Guest Author: Shawna Henderson Reprinted with Permission
What’s the use of a high performance envelope if it doesn’t make the grade?
In the US, there’s a requirement for HERS raters to determine if batt insulation has been installed properly. There are three ‘grades’ of batt installation, with a Grade 1 installation being the best and Grade 3 being the worst.
When batt insulation is installed properly, it touches all six sides of the cavity into which it is placed.
For walls and rim joists, that means it touches, completely, the top and bottom plates, the sides of the studs, the back of the exterior sheathing or rigid backing, and the back of the drywall.
For floors, it means that the insulation is in complete contact with the subfloor surface.
When it’s not installed properly, there are gaps and voids in the coverage, and insulation is compressed. These cause the rated performance of the insulation to go down.
Review some crib notes on conduction:
- Conduction is heat loss through solids
- Uninsulated surfaces lose heat primarily through conduction from warm side to cold side
- Conductive heat loss can be slowed down by isolating the exposed surfaces from temperature differences
- Insulation works by slows down the rate of conductive heat loss
- Insulation must be in contact with the exposed surfaces to ‘share’ it’s poor conductive properties
- Where there is no insulation, heat loss will continue until both sides of the surface are at thermal equilibrium
There’s a bunch of stuff that relates to convection and radiation too, but conduction is the key issue we’re talking about right here.
Inside those walls, it’s like the Wild West
The grading of batt insulation jobs is important, because too often (waaaaayyyy too often), compression, gaps and incomplete coverage are the norm. In the US, the insulation installation grade is a factor in calculating the HERS rating (HERS is the US equivalent of the EnerGuide for Houses). In the US, ENERGY STAR and and DoE Challenge Homes require a Grade 1 installation.
We don’t have any requirement for insulation installation to be graded in Canada. This is not to say that installers are not making the grade, or that builders are not requiring it. But it’s not part of our building code, and it’s not part of any requirement of any Canadian high-performance building program. Sure, there’s language around ‘proper installation’, but there’s no clear definition of what that means, nor is there a way to ensure that it has been done.
If you talk to any builder, Energy Advisor or other building science wonk (ahem), you will hear endless horror stories about crappy batt installation. It’s an itchy, grimy job and those who do it don’t get enough credit by half in my books.
Fibreglass batt insulation is still the most commonly used material in Canadian and US walls and floors. The fact that our high performance housing programs such as R-2000, ENERGY STAR for New Homes and the CHBA’s new Net Zero Energy program require higher levels of insulation but do not specify the standard to which that insulation is to be installed is a potential big black eye for the industry.
Why the black eye?
It’s not a mystery that, in combination with good air sealing, insulation that performs close to it’s tested R-value is what we rely on to create a high performance house. Not the framing, not the double, triple or quad glazing (windows are always going to suck), not the high-efficiency equipment.
The less-than-sexy, boring but itchy batt insulation.
So pack more insulation in there, nice and tight so it really touches all six surfaces, right?
When you compress batt insulation, it’s true that the R-value per inch goes up, but at the same time, the overall insulation value goes down, because now you have a skinnier batt than the one you bought that was tested and rated for a certain thickness.
The rated R-value that’s stamped on the batt is based on the manufactured density of the insulation. An R-19 batt jammed into a 2×4 cavity is going to perform more like a 3″ thick batt of R-11 in the same 3.5” stud cavity. Yes, that’s an exaggerated example, I know.
But we’re modelling energy performance based on the rated or nominal R-value for batt insulation, and what’s being installed in the field is a different beast. Compressed batts, incomplete coverage and no way to monitor or verify the quality of the installation affect the performance of the house.
HERS raters in the US actually has a calculation for this, my fellow Canucknuckleheads. They have to inspect the installation and record not only the compression but the degree of coverage as well for their final rating. Because, guess what? It impacts the energy modelling.
It goes like this:
Let’s say we have a 6.25” thick R-19 (regular density because it’s cheaper, right? That’s why they get put in) to put into a 5.5” wall cavity (nominal 2×6 construction).
Subtract the cavity depth from the thickness of the batt: 6.25 – 5.5 = 0.75”
Determine the percent the batt is compressed by dividing 0.75” by the thickness of the batt. 0.75/6.25 = 0.12, 12% compression
The initial R-value of the batt (R-19) decreases by roughly half the percentage of compression, so:
19 * 6% = 1.14
The R-value loss figure is then subtracted from the original R-value of the batt:
19 – 1.14 = 17.86, round up to R=18.
BTW – here’s how to achieve a Grade 1 batt insulation installation. You should study it, memorize it, devour it and spit it back out again on site, completely and perfectly. This is a great resource from NAIMA (the North American Insulation Manufacturers’ Association).
Also, all leading insulation manufacturers are able and interested in offering training to contractors and builders to ensure Grade 1.
Making the grade = performing well
Did I mention that the insulation grade is a factor in calculating the final HERS rating?
We’re looking at Net Zero Energy being incorporated into our building code here in Nova Scotia by 2022 — that’s five years from now. As we push forward to higher performance buildings, with higher insulation targets and requirements, we’re going to smack into severe problems meeting performance requirements if insulation installation is not up to par.
A house that is, on paper, marginally code-compliant for energy efficiency, or that is being rated on a performance path, might not actually be code-compliant or meet the required energy rating if it had the equivalent of a Grade 3 installation. Without having a way to gauge the effectiveness of a batt insulation installation, we’re not doing anyone any favours with increased performance requirements. Especially if the solution to reaching R-24 or more in a wall is to jam a +6” regular density (ie, less expensive) batt into the 2×6 cavity.
Many approaches to NZE and other high-performance targets rely on exterior insulation to eliminate thermal bridging and add the extra punch to the wall R-value. All of the houses in the recently completed pilot project on NZE houses funded through NRCan’s ecoENERGY program used exterior insulation. The aim of this project was to showcase ways in which production builders can reach NZE houses with little or minimal premium. Five builders and twenty six houses later, they’ve done it, more or less.
The exterior insulation diminishes thermal bridging substantially, and therefore reduces heat loss via conduction. To reach NZE however, the production builders relied on batt insulation within the cavity to account for 50 to 75 percent of the total wall R-value. Once again, if the batt insulation is not installed properly, the wall will not perform as it was modelled.
I am not pointing a finger at the houses or builders in this project and saying their insulation installations suck. Not at all, I imagine it’s the exact opposite on such a high-profile project. What I am pointing out is the fact that a fairly standard and economical way of creating a high-performance thermal envelope is still heavily reliant on the quality of the batt insulation installation and there is no regulatory mechanism in Canada that requires insulation to be installed to a certain standard.
It’s likely that the problems that stem from poor batt insulation installations will get exponentially worse as we get to tighter envelopes. Which means, that, on top of purchasing a house that doesn’t perform to the promised energy consumption target, homeowners will have building shells that could have significant conductive heat loss and condensation in the walls, and they will end up dealing with the resulting moisture damage and eventual rot.
As an industry, we need to come to grips with the fact that a high-performance house requires much more due diligence than we are currently required to carry out, and that’s right across the board. High-performance house building requires grading of insulation, blower door testing, and proper system commissioning. Without this due diligence, we simply cannot supply a well-tuned house, no matter how good it looks on paper or in our energy modelling software.
About the Author
Shawna Henderson is CEO of two companies: Blue House Energy, providing online training for the homebuilding industry, and Bfreehomes Design, providing design and consulting services for new construction and retrofit projects in Atlantic Canada and beyond.