New Construction – Fiberglass Insulation

Difficulty of Project:      Average Job Duration: 1-2 Days    Energy Savings: 40%

Fiberglass is the most common type of insulation used to date and is actually growing in popularity once again. 55% of newly built U.S. homes are choosing fiberglass according to a 2013 study. The reason? There are actually a few, and they could all drastically effect the homeowner and builder’s bottom line if not chosen carefully.

Did you know

Fiberglass was accidentally created in 1932 by Russel Games Slayter, when he shot a jet of air into molten glass, and small strands of fiberglass were all that remained.

 

How Fiberglass Compares to Other Insulation

The most important factor when it comes to home building is material performance. Whether or not the product works is always going to be the major deciding factor of choosing it. Take a look at this chart below to see where fiberglass stacks up.

As you can see, fiberglass comes in at the bottom of the list. This is a problem right? Not necessarily. Fiberglass can always be easily added to, which means you could match the r-value of other types of insulation without issue. The main issue with fiberglass is the fact that it has no air sealing properties. This is the area that spray foam insulation really shines, it has the ability to stop air flow (air loss) and thermally insulate at the same time. Now you might be asking yourself – so why shouldn’t I just go with foam? At the end of the day you could, and you would have a well sealed and insulated home, but this is where the cost factor creeps in.

 

Fiberglass vs. Foam Cost

When builders see the cost of foam this is when they usually start to look into other options. Typically on new construction, the cost of foam vs fiberglass can be 3-4 times as much, and can go even higher if there is a crawlspace or closed cell foam involved.

The cost of foam not only comes at dollar for dollar expense, but the expense of having downtime on the job. Fiberglass can take anywhere from 1-2 days, while foam can take 3-4 days or more. The main difference being, other crews can not be on the job site while foam is being sprayed. This holds up the sheetrock crew and everything following after.

 

But What About Air Sealing

At this point, it’s quite clear that fiberglass has no beneficial air sealing qualities while foam does. So what do you do? You use foam. Just not in the way you are thinking. Foam doesn’t have to be installed on the roof decking for it to work properly. It can be installed from the inside of the home, and yield all the same benefits. The technique most commonly used now, is to foam every penetration and air leak in the home, then install fiberglass insulation over it.

 

This is how the whole process works

Step 1: Caulk around entire bottom plate of home

Step 2: Foam every wiring, or plumbing penetration running through the top plates (interior and exterior)

Step 3: Install Insulation

Bonus: After sheetrock is installed, foam or caulk every top plate to sheetrock joint

 

Choose What Works For You

At the end of the day, there is no right or wrong insulation, it all comes down to needs and personal preference. Just remember, each method can get you the same final result, it’s just a matter of how much you want to put in to get to that same goal.