why is there frost in my attic???

Question

I bought a house and the roofing looks good. Seller says its a newer roof. I am putting a floor down in the attic with plywood an noticed frost on the boards, and as it warms up with the heat going up from downstairs it melts an dries up.I have three roof vents on the back side of the house and one in each of the two peaks at the ends. Should I close them or leave them open for the winter?People tell me the house has to breath and thats why the vents are there. But im afraid of the roof rotting in time and I cant afford a new roof right now. The house is 850 square ft built in 1954. Attic floor has insulation but none in the roof area.What do i do?

Answer 1

It sounds to me like your insulation is doing it's job. It's there to keep heat excaping from the living area into the attic. And that's a good thing - if it didn't do that, there would not be frost on the underside of the roof.

I don't know where the moisture is coming from, but whatever you do, DON'T BLOCK THE VENTS. They are there to let air move in and through the attic, and to carry the moisture away. You could look into getting a powered vent - this would be basically an exhaust fan at one of the 2 vents in the peaks at the ends. It would draw air out of the attic and blow it outside.

Did you have the house inspected before you bought it? If so, call the inspector, and tell him what you found. He would be able to say if you need a powered vent.

If not, I would call a couple of local roofers or builders, and ask them to look at it. They would be able to look at it and either recommend it or not. This will cost you maybe $100-200, but it's a lot cheaper to pay for professional advice that will save you a rotted roof in the long run.

Answer 2

Don't block your vents, you need them year round. You already looked at the roof. My next recommendation would be to ask where does your bathroom exhaust fan vent to? They really should go outside, but a lot of times they let them dump into the attic, and will cause what you describe.

Another source of excess moisture in winter can be a ventless gas heater or fireplace (propane or natural gas). These don't use flues, and vent right into your home, like you typical gas stove or oven would. The combustion process generates quite a bit of moisture, and can enter your attic by creeping around your attic access door or panel and create frost. In this case you might need to crack a window upstairs to permit the excess to escape (we're talking less than a 1/4" crack here).

Answer 3

Do Not Close off your vents, your system is working fine, you want good circulation in your attic or you WILL end up with plenty of mold. What you should do is lay another layer of fiberglass insulation going the opposite way it's going now. YOU WANT YOUR ATTIC TO BREATH and sounds like it's doing it's job.

Answer 4

We had this problem and ended up getting mold in the attic, we got it all cleaned out and put in a dehumidifier, you should insulate the roof as well.

Answer 5

Sounds like you need new insulation.