Mixing Attic Insulation: Genius Move or Recipe for Disaster?

Most people don’t consider checking or inspecting their attic unless something goes wrong. Cold drafts in winter?  A/C not turning off in summer? Heater working overtime during winter? It is time to check the attic. Because within this area above your ceiling lies the key to comfort, energy efficiency, and lower hydro bills, which is proper attic insulation. 

But what if your attic has more than one type of insulation? Is that a problem? Or could mixing insulation types actually be a smart way to reach the needed standard of thermal resistance (R-value)? 

Briefly, what is R-value? And why should you care about R-60 here in Quebec? 

R-value is a measure of thermal resistance, in other words, how well the insulation resists the flow of heat. The higher the R-value, the better the material is at keeping heat inside during winter and outside during summer. In most of the regions of southern Quebec, R-60 is often considered the optimal thermal value for having proper attic insulation. 

But getting to R-60 isn’t just about piling insulation up there! 

Attic insulation comes in various forms: Fiberglass batts (Big, fluffy pink or yellow rolls), Blown-in cellulose (Recycled material), Spray foam (Expands to provide air sealing) ... 

Each type has its specifications. But what happens when you mix them? Is it Helpful or additional Headache? 

Pro: Achieving R-60 more affordably: Sometimes, topping up existing fiberglass or cellulose with a second type could be a budget-friendly way to hit R-60 without tearing everything out. 

Con: Airflow confusion: Some insulation types (like fiberglass batts) don’t block air well, especially in tight and problematic areas within the attic. If you install another insulation above it, you can end up with moisture traps and thus deteriorate the insulation’s performance.  

In addition, mixing materials can also get tricky with fire safety ratings and building codes—especially if you DIY your attic insulation job. 

If your attic looks like a nasty mixture of insulation materials from every decade, it’s worth having it inspected. At Systèmes Éconergie, our team of attic experts can assess your current setup, calculate your actual R-value, and recommend how to reach that comfy R-60.  

Need help inspecting your attic? Let’s take a look. No judgment, we’ve always seen worse.