Installation Guide

Floor Insulation:

How to Install Underﬂoor Insulation

Underﬂoor means the ﬂoor above an unheated crawl space or basement. Once the underﬂoors are properly insulated, you will

increase the overall comfort of your home because underﬂoor insulation provides valuable sound control and thermal control.

The procedure for installing insulation in underﬂoors is similar to installing ceiling insulation. Follow the installation tips below to

ensure that you do a professional job.

1. Caulk where wiring runs through the ﬂoor joists and around the top of the wall.

2. Gently press the insulation between the joists. If you’re using unfaced batts or rolls, allow friction

to hold the insulation in place (called “friction ﬁt method.”) If you’re using faced insulation, install

it with the vapor retarder positioned up toward the subﬂoor. This product would also be installed

using the friction ﬁt method. The vapor retarder side is installed up against the subﬂoor.

3. Expand the insulation to its full thickness in the joist cavity to insure complete coverage. However,

avoid compressing the insulation material, because compression will reduce its R-value.

FLOORS

The easiest and most effective method of holding insulation in place is to use straight, rigid wire fasteners (preferably

galvanized), with pointed ends. The fasteners are made for joist spacings of 12, 16, 18, 20 and 24 inches, and may be used against

wood, metal or concrete. The fasteners, which are slightly longer than the joist spacing, are placed by hand between the joists

and bowed upwards into the insulation, causing the insulation to be in contact with the subﬂooring. Install the fasteners so

they hold the insulation in contact with the subﬂoor but avoid unnecessary compression. Spacing of fasteners is as required to

prevent sagging of the insulation, normally 12 to 24 inches apart and not more than 6 inches from ends of the insulation.