• By radiation from a warm surface to a cooler surface through an air space as infra-red heat
• By conduction through solid or fluid materials resulting from direct contact
• By convection, which involves the physical movement of air - warm air rises

Heat moves through walls or between roofs and floors by a combination of radiation, conduction, and convection with radiation being the dominant method of heat transfer. Research shows that control of radiant heat transfer is the core of heating/cooling climate control.

Radiation is the transfer of heat (infra-red radiant energy) from a hot surface to a cold surface through air or a vacuum. Radiation is the dominant method of heat transfer in a building accounting for 65-85 percent of all heat transfer through walls, roof, and floors. Aluminum foil is an effective barrier against radiant heat transfer because it reflects back almost all of the infrared radiation striking its surface and emits very little of the heat conducted through it.

Traditional fiberglass insulation has no effect on radiant heat transfer. Estimates are between 80 and 90% of the radiant heat striking fiberglass will pass right through it. Aluminum foil reflective insulation, which can reflect up to 97 percent of the radiant energy that strikes it, has proven to be an outstanding radiant heat barrier. All new steel buildings that will hold people or animals should incorporate a radiant barrier including buildings in mild climates where you do not need to air-condition the building for part of the year.

Reflective Insulation Installed as a Radiant Barrier in a Steel Building

Metal buildings are very good conductors of heat. Radiant heat from the sun that strikes the metal roof will be carried inside very efficiently unless a radiant barrier is in place. Installing a radiant barrier will reflect the sun's infra-red rays back into the atmosphere so they will not penetrate the building. This will keep the interior much cooler and save money on lower air conditioning bills or eliminate the need for air conditioning entirely.

Radiant barriers are made of aluminum foil sheeting with a backing for stability so it can be installed without tearing. They have become increasingly popular because tests by the Florida Solar Energy Center (FSEC) and Oak Ridge National Laboratories throughout the 1980s and 1990s show that they work, and also because manufacturers have improved the quality of radiant barrier materials making them easy and affordable to install.

Click here to read a detailed article on the physics of foil.

Adding thermal insulation in a steel building is important for interior comfort if people will be working inside. Thermal insulation will help maintain a constant air temperature and lower costs for heating as it impedes the movement of heat to the outside. Local building codes will provide guidance on the R-values of insulation necessary for steel building walls, floor and roof depending on the climate.

Condensation can be a more significant problem in a steel building than temperature control. Moisture from humidity, rain, groundwater and human activity like washing and breathing creates the potential for several problems in steel buildings. First, the presence of water or ice in the insulation seriously degrades both the thermal performance and service life of fiberglass, paper, wool and other traditional insulation materials. Second, water in contact with metals contributes to corrosion and lowers the service life of the building. Third, collection of water can lead to dripping, staining, mold, mildew and odors.

All of these problems can be solved with a properly installed insulation/vapor barrier system. Even in only moderately humid climates, condensation can cause serious problems in an unprotected steel building. To avoid this problem, adequately ventilate the building and install a vapor barrier even if you do not plan to insulate.

Use reflective foil insulation - it will never get wet and have to be replaced like fiberglass batts. Reflective insulation acts as a vapor barrier or vapor retarder by limiting the passage of water vapor thereby preventing condensation within the insulation or on the interior surfaces of the building.

Click here for a detailed article on condensation control in a steel building.

Reflective insulation is the builder's choice for steel buildings as it provides thermal insulation, a radiant barrier and a vapor barrier to eliminate condensation problems in one product. The reflective surface also enhances the lighting efficiency inside the building. It is commonly used in walls, under the roof decking, under the floor, and around ducts.

Reflective insulation is made of two layers of foil with a core layer of foam or plastic bubbles in between creating an air space. Reflective insulation products incorporate trapped air spaces as part of the system to retard the convective flow of heated air the same way fiberglass insulation does.

Radiation accounts for 65-85 percent of all heat transfer through the walls and roof. Reflective insulation is an effective barrier against radiant heat transfer because it reflects back almost all of the infrared radiation striking its surface and emits very little of the heat conducted through it. The aluminum foil component in reflective insulation will reduce radiant heat transfer by as much as 97 percent. This keeps the building from getting hot inside.

Reflective Insulation for Steel Buildings

The benefits of using reflective insulation instead of conventional bulk insulation are numerous:

• Clean, lightweight, flexible and very strong
• Very thin - can be used effectively in small spaces
• Easy to install
• Installation requires no special tools or clothing
• Easier to cut than fiberglass batt and bubble wraps
• Convenient flange tabs on sides
• Can be stapled, nailed, glued or sewn
• Non-hazardous/Non-toxic/Non-carcinogenic
• Safe for workers to use as there are no fibers to breath or cause skin irritation
• Provides up to 19DB of soundproofing
• Works in temperatures extremes as low as (minus) -20 degrees Celsius and as high as 80 degrees Celsius (and if an air space is added it can go up to 300 degrees Celsius)
• Vapor barrier, waterproof, non-absorbent - reduces or eliminates condensation when properly installed
• Radiant barrier - reflects 97% of radiant heat
• Does not promote mold, mildew or fungus growth
• Does not provide nesting for birds, rodents or insects
• Is used in animal confinement buildings to reduce the "black globe effect"
• Provides Class A/Class 1 fire rated protection - meets fire and smoke safety requirements of most federal, state, and local building codes
• UV resistant
• Flexible at low temperatures
• Withstands fluctuations in outdoor temperatures
• Reinforced (Commercial Grade)
• Saves money and energy

Reflective Insulation Provides and Aesthetic Finish

• Reflective insulation has higher R-values (or resistance to heat transfer) than any other type of insulation per inch. ¼" thick reflective insulation has more insulation value than 6 inches of common fiberglass batt.
  

  Average R-values of Insulation Materials
  Insulation type	R-value per inch of thickness
  Fiberglass blanket or batt	2.9 to 3.8
  Loose-fill cellulose	3.4 to 3.7
  Expanded polystyrene board	3.6 to 4
  Extruded polystyrene board	4.5 to 5
  Polyisocyanurate board, unfaced	5.6 to 6.3
  Polyisocyanurate board, foil-faced	7 to 8
  Spray polyurethane foam	5.6 to 6.3
  2 layers of foil - polyethylene foam core	14.5 (1/4 inch thick) -- Details.
  2 layers of foil - fiberglass core	7.6 to 10.3 (1/4 inch thick) -- Details
  2 layers of foil - polyethylene bubble core	4.9 to 14.1 (1/4 inch thick) -- Details

• Reflective insulation is the only type of insulation that reflects radiant heat. Traditional fiberglass insulation has no effect on radiant heat transfer. Estimates are that between 80% and 90% of the radiant heat striking fiberglass will pass right through it. Aluminum foil reflective insulation, which can reflect up to 97% of the radiant energy that strikes it, has proven to be an outstanding radiant heat barrier.
• Reflective insulation is the only type of insulation that can be used as a vapor barrier. All other insulation requires the addition of a separate vapor retarder to prevent moisture accumulation in the walls and ceilings that can cause rot, mold, fungus, and dripping.
• Reflective insulation will not compress or absorb moisture - conditions that seriously degrade the performance of batt and blanket insulation.

When you insulate a metal-framed building, it is important to recognize that much more heat flows through steel studs and joists than it would through wood framing. Because of the high conductivity of steel, placing insulation between the wall studs, doesn't work as well for metal-framed buildings as it does for wood-framed buildings.

A steel building frame can make up as much as 15 percent of a wall or ceiling surface. In colder climates, these steel framing members will act as a thermal bridge allowing heat to bypass otherwise effective insulation. Heat will be conducted right through the steel studs to the outside.

For metal frame walls, you will need to place the insulation sheet over the outside of the wall frame, between the metal framing pieces and your exterior siding similar to whole house wrap. Taping all seams and taping at the floor and ceiling create the vapor barrier. If you have an attic with metal joists, you will want to place insulation between the joists and the ceiling drywall.

For new construction of a steel building:

• Install between framing and sheeting
• Place double-sided tape on frame
• Roll out insulation over frame
• Allow insulation to sag slightly (approx. 1 inch) to create air space
• Attach your sheeting as if the insulation wasn't there

To Retrofit an Existing steel building:

Use a combination of glue, tape or screws to attach to side or underside of metal beams. You may install between beams or run opposite direction over beams to avoid having to cut (this is the method to create a vapor barrier). Reflective insulation is most effective when incorporated with a ¾-inch or more airspace on at least the outer side of product.

Click here for comprehensive installation instructions using reflective insulation as Steel Building Insulation.

Cavity wall installaion in a metal building:

• Stick the insulation to the metal studs with double faced tape. Just stick it temporarily prior to the installation of the metal strapping.
• Install the metal strapping and drywall following the manufacturer's

Click here for comprehensive installation instructions using reflective insulation in the Cavity Wall of a steel building.

Oak Ridge National Laboratory
Radiant Barrier Attic Fact Sheet
http://www.ornl.gov/sci/roofs+walls/radiant/index.html

Florida Solar Energy Center
Radiant barriers: a question and answer primer
http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/index.htm

Parker, D.S., J. R. Sherwin and M. T. Anello
FPC Residential Monitoring Project: New Technology Development - Radiant Barrier Pilot Project
Contract Report FSEC-CR-1231-01
Florida Solar Energy Center, Cocoa, Florida, January 2001

Reflective Insulation Manufacturer's Association
Understanding and using Reflective Insulation, Radiant Barriers And Radiation Control Coatings
May 2002
www.rima.net

US Department of Energy, Energy Efficiency and Renewable Energy
Reflective Insulation
http://www.eere.energy.gov/buildings/info/components/envelope/insulation/reflective.html