White Roof Coating - Passive Anti-Solar Project for FL

33703: Zone 10a: for all of the Florida/Arizona/S Cali/etc... permies who have the opposite "winter" as the rest of the US (OMG, when will this heat end! I cannot wait for January!)

3/16/14: Put the 1st coast of white elastomeric roof coating on the roof today. I have about 1500 sq ft of roof (950 sq ft house) and a rolled tar & asphalt roof no/little space in the roof for insulation. Crawl space is als uninsulated and the house is a 1960's era cinder block home. I am hoping this will make a significant difference in the heat gain during the summer and reduce the power bills ($300+ in the summer (May-Oct)). Not so much concerned about the heat lost during the winter since that really only lasts about 60 days anyway.

Here is what the 1st coat looks like. Definitely needs a 2nd coat. Went thru 3.25 buckets (5 gal @ $75/bucket) and it took about 4 hours of actual work time, not counting rehydration breaks, lunch and the break that I took when I almost fell off the roof. Went thru two 3/4 inch nap rollers.

Lessons Learned:
If you are painting near your iPod doc, move the iPod doc. Oh, also if you are wearing your running shoes becuase you didn't want to dig thru the garage for your muck shoes, don't expect them to be your running shoes for much longer. Oh yeah, and if you are working backward, make sure you have awareness of where the roof ends.

Totally unscientific test. This is what the roof over my porch looks like vs the coated roof. Not too dark but still picks up a LOT of heat. This side of the house is on the East side and gets nearly full sun until about 4:00 PM. At 2:30, when I was finished, I placed my right hand on the unpainted porch roof and my left hand on the 1st coat of paint on the portion of the roof I had done 3 hour prior. To me, there was about a 10 degree difference. Today, the weather was about 80, full sun and really windy (~20 mph all day). UV rating was probably about 6-7 out of 10. My guess is that during the summer, when it is 95 and the UV rating is a full 10, I might see a 20-30 degree difference, or more. I can tell you that when I was up on the roof last May painting my eves, I had to lay a towel down bucause putting my bare knees on the roof was way too hot...at 10 AM and only 2 hours of sunlight.

NOTE: this stuff needs to have a 24 hour dry period...I messed up and got up too late on Saturday and realized today (Sunday), after I was finished of course, that there is a 90% chance of rain in the PM hours on Monday. Hopefully, I won't see any damage or runoff of white tinted rainwater coming off the roof.

Update to come in a couple of weeks when the 2nd coast is on...

***Update*** 3/30/14

Completed coat #2. Weather was about the same (Windy, Sunny, Warm but not Hot). The 2nd coat went on super fast so I was done in about 3 hours, instead of 4. I'm guessing that it went on fast because I had a smooth coat, versus the initial coat that sucked up all of the paint. Plus, I bought a different roller this time. This one was coated with Teflon so it didn't soak up the paint, just held it in its mass of fibers. This coat took just over 2 5-gal buckets, instead of 3.25 for the 1st coat.

When I was finished with the 2nd coat, I completed anothre unscientific test, placing my hand on an uncoated section in full sun and my other hand on a coated section. There was a significant different between the 2 temps (~130 vs cool to the touch, as if t were in the shade all day). I'm guessing there may have been an evaporative cooling effect going on so I am going to recheck it after it has cured for a few days and the heat really starts to kick in later in the week (85+ in FL this week already).

Next is looking at the AC bills from last year, same timeframe, versus the 2014 AC bills.

Gosh. I see this post has been here for weeks and no responses.

I was hoping to get some feedback on "Cool Roofs". Is it worth the money verses the savings. If you have an existing asphalt roof, what's the best Eco-friendly upgrade?
The roof is fifteen years old and needs replacing soon.

I've been upgrading/renovating for the last few years to make my MH eco-friendly. Added straw/clay insulation all around the exterior walls, additions are paper adobe and/or sawdust clay/slip, and more.....

Now I'm finally getting around to the roof. I want to make it as earth friendly as possible. A MH roof is crappy 2 x 2 trusses, with 1/2" plywood, and asphalt shingles. My thought was to put a cool roof coating over the existing shingles. not finding a lot of info about this online. Most sites do not recommend painting a cool roof product over shingles. I talked to ANVIL (makers of roofing products) and they said it's okay, but you must clean, and then seal the shingles first, to make them less porous and for a better seal between coating and surface. Does anyone on this list have any experience with "Cool Roofs"? Is it better to use elastomeric? or a ceramic coating? I've seen some sites that say it's all a waste of time and money.

E. Henderson: Did you seal the roll roofing? What white coating product did you use? Is a fibered elastomeric better? I live in the Southern USA. Hot from May to Oct.
My building renovation design philosophy has been to use natural insulations as much as possible. I'd like to the same with the roof.

build it solar has a similar project but they used lime to coat the roof (less toxic gick onsite, not sure of overall greenness, probably not the right answer for heavy rain areas).

I think that coating a roof and keeping the asphalt out of a dumpster for another 10+ years is a great plan.

If the roof is beyond that, then I would go with a metal roof. Rugged, non-toxic, can be diy, can add foam insulation to the roof at the same time, can be built to provide solar shading to the existing roof deck.

R Scott: I'd like to do a metal roof, but that's out of my budget. Covering the existing roof with elastomeric or a ceramic layer is more cost effective for me....

There are highly reflective asphalt shingles, but they cost more. A double roof is best to keep the heat from getting inside. The outermost layer should have good ventilation and the inner layer should be well insulated. People will often put a radiant barrier between the outer layer and the inner layer. There are too many configuration options to cover in one post.

I couldn't afford a double roof, so I used foil covered bubble wrap installed between the roof joists to form a channel for air to move from the eaves vents to a ridge vent. It seems to work well enough, as I am able to keep the whole house comfortable (if the kids keep their doors open at least 4 inches) with the same cooler I used before I doubled the square footage with a second story addition. I also installed my siding as a rain screen with vents at the bottom of the 3/4" gap, forming a channel to the eaves and on up to the ridge vent.

When I was in Texas, many years ago, I saw many trailer homes setup under pole barns. The shade of the barn made a big difference and was added protection against hail -- but not tornadoes.

A truly green option is to put up a light trellis over the roof and train some vines to grow on it to shade the house. The major drawback to surrounding a house with plants is mosquitoes. There is always a complication.

If you coat your roof anyway then coating it white is ok otherwise you are using a lot of sometimes poisonous materials and all the paint might have a bigger footprint as the whole project is worth it. If you heavily plant a lot of trees in your yard there is more effect on the temperature. They did temperature montioring in Brisbane years ago and there was one yard considerably colder than the neighbouring, when they looked it was because it was heavily planted (ornamentals only, nothing permie).

I put a steel roof on, with the same kind of paint as used on military vehicles to reflect the suns rays better. Jay

t ismy understanding that any metal roof will be hot.
In Australia I measured the surface temp. at 76 deg. C in full sun
When it was shaded by a solar panel 56 deg.
And when shaded by a safari panel system I designed it was 38 deg.
The safari roof consists of another sheet of steel installed 100mm off the roof on a frame, with a layer of top quality thermal insulation installed 50mm off the roof.
It works by shading, reflecting from the thermal sheet and by having air pass under the 2 new layers.
Any metal sheeting will be cooled dramtically underneath with good reflective film and rockwool.

The temperature on the roof also has an effect on the efficiency of the solar panel I believe.
Effect of temperature on solar performance

Interesting that the surface temp. of the panels was measured at 77 deg. close enough to my results also.

Home solar panels are tested at 25 °C (77 °F)  and thus solar panel temperature will generally range between 15 °C and 35 °C during which solar cells will produce at maximum efficiency. However, solar panels can get as hot as 65 °C (149 °F) at which point solar cell efficiency will be hindered. Install factors like how close the panels are installed to the roof can impact the typical heat of your solar system.

Being that I am a fan of paying attention to building science  I am not a great fan of doing what on the surface looks to be the easy solution.  I personally would not have used the coating.  I would have built up the roof.. added 4 to 5 inches of rockwool bat insulation.  Then put two layers of 2 x 4 on the flat screwed down on top of the insulation bats.  Each course of 2 x battens set at 45 degree offset from each other.. Resheath on top of these battens and then laid steel right over the top of the battens.. Why is simple.  The insulation could be as much as r 20 and being exterior it cuts 100 % of the thermal bridging that just transfers right into the house.  The battens allow the roof to be ventilated.  meaning that under the roof will be much closer to ambient temperature than 160 that is likely to be what is happening in the low attic of this house.    There was no mention of the framing of the house but being florida could well be cement block.. which also given that it is florida has no insulation or perhaps a couple inches if they framed the interior.  So they build with a great heat sink on the outside of the house.. The night temps are much like the day time temps down there so... I can only imagine what it is like living in an oven that the AC is running 24/7 just to make the house marginally bad to live in