Perhaps, like me, you’ve wandered up to your attic on a hot summer day. As you climb the stairs it feels as if are assaulted by a wave of heat. Immediately you start to sweat. If you’re lucky, you’re just there to get something and retreat back downstairs. If you’re not, it’s going to be a long, hot, miserable afternoon.
But wait, your attic is insulated, right? You can see the pink stuff in the rafters. If that’s there, why is it still so hot? To answer that question, one needs to understand that there are three ways that heat moves from one body to another.
1. Conductive – when heat moves from one body to another through direct physical contact. The fiberglass insulation is directly contacting the roof. Check.
2. Convective – when heat moves from one body to another via some adjoining liquid or gas. The fiberglass insulation baffles the movement of air. Check.
3. Radiant – when heat moves from one body to another through electromagnetic radiation. For example, on a warm summer day, you can feel the sun on your skin when you are outdoors. The fiberglass insulation handles this by…..oh. It doesn’t handle this.
In fact, as the roof gets hot, the heat from the roof radiates into the insulation. At some point, the fiberglass absorbs as much heat as it can. At that point of saturation, it becomes a radiator itself. This explains why the highest portion of heat loss or gain in a house is through radiant heat.
Right now you might be thinking “Why bother having fiberglass insulation if it’s this useless?” Trust me, if you removed the fiberglass, the answer would be obvious. The fiberglass still prevents a good deal of heat gain.
So what’s a homeowner to do? Move to a cooler climate? That would certainly solve at least part of the problem but it might be a bit involved and I hate moving, myself.
Enter reflective insulation. This is a product that’s relatively new – having only been around for about the past 20 years. The whole purpose of reflective insulation is to deal with radiant heat. How it works is simple and obvious when you think about it. The reflective insulation has a shiny (reflective) coating. This quite literally reflects the heat waves back to their source. In the case of your attic, it reflects the heat back toward your roof and prevents it from coming into your attic. When used in combination with the fiberglass, your attic is insulated against all three types of heat gain.
It looks and feels like bubble wrap used in shipping but instead of being clear, it’s opaque with either a shiny front or a shiny front and back. The reason for the double-sided insulation (reflective on both sides) is to account for winter and summer. In the summer, reflect the heat toward the roof. In the winter, reflect it back towards the living area.
Once I installed the reflective insulation in my attic, I was shocked. The temperature in the middle of a hot summer day was about 15 degrees lower. Clearly that’s quite a difference when you have to be up in the attic working. But even more interesting is what difference that makes to energy costs. It just makes sense that if your attic is not as hot, you will spend less money in cooling costs. The studies that I’ve read show that the energy savings in the summer months can be as much as 46%. I’m looking forward to that.
And here’s a bonus money-saving tip: After you’ve installed the reflective insulation in your attic you can use the scraps for packing materials instead of bubble wrap.