If you read my article last week, you know that most insulation materials don't stop infiltration, although it's commonly believed that adding insulation is the solution to a drafty house. That's only one of many limitations you need to be aware of with insulation. Another is that the quality of installation can greatly affect the performance of insulation.
When Version 2 of the ENERGY STAR homes program came out in 2006, RESNET updated the Home Energy Rating System (HERS) Standards at the same time. Both required a HERS rater to put a Grade - I, II, or III - on how well insulation was installed in house. Grade I is the best, grade III the worst. (Well, actually, uninsulated is the worst, but I'm talking about when you actually have insulation installed.)
A house could still qualify for the ENERGY STAR label with Grade III insulation in ENERGY STAR Version 2, but it took a hit in the home energy rating software if it wasn't Grade I. With Version 3 of the ENERGY STAR homes program, however, Grade I will be required in most cases. The only exception is in walls that have exterior insulated sheathing (foamboard).
So, you may wonder, what is it that determines whether an installation is Grade I, Grade II, or Grade III? There are two parameters that come into play here: Missing insulation (gaps) and compression or incompletely filled areas.
The photo above is a Grade I installation. It's in a modular home plant for a company that made the decision to build green modular homes, and the photo above is a big change from what I saw the first time I visited their plant (photo at bottom).
Notice that all the cavities are filled completely. The fiberglass batts are cut to exactly the size of the cavities they fill, they aren't compressed, and they fill the cavities completely. As you can see in the photo at right, the batts also surround the wires instead of being squeezed behind or in front of the wires.
According to the HERS Standards from RESNET, to get Grade I, an insulation installation should have only 'occasional very small gaps.' It can have compression or incomplete fill up to 2% of the insulated area.
I'll tell you right now, getting Grade I insulation with fiberglass batts is NOT easy. The photo above is one of only two fiberglass batt installations I've seen that have gotten Grade I.
The typical installation of batts is Grade III. The photo at left shows one that gets Grade III because of having more than 2% of the area uninsulated. In this case, it's an attic kneewall, and the insulators obviously didn't take much time to fit the batts properly to the cavities. Their job in most new home construction is to get in and out quickly.
The two sides of the other parameter, compression and incomplete fill, actually go together when a cavity is insulated with fiberglass batts. In places where the fiberglass is compressed, you're usually going to have incomplete fill in that part of the cavity. The photo below shows a wall with lots of compression, and is clearly Grade III. This photo is from my first visit to the plant of the modular builder that achieved Grade I six months later.
Grade I is definitely achievable, but it's difficult to do with fiberglass batts. To get their insulation contractors to do it, builders are going to have to pay a premium because it takes more time and attention to detail. Even then, I imagine it's going to be a constant battle. My friend Carl Seville, the Green Building Curmudgeon, went so far as to suggest the idea of banning fiberglass batts in his column at Green Building Advisor a few months ago.
If I were a builder of ENERGY STAR homes, I'd be looking seriously at other ways to insulate. Cellulose or other types of sprayed or blown materials are much easier to get Grade I installations with, though it's certainly not guaranteed. Although it's been all the rage in green building over the past few years, spray foam is not a miracle product.
With ENERGY STAR Version 3, new homes will definitely be better. The requirement for Grade I installation of insulation is one big reason for this improvement.
Note: Since I first wrote this article, ENERGY STAR revised the guidelines, and now assemblies can pass with Grade II insulation as long as that assembly has continuous insulation, too.
If you haven't read it yet, you can download our white paper on ENERGY STAR Version 3 now.