Insulation on attic ceiling and floor
whnh121
| Posted in General Questions on
I just put 5.5 inches of closed cell foam on my attic ceiling and gable walls to bring a pre-existing air handler and ductwork into the house envelope. Zone 5a so this is short of the recommended R49 but cost considerations required it. Prior to this the attic was vented with soffit and ridge vents and had some ~50 year old pink insulation under floorboards.
Is there any reason not to leave the existing insulation under the attic floor? It seems like it should provide some additional barrier between the attic and second floor but they may be other considerations.
Thanks
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Replies
https://www.greenbuildingadvisor.com/article/three-reasons-to-remove-attic-floor-insulation-in-a-sealed-attic
Just what I was looking for. Thanks. Seems that with the large majority of insulation on the attic ceiling I should be fine to leave as is
“Seems that with the large majority of insulation on the attic ceiling I should be fine to leave as is”
Only true if you spend the money to buy and operate the equipment necessary to keep the attic at more or less the same temp and humidity as the rest of your house.
Walta
What equipment are you referring to? I wasn’t planning on putting a supply register in the attic as it doesn’t seem to be necessary with closed cell foam based on what I’ve read here
The way I see it for attics you have 2 real options.
Vented and conditioned anything in between is a game of Russian roulette with mold and rot.
A vented attic is the safe lowest cost attic.
If your builder stuck your HVAC equipment in the attic (A very poor decision in my opinion) your left with bad options. Stick with paying 50% extra to operated the equipment. Condition the attic and only pay 30% extra or spend thousands and move the equipment.
Seems to me the smart move is to fix the bad decision and get the equipment out of the attic in the long run.
A conditioned attic will always have a larger surface area than the flat ceiling 20% maybe 50% by the time you count the gable end walls. A conditioned attic will almost always force you to use spray foam insulation the most expensive way to buy an R of insulation on. Since the SFI is so expensive and you need 20-50% more of it lots of people cut the number of R they are willing to pay for often well below code minimum. Hardly a month goes by when we don’t see a post about how someone’s spray foam install that went wrong.
The free lunch crowd tries be somewhere between vented and conditioned and calls the attic encapsulated. they ignore the high humidity in the attic acts surprised when parts of the attic get colder than the dew point of the air in the attic become wet and begin to growing mold.
My wild guess is if you did a manual J calculation the house the condition attic would be more than 50% of the load so you would need 50% of your register in the attic.
Most people move long before any of these fixes could ever begin to recover it costs.
Walta