My Cooling Odyssey

10 years ago

Hi HVAC Folks,

I am fairly new homeowner of an existing single story 2250 sq. ft. home in Auburn, AL. We are on the border between what I think is referred to as Zone 1 and Zone 2.

I have had some horrific cooling experiences. See http://ths.gardenweb.com/forums/load/hvac/msg0809362210118.html?12 for more detail.

I have been on an OCD rampage to get my unconditioned attic as cool as possible. The unconditioned attic is where the ductwork for my Trane 5 ton 14 SEER HP is located - as is the inside unit; laying on its side in the unconditioned attic.

When I first moved in, the entire attic of this home was ventilated by two anemic looking power vents and 22 soffit vents. Attic temps exceeded 145 degrees F (highest my therm would read).

Earlier this summer, in conjunction with a new roof, I had the roofers rip out the power vents and install ridge vents.

I want to reduce ambient air heat load on the inside A/C unit as much as possible. It is literally an oven in my attic.

My next plan is to ensure all the soffits are, in fact, clear and open to air flow (I later plan to install baffles and blow in insulation to R-40). I know insulating the attic floor will not help the attic unit's situation, just reduce the heat transfer from the cooled space below.

However, before I improve the insulation in the attic floor, I am considering installing a radiant barrier along the underside of the roof rafters.

My roof pitch is somewhere between a 5 and 6. Multiple spray foam insulation contractors have told me the roof pitch is too low to spray insulating foam in. It makes me wonder about the efficacy of a radiant barrier.

Given my low pitch roof, would a radiant barrier appreciably help lower my attic temperatures?

Any advice is much appreciated in advance.

Thanks,
PW

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Comments (3)

mike_home
10 years ago
Have the changes to the roof and attic ventilation helped lower the attic temperature?

Adding spray foam to the roof deck will help lower the summer temperatures. It seems like an unnecessary expense if you are going to improve the attic insulation to R-40. If you are worried about the duct work in the attic, then I suggest spending the money improving the insulation around the duct work.
roadking
10 years ago
An old study done in conjunction with a radiant barrier manufacturer (so beware the findings) found that attic temperatures decrease by an average of 18% with the barrier installed. (Texas location). Supply duct conduction losses were reduced by 30%. This doesn't mean that your cooling costs go down by 30%...just the losses attributable to the attic duct work temperature difference.

You need to weight the cost of the barrier installation versus what I think would be modest decreases in your AC bills.

Probably best to first look at duct work leakage and make sure all leaks are sealed. Assuming you've got flex duct check it's R value. Typically from R-4 to R-8...the higher the number the better.
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ionized_gw
10 years ago
Sealing duct-containing the attic and insulating the roof deck has become popular in recent years in hot-humid environments. In those cases insulation and vapor barrier is removed from the attic floor, knee walls, etc. It is unfortunate that you can not spray the roof deck.

If I were in your shoes, I would probably hire a local energy rater. One of those should know your climate and local building codes. They can see your house and its low-hanging fruit for energy savings. Interview some over the phone using general features of your house and see how they respond. Hire the one that you get a good feel for. You can find one at http://www.resnet.us. There are often local programs (government and utilities) that will pay for an energy use evaluation. Check around and ask the raters that you identify.

Another place you might do research is buildingscience.com

In your case, a cool metal roof might have made sense, but it is a little late for that suggestion :-( That would be your radiant barrier and a durable roof all in one step.