May 29, 2010 ~ House Parts: Insulation

OK, let's talk insulation.

The number one basic rule in creating an energy efficient building is 'first address the envelope'.

What does that mean? Well, when we say envelope we mean the outer shell of the house. The roof, all of the exterior walls. the bottom floor/ slab/ basement/ crawlspace (whichever the case may be.) So the first goal is to make that envelope a) very well insulated b) very well sealed by filling any holes, penetrations, nooks and crannies and cracks  c) protected from moisture infiltration and d) protected from air infiltration.

A lot of people's reaction to this is 'I don't want to live in a sealed box!' or 'Isn't it bad or dangerous to completely seal your house??' while it is true that a house needs to be sealed with care and that concerns about air exchange need to be addressed, you actually do want a well sealed home. AND just to ease your mind- addressing the air exchange in a well sealed house goes hand in hand with sealing the house. It is a given- like breathing- no architect or builder who builds well built, well insulated, well sealed houses will ever 'forget' to provide fresh air (unless they are a completely crazy or utterly incompetent and you will have noticed that long before you get to the building sealing stage! ) 

Basically I always use my swimming pool analogy. If you own a  swimming pool, you want to be in control of when the water leaves or enters your pool. If your pool was full of little cracks you would have no control over the water. You would have to continually fill the pool and constantly adjust and observe water levels, and all sorts of problems would occur in the area of the cracks (the cracks get bigger, deterioration of the liner occurs faster, dirt and critters collect there,etc, etc.) You want the same for your house. YOU want to control when and where air and moisture come and go. Simple. Logical.

Ok - back to the rules of the envelope list:  a) very well insulated b) very well sealed by filling any holes, penetrations, nooks and crannies and cracks  c) protected from moisture infiltration and d) protected from air infiltration.

The last 3 have to do with preventing the flow of air and moisture through the walls and are addressed through caulking and flashing and various tapes and sheet barriers (think Tyvek- tho we don't use Tyvek exactly). The reason you want to keep moisture and air from flowing back and forth through your walls is that air and moisture are the very things that cause building material deterioration, mold and mildew and dust (major allaergens), dust mites (which lead to spiders), insects and critters, etc. All are bad! bad! bad! for a house! never mind you the occupant. Remember the laws of physics: hot moves toward cold, wet moves toward dry. Air constantly wants to move through your walls and moisture travels on the air. We want to keep air and moisture from traveling through the walls. We want to control where and when it goes in and out ot the house and we will do it though ducts and vents and other specifically planned appetures. (AND we will talk more about how to do that in another post.)

One other thing that the flow of air and moisture do is that they reduce the functional R-value of your insulation.

SO now lets focus on the first item on the list - the insulation.

There are many types of insulation and they are all rated by one rating system and labeled with something called an R-Value. R-Value is a measure of thermal Resistance. The higher the R-value the better the insulation is at keeping heat or cool  inside your house at a steady temperature - this is because it is better at not allowing the heat to pass through it (either going out or coming in)...thus the term thermal resistance.

Most houses that were built in the post war era used fiberglass batt insulation (the pink stuff, the stuff you don't want to touch or breathe, the pink pather stuff, the stuff as one insulator I know says 'works GREAT as a filter! Cause the air passes right through it! which makes it not so awesome at thermal resistance' ) Usually we find houses of this era built with 2x4 studs so that means there is fiberglass batt insulation- about 3.5" thick slumping in the walls. Unless fiberglass batt is meticulously installed and unless it never aged and pulled itself off its staples overtime - its not really filling the wall cavity. Bottom line- its not the best insulator, it needs to be really well installed and almost never is, it falls and gets dirty over time, its bad for you to work with, critters don't mind it. We never specify it. We can't even believe people still use it as their primary insulation.

So what are the options. Well in the old days people used all sorts of things from straw to newspaper, to mud, tires, almost anything has been packed into walls. But we want something easily available, verifiably tested, regulated, readily installed, fire resistant, critter resistant, clean, mold and mildew free, etc. If we are going to make a good, well sealed, clean and healthy house we want insulations that work and work with our newer building methods.

The options we look at fall into these categories:

Blow in foams (Open cell or Closed Cell)

blow in 'other' (cellulose, fiberglass, cotton)

Batts (cotton or other)

Rigid Foam Boards (XPS, EPS, Polyiso)