Understanding Attic Ventilation When You Switch to Spray Foam

We see this one in our social media comment section all the time:

“Doesn’t spray foam block off the soffit vents? Isn’t that a problem?”

It’s a good question—and one rooted in traditional thinking about how attics are supposed to function. For decades, homebuilders and contractors have relied on passive ventilation (like soffit and ridge vents) to help control heat and moisture in attics insulated with fiberglass or cellulose. So, it makes sense that homeowners might feel a little unsure when they see us intentionally sealing those vents off.

But here’s the key: venting is only necessary in vented attics. When you convert your attic into a conditioned attic space using spray foam, sealing off those vents isn’t a flaw—it’s an essential part of the system.

Let’s break down how it works.

Traditional Attics: Why Ventilation Matters

In a traditionally insulated attic, the insulation is installed along the attic floor, and the space above it is left unconditioned—essentially exposed to the outdoor temperatures through soffit, gable, and ridge vents.

The goal of that setup is to:

• Allow hot air to escape in the summer,
• Prevent condensation buildup in winter,
• And reduce the likelihood of mold and moisture damage.

But here’s the catch: fiberglass and cellulose insulation are air permeable. That means hot air, cold air, and humidity can move right through it. In summer, the sun beats down on your shingles, superheating the attic space. In winter, cold air enters through vents and cools the attic, potentially leading to condensation issues on the warmer surfaces below.

Spray Foam Changes the Game

When we spray foam insulation onto the underside of the roof deck, we’re not just insulating—we’re sealing the attic from outside air. This turns your attic into part of the conditioned space in your home. That’s why it’s called a conditioned attic or unvented attic assembly.

So yes, we block the soffit vents—and we block the ridge and gable vents too. The idea is to eliminate all pathways for outside air to get in, because with spray foam:

• You don’t need airflow to manage temperature—foam keeps outside heat out and inside comfort in.
• You don’t need airflow to manage moisture—there’s no warm air leaking into a cold space, so condensation doesn’t form.
• And you don’t need airflow to prevent mold—because moisture-laden air is no longer cycling through the space.

What Happens to Your Attic Temperature?

This is where the real benefits kick in.

With a vented attic and fiberglass insulation, your attic might reach 130–150°F in the summer. That heat radiates down into your home, forcing your HVAC system to work harder. In the winter, the attic becomes freezing cold—robbing your home of warmth.

But with spray foam in a sealed attic:

• In summer, your attic stays around the same temperature as the rest of your home—usually 70 to 75 degrees.
• In winter, it stays warm—because it’s now inside your home’s thermal envelope.

People sometimes say, “I don’t want to waste energy heating or cooling my attic.” But here’s the truth: if your HVAC system is in your attic, you already are. And in a vented attic, you’re doing it very inefficiently. Spray foam stops the energy loss by keeping the entire space sealed and at a stable temperature—a concept known as steady state.

Why This Matters for Your Comfort and Bills

By converting your attic to a conditioned space, you:

• Reduce strain on your HVAC system (especially if your ducts run through the attic),
• Extend the life of your roof and equipment,
• Prevent moisture problems before they start,
• And lower your energy bills with improved insulation performance.

Blocking the soffit vents isn’t a problem—it’s part of the solution.

But What About Building Code?

This is another common question, and the answer is reassuring: modern building codes allow for unvented attic assemblies, provided they’re done correctly—with the right materials (like closed-cell spray foam) and proper air sealing. We follow all local and national codes, and we’re happy to walk you through how your project complies.

In fact, as energy codes continue to tighten, unvented, foam-sealed attics are becoming more common—even required—in many new construction homes.

Final Thoughts

If you’re still wrapping your head around the idea of sealing off attic vents, you’re not alone. It’s a shift from what many of us were taught about home construction. But with spray foam, you’re not just insulating—you’re creating a smarter building envelope that keeps conditioned air in, outside air out, and your attic working with your home instead of against it.

So yes—we block the soffit vents. On purpose. And it works.