Home Maintenance & Energy
UNL Extension — helping you turn knowledge into "know how"
The Right Insulation Options Can Meet Your Needs
Submitted by Lorene Bartos, UNL Extension Educator
Does your home have adequate insulation? Insulation works by having many tiny air pockets. These air pockets are not good heat conductors and therefore reduce heat conduction through the insulation. Insulation also reduces heat radiation and air convection within the cavities in which it is installed.
Improper installation, gaps, uneven installation, incorrect density, air convection, air leaks and water decrease the R-value of insulation materials. Seal air leaks in the interior and exterior of the building shell before insulating to increase efficiency.
R-value per inch is the resistance of a material to heat flow or movement. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness and its density.
Some insulation materials have an optimal density. If the density is less than or more than recommended, the R-value per inch will decrease. Adding denser insulation on top of lighter insulation in an attic or placing batts rated for one thickness into a thinner cavity will decrease the R-value.
Insulation placed between joists, rafters and studs does not stop or reduce heat flow through the actual joist or stud. This heat flow is called thermal bridging. This means the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation. Placing attic insulation to also cover the tops of the joists and using insulative sheathing on walls to cover over the studs reduces thermal bridging though the studs and joists.
Another factor to consider is whether or not the insulation components act as a vapor retarder. Avoid creating two vapor retarders in walls or ceilings. When water/moisture vapor moves into or through walls and ceiling cavities, it must get out. Perm ratings measure a materials resistance to moisture movement. The lower the rating, the higher the resistance to moisture moving through the materials. Any material with a perm rating of less than 1.0 is considered a vapor retarder.
Products with low perm ratings include aluminum foil, polyethylene plastic, vinyl wall coverings, asphalt-coated paper backing on insulation and some rigid insulations. Moderate perm ratings include kraft-paper backed insulation. Some building wraps stop moisture from entering through one direction of the product, but allows moisture diffusion back through to the other side to escape.
In our climate, if a vapor retarder is used at all, it is placed on the interior or warm site of the home. If you are adding insulation, do not place a vapor retarder between the two layers. Check local, area or state codes for any regulations concerning the use of vapor retarders.
Vinyl wall coverings, plastic coated surfaces and low-perm paint act as vapor retarders—try to avoid them as they reduce the ability of the wall surface to allow moisture in the wall components to escape.
Before purchasing a product, know the target insulating values for ceilings and walls, and which type of insulation will work best in each application—attic floor, walls, floor joist over a crawl space or crawlspace walls, etc. Nebraska has adopted the 2003 International Energy Conservation Code. Check local or state codes.
The approximate R-values for our climate, based on the U.S. Department of Energy recommendations, are:
-- Attic: R-49 to R-60
-- cathedral ceiling: R-30 to R-60
-- Wall cavity: R-13 to R-21
-- Insulating sheathing: R-2.5 to R-.6
-- Floor over unconditioned spaces such as crawlspaces, basements and garages): R-25 to R-30
-- Band joists or outside edges of floor frames: R-30
-- Slab (unheated): about R-6
The amount you are able to achieve may depend on existing or new home construction and other factors such as access. Check the product label to make sure the product is suitable for your intended application. Labels include a clearly stated R-value and information about health, safety, and fire-hazard issues.
Blown-in loose fill insulation bags should also be marked with an R-value and the amount of area the container will cover. Ask the contractor installing insulation to provide the product labels from each package. This will also tell you how many packages were used for the area to be covered. Attaching vertical rulers to the joists prior to installation will help you to assess the inches installed. However, some materials require a greater initial thickness to offset eventual settling or to ensure you get the rated R-value under a range of temperature conditions.
Correct installation of any insulation is extremely important. Professional installers should have a good understanding of codes, vapor retarders, air infiltration, ventilation, recessed lighting, water pipes and codes. The International Residential Code and other codes require maintaining a safe distance between fuel-fired equipment vents and combustible materials. The code requires installation of an insulation shield around fuel-fire equipment vents that pass through insulated spaces.
Avoid packing insulation around bare stove pipes, electrical fixtures, motors or any heat-producing item such as recessed lighting fixtures. Do not install insulation within three inches of recessed fixture enclosures, wiring compartments or ballast or above the fixture unless the fixture is labeled as suitable for insulation to be in direct contact with the fixture. Avoid covering or blocking attic vents.
In there is degraded or overloaded wiring or knob and tube wiring, contact a professional electrician to make the needed changes before insulating. National electrical codes do not allow loose-fill, rolled or foamed-in-place insulation around knob and tube writing.
For more information on R-values and insulating your home according to your zip code area, you can fine a computer program at http://www.ornl.gov/~roofs/Zip/ZipHome.html
For information on saving energy and conducting a do-it-yourself audit, go to http://hes.lbl.gov/
Now is a good time to check your home’s insulation. Correct amounts of insulation will help save energy and utility bills.
Contact InformationUniversity of Nebraska-Lincoln in Lancaster County
Web site: lancaster.unl.edu
444 Cherrycreek Road, Suite A, Lincoln, NE 68528 | 402-441-7180