FOR DECADES, WHEN INSULATING A HOME, IT HAS BEEN POUNDED INTO OUR HEADS
R-VALUE, R-VALUE, R-VALUE !
IN REALITY, R-VALUE IS NOT ALL IT'S CRACKED UP TO BE !
A HOME INSULATED WITH SPRAY FOAM INSULATION AT A LOWER R-VALUE WILL BE EASIER TO HEAT AND COOL AND SAVE YOU MORE MONEY THAN INSULATING WITH HIGHER R-VALUES OF FIBERGLASS AND CELLULOSE.
R-VALUE - A numerical value given as a materials ability to block heat transfer. This number is determined by applying a heat source to one side of a material and measuring how much heat comes out the other side. The higher the number the less amount of heat is transferred. This type of heat transfer being measured is CONDUCTION.
There are three ways heat is transferred or lost in a structure, CONDUCTION, CONVECTION and RADIANT.
CONDUCTION - Heat transferred or lost THRU a material.
Most insulating materials do ok blocking this type of heat transfer, as long as the conditions are perfect (no wind, no moisture, no radiant heat, no temperature change and no gravity). Fiberglass and cellulose insulation actually lose R-value over time. Both need to stay fluffy to retain R-value. The problem is that gravity takes over and eventually both fiberglass and cellulose compress and lose their R-value.
Also because of gravity, fiberglass and cellulose compact and drop inside the wall cavities. This leaves large voids at the top of the wall cavities and there is NO insulating value at all in these voids.
Spray foam insulation however doesn't compress much and sticks to the surfaces it is sprayed on. Thus keeping its R-value for a much, much longer time. Spray foam by the way has a higher R-value than fiberglass and cellulose.
CONVECTION - Heat transferred or lost THRU or AROUND a material by air movement
HERE'S THE BIGGY AND WHERE R-VALUE DOESN'T MEAN A THING !
In any structure this is the way most of the heat is lost. Insulated or not, warm air naturally rises and starts the air moving. When this warm air escapes thru cracks and small holes at the higher levels of the structure, cooler air is actually PULLED in at lower levels to replace the air lost. This is DRAFT EFFECT.
Fiberglass will let air pass thru it (fiberglass is used for furnace filters. It stops the dust particles and lets the air go thru.) Also there is no way possible to seal fiberglass to the sides of the framing members in a house. Air moves thru and around every piece of fiberglass installed.
Now the great thing about spray foam...as spray foam is installed, it is in liquid form and sticks to the sides of the framing members and other surfaces. Then it expands as much as 150 times its volume creating the foam, sealing every little nook, cranny and void. Extremely slowing down the air trying to leave the structure. No warm air leaving, no cold air coming in !
It is a whole lot more efficient for your furnace to reheat warmer air than to try and heat the cold air coming in. Your furnace runs less and saves you on heating bills. Also you don't have the cold drafts and cold spots in your home.
RADIANT - Heat transferred by means of electromagnetics (radiant heat from the sun)
An insulations ability to block this type of heat transfer is more about the insulations ability to DEFLECT the radiant heat. Also an insulations duty against radiant heat is geared more toward cooling a structure.
In the hot summer months the radiant heat from the sun can raise the temperature of a roof and attic space up close to 140 degrees even though the ambient air temperature outside is around 80 - 90 degrees. That temperature will eventually radiate down thru the ceiling and into the living space. Spray foam has great radiant heat deflecting properties (better than fiberglass or cellulose) especially when applied directly to the bottom side of the roof deck; it adheres to the surface and becomes a thermal break.