How To Insulate Your Home
Insulation is a material that you probably don’t spend much time thinking about because it is silently buried in your walls and has no moving parts that need to be repaired. Then you get hit with subzero (or scorching!) temperatures, a three-digit electricity bill, or frigid drafts, and you start to think about it a lot more seriously. Your thoughts turn to whether it is worthwhile to invest the time and money to install it in your ceilings, walls, and basement. When you get to the store, you ruminate about which type, thickness, width, and density to purchase. And when you put it in place, you start to wonder just how good “good enough” is.
Manufacturers and installers of home insulation were asked which questions they were asked frequently—and which mistakes they saw the most. The following are six things they (as well as we) believe you should be aware of.
Air Bypasses Should Be Closed First and foremost, attics are one of the most straightforward and cost-effective ways to insulate a home. The effectiveness of home insulation will, however, be significantly improved if you first seal up air bypasses (Fig. A), which include areas around chimneys, plumbing vents, wires, interior walls, and exhaust fans — areas where warm, moist interior air escapes into the attic and is lost to the atmosphere.
As a natural phenomenon, heat has a natural tendency to rise and travel to colder locations. Air bypasses can impair the efficacy of attic insulation by 30 to 70% when these two tendencies are combined, as demonstrated above. By raising the present attic insulation and looking for dark patches of moisture or dust, you can discover where the bypasses are located. Alternatively, on a cold day, go up to the attic and feel for pockets of warm air, or use a stick of incense to check for drafts in the house.
Before you begin installing (or adding) attic insulation, follow these guidelines:
Closing air spaces around pipes, ducts, and electrical cables that enter the attic with caulk and expanding foam (the fire-resistant variety) is a good idea. Make use of the fire-resisting kind.
Strips of 24-gauge sheet metal should be cut and fitted between the brick chimney and the wood framing surrounding it. Caulk the joint where the flashing meets the chimney with high-temperature caulk to keep water out.
Install weatherstripping around the perimeter of the attic access opening, and then use screw hooks to tighten the hatch against the weatherstripping to prevent it from opening accidentally. Glue the firm extruded foam house insulation to the top of the hatch with a hot melt glue gun.
The R-value of the insulation can be increased by using proper installation techniques.
It is estimated that leaving 5 percent of a wall uninsulated will result in a 20 percent reduction in the overall R-value (resistance to heat flow). In order to correctly install fiberglass insulation, it is not necessary to spend much extra time (Fig. B). The most significant actions you can do are as follows:
Fill up the stud cavity from top to bottom and from side to side, starting at the top. When insulating walls constructed using standard 92-5/8-inch-long studs, acquire and install precut fiberglass batts that are 93 inches long and 15 inches wide to eliminate the need for guesswork. Cut the batts 1 inch higher and wider than the space you’re filling when you have to custom-cut them at wall corners and other locations, such as around windows and doors.
Divide your insulation in half so that half goes in front of electrical cables and the other half goes behind them. Insulation’s R-value is reduced when it is compressed.
Instead of compressing the batt around electrical boxes, cut a notch in the batt and tuck the cutout beneath the box. In order to assist prevent frozen pipes, simply insulate the cold side of the pipe.
You Most Likely Do Not Require Kraft-faced Insulation
Kraft paper, the brown paper front that is impregnated with asphalt and used on insulation, is no longer often used these days, thanks to advances in insulation technology. Initially, insulation was only an inch or two thick, with the attached kraft facing stapled to the studs to prevent it from sagging. In today’s world, insulation is so “full-bodied” and entirely fills stud and joist cavities that it prevents the walls from settling, even when the walls are deliberately vibrated in tests.
Kraft paper does serve as a vapor retarder, allowing interior moisture to move more slowly through the wall cavity and insulation than without it. In the long run, however, a continuous 6-mil plastic sheeting vapor barrier is far more effective, especially in high-moisture regions such as restrooms and other such locations. On horizontal or sloped surfaces, Kraft paper can still be used to temporarily hold the insulation in place while the insulation is being installed. Furthermore, when retrofitting insulation in the floor of a crawlspace (Fig. D), putting the kraft-faced insulation paper side up offers an acceptable vapor retarder for the crawlspace floor. Inflammable Kraft paper and its underlying asphalt glue should always be covered with drywall or other fire-resistant material to prevent them from catching fire.
The use of kraft paper (or plastic vapor barrier) on the inside side of the wall, rather than the outside side, is another significant consideration, unless in extremely hot coastal regions. In warmer climates, vapor barriers are frequently deleted or relocated to the outside of the stud wall structure. If in doubt, seek the advice of a local building inspector.
High-density home insulation has the potential to pay off.
The resistance to heat loss (R-value) of insulation is measured: the greater an R-value is, the more insulating value is provided by that particular material. Standard fiberglass insulation has an R-value of approximately 3.5 per inch of thickness (Fig. C), resulting in an insulating value of R-11 for 2×4 walls and R-19 for 2×6 walls for the same thickness. However, if you are serious about reducing your energy use, you can invest in higher-performing products. High-density fiberglass insulation, which has more fibers and air gaps per square inch than standard fiberglass insulation, can provide R-values of up to 4.25 per inch. Two-fourths walls are provided with R-15 insulation, while two-sixth walls are provided with R-21 insulation. High-density insulation is also available for use in ceilings and attics. Despite the fact that high-density insulation may cost you more and may require special ordering, it will provide up to 35 percent more insulating value per inch than standard insulation.
You can also cram 5-1/2 inch thick insulation into a 3-1/2 inch thick wall to raise its R-value, but the compressed R-19 batt will only provide an R-value of about 17, and it will make it more difficult to get the drywall to lay flat against the wall during the installation process.
What Level of Insulation is Sufficient?
The first three inches of house insulation that you apply to a bare ceiling or wall will result in significant savings over time. The addition of another 3 inches will boost energy savings, but not to the same extent as the previous 3 inches. Check out the insulation manufacturers association’s website, naima.org, for charts indicating the ideal quantities of home insulation to install according to the Department of Energy. Their suggestions are based on a variety of factors, including climate, gasoline costs, and other considerations. Adding more will result in a decreasing rate of return on your initial investment.
Even though the payback period for installing home insulation varies widely, studies have shown that the additional insulation pays for itself in reduced energy expenses within 5 to 10 years on average. In Minnesota, a typical repayment term may be five or six years, depending on the circumstances. Although the payback period in more temperate climates is longer, keep in mind that home insulation lowers air conditioning costs as well.
Attics and crawlspaces should be ventilated.
Because home insulation alters the way attics and crawlspaces “breathe,” it’s vital that you maintain or build adequate ventilation in these places (Fig. D). At first glance, it is strange to add insulation for warmth while simultaneously creating ventilation “holes” to allow cold air to enter. Instead of doing so, however, you are putting yourself at risk for moisture problems in your home.
When adding insulation to attic rafters and attic floors, it’s critical to provide at least 1 inch of continuous air gap between the insulation and the roof sheathing from eaves to ridge. Moisture is flushed out of the system through this air gap. It also contributes to the preservation of a “cold roof,” which helps to prevent the formation of ice dams in the winter and the destructive effects of excessive heat on shingles and the increase in cooling costs in the summer. The most common mistake that homeowners make when installing siding is to install it in such a way that it limits the passage of air at the eaves. Putting up affordable air chutes to keep the gap open is the most effective method of preventing this problem from occurring.
Crawlspaces that have been newly insulated require adequate ventilation as well. It is customary practice to insulate both the ceilings and walls of unheated crawlspaces, as well as the walls of heated crawlspaces. If there is no slab, a 6-mil polyethylene vapor barrier should be installed on the ground in both circumstances to prevent moisture movement. When installing ventilation, it is recommended that one square foot of ventilation be provided for every 1,500 square feet of floor area. In addition, see How to Install a Vapor Barrier in a Crawl Space for more details. When it comes to insulating crawlspaces and attics, there are regional variations as well as different codes and interpretations. Make an appointment with a local building authority to ensure that your home remains code-compliant.
How To Insulate Your Home 