Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
INSULATION INSPECTION & IMPROVEMENT
ACOUSTICAL SEALANT CHOICES
AIR LEAK MINIMIZATION
ASBESTOS IDENTIFICATION IN BUILDINGS
BASEMENT CEILING VAPOR BARRIER
BASEMENT HEAT LOSS
BUCKLED FOUNDATIONS due to INSULATION?
CATHEDRAL CEILING INSULATION
CATHEDRAL CEILING VENTILATION
CEILINGS, DROP or SUSPENDED PANEL
DEW POINT TABLE - CONDENSATION POINT
DUCT INSULATION, ASBESTOS PAPER
FIBERGLASS PARTICLE CONTAMINATION
FIBERBOARD INSULATION SHEATHING MOLD
FIBERGLASS INSULATION MOLD
FIREPROOFING ASBESTOS SPRAY-ON
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FRAMING METAL STUD PERFORMANCE
FREEZE-PROOF A BUILDING
HEAT LOSS in BUILDINGS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSE DOCTOR, how-to be
HUMIDITY LEVEL TARGET
ROOF ICE DAM LEAKS
INSULATION AIR & HEAT LEAKS
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INSULATION CHOICES & PROPERTIES
INSULATION FACT SHEET- DOE
INSULATION INSPECTION & IMPROVEMENT
INSULATION MOLD TEST
INSULATION R-VALUES & PROPERTIES
LEED GREEN BUILDING CERTIFICATION
LOG HOME ENERGY EFFICIENCY
MOLD in FOAM INSULATION, RESISTANCE
MOISTURE CONTROL in BUILDINGS
NOISE / SOUND DIAGNOSIS & CURE
RIGID FOAM USE INDOORS
SHEATHING, FOIL FACED - VENTS
SLAB INSULATION, PASSIVE SOLAR
STAINS on & in BUILDINGS, CAUSES & CURES
STRAW BALE CONSTRUCTION
STUCCO WALL METHODS & INSTALLATION
STUCCO OVER FOAM INSULATION
SWEATING (CONDENSATION) on PIPES, TANKS
THERMAL EXPANSION CRACKS in BRICK
THERMAL IMAGING, THERMOGRAPHY
THERMAL MASS in BUILDINGS
THERMAL TRACKING Indicates Heat Loss
TRUSS UPLIFT, ROOF
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VENTILATION in BUILDINGS
WALL CONSTRUCTION BARRIER vs CAVITY
WIND WASHING INSULATION at EAVES
WINTERIZE A BUILDING
Radiant barriers and reflective foil insulation in buildings: this article discusses the effectiveness and installation options of foil based radiant barriers as building energy savers. We explain where a radiant barrier should be located, which way to face the foil, and we describe the circumstances in which radiant barrier "insulation" can be effective.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
Where to Install a Radiant Heat Barrier, & Which Way to Face the Foil?
Our radiant barrier photos just above show the installation instructions printed on the kraft paper facing of ALFOL, an aluminum foil radiant barrier "insulation blanket" product sold and installed in many homes in the 1940's. The waterproof kraft paper covering of this radiant barrier "insulation" product faces down into the attic space - a design later research showed was not the best performer. Dead air trapped between the double layers of foil above the kraft paper provided a slight increase in the R-value of this product.
A radiant barrier interrupts the radiant heat transmission using a reflective barrier (see our page top photograph of a radiant heat shield installed in a 1950's home). Research by the Florida Solar Energy Center (FSEC) found that radiant barriers work best when installed with foil-face down (towards the building interior) and applied under the roof sheathing.
This roof heat transmission mechanism explains why air conditioning equipment or duct work located in a hot attic or roof space will have to work extra hard to cool the building unless it is adequately insulated from these hot conditions.
What are the Energy Savings from Radiant Heat Barriers?
Remember, this advice was for Florida, primarily a cooling climate, not a heating climate. Cooling cost savings are a net advantage in the U.S. about as far north as Baltimore.
Roof Ventilation and Radiant Barriers
-- Adapted with permission from Best Practices Guide to Residential Construction.
Details about combining roof color, roof ventilation, and radiant barriers to reduce cooling cost are found at: xxx
Besides the radiant heat barrier article linked-to above, we need to issue a radiant barrier warning and to raise a question or two about this energy savings approach:
Radiant barriers are not a substitute for insulation in cold climates
In older homes built between 1950 and about 1965 we have found radiant barriers installed alone, with no building insulation. In cold climates such as New York and New England, an uninsulated home may be cooler in summer with a radiant barrier installed, but this system provides only modest heat loss savings in cold weather.
In the our radiant barrier "insulation" photograph at left and home shown in our page top photo of a radiant heat barrier, the foil was sold as "insulation" and no other insulation was installed. Each was a costly house to heat in cold weather - the new owners would want to install insulating batts in the attic floor.
In the Solar Age article above, radiant heat barriers are installed under the roof on a building at which insulation has been installed in the attic floor as well as the building walls. That's the way to do it.
Installing radiant barriers as a substitute for actual building insulation performs poorly. Radiant barriers work best blocking radiation of heat downwards towards the occupied space. In cold climates the radiant barrier actually prevents desired heat gain in the home during daylight hours. The Solar Age article above correctly concludes that while a radiant barrier may provide a small net heating cost savings (over no insulation at all) a better approach would be to add insulation to the building. "According to ASHRAE data, a radiant barrier at a 45 deg. slope with heat flow upward is worth about R-2.5."
The article adds that installing radiant barriers on building walls is less effective than under roofs. "A radiant barrier facing a 3/4" [air] space provides about R-3. If the barrier is included as part of an insulation system (such as foil faced insulation that includes this material as a vapor barrier) that's great. But don't use radiant barriers as a substitute for wall insulation.
Radiant barrier researchers think roof venting is unnecessary - are they right?
According to the Solar age article above, researchers think that venting the roof cavity above the radiant heat barrier is unnecessary because "... the radiant barrier does such a good job of blocking attic heat gain".
What is missing from that analysis is a more comprehensive consideration of how building work in all weather and moisture conditions, especially in cooling and humid climates, and also missing is a possible impact on roof shingle life when the roof is allowed to heat to the highest possible temperatures.
We prefer to provide under-roof ventilation in buildings, not just to permit hot attic air to escape in summer (drawing in cooler air from outside at the roof eaves), but also to permit un-wanted moisture to escape year-round. Failure to adequately ventilate attics has been shown to lead to condensation in cold weather and in some homes, severe mold contamination.
In our REFERENCES list below we provide links to the full set of US Department of Energy Documents giving extensive research data and installation advice for radiant barriers. Of those documents, we recommend in particular, the following:
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
Frequently Asked Questions (FAQs) about radiant barriers used in buildings to save on heating or cooling costs
Questions & answers or comments about installing, using, & benefits of radiant barriers and foil "insulation" in buildings.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References