Ice in the attic

[John Kogel]

Got some cool pics in this attic. []

The two plumes of frost are at the walls of an upstairs bathroom. This bathroom is not being used, no shower curtain so no long showers, no exhaust fan to leak, just a light fixture on the ceiling that is probably leaking some air. An elderly couple only use the downstairs master bathroom.

The insulation between these two frost plumes is wet on top, where you see black on the white fiberglass. Moldy dust, I call that black stuff.

The heat pump was going strong to keep the main floor at 68 F. Up in the bathroom, a register is pumping heat in, and a vaulted ceiling above the downstairs living room is supplying even more heat.

I think they should pull back the insulation and look for leakage at the wall top plates.

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[Jim Katen]

I see it all the time.

My theory:

Cold day.

Heat loss through walls.

Air film next to walls gets warm and rises.

Rising air gets sucked up onto the soffit vents and condenses on the cold sheathing surface.

[John Kogel]

Hello Jim. When the frost or stain is at the baffle openings, yes, it must be coming in from outside through the soffits.

But here, there is frost only in these two places, between the baffles but directly above the interior walls. The one truss is also black. So I think there is a poor seal where the walls meet the trusses. The attic hatch is adjacent and needs some weatherstrip, so some warm air is likely leaking in from there as well.

[Garet]

So I think there is a poor seal where the walls meet the trusses.

I could easily see an uninsulated framing cavity where an interior wall meets the exterior wall as a place where more air leaks out of the house, making its way up into the attic.

[Marc]

The position of the H clips seem too high for the roof panel to reach down to the eaves. Maybe there's a horizontal seam in the decking just below the top of the baffles, out of site, that provides the little extra cooling needed to put conditions barely within range to make ice.

Marc

[Tom Raymond]

I see it all the time.

My theory:

Cold day.

Heat loss through walls.

Air film next to walls gets warm and rises.

Rising air gets sucked up onto the soffit vents and condenses on the cold sheathing surface.

A little sunshine does the same thing. IIRC Dr Joe measured air film temps as much as 20 degrees higher than ambient.

Add some more baffles and blow in 8-10 inches of cellulose. That should be dense enough to seal things up. Blown glass is almost useless as insulation.

[Eric B]

Not sure how you guys are making your determinations. For me there's too little information about the home. There can be quite a variety of possibilities.

[John Kogel]

More info? Sure. It was a frigid day, about 2 degrees below freezing with a skiff of snow.

There is plenty of soffit ventilation as seen by the baffles, a poly vapor barrier and about 14" of insulation. The upstairs bathroom was quite warm due to a wide open register and like I said, the thermostat down in the living room with a double height vaulted ceiling. There is minimal staining anywhere else, 12 yr old house.

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[ghentjr]

If the bathroom heat is under the location of the ice the humidifier may be set to run continuously creating excess moisture. If the plumbing vent we see is connected to an appliance in the outer wall it could be disconnected or cracked.

[John Kogel]

There is no humidifier, don't need them here. The air is either moist or frozen.

The plumbing vent comes up behind the sink in the right interior wall, then crosses over to the roof jack above the left, suspended by the strap in pic3. Yes, warm air could be leaking out around the hole in the wall plate or the pipe itself.

[kurt]

Conventional framing practice creates a number of thermal bypasses @ exterior wall & roof structure junctions. It's a great picture showing how it works.

[mjr6550]

Got some cool pics in this attic. []

The two plumes of frost are at the walls of an upstairs bathroom. This bathroom is not being used, no shower curtain so no long showers, no exhaust fan to leak, just a light fixture on the ceiling that is probably leaking some air. An elderly couple only use the downstairs master bathroom.

The insulation between these two frost plumes is wet on top, where you see black on the white fiberglass. Moldy dust, I call that black stuff.

The heat pump was going strong to keep the main floor at 68 F. Up in the bathroom, a register is pumping heat in, and a vaulted ceiling above the downstairs living room is supplying even more heat.

I think they should pull back the insulation and look for leakage at the wall top plates.

013126214656_AttcFrost2.jpg[/img]

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I think you nailed it.

[Eric B]

How many people live in the home, do they use exhaust fans, how tight is the home, what was the outdoor temp prior to your visit,what's the humidity in the home, so there are baffles - is there daylight from the soffit vents? This is the kind of stuff I consider.

[AbsoluteInspector]

I just came across a home last week with a huge leak from a missing facia board near the ridge running snow and rain right into the attic and through a huge hole in the living room ceiling (they didn't need an inspector to spot that) It was all iced over at the time.