how effective are Radiant barriers?
Without proper roof and attic insulation, unwanted solar heat gains will flow into the living space.
And that’s where radiant barriers may enter. Radiant barriers (reflective insulation materials) are a way of cooling the attics in warm climates.
But are they effective enough?
Radiant Barriers Effectiveness
Radiant barriers are lightweight, clean, non-toxic and easy to handle and to install. But that doesn't make them a good product.
In new construction they are at least as expensive as conventional insulation materials, and may produce very poor results.
Do not be fooled by radiant barrier manufacturers' claims. They are not effective enough in cold or moderate climates, and they do not really replace conventional insulation materials (cellulose, fiberglass, foams).
RADIANT BARRIERS: A PRODUCT FOR HOT CLIMATES
Radiant barriers can be a useful product
to reduce attic temperatures, in hot climates. Just that.
The best way to avoid the heat transfer from the roof and the attic into the living space is to use high levels of attic and roof assembly insulation (provided by materials such as cellulose or rigid foams).
Radiant barriers are part of a larger set of products or strategies to solve attic overheating problems, also involving reflective and light-colored roofing materials and attic ventilation.
Radiant barriers can help reduce temperatures in the attic, in hot climates, but the overall results are questionable, even in hot climates.
Highlights
» Roofs and ceilings are responsible for unwanted heat gains, in many buildings.;
» And the are also a cause of huge energy loss in cold weather
» The best strategy to prevent overheating and heat loss, in new construction is a very airtight attic with very high levels of insulation on the ceiling plane (or on the roof assembly).
Reflective Roof Insulation (Radiant Barriers)
Radiant barriers (reflective roof insulation) are mostly used in hot climates. They use reflective surfaces, typically foil coated sheet and heavy foil.
They are available as sheets (sarking), concertina-type batts and as bubble multi-cell batts and radiant barrier chips.
Bubble radiant barrier batts are used in irregular or obstructed places, while sarking and concertina RFLs (reflective foil laminate) are used in more standard spaces, typically between studs, joists and beams.
Radiant barrier chips are especially designed for horizontal installation on the attic floor.
Radiant barrier prices vs. Conventional insulation materials
When buying standard radiant barriers, consider a shiny foil. Look for radiant barriers with high reflectivity (0.9+) and low emissivity (less than 0.1).
Prices may go from, say, $.30 to $.70 cents per square foot - which isn't exactly an inexpensive option. Foil-faced bubble wrap (prices around $.40 - $50 per square foot) may cost more than, say, R-5 extruded polystyrene.
Radiant barrier chips may cost you $1 to $1.50 per square foot.
Installation
Radiant barriers are easy to install. Just pay attention to the manufacturer’s instructions and check fire and building codes.
For a better performance, standard radiant barriers are installed at the top cord of the trusses, or draped over them.
When installing a reflective material, make sure there is a small gap (about 1 inch/2,5cm) between the roof material and the radiant barrier. If using sarking, you should install it between the battens and the rafters, with the shiny side facing down.
The images at right, from RIMA (Reflective Insulation Manufacturers Association), show two typical installation methods.
Installing standard radiant barriers on the attic floor will not provide any significant advantage.
See:
Roof Energy Savings Guide
Cooling & Insulation
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