Insulating for A/C

[MiddleMike]

Originally Posted by Tofuball

I know when you insulate for heat, you want to start from the top of the house and go down, and ways to do that include properly insulating the attic, caulking and sealing around recessed lights, vents, etc, and working down from there.

My question is, is insulating for A/C simply the reverse?

You insulate the house as if you are insulating to save energy costs. There is no pre-defined "order of operation" I know of that cannot be hotly contested. Insulate the attic first for heat? Ok, fine, but then you don't seal the basement or insulate it, and that nice cool AC air you paid good money for quickly flows right down into the unsealed and uninsulated basement and seeps into the earth lickety split. Contrary to popular belief, you cannot ignore a basement in your insulating scheme because "earth is a good insulator". It may well be, or not, but once the energy is outside your cinder blocks all you're doing is keeping/retraining the heat/cool outside your house.

Insulating and sealing, ideally, would be attic/walls/basement, at once (or as close to once as you can get). R38 (for temperate zones) and then top it off with a good radiant barrier in the attic. Remember to seal every wire/pipe entry you find in all areas first (there are exceptions of course, chimneys you have to block around and bathroom vent fans you don't cover either), and don't forget to seal the sill plate area where the basement and house pad meet with a good 20 year caulk (highly important). Also ensure you have very good circulation in the attic, that your soffit vents are clear and that your gable/sill vents are open and clear and moving air through convection (or fan if need be). The next best thing to do is to add some kind of shade (artificial or natural) to all windows that are exposed to the sun for any length of time during the day. Exterior shade is far better than interior shade (curtains) since it stops the heat/radiant heat from ever getting in to dissipate.

Ideally you insulate where you can afford to do so, regardless of order of operation. Most folks pick the attic because it's the easiest to get to, then neglect the other areas thinking they've done their job. The energy consumption improves, sure, but not nearly as much as if they'd taken on the whole house holistically as they should have. A well sealed and insulated house with windows shaded to keep out maximum radiant heat can obtain 50% to 70% less average energy consumption than a normal mass production home like most people live in.

See here: http://www.builditsolar.com/Projects...nservation.htm

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