Inference about leaking heat
I have a 2 story, 100+ year old, wood framed, poorly insulated home in zone 5, with oil fueled hot water baseboard heating.
Conditioned space ends at the ceiling of the second floor, above which there are 2 layers of rockwool — the first between the ceiling joists, the second perpendicular to the first and laying on top of both the first and those ceiling joists.
The attic is above the layers of rockwool and below the plywood sheething with asphalt shingles on top.
Below is a graph where I track the temperature on the second floor, the outside temperature, and the temp inside the attic across the time of day.
I have a general understanding that the sun, even in the Winter, will heat the attic, and that that heat will take some time to dissipate when the sun goes down.
But I'm looking at the graph and there is a substantial difference between the outside temp and the attic temp (even at nighttime) and I'm wondering if that difference is a good indicator of heat loss from the second floor into the attic.
I'm hoping that the experienced and excellent minds here can share their thoughts on my hypothesis.
Here are two graphs:
Comments
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Well you certainly are losing heat — most likely warm air rather than by conduction — into the attic. That is to be expected. Rockwool is a good insulator, but it isn't much in the way of a draught barrier. What interests me, though, is the increasing split on the 19th as compared to the 18th. What else was going on?
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
I noticed that increasing split and wondered the same. There is nothing person-caused that would explain that (the house is not occupied and hasn't been entered or changed in any way in over a week).
I think that only leaves nature-related explanations such as the amount of sunlight and the temperature.
I've been giving some thought to draught (or as we butchers of English might say, draft). The ceilings of the second floor are sheetrock, with only one centerof room light jbox in each of the 4 bedrooms, a ceiling fan vent in the bathroom, and a hatch for attic entry in the hallway.
I checked for draft using an incense smoke test and do not see a leak, but it's possible the test wasn't performed very well.
Do I understand correctly that your reading of the graphs indicate a heat transfer from inside to the attic?
Thanks!
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You really wanna see how bad the leakage & infiltration is, shoot the home with an infrared camera. Mad Dog
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I don't have much experience doing that.
Would I go up into the attic with the IR cam? Or while standing on the floor of the 2nd floor pointing at the ceiling? Or am I totally not understanding?
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View from both inside and out. Small inexpensive IR devices hook to your phone.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
IRcameras are nice but when attempting to tighten up attic it’s all about blocking penetrations. Each penetration acts like a chimney venting conditioned air out while pulling in outside air. An effective first step foaming the tops of all light, fan and smoke detectors up in the attic, think foam igloos. Next seal all wire penetrations through attic ceiling or wall plates.
Once you’ve sealed the penetrations, look at boosting amount of insulation.
IR cameras are very helpful tool to locate heat loss in wall, basements and around doors windows. The image below illustrates reduce temperature of foundation wall with 1.5” XPS applied (right) versus portion of wall with no insulation (left).
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I'm guessing the difference is due to varying wind levels. Wind blowing on one side of the house will positively pressurize the interior if it is reasonably leaky, as most old houses are. Our 100-year-old house has measurably worse heat loss on windy days. So a calm day wouldn't force as much warmed air out of the house and into the attic, etc, via air leaks, while a windier day would.
Also, by coincidence, I just went around our house the other day with a thermal imager, and I noticed that the air coming out of the attic vents was at around 44 degrees, on a day when the outside air temp was in the mid-30's, and the outer surfaces of the rest of the house were in that same range. So the air coming out of the attic was 10+ degrees warmer than ambient, and that was with 10" blown cellulose in the attic. And that was on a low-wind day. I'm sure it would be worse in higher winds.
We failed to do adequate air sealing in the attic before insulating, which I now recognize was a mistake.
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Thank you all!
First step is to seal up all penetrations — lights, smoke detectors, bathroom fan.
Very hard to check for air coming up from the walls — that is, the perimeter of the attic. The house uses balloon framing, and the roof touches the tops of the wall studs (possibly with a top-plate).
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Sealing the top plates is important, especially in balloon framing. You might find this comparison informative. One house had the top plates sealed; one did not. If I had read this before insulating our attic, I would have spray foamed the top plates first.
https://energysmartohio.com/uncategorized/a-tale-of-2-houses-low-hanging-fruit-is-poisoned/
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I dense pack fiberglass into large gaps like this one commonly found with balloon framing. Also meets fire blocks requirements. Best if you by unfaced fiberglass but you can remove the paper if you have faced. And wear a mask and long sleeved shirt!
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Be very careful about sealing or insulating around any lights which are ceiling mounted. They can get very hot it they are too tightly insulated or sealed around.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England2 -
Good point @Jamie Hall. Applies to lights mounted through drywall; I.e can lights which need “huts” with sufficient airspace for cooling. Low profile halo lights also need small huts built over them before sealing but this is primarily for service access.
https://www.homedepot.com/p/Tenmat-Recessed-Light-Cover-FF130E/204286308
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In typical older plaster and lath houses, there is a gap at the top between of the wall and plaster. This creates a nice little channels to leak air into the attic. Unfortunately your batts won't slow any of this airflow down, you need to plug these holes with something solid like canned foam or with larger gaps, pieces of rigid insulation sealed in place with canned foam.
Stuffing batts of any kind won't work as they will simply just filter the air leaks and won't stop them, the exception is dense packed cellulose as that is pretty restrictive.
Would have been an easier fix before the insulation went in, but not too bad as you can pull the batts up in sections as you work and relay them once done.
A budget thermal camera can show you where the major hotspots are in the attic.
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I just did a smoke test again and there is no smoke movement whatsoever around any of the lights (which are plain j-boxes.
But, there is substantial smoke moving up into the bathroom ceiling vent.
The bathroom has a window, so I'm wondering if I should just remove the vent (patch the ceiling).
I hear that now that the balloon walls are complicated/complex/substantial to block the airflow and insulate.
The next step for me will likely be the IR camera.
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Smoke test unfortunately won't show leaks inside walls, especially if balloon framed, those can be quiet substantial. Generally if the outside walls feel cold (less than 60F if there is insulation in it), you have air flowing through your walls.
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What is the hatch into the attic like? Those are notorious for being poorly sealed.
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”Stuffing batts of any kind won't work as they will simply just filter the air leaks and won't stop them”
Not so; dense packed fiberglass is highly effective. But you need to really pack in there. Or it’s just a filter as @Kaos said.
Dense packed fiberglass is better for the fire block applications since you can stuff it by hand wherever required. Not the case with cellulose which has to be blown into a closed space.0 -
Got it. Will need to work with an IR camera.
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