Disclaimer: while I think all the information presented here is accurate and scientifically valid, you are advised to consult a *professional before changing your home. This article covers just one component of your home. Your specific home may have conditions that override the comments contained herein.
*By professional, I mean an experienced building scientist, not your local carpenter or roofer or even a structural engineer or architect. While many of these people are artists in what they do, most have no training in building science or engineering and cannot be trusted to properly design a roof assembly. Likewise, you wouldn’t hire a building scientist to swing a hammer and build your roof! Cathedral ceilings are very popular – they give rooms a feeling of openness and an added aesthetic dimension. At the same time, they are responsible for a variety of building problems and homeowner heartbreak. What causes these problems and how do you avoid them?
There are a variety of climate zones. The south-eastern United States is hot and humid, while the north east is cold. The mid-Atlantic states, where I live, is mixed – during the summer it is hot and humid, during the winter it is cold. The south west is mostly hot and dry and the northwest is moderate in temperature but very humid! Each of these climate zones has its own particular building details. However, all must follow the laws of physics.
Physics tells us that moisture moves from areas of high humidity to areas of low humidity. If it’s more humid outside, moisture wants to come in. And when it’s more humid inside, the moisture will move toward the outside. Simple!
Signs of moisture and air flow in fiberglass insulation
When you climb into an attic and see this, you know something is seriously wrong. In fact, if your home isn’t very old, your insulation should be clean like when it was installed. The reason you get black insulation like this is because air and moisture are moving through the insulation, and it’s acting like an air filter.
The reason I’m showing you this picture is because it’s an example of the wrong insulation being used for a job. I feel pretty strongly about this because I’ve seen numerous homes where fiberglass has been installed in open walls like this and in almost every case, the insulation was seriously compromised – it was buckling under its own weight or simply falling out of the wall cavity. Or, in cases like this, it was hiding a big hole in the wall that should have been air sealed.
Let’s walk through the different insulation types and compare their main attributes: R-value, ability to reduce air movement, suitability for retrofit applications, and other characteristics.
In part 1 of this series, I gave you an overview of the different insulation materials and the various forms they come in. This article covers where insulation goes and why. Knowing this helps you understand why you’d want to use a particular type of insulation for specific applications in your home.
Where do you use insulation?
On the attic floor
In attic cavities
On an attic knee wall
On the attic ceiling
In the walls
Around the windows and doors
Around pipes and other holes in the wall
In the basement and crawlspace ceilings
On the basement and crawlspace walls
Under the slab
Outside the foundations
Each of these areas really deserves an article of its own. In fact, if you look on the Building Science website, you’ll find highly detailed articles doing exactly that. If you want to go straight to the source, consult these references.
Let’s look at some photos to get an idea of several of these cases…
When you insulate your house, you’re going to be confronted by a dizzying array of choices. How do you know which one to use? How much do they cost? Are some better than others or is it all hype? In this article, I’m going to do my best to sort through the options and help you make sense of them. Be warned – there’s a LOT of material here, so I’m going to have to break this into several articles.
First, let’s survey the types of insulation that you’re likely to encounter. I’m also going to provide links where appropriate.
This list is long enough. There are other insulation materials that have been used over the years, from vermiculite to horse hair to rice hulls to straw bales, but I’m not going to touch on anything that isn’t commonly available in the United States. Sorry!
Before we go into analyzing all the details of insulation materials, let’s spend a moment defining the basic characteristic of insulation – the R-value.
The typical attic hatch is drafty and improperly insulated. Fixing it can reduce the energy loss of a room by half. This afternoon project is simple and cost effective providing results you can enjoy year-round.
A properly insulated attic is supposed to have about R-40 insulation everywhere. This means that the insulation reduces heat loss by a factor of 40 – pretty simple eh? That also means, R-20 roughly equals twice the heat loss as R-40. R-10 is four times the heat loss and so on.
So what’s the R-value of an area of ceiling with no insulation? As it turns out, bare sheetrock on the ceiling has an R-value of about R-1. This means that every square foot of uninsulated ceiling loses about forty times as much energy as a square foot of properly insulated ceiling!
Put another way, if you have one square foot of uninsulated ceiling, it’s losing as much energy as forty square feet of normally insulated ceiling. So what happens when you have a hundred square feet that are uninsulated, like in this photo? Well, the energy loss from this section of attic are about what the energy loss of a 4,000 SF attic would be!
The take home message is – details matter! Every square inch of your attic should be fully insulated. And if you’re an electrician, take the time to put insulation back carefully after you’re done running wires in the attic. If you don’t you’re basically robbing your customers.