Friday, July 16, 2010

Radiant Barrier Performance Data/Update

As I was working on the fabulous image you see below, #2 came around wanting to go do stuff with me outside the house. His mother turned him out to play in the back yard for a little while. He went under the shaded deck cover (the coolest part of the yard) and swung on the swing for literally about 20 seconds. He came straight back inside and said "It's hot outside."

. . . which made it a perfect day to record some performance numbers for my DIY radiant barrier in the attic! It is 95ºF outside, and the sun is blasting down, with no clouds to stop it and barely any wind to speak of. I went over to my garage with the ol' digital thermocouple thermometer and did some measuring.

At the underside of the garage ceiling, it is 87º. On top of that single 5/8" layer of uninsulated drywall, it is 92º. I went straight for the big money: on top of the barrier material, between the barrier and the roof deck. 132º I left a gap at the top of the foil, to accommodate ventilation when we can finally get a ridge vent installed. This house currently has NO soffit vents and only two gable end vents. The foil over the garage is folded back over the garage ceiling as shown below, to keep the eventually-to-be-blown-in insulation from clogging the eventually-to-be-installed soffit vents. There is NO source of cool air in there, aside from the scuttle used to access the attic. There is a river of HOT air flowing at the top of the attic, where the air flows out from over the barrier material, on the way to a gable vent on the other end of the house.

I have mentioned before how, near the floor of the attic, it is relatively pleasant. Standing up in the attic is like stepping into a furnace, literally. Two feet down from the peak of the roof, in the stream of hot air, it was 112º. Two feet further down, mostly out of the stream, it was 102º, and then as mentioned before it was "only" 92º on the floor of the attic. Curious, I moved over two yards to the end of the garage. The end of the garage, where the attic is open to the attic over the rest of the house. The end of the garage, where the radiant barrier installation stopped at the last work day. 6 feet over, there is no barrier yet, and it is hot, just moving over to that part of the attic. I laid the thermocouple on top of the 4" of insulation between the attic air and the ceiling below. The top of the insulation was sitting at 105º. That insulation is separated from air-conditioned inside air by a 1/2" sheet of drywall.

No wonder our old air conditioner couldn't keep up. It was working in a blast furnace all day. The new one, working under this radiant barrier, shrugs off 95º like water off a duck's back. I have GOT to get the rest of that radiant barrier in. Then, as promised: PICTURES! :D

Click to see full size:
My Paint skillz, admire them:

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