How to Insulate a House

©2006 Publications International, Ltd. Insulation should go between the floor an either the unheated crawl space or basement, between the ceiling and unheated attic (between the attic and roof if the attic is heated), and inside all exterior wall (including those adjacent to an unheated garage.

Inadequate insulation lets heating or cooling energy escape through your walls and ceilings. To keep this energy in, and to keep your heating costs down, you need to wrap the entire living area of your house in the proper amount of insulating material. Easier said than done, right? Well, in this article you will find the answer to all of your insulating queries -- where to insulate, what to insulate with, and how to tackle tough insulating projects. Let's begin with a little introductory information about insulation.

Where to Insulate

Insulation should go between the floor and either a crawl space or unfinished basement, between the ceiling and an unfinished attic, between the attic and the roof if the attic is finished, and inside all exterior walls including those adjacent to an unheated garage. The goal is to envelop the entire living area in insulating material.

Types of Insulation

Insulation requirements are defined in terms of the R-value. A material's R-value means its resistance to heat passing through it. The higher its R-value, the greater the material's insulating qualities.

©2006 Publications International, Ltd. Insulation is available in blankets, batts, and loose fill. Batts and blankets can have an attached facing that serves as a vapor barrier, or they can come unfaced.  Batts are easier to install in attics than blankets.

The insulation materials available to the homeowner include a variety of R-values. But since these materials also vary in terms of installation ease and flammability, selection is not merely a matter of picking the one with the highest R-value. The R-values of insulation for specific homes depend on local climate and building codes. To make an intelligent choice, you should be familiar with all the properties of the most common insulating materials.

Here are some things to consider about the different types of materials commonly used for residential insulation.

  • Vermiculite is low in cost, widely distributed, and easy to install. A loose-fill material, vermiculite can be poured in and then raked, or it can be blown into place. It is an expanded mineral type of material that is easily introduced into hollow spaces, but it has the disadvantage of packing down from its own weight after several years. As it packs down, it loses thickness and thus its R-value is diminished. In addition, vermiculite absorbs moisture, causing even more packing, and the water itself greatly reduces the insulating qualities of the material. Therefore, vermiculite is not well suited to wall applications, where its settling tendency would leave uninsulated voids at the top of the wall space. Vermiculite is fire resistant.
  • Perlite shares almost all the qualities outlined for vermiculite, but has a slightly higher R-value.
  • Fiberglass, a popular insulating material in wide distribution, comes in batts, in rolls called blankets, and in pellets for loose-fill applications. It is relatively inexpensive and usually very easy to install. Fiberglass itself is fire resistant, although the heavy paper facing frequently found on fiberglass batts and rolls is not fireproof. Fiberglass can also be faced with better materials that form a good vapor barrier, and it is available in an unfaced version for adding atop existing insulation. Its few disadvantages are that fiberglass is a skin irritant when handled and that it develops an odor when dampened.
  • Rock wool offers almost the identical qualities described for fiberglass. Even its cost and R-value are nearly the same. Like fiberglass, rock wool can irritate the skin when handled. About the only difference between fiberglass and rock wool is that rock wool does not develop an odor when wet.
  • Polystyrene, sold under the name Styrofoam, is a type of rigid board insulation and an excellent material to use in new construction. Because it is combustible, however, polystyrene cannot be exposed in its finished state. It can be covered with wallboard, exterior siding, or other material as specified by local codes, and since it is moisture resistant, it can be used below ground level, such as in a basement or crawl space. Polystyrene is often used around slab foundations and has even been used as a base to provide extra insulation under a poured concrete slab. Polystyrene boards -- which are very susceptible to gouges and dents -- are generally attached to the studs of new construction during the framing.
  • Cellulose is as fire resistant as fiberglass or rock wool; however, it offers a higher R-value and does not irritate the skin like those other types of insulation. Cellulose comes in rolls, batts, or loose fill. Loose-fill cellulose has a fine consistency, permitting blow-in installation through small access holes. However, make sure that the cellulose you purchase carries the brand name and treatment certification of a reputable manufacturer.
  • Urethane is a foam-in type of insulation that is quite effective when installed properly. Its R-value is very high, and it is very fire resistant. In addition, urethane foam possesses excellent sound-absorbing qualities. A foam-in material has the advantage of completely filling in any cavity to which it is injected, but it requires installation equipment that is too expensive for the average homeowner. Therefore, applying urethane insulation is not considered by most as a do-it-yourself project. In fact, even some of the professionals in the insulation business lack the knowledge and experience to do a competent job. If you do elect to use this type of insulation, be sure to hire a qualified contractor to perform the installation.

Caution: If the insulation you are replacing is asbestos, contact your local building department for further information.

©2006 Publications International, Ltd.With an unfinished attic floor, just measure the thickness of the insulation with a ruler. Then, if you know what the material is, you can estimate its R-value. If you don't know the type of material, take a sample of it to a reputable insulation dealer.

A floored attic presents a slightly different problem. If the boards are just butted together and nailed down, you can pry up a board to check. Usually the easiest place to start is at an exposed end at the attic entrance.If the flooring is tongue and groove, you can drill a hole (1/2 inch or larger) through the floor in an obscure corner. Be sure the hole is not over a joist and that you have a dowel of the proper size to plug the hole when you're finished checking the insulation. Use a flashlight to peer into the hole. If you can see that the insulation comes up to the flooring, you need only to find out what type of material it is. Use the hook portion of a wire coat hanger to retrieve a sample of the material.If the insulation doesn't come up to the flooring, lower a probe into the hole until it touches the top of the insulation. Mark the probe at that point and then withdraw it. If you know the depth of the cavity and the thickness of the flooring, you can figure out how many inches of insulation are presently under your attic floor.

©2006 Publicationis International, Ltd. If the boards of a floored attic are tongue and groove, drill a hold through an obscure  portion (not over a joist), and use a flashlight to see whether the  insulation comes up to the flooring. If it doesn't, lower a probe into the hold until it touches the material.

If you don't know the depth of the cavity, however, push the probe through the insulation until it strikes the solid surface below. Mark the probe at that point and then compute the depth of the cavity by subtracting the thickness of the flooring from the total depth indicated on the probe.

To measure the insulation inside a wall, you must again find an opening. If possible, use existing openings such as those around electrical outlets. Before you start probing, however, turn off the electric current to the outlet you have selected.

©2006 Publications International, Ltd. To check wall insulation, widen the opening around an electrical outlet.  Pull out some of the insulation with a wire hook.

Take the cover plate off the outlet and see if there is enough space to the side of the junction box to allow you to inspect the insulation with a flashlight. If not, widen the crack on the side opposite where the metal box is attached to the stud. Use a utility knife to widen a crack in wallboard; use a cold chisel if the wall is plaster. Be careful, though, to widen only as much as the cover plate can hide. Then inspect the insulation with a flashlight. If you don't know the type of insulating material used, pull out a sample with a wire coat hanger.

Now that you know what insulation you need and the type and quantity of the material already there, you're read to install. We will work from the top down, and start with insulating an attic in the next section.

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