One of the hottest topics in energy efficiency and building science is “how should you insulate your attic?” Why? Simply put, the attic has more impact on your efficiency and comfort than any other single part of your home!
Let’s summarize why the attic is so important:
The attic is the hottest part of the house in the summer and is cold in the winter
Hot air rises up to the attic / cold falls drops into the living space
Moisture rises and accumulates in the attic
Central heating/AC systems and ductwork are often in the attic
In the first two posts of this overly wordy series, we saw a few ways to insulate an attic while avoiding some of the worst problems that can lead to moldy, rotten attics and roofs.
If you recall, the big problem is that moisture from the house rises up through the walls and all the little cracks around light fixtures, hatches, wiring, and the moisture condenses on cool surfaces. Over time, this will lead to mold growth and potentially, rotten roofs.
How do you know if you’ve got a problem? I’ll give you a hint – if you have ice forming under your roof like in this picture, you had better do something before you have to replace your roof!
In the first installment on attic insulation, I discussed why it can be dangerous to add insulation to your attic without air sealing the attic floor first. Moisture can slip through tiny cracks in the attic floor and lead to rotten roofs. Given this information, we walked through the process of finding and sealing all those insidious air leaks in your attic, some easy, some difficult. But finally, after fixing all these problems, you could lay more insulation down on your attic floor, more confident that doing so wouldn’t lead to a humid, moldy attic.
But what if there’s an easier way?
Whether you’re building a new house or retrofitting an older one, you can make life much easier on yourself by using professionally applied spray foam insulation that air seals and insulates in one shot. There are two ways of doing this, each with their own benefits and disadvantages. We’re going to review both methods. One is spraying foam on the attic floor, instead of using loose fill or batt insulation. The other is spraying foam under the roof deck. Continue reading →
Many of my posts come back to air sealing and insulating the attic. Why is that?
If you’ve done any searching about home weatherization, insulation, energy efficiency or related topics, you’ve probably come across the picture shown above. And for good reason – it clearly shows all the common sources of air leaking into (infiltration) and out of (exfiltration) your home.
One subtle part of the picture is that the size of the arrows represents the relative amounts of air leakage from each location. See all those big orange arrows going up into the attic? Those tell you that large amounts of warm air from your house leak into the attic during the winter. This is why all us energy geeks keep spouting about the importance of sealing up the attic before you waste you time on things like replacement windows, sealing electrical outlets, and so on. You can spend thousands of dollars and countless weekends working on all these other areas and it probably won’t improve your home’s energy efficiency as much as just focusing on your attic.
Insulation filters the air leaks from your house, showing you signs of energy loss
You might have noticed some black insulation in your attic or maybe around the perimeter of your basement, where the house rests on the foundation. What does this mean? Is it moldy? Wet? Why is the insulation black?
In fact, black insulation is the energy auditor’s best friend because it tells us where the problems are. In just a few minutes of looking around the attic, you can find the most serious air leaks from the house. Here’s why…