Welcome to Structure Tech

Frost in Attics

By In Attic Bypass On February 17, 2009

This Minnesota winter has been an especially problematic one for frost in attics, and it seems that most people don’t understand why it happens or how to fix it.  There is a lot of mis-information floating around about why frost gets in to the attic and how to fix it, but I’m going to give you the real story.

This winter we experienced an unusually long cold spell in Minnesota, with temperatures never climbing above freezing for about a month.  This means cold attics.  When moist household air is allowed to escape from the house to the attic, it condenses on the roof boards in the form of frost.  When this happens for a long period of time, a lot of frost can accumulate.  When the frost melts, it soaks the insulation in the attic, stains the ceiling, and can even leak out through windows (I talked to someone last week who was having this problem).

I’ve heard several homeowners tell me they called their roofer out because they thought the stains on their ceiling were caused by a leaking roof, and of course it wasn’t a roof problem.  Nevertheless, the roofers typically suggest adding more ventilation to the attic space.  This will not fix the problem.  To suggest adding more ventilation to a roof to fix frost in the attic is like telling someone with a leaking water pipe to install a dehumidifier.  Ventilation is not the way to fix frost in the attic.

The fix for frost in the attic is sealing attic bypasses – these are passageways from the conditioned household space to the attic.  Bypasses are what allow moisture in the attic to begin with, and this is what needs repair.  While bypasses are certainly the most common cause of frost, there are other ways it can happen, and these are much more obvious.  Disconnected bath fans can be particularly problematic, and disconnected furnace flues can be catastrophic.  The photo below is one of my favorites – when the roof was replaced, the furnace flue came loose in the attic, which quickly turned the attic in to a winter wonderland.

Ice in Attic

If you’ve had frost in your attic, wet insulation in your attic, or stains on your ceiling, find your attic bypasses and seal them.  If you’re not sure how, read my related posts or give me call.

Reuben Saltzman, Structure Tech Home Inspections – EmailMinneapolis Home Inspections

About the Author


Reuben is a second generation home inspector with a passion for his work. He grew up remodeling homes and learning about carpentry since he was old enough to hold a hammer. Reuben has worked for Structure Tech since it was purchased by Neil in 1997, and is now co-owner and President of the company.


  • Lisa Van Cleave 3 YEARS AGO

    Several months ago we noticed that one of our bedrooms had a water stain on the ceiling. We contacted the builder and he said it was due to exposed nails. Now in the same area we noticed frost in the ceiling corner. Please advice me on what we should do to fix the problem or what type of specialist to contact. Our house isn't even 5 years old yet and our builder has been less than cooperative on fixing things.

  • Terry Szajkowski 4 YEARS AGO

    We have water leaking down the corner of a wall where our our existing house meets our new addition. In addition there is an ice dam on the roof just outside the corresponding area. Could this be do to poor ventilation of the existing attic space, an attic "bypass", or both? Is this an easy fix?

    • Reuben Saltzman 4 YEARS AGO

      Terry - the frost and ice dam are mostly the result of attic bypasses, but insufficient insulation may also be contributing to the ice dam. Ventilation won't have a lot to do with it. It's impossible to say how difficult the fix will be without inspecting the attic. I recommend you hire a qualified person to tell you what's causing the problem.

  • Sheila Jones 6 YEARS AGO

    I have this problem.How and where do I start to fix it?Who do I call?Is it covered under my home owners?What about the damage that has happened? Where DO I START????!!!!!!! Help I don't want a divorce.

  • Russ Addleman 7 YEARS AGO

    My question to you is. I have a bathroom fan/heater. What do I use to seal it and can I cover this unit with fiberglass blown insulation? Also a drop down sophet do you recomend insulation in it (not covering vents ofcourse). And how do you seal the sophet?

    • Reuben Saltzman 7 YEARS AGO

      Are you asking how to make sure the fan is airtight, and doesn't leak air in to the attic area? Your best bet would be to ask the manufacturer all of these questions; they're the only ones that can safely give you answers. Covering up the outside of the fan with foil tape would surely stop any air leaks... but this might also void the UL listing. Yes, soffits should always be insulated. The Minnesota Department of Commerce has an excellent handout with instructions on how to seal up soffits - see page four of this document http://www.structuretech1.com/AtticBypasses.pdf