GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted
Best Practices

Getting Good Results from Fiberglass Batts

This less-favored insulation type will do a good job of slowing heat loss, if key details are attended to during installation

Properly installed fiberglass insulation completely fills the cavity. It is neatly cut around ventilation openings and electrical boxes and split to surround wires. Source: Department of Energy

You didn’t want to use fiberglass insulation on this project. But you’re trying to avoid spray foam because of its outsized embodied emissions. You got a couple of bids for net-and-blow cellulose, excited by the carbon-storing capabilities of this recycled material. One bid was really high; it seemed like the contractor wasn’t interested in a small job like yours. The other was reasonable. But that contractor couldn’t get there for two weeks, which would mean losing your spot on the drywaller’s schedule. So here you are in aisle 18 of the big-box store, questioning your green credentials and hoping you can get your dolly through the parking lot without running into anyone you know.

An anecdotal truth

Fiberglass batts have a bad reputation among energy-conscious builders, with some justification. Compared to other insulation types, they are particularly susceptible to installation defects. A lack of proper training and slipshod work practices means that most batt insulation performs well below its rated R-value.

Despite their shortcomings, fiberglass batts remain the most popular insulation product in U.S. homes. They’re inexpensive, readily available, and don’t require special installation equipment. Compared to spray foam, foam board, and even mineral wool, they have lower emissions associated with their manufacture.

These considerations mean that sometimes, using fiberglass batts makes sense. Once that decision has been made, how do we get the best possible result? In this article, we’ll walk through best practices for product selection and installation. We’ll focus mainly on wall cavities but will also cover floors, attics, and cathedral ceilings.

Reasons fiberglass batts underperform

Standard-density fiberglass batts have a nominal R-value of about 3.8 per inch of thickness. Higher-density batts can provide about R-4.3 per inch. These numbers bracket the same general range as cellulose, mineral…

GBA Prime

This article is only available to GBA Prime Members

Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.

Start Free Trial

One Comment

  1. Expert Member

    Another technique which helps, (but does cost more time and materials) is to run all your horizontal wiring runs on the bottom-plate, and the vertical ones on the side of the studs, with none bisecting the bays.

    I just insulated a 900 sf workshop with fiberglass batts. I tried to be diligent, but doubt even a charitable observer would call it a grade 2 installation.

Log in or become a member to post a comment.



Recent Questions and Replies

  • |
  • |
  • |
  • |