Batt Insulation….Exposed

We all know that insulation is important to keeping our homes and buildings warm in winter and cooler in summer. The most commonly used type of insulation is fibreglass batts that come in bags.

Is this fibreglass batt insulation effective? For the most part, no. The most critical aspect is if the insulation is properly installed and (here’s the kicker that’s often overlooked) that it is incorporated effectively into a wall or ceiling system. The fact that this insulation exists in your walls does not make it effective. In fact, an alarmingly high percentage of building envelopes (see my previous post on this) are not properly installed, making the insulation much less effective than the R-value of the product. More precisely, the biggest factor is air leakage and flow through the building envelope. Air leakage accounts for more heat loss than the effective R-value of insulation.

You can look at a bag of fibreglass batt insulation and it will tell you it is, for example, R20. In a lab, under ideal conditions, with no air flow and no moisture present, it will indeed perform at R20 – through the middle of a nice, perfectly fluffed-up batt. Exactly the kind of conditions that are almost NEVER found in the real world in an actual installation. In a real-life situation, batts are stuffed in tight spaces, pushed around pipes and wires, have gaps around the edges and end up inside a wall cavity that will have cold, damp air flowing into, around and through it. When batt insulations are compressed or encounter moisture (fog and high humidity anyone?) their effective R-value drops dramatically. Allow air to flow through or around them and the same thing happens – large drops in effective R-value.

Ahhh, but the modern “efficient” house is well air-sealed you say? And it has blower-door tests that prove the air-leakage is reduced? Let’s look at what, exactly, this tells us. Sure, the low air-leakage is a good thing, but what does the blower-door test really tell you? It tells you how much air is leaking past the air/vapour barrier. And where is this air/vapour barrier? In a typically constructed house, it’s up against the back of your drywall; yes THAT drywall that people will later poke holes through to hang picture frames, decorations, etc. So what it tells you is that only so much air gets past the drywall, however when you think about it, that means that cold air is flowing up against the drywall, creating heat loss. If it’s getting to the drywall, that means it has to go through and around the batt insulation, and we just talked about what that means – dramatically lowered effective R-values in your walls.

It is for the above reasons that I will not use fibreglass batt insulation in a building. It is an outdated, ineffective way to insulate a building and it is time we retired it.

In a future post, I’ll discuss other types of insulation and wall systems, including my InnovaWall System, and how they work.

Until next time.

3 responses to this post.

  1. […] This post was mentioned on Twitter by Andrew W Alcorn, Andrew W Alcorn. Andrew W Alcorn said: Batt Insulation….Exposed […]


  2. Posted by Cdn Reader on February 15, 2011 at 3:54 pm

    I always wondered about all those holes we make in walls and whether they compromised the vapor barrier. This confirms my suspicions. I’ve already changed my mind about how to insulate the section of wall we need to replace!


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