QA-spotlightheader image
Helpful? 0

Staying Cool with a Metal Roof

Metal roofs are durable and recyclable — but do they really save energy?

Posted on May 21 2012 by Scott Gibson

David Martin is intrigued with the idea of replacing his existing roof with a standing-seam metal roof. It should last longer than the alternatives, he says, and it would be compatible with photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. panels should he decide to add them in the future.

So what’s the issue?

David Martin is troubled by some of the advertising claims he’s seen about metal roofing, specifically a statement from the Metal Roofing Alliance that a “cool metal roof can save 25% in energy costs compared to a dark grey asphalt shingle.”

“I've searched around the Internet and found a lot of the industry's advertising,” David Martin writes in a post at GBA's Q&A forum, “but I'm a bit skeptical, especially after reading what [GBA senior editor Martin] Holladay says about the dubious claims made by manufacturers of bubble foils, radiant barriers, and open-cell spray foam.”

It seems to David Martin that the biggest variable in energy efficiency is whether they roof is vented. “I figure there would be a negligible benefit, if any, on a vented roof,” he says. “On an unvented roof, would the benefit be comparable to a radiant barrier on the underside of the rafters?”

His questions about the energy benefits of a metal roof are the subject of this month’s Q&A Spotlight.

Rating the cool factor

David Meiland also likes metal roofing — for its durability, recyclability, and ease of removal if the need arises. But he suspects that light-colored asphalt roofing would perform similarly, with or without ventilation. “Comparing a ‘cool metal roof’ and ‘dark gray asphalt shingle’ is apples to oranges,” he writes.

Kevin O’Meara says the difference in energy performance is due to more than just the color of the roofing. “The paint that the metal companies apply to the metal has added chemicals that are designed to reflect infrared wavelengths,” he writes. “Most metal companies will list these ratings under each color. There exists a ‘cool roof’ tax credit and a website for approved metal roofs.”

Indeed there is, as Meiland discovers. A products directory maintained by the Cool Roof Rating Council lists solar reflectivity and thermal emissivityAmount of heat radiation emitted from a particular body or material. Emissivity is expressed in a fraction or ratio, with the lowest values indicating low emissivity and the highest indicating the high emissivity of flat black surfaces. values for hundreds of brands of roofing.

Meiland finds that many shingle/shake products are not as reflective as the most reflective metals, although there’s a wide variation in metal colors as well.

“You need to look at the published specs of the roofing material and that will tell you how ‘cool’ it is,” adds Bob Coleman. “In some areas it may not be the best if you want some of the sun’s heat...Also, venting the roof underneath changes things. There is no magic bullet. It’s all part of a system that should be geared toward your solutions.”

And as to the claim of a 25% energy savings?

“Ridiculous,” says Holladay. “That would only be true in a very poorly designed house (one that doesn’t meet code and is therefore illegal). Assuming that the home is equipped with a properly installed layer of deep insulation, roof color doesn’t matter much – unless the ducts are installed in the attic. But as we all know, ducts belong inside the home’s conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .”

Winning an Energy Star rating

Roger Brisson likes metal roofing over asphalt for a variety of reasons, too, but some of his claims may bear more checking. “With all things being equal,” he says, “and standard underlayment, metal roofing performs much better than asphalt in its overall insulating capabilities; this is why the Energy Star label is applied to metal and not to asphalt roofing.”

He adds that metal roofing is “incomparably better” for the environment than asphalt shingles.

“Asphalt roofing is a [wasteful] disaster,” he says, “and yes, its lifetime is generally much less than what it is rated (at least here in coastal New England). Replacing asphalt roofing is dirty and messy work, which is why cheap, immigrant labor is used for it. And there's no way asphalt will perform as well as quality Energy Star metal roofing over the course of 50 years (the rated lifespan of most metal roofing). This is why in more technologically advanced countries asphalt roofing is virtually non-existent. It is prevalent in the US for one reason: the upfront costs are cheap, cheap, cheap, which is also what you get.”

Holladay is quick to reply, pointing out that asphalt shingles, in fact, can be Energy Star rated, as is the case with Duration Premium Cool Shingles manufactured by Owens Corning.

David Martin adds that the EPA’s Energy Star website notes that roofing material itself has nothing to do with whether it can be Energy Star rated, only its measured reflectance.

As to Brisson’s comments on immigrant labor, Holladay adds this: “This comment does not deserve to be dignified with an answer, since it implies that immigrant workers are only fit for dirty and messy work. My only comment: I used to work as a roofer, tearing off asphalt shingle roofs and installing new asphalt shingle roofs, and I was born in the U.S. Moreover, I have the highest respect for the work ethic and skills of most immigrant workers in the U.S.”

Our expert’s opinion

Here’s how GBA technical director Peter Yost sees it:

All “cool” roof claddings work based on their surface properties: initial reflectance, “aged” reflectance, and emissivity. The difference between the first and the second is how the surface (shiny and smooth out of the factory) degrades to some degree over time (duller and dirtier). In the case of an Energy Star-rated roof product, “aged” means after three years of standardized exposure. Emissivity is important because heat not reflected becomes heat absorbed, and you want high emissivity to re-radiate that absorbed heat.

Energy Star includes in its specs that “roof products can help reduce the amount of air conditioning needed in buildings, and can reduce peak cooling demand by 10–15 percent.” Big difference between claims of 25% reduced energy consumption and possible 15% reduced peak cooling demand.

EPA Energy Star bases its ratings on initial and aged reflectance but also reports emissivity values. Not surprisingly, the best performers are white metal roofs (ACM Regal White metal roofing with initial reflectance – 0.68; emissivity – 0.86) with some asphalt shingles qualifying, but with much lower reflectance values and similar emissivity (CertainTeed Star White shingles with initial reflectance – 0.29; emissivity – 0.90). You can download a pdf or excel file for all qualified products with their performance properties.

NOTE: the paired terms reflectance and reflectivity; emissivity and emittance are often used interchangeably. Though similar, the “-ivity” terms refer to the property of materials in general and the “-ance” suffix refers to the specific value of a specific material.

When it comes to venting (dead end air space between cladding and deck) and ventilating (open ended air space between cladding and deck), there is no doubt that they can have an effect on the energy performance of the roof but their main purpose is increased concealed free drainage (venting) and drying potential (ventilating gives both), not increased energy performance. And no doubt ventilating the back side of a roof cladding (air flow) would be more effective thermally than just venting, but I don’t think their effects have ever been measured.

I suppose making metal roofing with a low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. surface on the back side could help some, but manufacturers are unlikely to fuss with the backside surface of their metal roofing with the uncertainty of that surface facing an empty space.


Tags: , , , , , ,

Image Credits:

  1. Scott Gibson

1.
Mon, 05/21/2012 - 16:29

Cool roofs are not for high-slope roofs in cool climates
by Dana Dorsett

Helpful? 0

Using a high solar reflectivity/moderate deep IR emissivity approach the steady state and peak roof temperatures under summer sun can can be brought down considerably, and even in a well insulated attic the roof can be a large fraction of the cooling load. The Lawrence Berkeley Nat'l Labs has modeled it fairly well, and has a freebie download spreadsheet calculator for "solar reflectivity index" (SRI) that reports the surface temps under standardized insolation and sky temperature conditions to compare apples-to-apples for materials of given solar reflectance and emissivity numbers:

http://coolcolors.lbl.gov/assets/docs/SRI%20Calculator/SRI-calc10.xls

Roof venting has a far lower effect on peak shingle temps than the SRI, and on medium and high-pitch roofs (greater than 2:12 pitch under cool-roof terminology), convection cooling on the exterior provides an order of magnitude more shingle cooling than any scheme for ventilation under the roof deck can.

(Other D.O.E. cool-roof calculators with energy savings modeling can be found on the LNBL site here: http://heatisland.lbl.gov/resources/5 )

This is all fine and good, if air conditioning is the primary energy hog in the home. But in US Climate zones 5 & up, the reduction in shoulder-season and heating season roof temp increases the average heating load, adding more to the heating costs than it reduces the cooling energy costs under a wide variety of heating & cooling fuel & equipment scenarios. The additional heating load of a cool roof is quite modest, and isn't likely to break the bank, but there's no reason to go out of your way to spec a cool roof finish in a cool climate.

In US climate zones 3 or lower it flips the other way, and for a very modest (or even zero) uptick in cost a cool roof will outperform a radiant barrier, and is "worth it".

The best cool roof "coating" is of course, a photovoltaic panel that shades it. While the albedo of typical silicon PV panels is comparable to lower than that of a cool-roof (and comparable to medium-dark asphalt shingles), the net increase in warming from the more absorptive surface is far less than from the offset emissions of the electricity produced, even in a cooling dominated climate.

Steel roofs are great in any climate from a longevity and sustainability point of view, but cool-roof finishes are best left for cooling dominated climates where they actually do some good.


2.
Mon, 05/21/2012 - 20:45

Just curious...
by Lucas Durand - 7A

Helpful? 0

Who is the expert?


3.
Mon, 05/21/2012 - 21:00

Edited Mon, 05/21/2012 - 21:01.

Maybe...
by Lucas Durand - 7A

Helpful? 0

...but cool-roof finishes are best left for cooling dominated climates where they actually do some good.

I'm generally not a fan of "geoengineering" but urban heat island mitigation is something that should probably be considered in all climates.


4.
Tue, 05/22/2012 - 06:12

Response to Lucas Durand
by Martin Holladay, GBA Advisor

Helpful? 0

Lucas,
Thanks for your question -- the usual identification of our expert, GBA technical director Peter Yost, was accidentally omitted from this article. We've fixed the error.

And thanks for your reminder that cool roofs mitigate the urban heat island phenomenon.


5.
Tue, 05/22/2012 - 16:16

Response to Lucas Durand
by Dana Dorsett

Helpful? 0

In cool/cold climates (US zone 5 and higher) the net annual benefit of cool roof strategies to buildings accrue only to higher density construction or on low-angle & flat roofs, single-family residential. When implemented on neighborhood/regional scale the net annual affect of higher albedo roofing lowers the average temperatures in the micro-climate/heat-island in the winter too, increasing the average & peak heating loads, increasing overall energy use for any less-dense construction within that micro-zone.

It's not a simple model, and in some locations (even in cooling dominated climates) the average air temperatures can increase, due to the effects of a higher albedo on a whole city on rate if cloud formation, etc. (even though the net energy benefit to the buildings is still greater than the modest increase in cooling loads from that effect.)

In cooler climates heat island mitigation via increased urban vegetation & reduction in paved area is probably a better approach than cool-roofs, cool-pavement or similar direct albedo boosting approaches that end up increasing heating loads.


6.
Tue, 05/22/2012 - 21:00

Response to Dana
by Lucas Durand - 7A

Helpful? 0

Dana,
You're right, it is not a simple model...

When implemented on neighborhood/regional scale the net annual affect of higher albedo roofing lowers the average temperatures in the micro-climate/heat-island in the winter too, increasing the average & peak heating loads, increasing overall energy use for any less-dense construction within that micro-zone.

In many cool/cold climates, during much of the heating season, I would guess that the net effect of high albedo roofing on heating loads would be made insignificant by the presence of snow cover...


7.
Wed, 05/23/2012 - 12:58

Another difference...
by Gavin Farrell

Helpful? 0

It all comes down to the testing numbers, but another reason why I imagine metal roofs would be superior at keeping things cool is the difference in thermal mass. Heavier, thicker asphalt shingles can absorb alot of heat and are continously radiating/conducting some of it to the sheathing and framing, and thereby to the interior. Metal roofs get hot too, but should have substantially less capacity to absorb heat and should cool off faster. The night-time cooling cycle should look substantially different for the two materials.


8.
Wed, 05/23/2012 - 16:30

Metal roofing cooler?
by Rock Termini

Helpful? 0

I guess I'm looking here at the 'bigger picture'. When I did the roof (and roofing) rip off, the plan was to super insulate with solid foam sheets. As Martin has said before, you don't want to pass up an opportunity to beef up insulation when it presents itself. So I installed 6 inches of solid foam on top of the decking, 1X4 horizontal strapping (with 10 inch screws), and then the metal roofing onto the strapping. I wanted metal for all the reasons others have mentioned. With the roofing raised, I have ventilation. The point I'm getting to though is how would you attached asphalt shingles? To the foam? To strapping? (lot of sagging.) In other words, to do an insulation retrofit, I assumed at the time asphalt was not an option. And likewise for someone looking at replacing their roofing (assuming it is at least 25 years old) wouldn't they want to upgrade the insulation rating at the same time? BTW, my upstairs 'seems' cooler since we installed, but that just anecdotal comments, and I can't separate the insulation effect from the metal roofing and ventilation effect.


9.
Wed, 05/23/2012 - 16:39

metal roofs Work!
by PoodleHead Mikey

Helpful? 0

First of all: shingles are very heavy and create a huge thermal storage for unwanted heat. Which is why an attic vent fan often runs well after sundown. I removed FOURTEEN TONS of shingles and installed about 1900 lbs. of metal roofing to replace them.

BTW: my previous shingles were all white. So-called because they are barely white to start with and within two or three years may as well be half-black.

With the previous white shingle roof my attic temps could be over 150º at times in the summers here in southern NJ. But now with the metal roof my attic temp was 79ª F. on a sunny 103º day. I have a probe up there and the first time I saw it I immediately thought an A/C duct had broken and I was cooling the attic space. But that wasn't it - the attic was naturally 79º on a 103º day.

In fact; I reduced my A/C systems from two 3 tons systems to two 1.5 ton systems after the metal roof was installed..

A metal roof (I have aluminum but steel is the same) is 100% recyclable, comes with a very long coating warranty, and could almost certainly be re-coated right in place if after 50 years that becomes required.

With the price of oil having the price of comparatively short lived shingles so high - installing a metal roof becomes a no brainer. My only regret is that I didn't think of it thirty years ago.

PHM
-------


10.
Wed, 05/23/2012 - 17:11

Cool Metal Roof
by Ross Williams

Helpful? 0

I live in Key West, FL where it tends to get a liitle hot. The Florida Solar Energy Center has studied this issue. You must have both high reflectivity (> .70) and high emissivity (> .75).

I can say from practical experience that nothing beats a white metal roof reflectivity (> .80 - .90) and high emissivity (> .80 - .90). Galvanized and Galvalume metal roofs are hot roofs. They have medium relfectivity and poor emissivity ( .15). Painting a bare metal roof with white house paint dramatically improves preformance. Radiant barriers, air spaces and added insullation all helps but nothing improves performance like keeping the heat out of the structure to begin with. A truely cool roof prevents the roofing, roof desk and rafters from heating.


11.
Wed, 05/23/2012 - 17:53

Response to Rock Termini
by Martin Holladay, GBA Advisor

Helpful? 0

Rock,
Plenty of people have installed rigid foam insulation on top of roof sheathing, followed by asphalt shingles. But you have to install a second layer of roof sheathing -- either plywood or OSB -- on top of the foam. This can be done by screwing the sheathing directly above the foam (with long screws), or with intervening ventilation channels (usually created with flat-ways 2x4s, installed perpendicular to the ridge).


12.
Wed, 05/23/2012 - 19:51

Cool roof in hot climates
by August Tassin

Helpful? 0

There are few green building choices smarter than a cool roof in hot climates. The best way to beat the heat is to not absorb it in the first place. Use light color metal roof with overhangs to shade the walls on the south and west sides.
I can tell you that my experience is that any metal roof is cooler than asphalt shingles. Even the dark metal colors retain less heat than the relatively light shingles. As my Florida friend stated white metal is the best and the University of Florida has done some good work on quantifying what works.
Asphalt should be against code in the gulf south. They are perceived to be the cheap solution but they are environmentally disastrous; not recyclable and they create death traps out of houses when your AC is not available. Look how many deaths in Katrina were from heat in houses under asphalt roofs.
Folks who add metal roofs in my area see their AC bill drop in half or less. I have no problem believing a 25% reduction because it depends on thermal mass. The metal roof is raised on 1x4 slats so direct conduction is reduced. They are ventilated so convection is your friend. And the radiation out of the back side is never more than the radiation from the top side so a metal roof will cut radiant heat by a large amount in any color.
No I don’t’ sell metal roofs. I own several houses which I rent to folks visiting the area. I want all of my properties to be houses that don’t kill people just because the electricity gets interrupted in the summer. Cool roofs are the best first step.


13.
Wed, 05/23/2012 - 20:07

Nice article - Question about concealed fastner systems
by Narendra Patel

Helpful? 0

I don't know if this is the right place to ask the question: I have workshop going up with 4 inch horizontal battens on a 14:12 roof pitch for metal roofing. Will the battens telegraph through the metal roof? Also, is standing seam best applied with a cleat system or through the metal itself. Both are concealed systems. Thank you!


14.
Thu, 05/24/2012 - 05:46

Response to Narendra Patel
by Martin Holladay, GBA Advisor

Helpful? 0

Narendra,
Q. "Will the battens telegraph through the metal roof?"

A. Only when the weather is cold. Frost patterns can telegraph because the temperature of the roofing above the air space is sometimes colder than the temperature of the roofing above a furring strip.

Q. "Is standing seam best applied with a cleat system or through the metal itself? Both are concealed systems."

A. As far as I know, most standing-seam systems use clips that do not require fasteners to penetrate the steel. (See photos below.) However, through-fastened steel roofing is common; it is different from standing-seam roofing.

Standing seam roofing clip 1.jpg Standing seam roofing clip  2.jpg


15.
Thu, 05/24/2012 - 06:00

Edited Thu, 05/24/2012 - 06:00.

To "cool roof" advocates
by Martin Holladay, GBA Advisor

Helpful? 0

"Cool roof" solutions are similar to radiant barrier solutions -- they work best on poorly insulated houses.

If you are getting a lot of heat flux downward from your roofing to your ceiling, something is wrong with your house. The usual flaws: bad air sealing or insufficient insulation.

In new homes with adequate insulation, there really shouldn't be much heat flow from your roofing to your ceiling. However, if you have an older house with insufficient insulation, cool roofing may make sense.


16.
Thu, 05/24/2012 - 08:47

To Martin, GBA Advisor
by Ross Williams

Helpful? 0

In hot climates cool roof choices almost always make sense when there is no cost penalty, i.e. you choose white metal roofing over gray, green or brown metal roofing, etc. In the vast majority of homes the rafters attach to the top plates and the top plates are insulated from the interrior by a little sheetrock. You can insulate your attic to the ridge and this does not change. There will still be heat bridging into the perimeter of your exterrior walls. Why allow your roof deck, rafters, top plates and insullation to absorb so much more heat with a poor choice of roof color. There is a reason we wear white shirts in the South.


17.
Thu, 05/24/2012 - 09:22

Response to Ross Williams
by Martin Holladay, GBA Advisor

Helpful? 0

Ross,
I agree completely with your statement, "In hot climates cool roof choices almost always make sense when there is no cost penalty."

Nevertheless, I'm going to continue to advocate for good roof design and good insulation details. There is no reason that framers of new homes should be using conventional roof trusses rather than raised-heel trusses; nor should framers of new homes be installing sawn rafters directly on top of top plates.

We've known about the need for deep attic insulation at the perimeter of roofs for at least 30 years. At GBA, we advocate good insulation details, and that includes deep insulation at the perimeter of an attic. It's essential that builders begin to get these details right, no matter what color of roofing they specify.


18.
Thu, 05/24/2012 - 09:56

Edited Thu, 05/24/2012 - 10:04.

Cool Roof Contemplations
by Cameron Taylor

Helpful? 0

This article is timely, as we are researching options for replacing our terra-cotta colored asphalt roofing shingles with metal. While we have decent attic insulation, and I've undertaken considerable effort to ensure the ceiling plane between house and attic is much more airtight than average, the "cool roof" aspect of a metal roof still sounds appealing, since our HVAC ducts are in the attic. We also live in a climate where the cooling season seems to be expanding with each passing year.

Reducing heat gain to the attic via roofing material choice is a large driver behind our interest, but so is durability, since we plan to be in this house a long time. Hailstorms in spring and fall are not uncommon, and I understand metal roofing materials fare better through hailstorms and high winds (we can get both from the same storm system). From this article, concerning the cool roof aspect, I've learned to look for reflectivity and emissivity information, which until now was missing from my research. Therefore, thank you for writing this blog, and for the links embedded within.

In response to Mr. Holladay's comment: "'Cool roof" solutions are similar to radiant barrier solutions -- they work best on poorly insulated houses", what I'm faced with is an adequately insulated ceiling plane pierced by marginally insulated metal HVAC ducting in the attic. Also, reducing heat gain into an attic at the source to me makes sense even if the ceiling level insulation minimizes heat flux into the conditioned space, especially in my climate where nighttime temperatures can remain elevated long after sundown, which reduces attic cooling potential overnight.

I also like the comment above about how a house should not cook its occupants should the electricity or HVAC fail during the summer. Every summer our local news will carry a story about someone being hospitalized or dying from heat exposure inside their house with failed or no a/c. Invariably, if an exterior shot of the structure is shown, it will have asphalt shingles. This has always seemed ridiculous to me; that a structure overheats so badly without a/c that it can injure or kill its occupants. Does not meet the concept of "shelter" in my mind, which I hold as the primary purpose of any building.


19.
Thu, 05/24/2012 - 10:06

Response to Cameron Taylor
by Martin Holladay, GBA Advisor

Helpful? 0

Cameron,
I agree with you completely: if you have ducts in an unconditioned attic, then cool roofing makes sense. That's why I was quoted in the article as saying, "Assuming that the home is equipped with a properly installed layer of deep insulation, roof color doesn’t matter much – unless the ducts are installed in the attic."


20.
Thu, 05/24/2012 - 11:01

Response to all y'all, especially Mr Gibson and Mr Holladay
by David Martin

Helpful? 0

Ok, ok, ok. Enough already.

If y'all are trying to make me feel guilty for learning so much from this website and not paying for any of it, well, it worked. My finances are a bit strained at the moment so coming up with the money to afford the membership fee isn't that simple. So I've decided to cancel my Netflix membership and become a paid subscriber to Greenbuildingadvisor. I've learned a ton here and looking forward to having access to all the rest of the valuable information that comes with being a member. I should have done it sooner.

You guys are great. Thanks, again.

I've done a lot of research on this metal roofing thing, and have a few more random questions and comments. I'll have to post them a bit later.


21.
Thu, 05/24/2012 - 11:25

Response to David Martin
by Martin Holladay, GBA Advisor

Helpful? 0

David,
Thanks for the vote of confidence. I'm glad you decided to subscribe to GBA.

Don't hesitate to post further questions -- we're here to help.


22.
Thu, 05/24/2012 - 12:10

Edited Thu, 05/24/2012 - 12:26.

Sound, heat, and UV
by David Martin

Helpful? 0

I feel like I've become a metal roof salesman with all the conversations I've had with people about it recently. I'm sold on them because of their durability, lightweight, recyclability, etc. They beat out other materials in total cost of ownership over a long time frame. I don't like the industry making dubious claims about their energy efficiency. I think exaggerated claims do a disservice to the industry.

You often hear people of the "green movement" make the "save the planet" claim. That may get people excited but the environment is in much more trouble than that. I think the entire system needs, and will get, drastic reform one way or another. Until then, its good for individuals to continuously make better decisions to lead a less damaging lifestyle.

Sound
One preconceived notion that many have is that metal roofs are very loud in heavy rain or hail. True in a barn, but I think that's a myth in an insulated home. I'm interested if there is a difference in the sound properties if the metal roof is raised on purlins. Rock Termini, what is your experience? Anyone else?

Heat
Metal roofs will expand and contract more with changing temperatures. That is one reason why exposed fastener types are less durable. The sheet will move around the fastener, causing deterioration.

UV degradation
The reason the coating deteriorate is due to ultraviolet light breaking down the polymers in the coating. Lower quality coatings will deteriorate faster. I think color choice comes into play here. True that lighter colors are cooler, but don't they degrade faster? Does anyone know? Dana, it seems like you've done or read a lot of research in this area. Can you answer that?

McElroy Metals has a really good handbook called the "McElroy Metal Retrofit Guide" . It's free from their site but you have to register to get it. It has good illustrations and doesn't seem to be full of industry hype.


23.
Thu, 05/24/2012 - 12:31

Edited Thu, 05/24/2012 - 12:32.

Response to David Martin
by Martin Holladay, GBA Advisor

Helpful? 0

David,
Directly above my bed is an insulated sloped ceiling / roof assembly. The roofing above is steel.

The sound of the rain on the steel roof above my bed is louder than it would be if I had an asphalt shingle roof (even though the roof assembly is insulated).

I like the sound. I don't hear it anywhere else in the house.


24.
Thu, 05/24/2012 - 17:36

Response to Martin Holladay
by Dana Dorsett

Helpful? 0

Whereas radiant barriers reflect radiated heat back to the roof deck raising the temp of the roof deck & shingles to radiate more heat back to the sky, the convection & conduction around the attic back into the attic still raises attic temps. Cool roofs radiate the heat back to the sky without the intervening complexity of roof deck- the surface of the roofing stays cooler, the roof deck stays cooler, and attic stays cooler, since the roof deck isn't running as hot. Cool roof materials do work measurably BETTER than radiant barriers, and are a sufficiently cheap improvement that independent of insulation levels or where the ducts are located, they're cost effective at almost any R-value.

The LBNL site is chock full of data to back this up, but the better performance/lower cost of cool-roofing is the reason why they are prescriptive under California Title 24, whereas radiant barrier and (usually much) higher R values are allowed as alternatives under the code where the building owner or contractor is unwilling or unable to use a suitable cool-roof material. Peeling 10-20F off the peak roof temperatures places a much lower delta-T across the insulation layers. Even at R50 cool roofs can produce a measurable cooling-energy savings compared to a low-albedo roof, even if it comes without a noticeable difference in comfort for the occupants.

Metal roofs are probably the most expensive (first cost) cool roof solution, but they also have a favorable life-cycle cost which shouldn't be ignored. From a long term sustainability point of view metal is a good deal, but cool roof shingles shouldn't be dismissed- they run cooler (increasing shingle life) and come in many colors other than white/off-white, often with zero up-charge. (In CA it's probably hard to find anything BUT CRRC rated cool-roof shingles.)


25.
Fri, 05/25/2012 - 08:22

Response to Dana Dorsett
by Martin Holladay, GBA Advisor

Helpful? 0

Dana,
Cool roofing makes sense in areas of the country with high cooling bills. It makes the most sense for homes with low levels of insulation and for homes with ducts in the attic. Because the incremental cost of cool roofing is low, it's a relatively inexpensive and sensible product to specify in those climates.

Cool roofing can reduce energy use in some, but not most, U.S. climate zones. As noted in one of the documents from the LBNL website, "Prior research has indicated that savings are greatest for buildings located in climates with long cooling seasons and short heating seasons, particularly those buildings that have distribution ducts in the plenum [attic]."

I haven't yet found any document that backs up your statement that "Even [when a roof is insulated] at R-50, cool roofs can produce a measurable cooling-energy savings compared to a low-albedo roof." I'd be interested to see a link to a document that backs up that statement.


26.
Mon, 05/28/2012 - 10:05

building in Guatemala
by David Anthony

Helpful? 0

This is about using two-seperate-layers of metal roofing, I am building a one-story-3-bedroom-wooden-house on three-foot-high-pillers, the narrow-end of the house is facing true-west.
A wrap-around-porch of eight-feet. I am considering for the roof a moderate-pitch using corrigated roofing over wood strips then a series of 2X4 spacers over this and under a top-roof of commercial-metal-roofing kept open at the ridge-line for air-flow between the two-layers of roofing.
I will not air-condition this home, but will have a heater for those damp cool winter nights. The ceilings are heirring-bone-pattern-wood with 3-inches of vermeculite over a plastic-membrane.
Any and all comments are welcome.


27.
Mon, 05/28/2012 - 12:48

Home insurance
by Van Boston

Helpful? 0

I live in Central Texas and installed a metal roof on my house twelve years ago over the existing single layer asphalt roof. One of the deciding factors in choosing metal was that my insurance company reduced my insurance premium considerably because of the roof's resistance to hail damage, which is a common insurance loss in this area. The savings in insurance premiums has just about paid for the roof at this point.


28.
Fri, 06/08/2012 - 22:49

Roger Brisson likes metal
by shane pavel

Helpful? 0

I was not very happy at all to read what Roger Brisson said about cheap labor. In my area and just like the rest of the country immigrant works are in ALL lines of work. Not just the roofing industry Mr. Bigot. The going labor rate is the SAME no matter what color your skin is and if you have an accent or not. I have myself paid the going rate to all types of people. And if Roger Brisson is a contractor then he should know that. Not very professional.


29.
Tue, 09/18/2012 - 22:27

Update on Cool Roof Contemplations
by Cameron Taylor

Helpful? 0

Well we did it. We now have ~4,000 sq. ft. of "solar white" standing seam metal roofing on our house. Architecturally, it looks outstanding, since it goes well with the mid-century modern look of the structure. As for the "cool roof" aspect, just two weeks ago we had daily highs over 100 degrees; now daily highs are in the eighties after a nice cool spell with gentle rain. The past two days I've been on the roof in late afternoon measuring surface temperatures with an IR thermometer. Standing seam in full sun (with ambient air around 84) read ~94 degrees. Neighbor's solid black asphalt roof read 122. I haven't measured attic temps yet as I need to revive those sensors, and will do so soon, along with installing a data logger up there.

We chose the standing seam option for the high reflectivity/high emissivity traits in addition to potentially adding solar cells at a future date. In my previous post I mentioned our HVAC ducts being in the attic, with no intention of moving them inside or altering the existing HVAC in any major way. While our ceiling plane is well insulated, and I've sealed every ceiling penetration to the attic I can find, the duct heat gain with our old terra cotta colored asphalt shingles, in spite of a spray-on radiant barrier added several years ago to the roof decking, was definitely reducing the actual delivered capacity of our a/c to each room. Not enough to cause us to be uncomfortable in summer, but enough to increase operating cost.

One thing I should note is that I realize we may see a slow payback with our roofing choice, much due to what I've outlined above. Honestly that does not bother me much, as we plan to be in the house a long time and will not be faced with reroofing costs for the remainder of our stay. In addition, the wind resistance of our new roof is much higher than before...we live in high wind/tornado alley, not to mention almost without fail in spring (and sometimes fall) we get hailstorms. Our old roof was damaged by hail, which prompted this entire project. The new roof may suffer cosmetic damage with large hailstones, but the water shedding integrity of the roof will not be compromised.

One benefit of our new roof we did not expect was that it has made the interior of the house more quiet from exterior noise. We live in the city, about four blocks from a major interstate. When the wind is from the north it carries the freeway noise with it. Before our new roof went on I could clearly hear it from inside the house, and I attributed it to our old single pane windows we haven't replaced yet. But now I'm sitting in the same rooms with the same old windows, and with freeway noise blasting us full on, but the room is noticeably quieter. Such a discovery is delightful, as it dovetails with my views on "shelter" not just being from weather, but from other exterior assailants such as urban white noise. Even when prop or jet airplanes fly over the house, more of the sound enters through the windows than it does from overhead (whereas I used to literally be able to know when the plane was directly over the house, since I could hear it through the ceiling).

Bottom line: we're already enjoying the new roof with the short time we've had it, and are looking forward to monitoring its long term performance in terms of energy reduction, comfort increase, architectural enhancement, and increased protection against severe weather.


30.
Sun, 03/02/2014 - 18:20

Edited Sun, 03/02/2014 - 18:22.

White elastomeric roof coatings
by ian Bernard

Helpful? 0

I am an avid green roofing supporter. The many advantages are numerous. If you use the reduce, re-use, and recycle thinking it makes so much sense. Think about all the roofing materials in the US that are torn off and replaced with new materials that came from a heavy industrial process leaving a negative green foot print.
I work in the commercial roofing industry and have gained a behind the scenes view point on green roofing. If all companies would take their existing traditional roofing system like EPDM, TPO, hypalon, BUR roofing, or rolled roofing and bring it up to a spray applied white elastomeric roofing system it would dramatically effect the heat island effect caused by traditional dark colored substrates that hold heat, not reflect it. (only if the current substrate is in sound condition or close to sound).
Once brought up at about 50-70% of a tear off replacement, all they have to do is keep it on a maintenance cycle that would lower their capital expnese over the course of time. It's a win win for the earth and their pocket book. A professional system applied by a qualified contractor comes with extendable warranties in 10 and 15 year periods.
It's amazing to be on these roofs applying white elastomeric roofing and walk from a finished section onto the old black roof sections. The extreme difference in temperature makes you a believer real quick. You can always learn more here: www.commercialpaintingservices.com
The advantages of using these types of systems on metal roofing is their able to flex with the large amount of thermal shock a roof receives from daytime high temps. They completely encapsulate your old roof with a monolithic single ply of elastomeric rubberized coating that is a water based formula manufactured with energy star ratings and green manufacturing process.
More info from Cool rating Roof Council can be found here: http://coolroofs.org/documents/CoolRoofsforArchitectsandRoofingSpecifier...


Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!