Is fiberglass insulation or blown in insulation the best?

Asked by Susan
Franklin, TN

We need to replace our fiberglass insulation under the floors due to excessive moisture buildup in the crawl space. Is there any reason not to replace with the same type of insulation?


Randy Potter

Answered by Randy Potter

Alameda, CA

July 1, 2010

The quick answer is blown-in insulation is always far superior in performance to fiberglass insulation.

There are several reasons for this, the primary one being that blown-in insulation, especially expanding foams, provide for a foolproof installation due to the nature of the way they are applied.

  • Expanding foams are blown in a liquid form which rapidly expands into every nook and cranny of the wall, making it virtually impossible to get a less than perfect application.
  • Fiberglass batts, on the other hand, are nearly impossible to get a perfect application, with over-compaction and voids being the norm, which then dramatically reduces the effective R-value.

Moisture problems?

The more critical issue is this -- is your moisture problem causing the need for new insulation? Certainly have your crawlspace looked at by a green professional to assess ways to reduce moisture and mitigate infiltration.

Another benefit of blown-in expanding closed cell foam insulation products is that they can provide a moisture barrier which will reduce future moisture problems.

Cost vs benefit

One thing for you to consider is cost vs. benefit. You will pay between 2 and 3 times as much for closed cell expanding foam as for fiberglass batts.

We generally think that this is a sound investment, however if you live in a house without ceiling or wall insulation and with old leaky windows then the extra money may be better spent elsewhere when it comes to renovations for an energy efficient home.

Would a home performance evaluation make sense?

Perhaps a home performance evaluation would make sense: a blower door test and thermal image will tell you where your heat loss points are and where it would make sense to spend the extra money.

If so, check Green Home Guide's Find A Pro directory to find an energy auditor near you.


For more information:

Read Andy Ault's Q&A "Do you recommend bio-based soy foam insulation?"

Also, check our home foam insulation Q&A to see what other homeowners and contractors are saying about closed cell vs open cell foam, etc.

Tagged In: insulation, spray foam, energy audit

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