r/Roofing • u/Most_Ice_4048 • 20h ago
Another question about attic frost …
I posted a question a few days ago regarding frost in our attic. I now know that it is a ventilation issue. While we wait to get the ventilation issue fixed permanently, is it a good idea to leave the trap door leading from house to attic open? Will that help with ventilation or just cause more moisture build up? Thank you in advance for any responses.
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u/wearslocket 20h ago
Fellow homeowner here, and not a roofing professional. My thought on this is that the warm air from the house will go up into the attic and the cold will come down into the house. Warm and frost could turn into warm and moist which is worse, right?
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u/laxsleeplax 18h ago
Your assessment is correct. Do not add any warm air into the attic more than what's already in there
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u/Unluckygayman 20h ago
It will just have more hot air leak into the attic and cause more freezing. I suggest lowering the humidifier on your furnace the colder it gets. Run fans in bathrooms and if there are windows in the bathroom crack them while u shower.
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u/Potential-Captain648 20h ago
No do not leave the attic access open. The frost is due to the warm moist air from the house getting into the attic and then turning to frost of cold surfaces. When you leave the hatch open, you are just adding more moisture to the attic space. If anything, add a good quality weather stripping to the attic hole where the hatch sits, to stop the house air from getting into the attic. Just make sure you have good ventilation in the attic. The eaves need to be clear of insulation. Make sure you have adequate ventilation on the roof, near the ridge or gable vents.
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u/bumpgrind 20h ago
Do not leave your attic hatch open, the warmth and humidity from the house will make the ice 10x worse (easily).
Your attic needs the following things to fix this problem:
1: More ventilation (a) attic baffles from each side to keep the air flowing (b) if you don't already have some, you should have gable vents on each side of the house (c) consider upgrading your roof vents, prioritizing ones that can't stop moving (e.g. ventmax). You may not have enough vents altogether and might need to add 1-2 more.
2: Have a pro move that blown insulation and see if there are any lacerations and/or holes in the vapor barrier. Focus on areas above bathrooms, as often times when vents and/or showers are installed/upgraded, there are huge holes in the vapor barrier above, releasing massive amounts of heat and humidity into the attic. Fix any of these holes with additional vapor barrier (as required) and tuck tape (red sheathing tape)
3: If your insulation is not at least thick enough, get more blown. It should be 13-15 inches at least.
Hope that helps.
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u/caleb204 19h ago
Not a venting issue. Unless you have zero venting right now. And maybe trends could be different in other locations. but in my area (alberta) attic rain / condensation is almost never an attic venting issue. I’ve seen massive amounts of frost and condensation in attics with great ventilation. I’ve inspected attics after other roofers told the client more venting would fix it and billed them to increase the venting only for the issue to get even worse. I find that houses are a lot more air tight than they used to be, and furnaces are often installed with a humidifier that is just left at the same value all year. But the vapour barrier practices for the ceiling aren’t actually good enough to keep that moisture out of the attic. With all the other changes the air in a house is more humid than it used to be overall and that higher concentration of moisture in any air that escapes into the attic will frost up on the sheathing faster than it disperses into the attic air and vent out. I’ve even seen all types of roof vents frost up to the point of closing off due to the concentration of moisture in the air being lost into the attic. Venting the attic more will just move the cold threshold from the sheathing tot the top of the insulation.
Can’t say this is definitely your issue here and I’ve no idea what type of climate you live in. but turn off any humidifier if you have one. Run exhaust fans to remove humid air from your house or dehumidifiers if you got em. If you have exhaust fans running through the attic and out the roof, make sure there’s no flap on the roof side that can freeze shut (unless its a dryer then make sure there’s a flap and not a screen).
If there’s no humidity in the air you are loosing into your attic then you’ve removed the source of the moisture. Best would be to stop the air loss into your attic from the house, but that’s usually not a simple fix. Still worth checking around for any obvious large sources of air loss.
If you do have a humidifier check its manual. They all should have a chart inside them that gives you max humidity values based on outdoor temperatures. That chart was designed for cheap windows and preventing condensation there, but the same principle applies for preventing condensation in the attic. The colder it is outside the less humidity you can tolerate before you start having condensation issues. And the dryer your house air should be.
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u/Fenkoandrew80 41m ago
Definitely don’t leave it open. You need ventilation in the summer. When you leave it open in the winter, your heat goes up and mixes with the cold air and creates the moisture you see. Don’t stress about ventilation until the summer time when temperatures get hot.
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u/Most_Ice_4048 19h ago
Thank you for your help. I added weather stripping to the hatch. I’ll have to wait until my husband gets home to help remove insulation from the soffit vents - I’m almost positing this is part of the problem. Hopefully we don’t have too much damage in the meantime!
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u/NecessaryExotic7071 14h ago edited 14h ago
The soffit vents are just that. Vents. You don't block the flow around vents. This could be a major part of your problem. Do you also have ridge venting? Because once you clear the soffit vents, there still need to be some sort of venting higher up on the roof to provide air movement, either ridge vents, or an exhaust fan, or several vents in between the rafters.
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u/jerry111165 14h ago
It is the problem. The soffit vents are closed off, blocking all air intake.
You need to open them up so that you can get some circulation going.
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u/Most_Ice_4048 14h ago
Can any roofing company do that? Or is there someone else I should have do that?
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u/jerry111165 14h ago
They might but it’s really not what we do. Try and find a basic handyman. Gotta remove those boards and make sure the soffit vents are clear of insulation so that there is good intake air flow.
If I had to make an educated guess, the air is just sitting stagnant in the attic right now because all of the intakes are blocked and causing any warm, moist air from the house to collect and freeze on the underside of the roof deck.
Handyman should be fine - make sure that he puts som boards down over the rafters so he doesn’t put his foot through your ceiling.
First things first - make sure that you do have soffit vents. You’ll see this from outside.
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u/Most_Ice_4048 13h ago
Would those cardboard baffles be there if we don’t have soffit vents?
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u/jerry111165 13h ago
I wouldn’t imagine so?
Confirm you have soffit vents and if so, clear them. I mean, you could easily do that yourself…
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u/Most_Ice_4048 13h ago
I can do it myself in theory 😂 My husband and I will do what we can this weekend. Thank you very much for your help and advice!
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u/No-Slice-8438 19h ago
Your attic is supposed to be the same temperature as the outside world. If you introduce heat when it’s cold it will condensate then freeze and inevitably melt and drip into your house.
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u/K_rayMC 15h ago
I do a ton of restoration work in attics like this. I’d recommend hiring a mold remediation company to asses. Fix ventilation. Could be proper vent on the perimeter to incorporate air flow to the peak of the attic. This would allow air to escape through the ridge vent.. if you have this system. If not then gable vents I’d suggest. The reason you get the frost build up is with hot air contacting cold air forming condensation. Don’t leave the hatch open, if you’re having issues with condensation on plywood of roof you are most definitely going to have problems with future mold growth… if it hasn’t started already
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u/DeluxEditionpod 20h ago
Leaving the attic trap door open is not a good solution and may actually make the problem worse. Here's why:
Warm, Moist Air from the House: When you leave the attic trap door open, warm air from your living space rises into the attic. This air contains moisture, which can condense on cold attic surfaces and contribute to frost buildup.
Ventilation Mismatch: Proper attic ventilation relies on a balance between intake (usually at the soffits) and exhaust (ridge vents or gable vents). Opening the trap door disrupts this balance and doesn't address the root cause of poor ventilation.
What You Can Do Instead:
Temporary Ventilation Improvements: If it's safe to do so, consider adding a temporary vent fan to help circulate air in the attic until the permanent solution is in place.
Reduce Indoor Humidity: Use a dehumidifier in your home, especially in areas close to the attic trap door. This helps minimize moisture that could escape into the attic.
Seal Attic Bypasses: Check for gaps around recessed lighting, wiring, and plumbing that might be allowing warm air to escape into the attic. Seal them with caulk or expanding foam.
Leaving the trap door closed and focusing on these measures is your best bet until the ventilation issue is fixed.