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Unread 07-24-2021, 05:18 PM   #1
makethatkerdistick
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Reflective metal roofing in hot climate

I just wanted to share my experience with the positive impact the installation of my white metal roof has had on energy consumption and climate control in my house.

I had a white 24 gauge standing seam roof installed at my house last year. I chose the PVDF/Kynar paint system which has an excellent track record for durability. The roof was expensive. Furthermore, a substantial installation error led to a battle with the installing contractor which cost me lots of sleep and nerves. Thankfully, I was able to get him to help me correct the problem. Anyway, I digress.

Overall, there is no doubt in my mind that this roof is the right thing for me and my family, especially given our very hot and sunny climate here in North Texas. I am impressed with the roof's ability to reflect sun light and the high emissivity of metal, leading to rapid cool-down after sunset.

I installed a remote temperature sensor in the attic which gives me a constant readout and lets me track the temperature rise throughout the day. Believe it or not, this roof keeps the attic temperature at or near ambient outdoor temperature. It often runs slightly above ambient, but reaches no more than a 10 degrees F difference. Typically, the attic is about 5-6 degrees F warmer than the outside. Imagine going into an attic in the middle of a sunny Texas day and not dying. From my old shingle roof I know that attic temperatures routinely reach 140-150 degrees F.

Since all my ductwork is in the attic, this dramatically improves the efficiency of my HVAC system. Furthermore, my ceiling is also completely air-sealed and very well insulated, thus I have no more warm ceiling spots. The comfort level is truly amazing!

Clamping on solar panels and associated racking is extremely easy with a standing seam roof. One attaches clamps to the seam in lieu of drilling through the roof. No penetrations were necessary.

The roof surface itself is only slightly warm to the touch in full sunlight. It can be accessed without burning your hands or feet. Naturally, metal roofs are slippery and more dangerous to walk and work on. I got myself some magnetic roofer's boots for that purpose.

Since this is installed on full plywood decking, I only notice a minimal increase in noise during rain events, if even that.

I've been logging my energy consumption in the past 30 days. The average daily high was probably in the mid 90s, the average daily low in the mid 70s. A total of 840 kWh was used between June 21 and July 21. According to my energy monitor, approximately half of this is used to cool the house. We keep the thermostat set to 73 degrees. Most of my neighbors consume three to four times the amount of electricity to achieve the same.

In a nutshell, white metal roofs offer longevity, comfort, and tremendous energy savings in hot climates such as mine. They perform so much better than composite shingle roofs in every possible aspect.

I just wanted to share this in case anyone might find my informal case study useful.
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Unread 07-25-2021, 07:19 AM   #2
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Thanks Wolfgang! Love this kind of information
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Unread 07-25-2021, 07:26 AM   #3
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If I were still building, I'd convince one of my customers that we needed one of them fancy white metal roofs just so I could test your data, Wolfgang. I've done a lot of metal roofs and never had an attic that had only a 10 degree above ambient summer heat gain. And I build a pretty good house if I do say so myownself.
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Unread 07-25-2021, 10:09 AM   #4
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Quote:
Originally Posted by CX
I've done a lot of metal roofs and never had an attic that had only a 10 degree above ambient summer heat gain
We have a standing seam roof, galvalume, and closed cel insulation underneath. The temp in the attic is only slightly higher than inside the house. The temp in the house is set to 76-78º, depending on who is messing with it, and it's probably no higher than 85 in the attic even tho it's 90-95 and sunny outside.

Very easy to work in the attic, which is rare anyway. Our last house had shingles and blown in insulation. We had the ductwork replaced and the ac guy's price was 50% higher if we wanted it done in the summer.

I couldn't be happier with the insulation and standing seam combination. With that said, I didn't even consider white. Probably would after reading this tho.
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Unread 07-25-2021, 11:10 AM   #5
makethatkerdistick
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Here's a picture of my thermometer. As you can see, my attic temperature vacillated yesterday between 73 and 102. I think the weather report said it was sunny with a high of 95. That would make it a 7 deg. difference at peak.
I noticed that in the morning the attic will lag behind a few hours before it slowly rises above ambient. This is owed to the emissivity of the metal and its ability to quickly shed thermal energy at night, giving me a thermal buffer in the morning.

For this sort of reflectance you have to go fully white. Light grey won't do it. Beige won't do it. They will still run cooler than a dark color, but there is a distinct difference between a white white and anything else. Really, it's just simple physics. Metal manufacturers will also post very detailed spec sheets that show solar reflectance and other thermal performance indicators. This will very precisely predict field performance. It's all there in the data, really.

I noticed that of late in my neighborhood charcoal-colored shingle roofs have become all the rage. It's the darkest shingle color one could imagine, literally turning your house into an oven. And if you lose power or your AC fails, then very quickly your house becomes a death trap. Texas has seen this happen during Katrina. To me, this violates what housing should be about first and foremost: providing shelter and keeping us safe.

People will often say that shingles are so much more affordable than metal. And while that is true, once you factor in the cost of additional energy needed to condition your house, I think the price gap shrinks quickly.

Naturally, white roofs only make sense in certain climates, but they are hard to beat. And there seems to be the barrier of aesthetics. Most people are used to certain roof colors which they deem aesthetically pleasing and "normal." But that is a cultural value, not based on performance. If you play with Google Earth, you'll see that, for instance, white roofs are much more common in New Mexico and Arizona. Texas, not so much.

Jerry, we considered spray foam to make the attic a conditioned space but chickened out. I was afraid of small leaks and ensuing condensation issues.
Instead, I opted for air-sealing the ceiling area very carefully yo make it as airtight as possible. That alone made a big difference, even when I still had the old shingle roof. But whole-envelope spray foam is the best insulation, really. Especially closed cell. Your combination of metal and foam is very solid. You wouldn't gain much by going white at this point.
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Unread 07-25-2021, 02:38 PM   #6
Davy
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Just wondering, would your home insurance be higher with a metal roof since it's more expensive to replace? Does the metal hold up better in a hail storm?
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Unread 07-25-2021, 03:33 PM   #7
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Short of a catastrophic event (such as a tornado hit), 24 gauge metal will not fail in a hailstorm. It could, however, be cosmetically impacted, but to my understanding that would require extremely big hail. The thicker the gauge, the better. Same with the solar panels: It would take extremely big hail to break the tempered glass that protects them. I have had them for eight years, and they've weathered all hail events just fine so far. In fact, they're super robust.

I got a nice discount on my Liberty Mutual insurance policy when I shopped around after the installation. My old insurer (Nationwide) actually wanted to charge me more (and they didn't even pay for the replacement). That was their way of saying thank you for five years of being a customer without a claim.

The consensus is that, yes, you can get a discount with most insurers. It's generally known to insurers that metal roofs will reduce the risk of storm-related damage to the rest of the house. What you should never do with a metal roof is sign a cosmetic-damage waiver. If you get dents and want to file a claim, they won't pay a cent in that case.
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Unread 07-25-2021, 07:36 PM   #8
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Thanks for the info.
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Unread 07-25-2021, 08:34 PM   #9
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Insurance companies like metal roofs in general because it helps prevent fires spreading from your neighbor's burning house. In the last neighborhood where I lived last time I lived in the Ft. Worth area, wood shingle roofs (what I had) were finally outlawed completely as too much of a fire hazard. Well, I don't think the roofing was outlawed, actually, but you could not get insurance on a house with such a roof and therefore you could not obtain a mortgage. Same as being outlawed, for all practical purposes.

I've seen 26 gauge metal roofs damaged from hail storms in my current area. It's actually all cosmetic, but the insurance companies call them "destroyed," anyway. Now, the cheapo 29 gauge roofs will sometimes actually crack in such storms. When I was building, the 24 gauge Wolfgang has was not available in my area that I'm aware of. Wouldn't be much fun to work with, but sure would make a nice roof.
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Unread 09-18-2021, 09:43 PM   #10
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I thought of your roof when I read this and thought I would share


https://www.usatoday.com/story/news/...ng/8378579002/
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Unread 09-19-2021, 11:20 AM   #11
makethatkerdistick
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I had heard about this Purdue research project. The problem is that all whites exposed to the elements will somewhat dirty, reducing their effective solar reflectance. In theory, this paint reflects more than the typical white. In practice, it might make very little difference compared to what is already available.
In many hot climates, you will still need cooling as the ambient temperature rises above what is comfortable and as insulation, even the best, only retards the movement of thermal energy. Still, a house properly done with what is currently available, you can succeed and only need very little cooling.

But yes, white roofs should be a no-brainer in hot climates. It is an old tradition to whitewash buildings in many cultures and countries. Nothing new there. Actually, a hydrated lime whitewash is one of the whitest whites I have ever seen. I attempted that with my old shingle roof, and it lasted a few years and eliminated attic heat quite well. Cost me $80 for the lime, but ended up looking ugly after five years. You need to redo the finish every so often.
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