Insulation drastically slows the migration of heat with thermal barriers and air seals. A thermal barrier prevents heat from traveling through walls and ceilings, often using materials that trap air to resist heat conduction. This resistance to conduction is known as R or R-Value. A higher number indicates better resistance (see below for a detailed explanation).
Air sealing prevents the movement of air though gaps and crevices. Air sealing is particularly important around doors and windows where gaps may exist between frames and wall structures, but the structures of homes and buildings are rife with small openings. Such gaps allow air to leak in and out of your home, carrying heat along with it.
When we talk about R-value -- usually insulation -- we're talking about a material's ability to resist heat flow. The R-value of any material measures how well a material resists the transfer of heat if the temperature on one side of it is higher than on the other side. The higher the R-value, the better the material insulates.
Most people think R-value is important because it keeps our homes warm in the winter. But as the spring and summer comes and with it, the warmer weather should we forget about it until the fall? Well, that depends. How warm does your house get in the summer? Just as insulation's R-value protects our homes from heat loss in the winter, it also protects it from cool loss in the summer, and we can't go losing our cool!
We need to make sure our homes are properly insulated, so they can retain the cooler temperatures inside, and keep the heat outside. If not, our air conditioners will work overtime, which isn't good for the environment . . . or the wallet.
So what kind of insulation gives you the best R-value? I wish there were a clear answer, but there are a lot of things that affect a material's R-value. Number 1 is the thickness and density of the material. But this, of course, changes all the time, for every single job.
For example, batt insulation usually has a rating of 2.5 to 3.5 per inch. Multiply that by the number of inches your contractor will be installing, and you'll get the total R-value of whatever is being insulated, whether it be a wall, floor, roof, or attic.
Does thicker mean better? Again, it depends on the specific material and brand your contractor is using, and how that material is applied. Let's look at batt insulation again. Batt insulation is usually made from fibreglass or mineral wool. Within it, there's also a lot of trapped air. This air actually adds to the insulation's R-value; it plays a huge role in the overall effectiveness of the insulation. That means that, if batt insulation is compressed, its R-value is going to decrease. That's why you never want to stuff as much batt insulation as you can into a wall. By crushing or pressing it, you damage it. And that means you're wasting your money.
Can you have too much insulation? The answer is 'yes,' especially in the attic. Loose fill or blown-in insulation has an R-value of about R3 to 4 per inch, around the same level as batt insulation. It's what most contactors use to insulate attics, and it's crucial that a professional installs it. Why? Because non-experts tend to randomly fill in the attic space, covering the soffit vents and cutting off the ventilation in the attic. Or some pile it so high, it fills the entire space, not allowing for air movement. If there's no airflow in the attic, we've got big problems. This will lead to ice dams on your roof and downspouts, which will start to damage your roof. So more is definitely not better.
R-value is a helpful indicator, but it doesn't tell you everything. For starters, R-value performance tests assume there's no air movement. What does that mean? No matter how high a wall's R-value, if you don't protect it properly against drafts, the R-value has no value.
Every home renovation or construction will, or should, have different R-value targets if insulation is going to be used. And these will be different in different areas of the home. For example, you may want a total of R60 in the attic, but R28 for a living-room wall.