Introduction
I would like to take this opportunity to welcome you. I've put together what I believe to be a comprehensive list of some of the more fundamental topics of residential home insulation. I've done so simply because there is so much controversy about it. I will not take a position on what I believe to be the best system, just share some of what I have learned over the years.In today's market place there are so many different kinds of products. It is quite hard to made an informed choice. Further, such decisions shouldn't solely be fueled by the pressures of contractors, sales people or manufacturers. I believe that with a little understanding of the concepts that drives the thermodynamics of a living space that such a decision can be made.
Some key issues at this time are based around information that has been gathered over the last twenty years. Whether fiberglass or cellulose insulation is best, a better question might be in what application is one superior to the other. The use of air/vapor barriers has come in to question of late. Hi-tech house wraps have grown in favor over their felt paper counter parts. New types of heating systems like radiant floor heat have come of age. Fresh air standards for tight house construction are also an issue. To vent or not to vent your attic is one of the hottest question today. We will take a look at the theory behind these systems and try to separate fact from fiction.
At this time, I feel It's important to emphasize that most systemsfail due to improper installation or a misunderstanding of the proper application of the system's components. In most cases only badly designed systems, installed correctly, will fail. I'm not saying you need to be a scientist to understand this stuff, you just need to do the best possible job you can at understanding and installing the parts of what ever system you choose to employ.
I would gladly enjoy reading your commits, positively or negatively. E-mail Me.
Fiberglass Insulation
Fiberglass insulation is made from mineral substances (hopefully some recycled glass) processed from a molten state to an incombustible fibrous form. This material is spun to create a hair like structure. Because this material is a "poor" conductor and coupled with the "trapped" air (which is also a poor conductor) between the fibers, it makes a very good insulator.
Facings Facts
Standard facings will burn and should not be left exposed. Residential facing should always be installed to the warm (heated) side of the dwelling for vapor barrier application. Vapor barriers must have a rating of 1 perm or less.Flame Spread, Combustion, and Federal Testing
Unfaced fiberglass blankets, Unfaced Metal Building Insulation, FSK 25 and blowing wool have a class "A" rating of flame spread of 25 or less and smoke developed of 50 or less in accordance with ASTM E84 test method. Unfaced fiberglass blankets, Metal Building Insulation, and blowing wool have been tested and have passed the requirements of ASTM E136 combustion characteristics and are considered non-combustible by major building codes. The federal specification of HHI-521F for mineral fiber insulation blankets has been canceled and replaced by ASTM C665.Sound Facts
Fiberglass insulation increases the sound transmission class (STC) rating when properly installed in building assemblies. It has been determined that thickness has greater value in sound control than density.
Airflow/Vapor Barriers
Inside
This one is a little "tricky" to explain. This barrier is supposed to stop the migration of vapor. They are made out of paper (which is impregnated with something like tar), foil (made from aluminum) and plastic. Do they work? I really don't know. I can fill a zip lock bag with water and it doesn't leak, so odds are they do. I have used 4 & 6 mil polyethylene as barriers. I do know that they stop airflow from one side to the other. If you install one you should install it to the warm side (heated side) of the structure. I can see this vapor/airflow barrier as being more important to install with fiberglass insulation then with cellulose insulation.
I've always installed unfaced fiberglass insulation in stud, rafter and joist bays when ever possible and applied a plastic air/vapor barrier over in. I've had no ill effects with this system to date.
Outside
This one too is a little "tricky" to explain. This one is supposed to stop airflow and let moisture out. For the longest time many builders used felt or building paper in varying weights (15lb, 30lb or even 60lb). Building paper has it's problems, it doesn't do a good job of letting moisture out. One could also say it doesn't do a good job of keeping air out either (this is a function of how well you install it). As a matter of fact for it to do a good job at either one, it gives up the ability to do the other. To prevent airflow it has to be installed very tight. If it's very tight moisture can't pass through it. If it's not tight, moisture can and so can air, get the point?In light of this the new technology is what some call the whole house wrap. One trade name is Ty-vex. There claims are that they keep air from migrating in, but still let moisture out. Whether or not they work in the very dynamic environment like a house, the jury is still out.
Notes
Ok from what we have so far, we can see a real concern about moisture "getting" into the wall cavity. The concern is that it will cause damage to the framing namely rot. The inside barrier is supposed to keep it from getting in and the outside one is supposed to let it out if it does get in (neat eh).
Does all this work? Well, that all depends on who you ask.
Continuous Ridge Venting
This is accomplished by first undercutting the roof sheathing about 2-1/2" to 3" from the ridge itself. You must not paper or shingle over this gap. Shown below is a picture of how the vent looks.
One important feature of any ridge vent is that it must not allow water to enter in! This is accomplished by different means by each manufacture. The "Killer" of any ridge vent is wind driven rain/snow. This is one of the components of a vented roof system. If you choose this type of system it's proper installation is imperative to it's success!Continuous Soffit Venting
This is accomplished by providing an unobstructed air way at the soffit . This is also a component of a vented roof system.
The idea behind this is that as warmer moist air exits through the attic ridge vent, cold air is taken in through the soffit vent. This is what is known as a convection current or chimney effect. The final component to this system is to supply a continuous airflow path from soffit to ridge vent.
Rafter Baffles (providing a continuous path)
The final part of the vented roof system is to ensure that a continuous path from soffit to ridge exists. You can accomplish this in a few different way. The most economical would be to install rafter baffles. They provide a continuous air path form soffit to ridge by not allowing the insulation installed in the rafter bay to come in contact with the roof deck. They usually provide about an 1-1/2" space for the air to flow through.Gable End Vents a No No in any System
This is an example of a bad idea. In my humble opinion there is absolutely no reason for ever having to install these vents. They really are very hard to get to work right. Why bother, you don't need them.
Note: For more on this subject CertainTeed was
a worderful site, if you have the time visit it.
The Chimney Effect
Ice Dams
Airflow Sealing
Blower Door Testing
Heat Energy Transfer
Radiation
The transfer of heat by radiation is self evident if you stand outside on a sunny day. You can easily feel the warmth of the sun on your skin. Solar radiation is transmitted in the form of rays called infrared waves. The actual way that energy is transferred by waves is a bit complex. It's worth mentioning here that we usually think of heat as being transmitted in the radiation process, strictly speaking this is not true. The heat of a radiating body is transformed, at the instant of radiation, into radiant energy. The heat from the sun, for example, is transformed into radiant energy and travels in that form throughout space; it is retransformed into heat when it strikes an object.The only thing that is important is that you understand that the energy can be transmitted through empty space, a vacuum (well almost anyway). This is different then conduction or convection in that both of these forms use an existing medium to transfer heat.
Note: Since heat is energy, it's important to understand The Law of Conservation of Energy. In it's simplest form it states that; energy can never be created or destroyed only transferred.
Conduction
Conduction is the ability of a material to allow the transfer of heat energy directly through it. How well a substance does this has to do with the electrical bonding of it's molecular structure. Substances with a 'loose" outer electron, conduct heat (and electricity) well. Metals are the best conductors of heat and electricity for this reason. We could use a spoon and hot cup of coffee to demonstrate this.... If you put the spoon in the cup and hold the handle you will slowly feel the handle "warming" up. It will eventually get quite hot! If a material possesses this ability it is commonly referred to has a conductor, if not, it is referred to has an insulator. Some good conductors are copper, brass and iron. Some good insulators are wood, cork, water and air. In homes that use steam or hot water heat baseboard or radiators, people sometimes confuse radiation as the method of heat transfer. This is not the case. The energy that is contained in the steam or hot water is transferred to the "radiators element" by conduction. These are usually made from cast-iron, copper or aluminum. How the heat gets from the radiator to warm a room is explained in convection.
Convection
The most common places for a convection current to occur is in masses of air (gases) and water (liquids). The medium, air or water, needs to come in contact with the heat source in order for the heat to be transferred. Lets take the radiator as an example. Once the immediate volume of air that surrounds the radiator makes contact, heat is transferred, you guessed it, by conduction. This air then begins to expand (the molecules of air move farther apart from another) and hence become less dense then the air around them.This air mass rises because colder air moves under and forces the column of warm air to rise. This colder air then makes contact with the radiator surface and heat is transferred once again, repeating the cycle. It's also important to remember that the expansion of air is a cooling process. As warm air rises it cools and "falls" to continue the current. This will continue as long as there is a heat source and some air.
Temperature
Most people believe that temperature is a measure of heat energy, which is caused by the frequency of molecular collisions within a substance. This is not the case. Air molecules are constantly moving. The speed of air molecules corresponds to their kinetic energy, which in turn corresponds to the amount of heat energy in the air. Air temperature is a measure of the average speed at which air molecules are moving; high speeds correspond to higher temperatures. In every day life we use a thermometer to measure the temperature of a substance.
BTU (British Thermal Units)
This is a measure of a heat energy. It is defined as the amount of heat energy needed to raise one pound (lb) of water one degree F. If you have one pound of water at any temperature and you want to raise it 10 degrees F. you must add 10 BTU's of heat energy to do it. Another system for measuring this heat energy is the Calorie. It is defined as the quantity of heat energy that needs to be added to one gram of water to rise it one degree C.R-Value
R-Value means the resistance to heat flow. The higher the R-Value the greater the insulating value.Hidden Heat
This issue might seem odd at first glance. Its major impact in relation to the "living space" comes in winter. The processes by which water changes "state", from liquid to gas and from solid to liquid are referred to as "Heat of Fusion and Melting of Fusion." In both case, although heat is constantly added to the solid or the liquid, the temperature of the solid or liquid remains the same. It seems to appears that the added heat has disappeared into the heated substance without changing its temperature. If heat is energy, it must be conserved, this hidden heat cannot be lost.Melting or Fusion
If heat is conserved, this heat can not be lost. To find out what happens to this heat, we must first consider the change in state at which a solid becomes a liquid. This change is called fusion or melting. In particular consider what happens to the heat that is absorbed by the particular solid, ice, it melts to become water. You could see this at home if you took some ice cubes and put them in a pan on the stove. Put a thermometer in the pan and see what it reads. No matter how high you turn up the flame, the temperature of the solution will not raise about 0 until all the ice is melted.Heat of Fusion
The above illustrates two important facts concerning fusion or melting. First, to melt each unit of mass of a solid like ice, a definite quantity amount of heat must be applied to it. Second, in crystalline solids like ice, although heat is added to melt the solid, the temperature remains the same during the melting process. The heat needed to melt one gram of a solid at its melting point is called the heat of fusion. The temperature at which a solid melts is called it's melting point. For ice, (which is something we see a lot of in winter) we know that it's melting point under normal atmospheric conditions is 32 degrees F. or 0 degrees C.It is a fixed quantity of heat for any particular solid crystalline substance but different from substance to substance. The heat of fusion for ice is 80 calories per gram. All this means that it takes 80 calories for heat to melt one gram ice at 0 degrees C. without changing it temperature!
Vaporization
The change in state of which a liquid changes to a gas is called vaporization. The temperature a which a liquid vaporizes under normal atmospheric conditions is called it's boiling point. Different liquids have different boiling points.This important to also understand that it takes a definite quantity of heat to change a give mass of a liquid into a gas. In the case of water that quantity is appro. 540 calories per gram. This means that once water reaches 100* C. an additional 540 calories of heat is need to change one gram of water to steam.
Condensation a Heating Process
As in the case of steam, if at 100*C. steam is allowed to cool, it will begin to change back to water at the same temperature (100*C.) In this process the steam is losing heat but, it's temperature remains the same at 100*C. The change in which steam turns back to a liquid is called condensation.Condensation and boiling take place at the same temperature. However, in condensation heat is being given up by a substance, while in boiling, heat is being absorbed by the substance. In the case of water, for every gram of steam the turns to water 540 calories of heat is released.
Evaporation a Cooling Process
The gradual change of a liquid into a gas without boiling. The molecules of any liquid are in a constant state of motion. The average speed of the molecules depends only on the temperature, but individual molecules may be moving at a speed far greater or far less than the average. At temperatures below the boiling point, individual molecules approaching the surface with above-average speed may have enough energy to escape from the surface and pass into the space above as gas molecules. As only the fastest molecules escape, the average speed of the remaining molecules is lowered; and since the temperature, conversely, depends only on the average speed of the molecules, the temperature of the remaining liquid is also lowered. In other words, evaporation is a cooling process; a drop of water placed on the skin feels cool as it evaporates; a drop of alcohol, which evaporates more rapidly than water, feels even colder.
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