well-detailed hot roof can work. But it must be sealed tightly, insulated correctly, and built with high-end materials. These situations are the exception, not the rule.