Gaines Group Architects
fiberglass insulation

You can find air leaks in your thermal envelope by looking at fiberglass insulation

I do a lot of energy audits for Harrisonburg Electric Commission, they offer them free to their customers. The problems I find in most houses are very similar and are caused by lack of building science understanding. Air leaks in your thermal envelope are the biggest source of comfort issues and wasted energy for heating and cooling. You can find air leaks in your thermal envelope by looking at fiberglass insulation. 

fiberglass insulation

Find places where your pink fiberglass is black and this is an air leak.

fiberglass insulation

This yellow insulation shows air moving through the wall from an unconditioned attic into a conditioned space. Stop the leaks and you will improve comfort and reduce wasted energy. It is easy to fix this kind of leak. You can remove the insulation and spray foam the cavity or you can cover the leak with a solid surface material and caulk the joints. These leaks add up quick and cost you a ton of comfort and money. You may hear from framers that you don’t want a house that is too tight. That is true, but you don’t want random air leaks around your house that add up to the size of a window. Control your air intake through your HVAC system and plug the air leaks in your home.

What do you think of fiberglass insulation? I am reevaluating my negative opinion

I am always looking for experts in the construction industry to discuss best practices. At Construct this year I met Andy McIntyre with Knauf Insulation. Our discussion went something like this:

Me: “Andy, great to finally meet you, I don’t have any use for your product.”

Andy: “Here are the many many reasons why you are wrong and should use my product on a regular basis.”

Ok, that is not exactly how the conversation went, but I am not stretching too much. Andy is an expert. I pretend to be an expert. We had a discussion, Andy gave me enough valuable information to reconsider my “expert” ideas about fiberglass insulation. I asked him to put in writing his reasons to continue our discussion. This is what he sent me. Let me know your thoughts:

“Not your father’s insulation: Today’s glass mineral wool insulation is a high performance, proven, sustainable product perfectly suited for green building. Today’s glass mineral wool products, in batt, blanket, or blown in form can achieve R 4.2 per inch, placing it as the highest performing non-foam material available. Glass wool insulation is comfortable to work with. Prior formulations with larger fibers and a Phenol formaldehyde binder (PF) had caused brashness in the product. In today’s products, PF has been replaced by bio based binders derived from corn.


Glass wool insulation is safe, and is no longer considered a possible carcinogen. No other building material has been as exhaustively tested as glass wool, aka fiberglass. It has been completely exonerated. Any claims otherwise are completely false, and misleading. Today’s glass wool is unsurpassed in sustainability. Featuring high post-consumer recycled content, today’s materials meet stringent Red List Free status, and have Environmental Product Declarations (EPD’s) available. Today’s glass wool products are comfortable to work with, offer proven high performance, and are sustainable.”

So, which insulation product on the market is the best for a high performance healthy house in your opinion?