Is my attic a problem?

josephny

I have a ~100 year old, 2 story frame house. It has a Burham oil boiler with a zone for each of the 2 floors.

Above the 2nd floor ceiling (between the ceiling joists) is 6" of mineral wool.

Above that is an uninsulated (vented) attic.

I put a temperature sensor in the attic (and everywhere else I could think of), and I notice that the attic is always substantially warmer than the outside temperature. I understand that the sun will warm the attic, so I'm only looking at the night temps.

For example, last night the outside temp hit a low of just under 13*F.

The attic low temp was 22.

The 2nd floor low temp was 61.5.

Below is the graph.

Does this indicate that heat is moving from the 2nd floor into the attic? If so, is it doing so to an extent worth doing something about?

Thank you.

Mad Dog_2

Hot goes to cold...always. We merely try to slow it down. Mad Dog 🐕 

josephny

Understood -- learned that (slowly) here.

Does an average 10*F difference between outdoor temp and inside-the-attic temp indicate an unacceptably/undesirably rapid movement of heat from 2nd floor to attic?

Night before last the outside temp was higher, and the difference was generally less. I wonder if that is informative?

PC7060

The only way to solve the problem is to remove all of the existing insulation from a section ant a time and then use foam in a can to seal all penetrations from the living space to the attic. You can reinstall the existing insulation once you’ve sealed the penetrations. 

My house had multiple location where lower level walls opened directly up into the attic creating a chimney for movement of warm air into the attic.  Openings around light fixtures and wiring are also big contributors.  I use the orange foam in the can to make igloos overall light and smoke detector penetrations.

Dense, packed fiberglass also works very well to plug large openings. Just keep stuffing it in the opening do you have a solid plug of insulation. Also access an approved fire barrier.

My case I had all the insulation professionally removed, then later used BIBS (blown in blanket system) Insulation. The system puts a net down first, and then blows in dense, packed, fiberglass, which insulates and limits air movement.

Sylvain

One doesn't need to remove all the isolation if one knows where the penetrations are.
Why waste the existing insulation?
You have to investigate what happens at the top fo the frame walls.
Then, You could also add another insulation layer.

josephny

I added the insulation myself (replaced nasty old fiberglass) about a year ago. Put a nice thick amount.

I did not seal around openings in the sheetrock of the ceiling below because the insulation covers it completely.

Taking a look at the top of the perimeter frame walls makes sense. The tops of those walls in the attic is where the soffit vents are, and my recollection is that I was focused on making sure not to block the soffits and was not focused on heat travelling up within the walls and into the attic.

Thank you!

Intplm.

Roof ridge vents and soffit vents play a large roll in how your Attic feels in the winter. They allow air, cold or not to circulate through the roof.
This circulation of air is helpful in protecting the roof.

So to answer your question, "Is my attic a problem?" I would answer no it is not a problem.

jesmed1

The temperature differential in the attic will depend mainly on two factors: (1) the rate at which heat is being transferred from the heated interior of the second floor through the ceiling and walls into the attic, and (2) the rate at which heat is lost from, and cold air transferred into, the attic.

Since (2) is largely dependent on venting configuration, vent area, etc, there's no way to say how your 10-degree attic differential compares to another house with a different configuration.

What you can say for sure is that, whatever the R-value is of your second floor ceiling/attic insulation system, you're losing more heat through it than you would predict from just the R-value, because of air leakage.

For example, you say you have 6" of mineral insulation. That gives you a nominal R-24. Then you gain some R-value from the second floor ceiling materials, but you lose some from thermal bridging across the ceiling rafters. So let's just say for argument's sake that the assembly R-value of the whole system is R-20. Then at (say) a 60-degree differential between indoor and outdoor temps, in theory you're losing 60/20=3 BTU/hr per sq foot. So in a 1000 sq ft attic, you're losing (in theory) 3,000 BTU/hr at that temperature differential. Over 24 hours, that's 72,000 BTU, or roughly 1/2 gallon of oil.

But in reality, your attic is much worse, because of air leaks. You could easily be losing twice that much heat through the attic because of air leaks through the ceiling and the top plates of the walls.

A few years ago we had 10" cellulose blown into our under-insulated attic. I expected big savings based on the expected R-value of 30+. We did not get the savings you would predict just from the R-value, to my disappointment. I now believe one reason is that we didn't do sufficient air sealing in the attic before blowing in the cellulose.

I later found an article saying that air sealing the top plates in the attic is important, and it's something I wasn't aware of and we didn't do. I wish now that I'd found this article earlier, and that we had sealed the top plates. (see link below)

Note that near the end of this analysis of two house that were air sealed and insulated, the paragraph "What Really Made the Difference?" mentions in item #3 that the house that saved a lot of energy had its top plates air sealed, while the other did not. Of course that's only one item in a list of improvements, but if you have access and can air seal your top plates, that's what I'd do first.

https://energysmartohio.com/uncategorized/a-tale-of-2-houses-low-hanging-fruit-is-poisoned/

PGB1

After sealing openings & wire penetrations, as others mentioned, I installed perforated radiant barrier on top of the insulation in one of our attics. At 19 cents a square foot, I think it paid for itself in about 2 days.

We live in a sort-of cold climate (Detroit) and the rooms below that attic became suddenly much more pleasant. The rooms could not maintain 70-F on a 20-F day. Now, the radiators are throttled down. Proof enough for me. (Two mini duct A/C vents in each are now closed as well.)

I installed that one on a, perhaps, 95-F day. The thermostat's thermometer in one of the rooms below was pegged full scale before starting and dropped to the low 80's after (without the cooling system on) when I was half done.

I did another of my attics in winter and did a crawl space under a bedroom in winter. For both, the next month's heating invoice cycle was colder outside but the cu-ft used was much lower. (I had degree-day records, but the computer ate them somewhere.)

In winter, my brother & I installed perforated barrier in his 4,000 ft-sq attic which is 9+ feet tall, mansard style. The entire house became warmer. His steam bills dropped dramatically.

I've been on lots of government, commercial and industrial projects that incorporated radiant barrier. Despite negative comments, it actually works.

Ask a legitimate seller (below) for a sample. Lay it on an inverted cardboard box with a thermometer poked inside. Shine a hot lamp on the foil. Check the temp. Now remove the foil & watch the temp rise.

Four Keys:
A) Use real radiant barrier that is 100% aluminum and un-coated. The bubble stuff is coated.
Watch for fake stuff. It's everywhere on line & in stores.

IMPORTANT: Use perforated if it is over an existing surface. Moisture must escape.

C) CRITICAL: Leave a radiant gap of 19mm or more on either side. (The gap makes the barrier a good reflector on the gap side and a low emitter on the non-gap side if there is a gap on the other side. Aluminum is 97%/3% rated. Silver: 98/2 Gold: 99/1

D) Radiant barrier with scrim is very strong and easy to work with. It'll never tear.

AtticFoil Com sells legitimate product & are nice people.
AFS Foil was where I learned (the owner was chairman of DOE's radiant energy committee). But, I think they got sold when he died. Don't know if they are still legitimate.
I'm sure there are other legitimate suppliers out there.

Paul