White Metal Roof

White Metal Roof

24. May 24, 2012 5:36 PM ET Response to Martin Holladay by Dana Dorsett 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.)
white metal roof 1

White Metal Roof

Response to Martin Holladay by Dana Dorsett 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.)
white metal roof 2

White Metal Roof

Hi Patrick, No three layers of shingles is a no go. They need to be removed, plus the deck needs to be inspected before a metal roof is put on. Darker colors will help the snow melt for sure. How low pitch is the valley? What type of a metal roof is this? Standing seam, metal shingles, ribbed with exposed fasteners? Make sure the slope of the valley is in line with what the roofing system is designed for. I would say a minimum slope of 3 to 12 for standing seam. Metal Shingles would be 3 to 12 or 4 to 12 pitch depending on the systems. Once the tear off of the old rood is completed, have the deck inspected, you will probably have rotten or damaged wood from roof leaks in the valley. Make sure that a breathable synthetic underlayment is installed underneath the metal roof. — It’s a roof underneath the roof, plus it allows your roof deck to breathe.
white metal roof 3

White Metal Roof

10. May 23, 2012 5:11 PM ET Cool Metal Roof by Ross Williams 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.
white metal roof 4

White Metal Roof

Cool Metal Roof by Ross Williams 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.
white metal roof 5

Cool Roof Contemplations by Cameron Taylor 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.
white metal roof 6

A cool roof does not necessarily cost more than a non-cool roof, especially if you are installing a new roof or replacing an existing one. However, converting a standard roof that’s in good condition into a cool roof can be expensive. Major roof costs include upfront installation (materials and labor) and ongoing maintenance (repair, recoating, and cleaning). Additional cool roof costs include specialized materials and labor.
white metal roof 7

The color of your roof plays a major role in helping make your home more energy-efficient, so taking this into consideration will help you save money on your monthly electric bill. Lighter color roofs reflect sun’s heat much better than darker colors. In fact, a white metal roof is Energy Star rated as a cool roof, and can be 50 to 60 degrees cooler than a dark color asphalt shingles roof. It is best to choose a light color metal such as white, light bronze, beige, peach, light green or blue, if you live in a region that has a lot of sun and a hotter climate. A light color of the roof will protect your home from unpleasant heat, as well as help to lower your monthly energy expenses by as much as 20-30%. On the other hand, if your home is located in a cooler climate and remains rather cold even in the summer, it is better to choose a darker color, as it will absorb heat from the sun, helping keep your house warm.