I live in a 1926 co-op building in PNW USA (3 stories + partially underground ground level) with radiator heat served by a gas boiler.
The attic insulation is pretty minimal. We can get some money from the city to pay for insulation. As far as I know the attic is moderately well sealed from the top floor (there is ongoing work to seal other aspects of the building envelope, see below), and in any case we can't get money to fix the sealing.
The top floor gets very hot in the summer and rather cold in the winter, as you'd expect. The other floors don't seem to be quite as bad but nonetheless are not necessarily comfortable. Notably some first floor residents have complained about cold.
There are 2 temp sensors for the boiler, in one unit on the ground floor and in one unit on the third floor.
The boiler fires once in the evening and once in the morning, and is otherwise off. No central air, some residents have individual A/C units.
It has been argued that the proposed attic insulation project will only benefit the top floor and thus is not really worth it for the bottom 2 floors. This doesn't make a whole lot of sense to me, because conduction of heat up towards a cold leaky attic will necessarily cool bottom floors in between firing cycles. Likewise, a hot third floor will heat up the second floor (even if to a lesser degree). Looking around on trade forums and similar mixed-reliability places, I can find arguments either way e.g.:
- https://forums.jlconline.com/forums/forum/jlc-online-expert-forums/building-science/50921-heat-loss-insulation-in-tall-buildings
- https://www.jlconline.com/training-the-trades/heat-transfer-through-buildings_o
- https://www.greenbuildingadvisor.com/question/will-insulating-attic-have-a-noticeable-effect-on-lower-level
None of these are particularly convincing in that none of them are very quantitative. So I pose a more quantitative question: could one reasonably expect insulating the attic to make the second floor at least 1º F cooler in summer or to make the ground floor 1º F warmer in winter (at least when the radiators aren't running)?
In other words, is the top floor the sole beneficiary of insulation, or can we expect any perceptible difference in comfort in the lower levels from additional insulation?
I don't need a precise answer or a "yes in all cases" answer, more of a "reasonable expectation" yes/no type of answer.
Additional info:
- We are well aware of the possible energy efficiency / cost benefits of insulation, I am specifically interested in comfort.
- There is a separate effort to seal the building envelope with upgrades like replacing the original windows. We understand that these efforts will necessarily complement each other. I'd be happy to hear whether this impacts the answer.
