Radiant heat barriers (Post: bills, installation, required)

[10scoachrick]

Originally Posted by CptnRn

A metal roof, if it is white or very light in color can be very effective in reflecting away the sunlight that causes a roof to heat up.

Cool roof - Wikipedia, the free encyclopedia

However, any metal roof that is not highly reflective would heat up the roof deck just like any other roof. As I understand it, a radiant barrier needs to be between the hot roof deck and the attic insulation, with an air space separating it from the deck.

So it appears that some metal roofs could also benefit from a radiant barrier.

Before we left Atlanta, a neighbor installed a standing seam metal roof on her mid-'50s salt box house. The metal went on top of two 3" layers of rigid foam insulation. She said she could tell a dramatic difference immediately. Also, she said the only sound of storming rain she could hear was the rain hitting the ground...the rigid foam was a fantastic sound insulator as well as protecting the home from heat gain.

I had an over-the-phone estimate of the cost of a radiant barrier retro-fit on our rather large house. In loose numbers, the minimum cost was $1500 and that would not include insulating in attic areas that were difficult to reach. With the excellent attic floor insulation we have, we would have had a much cooler empty attic, but little improvement in our living space. Even at a 'generous' utility bill decrease, the payback period would have been too long to interest me. Even factoring in the lower stress on the cooling system didn't make the numbers work. HOWEVER, there is no way I would build new without a radiant barrier and serious blown in insulation--well in excess of standard...just too easy to build it in rather than trying to add later.

I have noticed that the 'spray-on' radiant barrier folks have not been as active this year. That method was questionable for a number of reasons and I suppose a percentage of those installers have moved along to another line of work. The changes in the tax credit structure factored in, I'm sure.

[nonexpat]

We have a brand new home with a radiant barrier and extra insulation in the attic. Our new home is 3500 square feet as compared to our older home in Plano which was 2700 square feet. During the height of summer--July and August--our electric bills are at least 100 dollars cheaper per month even with a much bigger home.

[kiacook]

I should clarify that the "radiant barrier" I had done was the spray-on kind.

[CptnRn]

Originally Posted by 10scoachrick

I had an over-the-phone estimate of the cost of a radiant barrier retro-fit on our rather large house. In loose numbers, the minimum cost was $1500 and that would not include insulating in attic areas that were difficult to reach. With the excellent attic floor insulation we have, we would have had a much cooler empty attic, but little improvement in our living space. Even at a 'generous' utility bill decrease, the payback period would have been too long to interest me. Even factoring in the lower stress on the cooling system didn't make the numbers work. HOWEVER, there is no way I would build new without a radiant barrier and serious blown in insulation--well in excess of standard...just too easy to build it in rather than trying to add later.

That is good information.

It sounds like it will take 10 to 11.33 years to payback the cost of a radiant barrier retro-fit with energy savings, maybe a little less with rising energy costs.

For comparison I just added about R-20 insulation to our attic and I calculate that payback will be around 3-4 years. Looking forward to seeing my next few utility bills to verify that.

[gpurcell]

Originally Posted by CptnRn

A metal roof, if it is white or very light in color can be very effective in reflecting away the sunlight that causes a roof to heat up.

Cool roof - Wikipedia, the free encyclopedia

However, any metal roof that is not highly reflective would heat up the roof deck just like any other roof. As I understand it, a radiant barrier needs to be between the hot roof deck and the attic insulation, with an air space separating it from the deck.

So it appears that some metal roofs could also benefit from a radiant barrier.

No air gap needed; when installed as part of a roof installation it's simply the interior side of the new plywood decking for the roof.

[Mel Presswood]

The radiant energy is reflected back through the roofing system. Subsequently, the roofing system is exposed to the radiant energy twice instead of once. That equates to a reduction in the life of the roofing system. Does the decrease in roofing system life and subsequent cost of replacing the roofing system negate the potential energy savings and cost of installation of the radiant barrier? In addition, each time you'd replace the roofing system, you might also be removing the radiant barrier if the deck is damaged due to the increase in expose to radiation. I've never seen a life cycle cost study to justify installation of a radiant barrier. If anyone has one, I'd like to see it.

[CptnRn]

Originally Posted by CptnRn
A metal roof, if it is white or very light in color can be very effective in reflecting away the sunlight that causes a roof to heat up.

Cool roof - Wikipedia, the free encyclopedia

However, any metal roof that is not highly reflective would heat up the roof deck just like any other roof. As I understand it, a radiant barrier needs to be between the hot roof deck and the attic insulation, with an air space separating it from the deck.

So it appears that some metal roofs could also benefit from a radiant barrier.

Originally Posted by gpurcell

No air gap needed; when installed as part of a roof installation it's simply the interior side of the new plywood decking for the roof.

That is not what I read in several places, the radiant barrier is not effective if there is no air gap.

[10scoachrick]

Originally Posted by Mel Presswood

The radiant energy is reflected back through the roofing system. Subsequently, the roofing system is exposed to the radiant energy twice instead of once. That equates to a reduction in the life of the roofing system. Does the decrease in roofing system life and subsequent cost of replacing the roofing system negate the potential energy savings and cost of installation of the radiant barrier? In addition, each time you'd replace the roofing system, you might also be removing the radiant barrier if the deck is damaged due to the increase in expose to radiation. I've never seen a life cycle cost study to justify installation of a radiant barrier. If anyone has one, I'd like to see it.

The only 'numbers' I've seen for an increase in the roofing material temperature was 3-4 degrees when the roofing was placed over a radiant barrier deck. I'll have to do a bit of digging to find the source. In essence, the study was refuting the notion that a roofing material's warranty 'should' be voided when the roofing is placed over a radiant barrier deck. After all, the temp up there is routinely over 120 degrees.

[10scoachrick]

Originally Posted by gpurcell

No air gap needed; when installed as part of a roof installation it's simply the interior side of the new plywood decking for the roof.

Originally Posted by CptnRn

That is not what I read in several places, the radiant barrier is not effective if there is no air gap.

I think we are talking about different types of radiant barriers.
A) The spray-on barrier(like 'paint', not spray foam) AND the 'built-in' decking barrier are applied directly to the decking...as such, no air gap.

2) The foil or rigid foam barriers are typically installed WITH an air gap of 1/2" or more...often applied to the 'bottom' side of the roof rafters. Same when insulating your garage doors with rigid foam or foil...best to leave an air gap or 'dead space' between materials...so they say.

[Mike78613]

Low E3 windows are better investment than Radiant Barrier. If it comes w/ the new house along w/ Low E3 windows; YOU'RE a WINNER!!!!!!!!!!!!!

If you are in an older home, I would get the Low E3 or E4 windows over RB