Increase the R-value
The question only keeps total nerds awake, but if you’re concerned with how well the insulation in your attic is actually working, you want to pay attention. Allison Bailes, physicist at the always entertaining Energy Vanguard blog, explains it all rather nicely, with mathematics and impossible to dispute commentary. In essence he explains: “…if you see an attic with lumpy insulation, get in there with a rake and smooth it out. In the example I just worked out, you’d nearly double the R-value without adding any extra insulation!”
Another thing I see all too often is the mouse infested attic, where stampedes of mice trample down insulation into innumerable trails. In addition to mice (which I hate!), they ruin the insulating effect of your insulation. (How to get rid of mice will be addressed in a coming post, and surprise, your pest control person isn’t usually the guy that’s successful at getting rid of them.)
Pull down attic stairs
Allison also explains why pull down attic stairs can reduce the effectiveness of your insulation by as much as 25%. In addition to killing insulation R value, the cheap stairs might kill you. If you’re going to have one of these things, make sure it’s a good one that doesn’t collapse on you when you’re trying to put away the Christmas lights for the season.
So, all those DIY’ers dumping bags of insulation in the attic don’t do much if it’s not installed at a uniform and consistent thickness, and if you’ve got a pull down stair, it doesn’t do much of anything at all.