What is insulation and why is it so important? Some of us may not realize the role it plays in making our lives more comfortable as well as more affordable. Even though you can’t see it, it’s there alright – or at least it should be – and it’s one of those things you have to factor into your budget when designing a building or room that will house people. There are several aspects to insulation and their different uses.
Insulation is broadly defined as a non-conductor that insulates a conductor against conducting bodies. These “conducting bodies” can technically be anything from sound to heat to electricity, but we’ll be focusing on heat in this article. Insulation can be used to prevent heat from entering your home, or to prevent it from leaving – or both. There are 3 forms or modes of heat transfer:
1. Conduction. – The transfer of heat due to a temperature difference from one body to another, ie, from your warm fingers to a cold glass of ice water.
2. Convection. – The transfer of heat due to the movement of heated fluids (in this case, the air).
3. Radiation. – The transfer of energy from one body to another, resulting in the latter increasing in temperature, which in turn transfers heat to its surroundings via convection.
Physics tells us that the denser a material is, the better it will conduct heat. Obviously, we don’t want any kind of heat conduction because that means it will absorb the heat that we don’t want it to, whether it’s summer or winter. So we need to find something with as little density as possible so as to minimize heat conduction. What comes to mind when you think of something with very little density? – Air!
This explains why insulation material is often “airy” and lightweight. There is a sensitive balance that must be struck in blocking the above 3 modes of heat transfer for insulation to be effective. The primary role of the “airy” types of insulation is to trap the air within itself, rendering it into trapped, stagnant air. This will essentially rule out convection as a viable mode of heat transfer, but will at the same time increase conduction compared to that of still air.
Many kinds of mineral wool insulation combine measures to counter both convection and radiation by packing the mineral wool within sheets of reflective aluminum foil. This is a considerably effective kind of insulation due to its dual properties. A “radiant barrier” is the reflective sheet and is used to counter thermal radiation.
Thermal radiation is a bigger issue in warmer climates so it’s wise to make decisions regarding what kind of insulation to install based on local climate, as well as other things like cost, etc. Thermal radiation is what can seep mercilessly through your roof and attic via the sun’s rays, pretty much turning your home right into an oven. Think of radiant barriers as large sheets of aluminum foil stapled somewhere under your roofing – either on the underside of your plywood or bulk insulation.
One thing to keep in mind about your radiant barrier is that it can often act as a vapor barrier as well as a radiant barrier. What this means is that moisture or condensation can get trapped between it and whatever other material nearby, potentially causing decay etc. The solution to this is to use perforated radiant barrier to allow the moisture to escape while at the same time fulfilling its original purpose. Vapor barriers are not insulators and care should be taken when installing these on the interior of your home.
Along the lines of moisture, think of condensation on a cold glass cup on a summer day. The warm air is cooled against the cold cup and turns into liquid. This is a simple law of science, but it holds true with bigger things like housing too. If you live in a colder region, condensation will form to the inside of your main insulation, whereas if you live in a hotter region, it will form to the outside – in either case, wherever the greatest temperature change is.
Ultimately, humidity has the greatest effect on how much condensation will form. But as a rule, install perforated radiant barrier in humid climates. Ok, back to insulation. Have you ever pulled furniture away from a wall to clean or whatever and found to your horror that there was more green than any other color? This often happens during the winter months when rooms are heated 20 or more degrees higher than outside temperatures.
Well, isn’t that normal for winter months you might ask. Yes it is. But the difference here is that the ugly green stuff grows when there is insufficient insulation within the walls. In other words, your interior wall is acting as the “glass cup” from the example above, the outside temperature the cold water, and the room temperature is the warm air that will yes, form condensation on your inner wall.
With proper insulation, instead of your wall being the “glass cup”, the insulation barrier will. Insulation such as glass wool typically comes packaged with a moisture barrier on one side and a perforated lining on the other. Be sure to install it with the moisture barrier on the room side of the wall, and the perforated lining on the exterior side. This way, humidity will be absorbed into the insulation and not build up as condensation.
Thermal resistance in insulation is measured as “R-value”. The higher the number, the more thermal resistance your insulation has.
R-value is dependent on several factors, the main one being that it is strictly only the value of the insulation it represents. In other words, it does not take into consideration the heat lost through “thermal bridges” such as wall studs, windows, doors, and even air exchange. Practically speaking, R-value can be doubled but still only result in a 20% or 30% reduction in heat loss due to said thermal bridges.
Another main factor is installation. Product R-value is rated on specific test conditions so don’t think you can do a shoddy installation job and hope to get the promised R-value! Stacking insulation vertically in a wall that is too wide for it to sit snug can result in some falling creating sections where there are 2 or more layers and sections where there is nothing. Insulation needs to be packed somewhat tightly with as few gaps as possible. It all adds up.
Animals such as weasels and ferrets are known to destroy insulation in their attempt to get up your walls and into your warm ceiling during the winter months. I have witnessed this first hand when I was replacing some walls. What used to be neatly lined insulation was reduced to little balls of mineral wool at the bottom of the wall, and there were bird bones and feathers everywhere.
I have also eye-witnessed a weasel disappear into a wall and by following its very audible rustling noises I could tell it was making its way straight up the wall – where there should have been tight insulation barring his way. One way to prevent this is to staple or somehow secure the insulation against your wall studs or ribbing, and leave an air pocket all the way up and down your wall.
This way, if you happen to get a weasel in there, it will have a clear path upwards and won’t have to destroy your insulation. However, the best solution is prevention. Do what you can to keep the animals out of your house. Find out where they are getting in and seal up cracks and broken vents etc. Animals are not magicians, they’re getting in from some physical entrance point and can be stopped from doing so. (See Attic Animals and Their Antics.)