Does Icynene Really Save Money?
I’m working on a new home and am considering using an icynene insulation system. I understand the superior air infiltration properties of this product, but have what I consider a fairly simple quesiton that I have so far been unable to get answered.
I understand that the icynene insulation on the underside of the roof will provide superior insulation to the traditional insulation on the attic floor. I also grasp the benefit of avoiding ridge and soffit vents.
But, since with the traditional system the attic space was not heated and cooled, what about the incremental cost of conditioning this space? In my planned home, this is a pretty large space.
So to summarize my question: Will the superior insulation qualties of icynene offset the incremental expense of heating and cooling unlivable attic space?
Replies
"But, since with the traditional system the attic space was not heated and cooled, what about the incremental cost of conditioning this space? In my planned home, this is a pretty large space. "
It cost NOTHING to condition SPACE.
Well not exactly. Actually the air in the space would need to be initially headed or cooled to the desired temp. But that could be done with a single 3" candle or ice cube.
What cost is the energy that transfers across the evelope.
Now the envelope, in this case the sq ft of the roof or attic floor, is somewhat bigger for the insulated roof than the insulated attic floor. Depending on the design of the roof and the slope it might be 20 to 50% more.
But in general attic floors are VERY POORLY INSULATED. One reason is the large number of openings for plumbing, electrical, sofits, flues, etc between the house interior and the attic.
And in many areas many of country HVAC stuff is put in the attic.
Building Science studys in the South or Southwest has show 30% reduction in cooling cost when going to conditioned attic space.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Good answers. I had not considered the that the HVAC system in the attic might not have to work as hard in conditioned space. If the 30% cooling savings are even close, this system will pay for itself in Atlanta fairly quickly. Thanks for the education.
had not considered the that the HVAC system in the attic might not have to work as hard in conditioned space
The (typically) R6 blanket on the ductwork does not do that much in the face of 130-140º attic temperatures--and pushing a plug of 95-110º air into your conditioned spaces every time the fan kicks on is not really "helping" the cooling any.
Now, with a conditioned attic, you really don't need the insulating blanket, but that can be just a little to far "out there" for some hvac people.
In Atlanta, it will be as 'big" an issue as in central Texas, but not running the furnace in a cold attic is also a pretty good deal, too.Occupational hazard of my occupation not being around (sorry Bubba)
what about the incremental cost of conditioning this space? In my planned home, this is a pretty large space.
The one I consulted on just west of the Brazos river from here, is a 1570 SF conditioned floor footprint. It uses a 6/12 roof, so there's about 5000 cf in the attic. It's currently "conditioned" with two 3" Ts off either end of the main duct trunk (was only the one, initally). Both are "throttled" down to about 25% open (3" was the easiest off-the-shelf stub T to knock into the trunk duct). From last year's high attic temp of 89º, the current high temp has been, middling consitently, right at 85-86º.
That's 2.5-3" on the existing roof deck, and 1-1.25" over all the rafters, and right down to the top plate, sealed up tight.
The savings in not operating the hvac in either 138º or 40-50º attic space more than makes up for the small amount of "lost" air cost.