‘Red Flag’ for the insulators: Poor batt install will waste energy and act like a bad marketing lightning rod until it is fixed or covered up.
Fiberglass batts are one of the easiest types of insulation to install poorly, so finding examples of bad batt installations on job sites is like shooting fish in a barrel. Except that it is a lot less messy than shooting fish in a barrel, with fewer chances of ricochet.
The discouraging part is that professional insulators ought to know how to stuff a batt in a wall cavity and make it work. Did a high-school kid do this?
Why does this matter?
If you want to get an Energy Star rating, then you need to make your insulation perform well. Fiberglass batts are designed to work perfectly when they perfectly fit the cavity that they are installed in (the test cavity is typically built to fit the batt, rather than the batt being cut to fit the cavity -- in a laboratory somewhere, rather than on a construction site...).
In order for batt insulation to work as expected, it must be installed perfectly. A 2% leakiness penalty can cost you up to 40% in performance. Pretty shocking, huh? If you see this kind of sloppy batt installation on one of your job sites, get it fixed before the drywall goes up.
How to do it right:
1. When installing batt insulation, make sure that the batts exactly fit the cavity they are going into – not too tall, short, wide, or narrow. That means framing like a pro -- lay out the studs accurately and nail them on layout.
2. Cut the batts to the correct length, If the stud cavity is shorter than the 8-ft length of the batt, use a template to cut length accurately.
3. Split batts instead of tucking them behind or in front of cable, tubes, and pipes. Cut around electrical boxes rather than tucking excess insulation behind the box.
4. Stop air from leaking into the wall cavity -- seal holes for pipes and wires on the inside and outside surface of the wall. Consider an air sealing system, like Owen's Corning EnergyComplete or a skim coat of spray foam to stop air.
The batts in this photo are too big in both directions, which means that the wrinkles will make air pockets in the stud cavities. These air pockets will allow convection currents within the stud cavity -- the outer surface will be a different temperature than the inner surface, and the tops of the cavities will be warmer than the bottoms.
Because fibrous insulation such as fiberglass works by trapping air, these convection currents will sabotage the fiberglass' ability to do its job: to slow the flow of heat.
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