Home>Discussions>INSULATION & HVAC>Wintertime Attic Frost and Insulation, how to address?
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Wintertime Attic Frost and Insulation, how to address?

Hi all, I just read about two hundred posts on attic insulation and couldn’t find my specific frost and condensation problem. I would be super appreciative of any DIY advice because I can’t afford to hire anyone right now. My current two winter problems that only show up when outside air is 30F or less: 1) condensation above/around bath exhaust fan box- there are water droplets on the nail heads through the sheathing, moisture everywhere and at times a very wet interior ceiling around this exhaust fan (there could be condensation/moisture in other parts of the attic that I haven’t seen or discovered). This is only when it is cold, NOT when the bath/shower is/was in use. 2) Attic frost on the eaves and roof sheets, but only in the northwest corner of the house (again, could be other parts I haven’t seen or discovered), and I get water condensing (or seeping?) at the joint of my interior wall and ceiling in this corner. At this corner of the house there are no canister lights, no plumbing vent stacks, etc, but I did notice the blow-in in the attic seems pretty sparse.

My set up: late 50’s single story ranch over a basement with a 950 Sq Ft crawl space attic under a 12/4 (maybe 12/6) roof that has overhangs, no soffits, no ridge venting, the ridge runs east-west, and gables (no fans) at each end, maybe 4’ x 4’. We’re in Washington DC area so it gets cold but not a lot of snow. I bought the house two years ago – at some point in the past insulation was blown in but I have no idea how much or how well it was done. When we moved in we had down lights and the bath exhaust fan installed and the electrician only halfheartedly replaced/put back the disturbed blow-in.

So I clearly have heated air making it into a poorly ventilated attic. I’m on a tight budget so what should I do? My DIY ideas are:

-Put in soffit vents? How do I figure out how many?
-Put in an attic fan at the east gable (we have mostly NW prevailing wind) on a humidistat? With or without soffit vents?
-Can I add blow-in by hand around the canister lights and fan box? In the northwest corner? Or should I try to add fiberglass batts or roll? Do I put down or add any kind of moisture barrier? Should I break out the caulk gun?

Finally, this house stays pretty cool in the summer thankfully. Thanks a million for any ideas!!

Re: Wintertime Attic Frost and Insulation, how to address?

Its hard to tell without actually seeing it, but it sounds like you may have a couple issues with the fan. First, the fan is not sealed between the sides of the fan housing and the ceiling so warm moist air can rise up into the attic around the fan and when the bathroom is not in use, cold air can fall from the attic into the bathroom. Second would be that the duct is not sealed to the fan housing so when the fan is running, it is blowing a little of its warm moist air into the attic.

I think you might have been better off without the fan, but now that you have it, it must be properly sealed.

Re: Wintertime Attic Frost and Insulation, how to address?

Condensation forms when warmer moister air meets a colder surface. Thinking that through will show you where to look for problems. Bath exhaust fans don't seal well- generally there's a hinged plastic door that gravity pulls into place and it doesn't seal the opening well at all. Insulated exhaust ducting may help that.

More importantly, before you cover any electrical parts with insulation, you need to know the exact specifics on how to do that from whoever made the item(s) or they may overheat and cause a fire. Lots of expensive unregulated heat that doesn't last the season when that happens :eek: You'll need the make and model number(s), not just the general type of thing in question, because they all have varied requirements. Some recessed lighting cannot be covered with insulation and some can- I hope you specified and got the type that can be covered.

As for the fan, well I've never seen any insulated but I have seen some covered with blow-in and it didn't seem to cause problems, so that might also help you. Do be sure it vents freely to the exterior of the house where it can't easily rise back into soffit venting- some codes now prohibit these vents in soffits without 3' minimum to the nearest soffit venting. I still prefer to not poke any unnecessary holes in a roof but that is a better place to vent this at. Also be sure there's no 'dips' in it's run that might collect moisture and allow it to drip back through.

Hope this has been of some help and let us know how it works out!


Re: Wintertime Attic Frost and Insulation, how to address?

1) the joint between the fan box and plaster was probably left poorly sealed or not sealed at all. if the gap is under a quarter inch it can be caulked. if larger you can tape the joint from below then go above and run a bead of canned foam sealant. The same can be done for the can lights. All fans are rated for direct contact with insulation and should be covered to prevent heat loss and condensation on the inside of the box. Some can lights are not rating for direct contact with insulation so a 5 sided box needs to be built over them to maintain an inch or two airspace between light housing and insulation. Check for loose or disconnected ducts as well.

2)It possibly to get water condensing on a uninsulated area of ceiling. Water could Condense on a vapor barrier on top of the plaster with no insulation above, or the frost you see melts and drips through the plaster joint. You could also have a small roof leak. Adding insulation to the attic will help if water is condensing on the plaster or vapor barrier. If the frost is caused by warm moist air leaking out of the house sealing leaks may be difficult if theres no obvious holes or cracks to be found. With a 4/12 roof its a tight squeeze to do any work in the attic clear out to the eaves so it may be easier to add a few soffit vents in the area of the problem. If its a leak from an ice dam soffit vents will also help but if the leak is caused by damaged shingles it needs patched promptly.

Re: Wintertime Attic Frost and Insulation, how to address?

Thanks all, I think you guys are spot on that my fan box and probably the exhaust conduits aren't properly sealed, or could be sealed better. I am going to get up there and attack that this weekend. I'm going to put a couple soffit vents in at the corner where I have that frost and monitor (really doubt I have a roof leak as roof is about 6 years old with architectural shingles, but I guess anything can happen over time).

However curious that no one mentioned a fan at one of the gables - waste of time or money or a worthwhile project? Thanks!

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