The Foil vs. Paint Question:
There are two basic types of products on the market today being sold as "Radiant Barrier", Foil and Paint.
The effectiveness of a Radiant Barrier, RCC "radiant control coating", or an IRCCS "interior radiation control coating" are measured by their emittance value. (note: Emittance and Reflectivity should have a sum of 1.0 or 100%.) For products to qualify as a Radiant Barrier according to (ASTM) a material must have an emittance value of 0.1 or less. This means it will reflect at least 90% or 0.9, and emitt no more than 10% or 0.1
You want the emittance value to be as low as possible.
First lets look at RB Foil, while there are numberous manufactures and grades or weights available, they are all for the most part made of very thin sheets of alumimun, double sided and laminated with a polimer or skrim to increase their tear resistance. Weight is the common factor to measure the strenght of these products. The emittance value of most Foil Radiant Barrier products is 0.03 or 3%, reflecting 97% of thermal radiation.
Foil is stapled to the underside of the roof rafters or laid on over insulation, either method is okay because there is an open air space between the heat source and the Radiant barrier. But there are a few things to consider when choosing which application will best serve you. "see applications"
Now for Paint, If you will look at the specs put out by the ASTM even the best reflective paint products DO NOT qualify as radiant barriers. They have value ratings of the best being 0.195 all the way down to 0.90. What this means is the best in its class only reflects 79.5% and the worst reflects only 10% of thermal radiation. These results can be futher effected by how thick the paint application is, and some (not all) thin or cut their product to reduce material costs. (remember a radiant barrier must have a rating of 0.1 emmiting no more than 10% and reflecting at least 90% of thermal radiation)
Here is how the (ASTM) classifies "PAINTS"
Especially formulated coatings and paints are used in building applications to conserve energy. A large number of products called "radiation control coatings (RCC)" are used on exterior surfaces to reduce the amount of solar energy absorbed by the surface and transported to the interior. A second class of products called "Interior Radiation Control Coating Systems (IRCCS)" are available for use on interior surfaces to reduce heat transfer from the adjacent interior air to the coated surface. Consensus standards for both product types have been developed by the American Society for Testing and Materials (ASTM). This evaluation was undertaken to determine the suitability of specific paints and coatings for use as IRCCS. see IRCCS ratings
Thermal Radiation moves through air, the energy transfered by radiation is HEAT. It does not warm the air it is travelling through but the material it contacts, this is a fundamental law of nature and we can do nothing to change it. Furthermore the material that has been heated will continue to transfer that heat to whatever it is in contact with through CONDUCTION. This conductive transfer of heat will continue untill an open AIR Space is encountered and the heat again begins to move as thermal radiation. So let us revisit the structure of your homes roof and attic.
The sun's thermal energy radiates to earth where it encounters your roof and heats it up, this heat is then conducted through to the felt below, which in turn heats up the decking, and if you have painted that deck it continues to conduct that heat to the paint, at which point there is an open AIR space and it radiates down through your attic to the insulation. Please refer to the statment above by the (ASTM) in red.
"IRCCS reduce heat transfer from the adjacent interior air to the coated surface"
One last time, if you paint somthing there is no AIR between that paint and the surface being painted !!!!!!!
True Radiant Barrier?
If someone tells you that they are going to "paint" a Radiant Barrier to the underside of your roof, they are generally misinformed.
There are two basic types of products on the market today being sold as "Radiant Barrier", Foil and Paint.
The effectiveness of a Radiant Barrier, RCC "radiant control coating", or an IRCCS "interior radiation control coating" are measured by their emittance value. (note: Emittance and Reflectivity should have a sum of 1.0 or 100%.) For products to qualify as a Radiant Barrier according to (ASTM) a material must have an emittance value of 0.1 or less. This means it will reflect at least 90% or 0.9, and emitt no more than 10% or 0.1
You want the emittance value to be as low as possible.
First lets look at RB Foil, while there are numberous manufactures and grades or weights available, they are all for the most part made of very thin sheets of alumimun, double sided and laminated with a polimer or skrim to increase their tear resistance. Weight is the common factor to measure the strenght of these products. The emittance value of most Foil Radiant Barrier products is 0.03 or 3%, reflecting 97% of thermal radiation.
Foil is stapled to the underside of the roof rafters or laid on over insulation, either method is okay because there is an open air space between the heat source and the Radiant barrier. But there are a few things to consider when choosing which application will best serve you. "see applications"
Now for Paint, If you will look at the specs put out by the ASTM even the best reflective paint products DO NOT qualify as radiant barriers. They have value ratings of the best being 0.195 all the way down to 0.90. What this means is the best in its class only reflects 79.5% and the worst reflects only 10% of thermal radiation. These results can be futher effected by how thick the paint application is, and some (not all) thin or cut their product to reduce material costs. (remember a radiant barrier must have a rating of 0.1 emmiting no more than 10% and reflecting at least 90% of thermal radiation)
Here is how the (ASTM) classifies "PAINTS"
Especially formulated coatings and paints are used in building applications to conserve energy. A large number of products called "radiation control coatings (RCC)" are used on exterior surfaces to reduce the amount of solar energy absorbed by the surface and transported to the interior. A second class of products called "Interior Radiation Control Coating Systems (IRCCS)" are available for use on interior surfaces to reduce heat transfer from the adjacent interior air to the coated surface. Consensus standards for both product types have been developed by the American Society for Testing and Materials (ASTM). This evaluation was undertaken to determine the suitability of specific paints and coatings for use as IRCCS. see IRCCS ratings
Thermal Radiation moves through air, the energy transfered by radiation is HEAT. It does not warm the air it is travelling through but the material it contacts, this is a fundamental law of nature and we can do nothing to change it. Furthermore the material that has been heated will continue to transfer that heat to whatever it is in contact with through CONDUCTION. This conductive transfer of heat will continue untill an open AIR Space is encountered and the heat again begins to move as thermal radiation. So let us revisit the structure of your homes roof and attic.
The sun's thermal energy radiates to earth where it encounters your roof and heats it up, this heat is then conducted through to the felt below, which in turn heats up the decking, and if you have painted that deck it continues to conduct that heat to the paint, at which point there is an open AIR space and it radiates down through your attic to the insulation. Please refer to the statment above by the (ASTM) in red.
"IRCCS reduce heat transfer from the adjacent interior air to the coated surface"
One last time, if you paint somthing there is no AIR between that paint and the surface being painted !!!!!!!
True Radiant Barrier?
If someone tells you that they are going to "paint" a Radiant Barrier to the underside of your roof, they are generally misinformed.
Heat flows naturally from a warmer to a cooler space or material. In winter, the heat moves directly from all heated living spaces to the outdoors and to adjacent unheated attics, garages, and basements - wherever there is a difference in temperature. During the summer, heat moves from outdoors to the interior of the house. To maintain comfort, the heat lost in winter must be replaced by your heating system and the heat gained in summer must be reduced by your air conditioner. Insulating ceilings, walls, and floors decreases the heating or cooling needed by providing an effective resistance to the flow of heat.
Conduction is the least efficient method of transferring heat and in a kitchen analogy, that would be an equivalent of boiling water in a pot over a stove. The fire heats the pot and the pot transfers its heat to the water and the water eventually comes to a boil. The key point here is that conduction is the transfer through direct physical contact. [any materials including radiant barrier will conduct heat when in direct contact with any other material.]
Convection is more efficient than conduction, and in our kitchen analogy, convection would be the use of an oven to heat food. Convection heat transfer is the process by which heat is circulated in an area through the air and/or fluid. The key point here is that heat is transfered through air circulation.
Radiant heat otherwise known as thermal radiation is the most efficient type of heat transfer and the best example in our kitchen analogy would be the use of a microwave. Radiant heat is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. In a home or building, radiant heat refers to heat radiated from objects and materials, such as incandescent lights, concrete flooring and the sun. It is also important to note that radiant heat moves through the air without heating the air, instead it will heat the first surface that it touches, and this surface will then conduct that heat to any material it is in contact with..
In General heat transfer in a home or building is bad and decreases the efficiency of the heating and cooling system. There are some special conditions where heat transfer is used to increase the efficiency, such as traum walls, thermal masses, and other natural heating and cooling techniques. But for the most part, in a typical home or building which relies on mechanical means of heating and cooling, heat transfer is the enemy.
Convection is more efficient than conduction, and in our kitchen analogy, convection would be the use of an oven to heat food. Convection heat transfer is the process by which heat is circulated in an area through the air and/or fluid. The key point here is that heat is transfered through air circulation.
Radiant heat otherwise known as thermal radiation is the most efficient type of heat transfer and the best example in our kitchen analogy would be the use of a microwave. Radiant heat is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. In a home or building, radiant heat refers to heat radiated from objects and materials, such as incandescent lights, concrete flooring and the sun. It is also important to note that radiant heat moves through the air without heating the air, instead it will heat the first surface that it touches, and this surface will then conduct that heat to any material it is in contact with..
In General heat transfer in a home or building is bad and decreases the efficiency of the heating and cooling system. There are some special conditions where heat transfer is used to increase the efficiency, such as traum walls, thermal masses, and other natural heating and cooling techniques. But for the most part, in a typical home or building which relies on mechanical means of heating and cooling, heat transfer is the enemy.
This site is dedicated to educating you, the consumer, about the facts concerning Radiant Barrier products and their effectiveness, in an effort to aid you in making an informed decision about what is the best way for you to make your home Energy Efficient.
Studies now show a large percentage of a structure's heat gain and/or loss is through radiant heat transfer. Winter heat loss 50% to 75%, and summer heat gain up to 93%.
Conventional insulation products were just not developed to address this issue.
Conventional insulation products were just not developed to address this issue.
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In order to help you to understand how a radiant barrier works, let us first begin by explaining a little about heat transfer. When talking about radiant barriers, insulation, HVAC systems and energy efficiency, it is important that we recognize that all of these things are about controlling heat.
Properly installed "Radiant Barrier" combined with attic ventillation and conventional insulation will improve the comfort of your home and significantly reduce UTILITY COSTS.
Installing Radiant Barrier to aid in the control of thermal radiation heat transfer is the most cost effective way of reducing utility costs and increasing the comfort level of your home.
Next we will look at how radiant barrier works and its relationship with the other materials in your home.
Next we will look at how radiant barrier works and its relationship with the other materials in your home.
Radiant Barrier understanding your options!
Now that we understand HEAT's "mode of tranportation" changes in direct relationship to the the object or space it is moving to and from, we need to understand the structure of your home and how to best choose the right product for the job at hand.
First let us consider our main heat source, the sun, radiant heat from the sun hits the earth every hour with enough energy to supply the worlds population with heat and electricity for an entire year. This sounds pretty incredible, but it is possible with the renewable energy products we have available today. But for now, let's look at how all of that energy effects our every day lives and we will start with your roof.
Remember that radiation does not heat the air it moves through but the surface it contacts, your Roof! On hot sunny days it can bring the tempurature of you roofing materials to 150 plus degrees. At that point the heat changes it mode of transportation to "CONDUCTIVE" it conducts down through the materials of your roof [1- shingles 2- felt 3- decking 4- "IRCC" interier radiant control coating] until it comes to an air space when it changes back to it radiant mode of transportation. Travelling through your attic untill it encounters another material, your insulation, whitch it in turn, heats up and CONDUCTS down through to your ceiling, where again, it hits an air space, "Your Livng Space" and radiates to the furniture, carpet, walls, etc. which absorb the heat again, and continue to re-radiate that heat untill your air conditioner has cooled all these materials.
Have you ever noticed or wondered why you home seems to continue warming up after sundown even though the night air is cooler? This is because the stored heat in your insulation, walls, and furnishing continue to radiate heat until they have cooled.
Remember up to 93% of summer heat gain is through radiant heat, and coventional insulation was not developed to address this source of heat, it cannot address the issue because thermal radiation's only mode of transportation is air! In order to block thermal radiation we must have an open air space bettween the Radiant Barrier and the source of heat "your roof deck".
Remember that radiation does not heat the air it moves through but the surface it contacts, your Roof! On hot sunny days it can bring the tempurature of you roofing materials to 150 plus degrees. At that point the heat changes it mode of transportation to "CONDUCTIVE" it conducts down through the materials of your roof [1- shingles 2- felt 3- decking 4- "IRCC" interier radiant control coating] until it comes to an air space when it changes back to it radiant mode of transportation. Travelling through your attic untill it encounters another material, your insulation, whitch it in turn, heats up and CONDUCTS down through to your ceiling, where again, it hits an air space, "Your Livng Space" and radiates to the furniture, carpet, walls, etc. which absorb the heat again, and continue to re-radiate that heat untill your air conditioner has cooled all these materials.
Have you ever noticed or wondered why you home seems to continue warming up after sundown even though the night air is cooler? This is because the stored heat in your insulation, walls, and furnishing continue to radiate heat until they have cooled.
Remember up to 93% of summer heat gain is through radiant heat, and coventional insulation was not developed to address this source of heat, it cannot address the issue because thermal radiation's only mode of transportation is air! In order to block thermal radiation we must have an open air space bettween the Radiant Barrier and the source of heat "your roof deck".
You may now have enough information to understand the basics of how a Radiant Barrier works, how important air space is, and how the method and more imporrtantly what the surface it is installed on is adjacent to, effects and or determines if it will even work at all.
So now lets look at Radiant Barrier Products available for controlling thermal radiation.
So now lets look at Radiant Barrier Products available for controlling thermal radiation.
Please take note of the underlined statement above by the (ASTM) it states everything you need to know about why painting the underside surface of your roof decking is not the proper application for these products.
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N© associated with this site in a sincere wish that you pass this information forward.
Beat the HEAT: "Lower Utility Costs"
SO LET US ASSUME FOR A MOMENT THAT AN EMMITANCE VALUE OF 20% VS 3%
WON'T AFFECT YOUR UTILITY SAVINGS OR THE COMFORT OF YOUR HOME
I am appologizing in advance for being a little redundant here but I really want you to understand this point.
This is the most important factor in your decsion about having Radiant Barrier installed in your home.
OPEN AIR SPACE
WON'T AFFECT YOUR UTILITY SAVINGS OR THE COMFORT OF YOUR HOME
I am appologizing in advance for being a little redundant here but I really want you to understand this point.
This is the most important factor in your decsion about having Radiant Barrier installed in your home.
OPEN AIR SPACE
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Radiant Barrier - Foil vs Paint Pros and Cons
Aluminum Foil
IRCCS (paint)
Pros:
Reflects 97% of radiant heat
Lowers attic tempuratures up to 50o
Has a Class A Fire Rating
Prolongs the lifespan of your HVAC system
Several choices of installation methods
Can be taken down and reinstalled in the case you need to do some work in your attic.
Reflects 97% of radiant heat
Lowers attic tempuratures up to 50o
Has a Class A Fire Rating
Prolongs the lifespan of your HVAC system
Several choices of installation methods
Can be taken down and reinstalled in the case you need to do some work in your attic.
Pros:
Very inexpensive, material and labor costs should not be significantly higher than painting any room of simular size.
Can be installed "spayed on" in a couple of hours.
Very inexpensive, material and labor costs should not be significantly higher than painting any room of simular size.
Can be installed "spayed on" in a couple of hours.
Cons:
Installation is labor intensive making initial investment higher, but this should quickly be offset by utility savings.
Installation is labor intensive making initial investment higher, but this should quickly be offset by utility savings.
Cons:
Unless you remove the insulation in your rafters, and apply the product to top side of you ceiling there is no surface to properly install these products in an attic.
If that were done it would increase matterial and labor costs to that of foil barrier or more, leaving your ducting system and replaced insulation in extreem tempuratures. It wouls still emmit 20% radiant heat vs 3% for foil. (C'ing M A, I am not recomending this method of installation)
Thickness of paint effects the performance
Can be thined by some, not all companys to reduce material costs.
Usually sold in combination with minimum purchace of conventinal insulation, no way to dicern which product actually worked.
In case of a fire puts off toxic fumes and can intensify the flames.
Seals the decking, reducing the evaporation, increasing the possibly of rotting in the case of a roof leak.
Unless you remove the insulation in your rafters, and apply the product to top side of you ceiling there is no surface to properly install these products in an attic.
If that were done it would increase matterial and labor costs to that of foil barrier or more, leaving your ducting system and replaced insulation in extreem tempuratures. It wouls still emmit 20% radiant heat vs 3% for foil. (C'ing M A, I am not recomending this method of installation)
Thickness of paint effects the performance
Can be thined by some, not all companys to reduce material costs.
Usually sold in combination with minimum purchace of conventinal insulation, no way to dicern which product actually worked.
In case of a fire puts off toxic fumes and can intensify the flames.
Seals the decking, reducing the evaporation, increasing the possibly of rotting in the case of a roof leak.
See also RIMA "Reflective Insulation Manufacturers Association International"
