I have a west wall (SW Texas; Austin/San Antonio area) that heats to 160-175 degrees in summer (IR thermometer reading). It is a composite plank/board, painted a medium dark green, about 10 years old and fading, chalking some. I know the lighter the color the more reflectance. I "think" the glossier the sheen the more reflectance? Preliminary research has found a Kelly-Moore "Enviro Coat Reflective paint. I've also seen references to "additives" that help reduce heat load ... some of the information seems a little snake-oilish :) I'd appreciate any education here I could get and advice on products. I am coming to the opinion that I should just go with a good quality, semi-gloss white ... and that would give me most of the benefits of the more expensive options? That was a question :) And yes ... the live oaks are planted ... should have reasonable shade in 35 years or so ... the oleanders don't seem to be helping in the short run, seems they need water ... mother nature isn't helping and there are city/county restrictions on outside watering, which I agree with. Thanks.

The ceramic nano-sphere additives only work when mixed with the purest mouse-milk- keep the snake-oil away- it'll contaminate it! :-)

Seriously- third party testing of that crap has sometimes shown INCREASED absorption of solar spectrum, if only slightly, and no thermal benefit in the non-nano-scale world.

High-gloss or low doesn't much matter from a reflectivity point of view- it's all about the absorptivitity/reflectivity of the pigments across the spectrum of incident light. Kelly-Moore Enviro Coat Reflective 1545 is low sheen (allegedly to reduce dirt-adhesion) but highly reflective over most of the solar spectrum due to the anatase titanium-dioxide white pigment it's based on. Titaninum white is about as intensely white as it gets in the pigment world, and it's not just visible-spectrum.) The other metal oxides & silicates they use to tint it to give it some color cuts into that reflectivity a bit which is why the TSR specs are in the 50-60 range and not 80+. The TSRs of different colors are listed in the table on p2 of the short-form spec:

http://www.kellymoore.com/userfiles/file/pdfs/1545tds.pdf

The higher the TSR, the more reflective it is.

Any pure-white paint that uses an anatase titanium dioxide pigment (as opposed to rutile TiO2 ) will have similarly high TSR, but many white/off-white pigments can be fairly absorptive in the infra-red, which is more than 1/3 of the total energy in the solar spectrum. We can't see in the infra-red, and as long as it reflects most of the visible portion it appears white, but not all white pigments are super-high solar reflectance, though most are probably north of 40 for a TSR / SRI. To compare the main TiO2 pigment types see figure 5 on page 7 of this docuemnt- they're not all the same.

http://www2.dupont.com/Titanium_Technologies/en_US/tech_info/literature/Coatings/CO_B_H_65969_Coatings_Brochure.pdf

The Cool Roof Rating Council keeps track of the reflectance of a number of mop-on coatings suitable for roofs, (some with initial reflectivity greater than 100) but none of those are likely to be cheaper than a decent titanium-white paint. http://coolroofs.org/

My gut says you're probably not going to do much better performance wise than the Kelly-Moore product.

That said, heat gain is far more about windows, attic-R, and shading factors that it is about the wall paint. If you have any windows on that wall, the heat gain through 10 square feet of window could easily be an order of magnitude more than the direct gain through the rest of wall. (Measure the temperature of the INTERIOR surface of the wall- if it's hot it's probably due to an insulation issue.) South windows can be shaded with awnings, but west facing windows would need exterior pull down shades, exterior shutters,or a really deep porch with roof.

Measured over an entire summer day, a white flat roof might save ~10% over a black one. Walls and steeply sloped roofs have considerably less savings (due to convection), perhaps to the point where some bushes or trees might be a better option (shade should bring the wall all the way down to ambient).

Posted By Dana1 on 25 Mar 2014 06:28 PM
The ceramic nano-sphere additives only work when mixed with the purest mouse-milk- keep the snake-oil away- it'll contaminate it! :-)

OK, but I have to tell you, I grew up on a dairy and have milked a lot of cows, a few sheep and goats, a couple horses but these mice are giving me hell. Seems like only 35 to 40% of the little critters I round-up are females, only a few of them lactating, and getting hold of those tiny little teats is hard ... why am I remembering a college girlfriend?

Seriously ... I very much appreciate the information. As in the past it has been most educational and helpful. Thanks again to both of you.