Posted by: greenpinkies | November 7, 2010

Conditioned spaces or “We All Live In A Yellow Submarine….” (The Beatles, 1968)

Perhaps the most difficult concept for us to visualize is that of “conditioned space”.  Try to imagine that our houses are like submarines.  Actually, we are trying to make them that way with all the insulation, air exchange mechanisms, and the dehumidifiers, etc.  And, ideally, the ductwork and the heating and cooling systems should be right along with us in that conditioned space.  Think: “…And our friends are all on board…”   This allows the systems to live with you, breath with you, and actually work less hard to keep your space at an optimum temperature.  Therefore the systems in your house, because they are as happy as you are, are not consuming excess energy to keep it that way.

But, how much of your house must be ”conditioned space”?  We all agree that the house itself should be, but what about the attic over your house and the crawlspace under it?  After all, in most cases our ductwork and/or HVAC units are housed either in the attic or under the house, out of the way.

This is actually what the ‘gurus of green’ are trying to steer us away from.  Ductwork that is left out in the cold (or hot), that is subject to extremes of temperature, will lower the efficiency of your system. This scenario takes more energy to keep you comfortable.

But, there are a thousand different opinions about how to make an attic “conditioned space” and how to make the crawlspace “conditioned space’.  Of course all these opinions come with a price tag. They are also new enough that there is not enough evidence, that we can find, that some of these alterations are worth the price.

For our project, it boils down to:  do we and our equipment live all together in the main part of the house or do we condition and include the attic and/or crawlspace in our ‘yellow submarine’?

The bottom line is that we really don’t know.  The decision should be based on where we wish to put the ductwork.  Owing to our magnanimity, the HVAC system itself  is already going to reside with us, albeit in a closet.

The technique of previous years, wrapping ductwork in insulation, is not energy efficient enough.  But, if the ductwork is in an unconditioned space, then the next best thing is to build boxes around the ducts and then spray foam the boxes. This renders the interior of the boxes, where the ducts are, the same temperature as the ducts. They are now ‘conditioned’.  There will be no energy loss as the hot or cold air travels through them.

For this Happy Hollow house, we have two options: First: put the ductwork in the attic and box and foam the ducts in. Or, Second: lower the ceilings in the hallway by 6 inches and put wide and flat ductwork right in the living space with us.  Since we have 8 foot ceilings currently, we’re not too sure about the aesthetics of the second option. We will run the numbers by William and Gary and see if there is a clear winner.

Conditioned Attics or “To Vent or Not To Vent, That is the Question”.

There are also two options for attics mentioned in the literature: vented attics and non vented.  Since we are in Arkansas, which is considered the ‘South’, our summers are hot and humid.  One camp suggests completely closing off the attic and using spray foam on all the rafters under the roof deck. There will be no air flow. The attic then joins up with the house as ‘conditioned space’.  All ducts can then happily reside there without feeling ‘left out’.  Although it really has no airflow with the house, the temperature should not vary too much from the interior of the house. For our house, the quote for the foam is in the $2,000 range.  Not good.

On the other hand, we can vent the attic and apply a thermal barrier just under the roof…looks like foil.  This method does require airflow.  The attic is considered ‘Unconditioned’  but, even so, will not have the same searing temperatures in summer that most attics have.  Ducts will, as said before, have to be boxed in and foamed to qualify as ‘conditioned’. (This “conditioned” is a requirement of the EVHA National competition).

The determining factor in why you would choose one type of insulation over another in the attic would be that, in summer, the air flowing into an attic has humidity (moisture).  Having no airflow with the outside would eliminate that problem.  In fact, in our houses here in Arkansas, we spend much of the summer trying to get rid of the moisture and humidity. Failure to do so is downright uncomfortable and smells are very magnified….usually not the good ones.



  1. Excellent illustration!! “A smart person is rendered so by speaking simply.”

  2. Whatever you decide about insulation and where to put it, suggest you consider an “Ice House Roof”. Ours was furnished by our designer, Stitt Energy Services. It consists of cardboard with aluminum foil laminated to one side. The cardboard is stapled between the trusses (rafters), spaced down from the roof decking, to provide an air channel. Use contineous ridge vents. Our attic stays within 5 degrees of outside air temperature with this system. Obviously dosn’t help heating costs but makes a big difference with cooling.

    By the way, we went with foam insulation on the floor of the attic rather than on the underside 0of the ice house cardboard because our house has a steep roof pitch, therefore a large attic area. It seemed like there would be too muich heat loss through that much larger surface area. Our ducts are in the attic, covered with spray foam, over the A/C installer’s insulation. We also have foam wall insulation.

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