Does Frost on my Roof Indicate Good Attic Insulation?

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Attic insulation is meant to be a thermal barrier between the conditioned space of your house, and the unconditioned space.

Here in our region of the country, (the Southeastern U.S.) vented attics are most common. In fact, until spray foam insulation arrived on the scene, all of us had vented attics over our houses.

If you have a vented attic, your thermal barrier will be the insulation positioned on the ceilings of your living space.

What About Vaulted Ceilings?

Rooms with vaulted ceilings can range from difficult to impossible to access. If the vaulted ceiling is directly attached to the roof joists, it’s next to impossible to access without major effort. But even in those cases, there is typically a baffle-system installed in the vaulted ceiling to allow for ventilation. And, like most all vented attics, the thermal barrier is the sheetrock ceiling.

Frosty Mornings

On a frosty morning, you may see roofs with frost on them, and other roofs with no frost, or roofs with a combination of frost and bare spots of no frost.

What is the explanation for that?

NOTE: My comments are directed to houses without trees or other interference from frost accumulating on the roof.

Frosty mornings mean cold, humid conditions. Those conditions drive us homeowners to heat our homes. Everybody has the heat on!


Good Attic Insulation = Frost!

If the attic has a strong thermal barrier between the ceilings and the vented attic, the frost will remain on the roof until it’s melted from the sunshine or higher temperatures..

Poor or No Attic Insulation = No Frost!

If the attic does not have a strong thermal barrier on the attic floor, the heat from the living space rises and escapes – to heat the attic. And because the roof deck is being warmed from the escaping heat, it melts the frost and prevents the frost from forming.

So, if you see a house with frost on the roof, and the house next door has no frost on the roof, you can assume that the folks with no frost need more attic insulation!

Spray Foam Insulation and Frost on your Roof

Several years ago we encapsulated an attic with spray foam. We had the sweetest, nicest homeowners to work with!

About a year or two later, I received a text with a couple of pictures from Mr Homeowner. It was a frosty morning, and right there near the bottom of his roof, was a bare spot about 1.5 feet wide and 2 feet long, that was completely bare of frost!

His text simply read, “Bob, did your guys miss a spot?”

Of course we had! Savannah immediately scheduled our team back to the house to spray that little spot. Our only explanation was that we missed it! No excuses.

Some time later I received a follow-up picture from him, of his roof with a beautiful consistent coverage of frost, with no bare spots!

Yes, you can say that frost on a roof is an indicator that the house has some insulation in the attic. How much? No one knows without looking.

But don’t get too confident – frost can also indicate that the heat isn’t on, so there is no heat being wasted in the attic.

Thanks for reading! On a frosty morning, if your roof isn’t covered with frost – you may want to take a look at your attic insulation. We can help!

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Check out this quick clip of a home we serviced and their lack of frost!!

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