If you’ve looked into insulating your home lately, you’ve seen that there are numerous facts and figures to be taken into consideration. The insulation industry itself cannot agree about the safety of some of its products and their insulating values. For an industry so well-established, and products so well tested, it may be surprising to learn that, except for lightweight urethane foam, the insulating materials used today were commonplace 20 years ago, and most of them long before that. Even the latest installation techniques are now over twenty years old.
So what’s the bottom line? All types of insulation’s work, but some work better than others in specific situations. This is always been true. What has made insulating more complicated today is the fact that building homes has become more complicated. While it’s agreed that sealing our homes against the elements increases are comfort levels and lower fuel bills, the improved insulating techniques have brought new worries like sick house syndrome and structural rot. Insulation and vapor barriers can cause these problems, but they can also help solve them. To understand about insulation you first have to understand how heat moves.
Whenever you find two areas of differing temperatures, you’ll find heat transfer, the hot moves to the cold. In a home this transfer takes place in three ways.
- It takes place by heat conduction through the materials your home is made up.
- It moves by convection, that is by currents of air within the house, the attic and wall cavities.
- Heat leaving your home by air leaking in of out through cracks, gaps and holes in the structure.
Insulating materials control the transfer of heat by slowing down the rate at which it moves through the homes envelope. R-value is the rating used to indicate the materials ability to resist the flow of heat. The half-inch drywall that usually covers interior walls as an R-value of approximately .4, but typical fiberglass insulation rates at 3.5 per inch or R-12 for a wall with a 3 1/2-inch cavity.
Filling your walls with adequate insulation is only part of the solution. Air infiltration through openings in the house envelope can account for 30 to 40 percent of a typical homes heat loss. Today plastic vapor permeable house wraps like Tyvek are typically used to cover the exterior of the home reducing the draught factor, as well as caulking and spraying foam into gaps around windows, doors and around holes in electrical and plumbing entrances.
A typical family of four generates 2½ gallons of water vapor every 24 hours through bathing, cooking, washing clothes, etc. This moisture, like heat moves from warm to cold areas, and the colder it is outdoors the greater the outward pressure. This natural migration can pose real problems for today’s moisture vulnerable building products. Water vapor moves through ceilings fairly easy, without doing much damage, but walls are closed and are more likely to trap moisture. Even a little dampness can degrade the R-value of most wall insulation. And when the vapor condenses it can rot structural members. To prevent moisture from entering the wall cavities, builders use vapor barriers. Kraft paper or four faced insulation slows moisture penetration and is a good choice in moderate climates with no more than a few really cold days. In northern states however, vapor impermeable polyethylene film is installed on all exterior walls just under the drywall. Except in a few very cold locations, plastic vapor barriers are not usually recommended on ceilings. Sealing a house completely not only traps water vapor inside but also harmful gases that may be present, like formaldehyde, radon or carbon monoxide.
Types of Insulation
Fiberglass and rock wool are considered mineral insulation because they’re made, at least in part, from sand or rock. Since the ’50s fiberglass has become the more popular of the two and, it now dominates the entire insulation market.
Fiberglass comes in two forms, batting (blanket type) and loose fill (for blowing in). Batting is available with a kraft paper or a kid aluminum foil glued to one side to serve as a vapor barrier. Normal thickness or depth are 3 ½ inches and, 5 ½ inches, six, eight and 10 inches ate available.
Fiberglass batting is made in various R-value’s; they are determined by alternating the density or fiber length. A 3 1/2-inch fiberglass batting for example is available in R-11, R13, and in R-15 versions with different pricing of course. Fiberglass batting is also available encapsulated in a plastic sleeve type bag, this makes application easier but does increase the cost by 15 to 20 percent.
Loose fill fiberglass is designed to be blown in. The traditional place for loose fill is in the attic and closed wall retrofits, in some cases it is also blown into open walls in new construction when remodeling. Known as blown in blankets the fiberglass is blown into stud cavities through holes in a polythene sheet stapled to the studs. Blown in blankets have three times the density of batting and are better at slowing convection. The R-value is approximately 4.1 per inch. Blankets require more work to install and usually you will have to pay 30 to 50 percent more.
Cellulose is made from ground up newspapers and other recycled paper products, with boric acid added as a fire retardant. By its nature, cellulose has greater density than fiberglass which makes it more resistant to air filtration and convection currents. Its R-value is around 3.7 per inch, it is the most affordable type of insulation. Like fiberglass, cellulose has been used for decades in well in attic and retrofit wall insulating. Like fiberglass, it can be blown into open cavities in new construction. In this type of application cellulose contains adhesive. When water is added, it can be shot into the cavities by machine. Any excess thickness or over spray scraped is then scraped away. Wet application cellulose makes a very tight wall tighter than fiberglass for loose fill cellulose, with an R-value of approximately 14 in a 3½-inch cavity wall.
Insulating rigid foam boards are made of either expanded, polystyrene (White in color), extruded plus tiring, (usually came to blue yellow or green). Foam boards range between R-4 and R-7 per inch and are available in many different sizes, the most common being 4x 8. Foam board is intended as exterior sheeting and is usually covered with a paper, plastic or foil skin.
Spray in place polyurethane foam is excellent at sealing gaps or cavities completely, stopping convection and infiltration of air. Polyurethane foam also boasts the highest R-value of any insulation delivering approximately R-7 per inch. On the downside, it is very expensive, modified lightweight urethane foam can also be used, sold under the trade name Icyene, this foam is applied like urethane, but water is used as a propellant. This foam remains soft and flexible when set, which means that can expanded and contract with the structure. It’s been thoroughly tested and produces no detectable vapors after 30 days; it is a good choice for those with chemical allergies. This foam can also be used in the walls of existing homes. Its R-value is less at 3.6 per inch but it does seal gaps or cracks. Spray foams are vapor impermeable, cutting down on the need for vapor barriers.
If you’re thinking of adding insulation to your existing homes but are unable to do it all at once, prioritize from the top-down. Heat rises and it makes sense that you’d lose more heat at the ceiling than at waist level. Even if a house is un-insulated, six inches of attic insulation will pay for itself in his little as a year, and will also improve the comfort level dramatically. After that the law of diminishing returns comes into play. Another six inches may take four to six years to pay for its self, and not noticeably improve the comfort level.
The effectiveness of the first six inches in the attic means that you are now losing relatively more heat for your walls than before, the next investment should be insulating the walls, including the rim joists. After this it’s time to focus on the windows, which are always the weak link in heat loss and will now be more vulnerable to condensation.
Replacing windows can be very expensive as well as having a long payback period. Caulking around the windows exterior trim, replacing the weather stripping around the sashes and adding plastic window covering in the winter are low cost alternatives that can make a big difference. Once you have taking care of the windows, it’s time to return your attention to the ceiling. After adding insulation there, focus on the basement or crawl space walls.
Payback on Investment
What is the best method of insulating your house, what is the most cost-effective? These are questions are going to have to ask yourself, the main factors to take into consideration are A: the cost of heating and cooling your home. B: have the years you intend to live in your home. If your utility bills are low any do not intend to live in a house for more than a year or two, the cost of insulating may be more than you would pay in higher utility bills. The decision is yours.
NOTE: If you are insulating an attic that does not have a lot of headroom, consider insulating to the top of the ceiling joists and covering the insulation with a Radiant Heat Barrier (An aluminum foil blanket). This will increase the efficiency of the insulation by reflecting heat away during the summer and reflecting it back into the house during the winter. The big saving is that the attic remains accessible.