Can thermal image tell you when “enough” insulation is present?
Hi,
I recently got a few sheets of some leftover 1″ fiber faced polyiso and have been using it to insulate my attic hatches.
I have 3 in various states of doneness, two in the ceiling and one in a wall.
1: 10″ polyiso
2: 2″ poly and 1/2″ XPS
3: 1″ polyiso
Out of curiosity I took some thermal images with a Klien TI-250. This is in Michigan with temps in the low 30s at the time and a vented attic insulated to ~R60 with blow in cellulose.
The hatch with only 1″ of foam is cooler than the surrounding wall by a couple of degrees (~66 vs ~68F). Wall is 2×6 dense pack cellulose
The other two with 10″ and 2.5″ are both at essentially the same surface temperature as the surrounding ceiling.
Does this mean that the 2.5″ is providing “enough” insulation? Is there something I am missing?
Appreciate any thoughts.
Jake
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Replies
Is there a reason they don't double batt R31 on the hatch to match the R60? That's what they do here.
Adding insulation has a diminishing return, as the halves getting halved are always getting smaller. By example, in my climate, R-19 ceiling insulation might reduce my heat loss by 45% compared to nothing, but double that (which costs 25% more for the material ) will only decrease the loss by another 5% or less. Another climate, with bigger temperature differences, will see a more elongated curve, but still nothing like a straight line.
"Enough" insulation is exactly right (if your air-sealing is good)--at a particular point, the increased material cost is unlikely to be recouped by the energy savings, even though the cost of energy is probably going to increase more than inflation, over time.
Exactly. For attic hatches, getting a very good air seal is the most important step. After that, insulation will certainly help, with diminishing returns as above. 2"-3" of rigid on the hatch goes a long way. A "pillow" of fluffy insulation made with a perforated bag would be cheap and it can simply sit friction-fit into the upper opening above the hatch, if you want to bring your whole assembly up to near the R-60 of the rest of the attic. Perforated is somewhat important to eliminate the possibility of moisture vapor condensation, but with good air sealing and rigid insulation on the hatch, this risk is low.