Cool your roof/house/planet
I’ve been having a conversation about roof cooling products (yes, I know solar is coming, etc..) – and, in the meantime – one can paint the roof with this or something like it. Please consider if you are having roof work done.
Here are some more comments on this from Mark Lakeman, one of the founders of The City Repair Project and a personal local hero of mine.
1. I spray painted two roofs this summer, took an hour and a half for one, two and a half for the other….immediate 35 degree reduction on the second floor !!
2. Pressure wash and sweep first! The paint needs no primer, but it does need two coats. Best to do first coat without trying too hard, because the porous roof just tries to soak it in. The second coat is when you care about about even coverage, but it freaking WORKS !!!!
3. The product is available at Sherwin Williams, called “Kool Roof”, latex, will extend the life of your dark roof by many years of you do it soon enough, before the old roof wears too far.. This could easily become a new business line for house painters or anyone who has the equipment for such + it doesn’t involve replacing a roof – just painting it (I know, not an easy task).
———–
Maria: What’s it made out of? Will it pollute the run off when the rains come?
Mark: Good question Maria. It should be much less toxic than the petroleum-based composite shingles that it covers. Of course composite shingles shed petroleum as well as fiberglass. On the other hand this latex paint Shields and caps that stuff and according to my biologist neighbor is relatively innocuous when it goes into the ground or even gets to a stream. The best thing about this is that it can extend the life of an otherwise dark roof by many years, which is really great for the Earth
Mark Lakeman About solar panels versus white roofs, I don’t think that they are mutually exclusive at all. Solar panels don’t tend to take up your entire roof surface, sometimes only a small portion. In fact you can paint your roof white right now and then install your panels later. Best, order your roof to be white when you first get it and use metal roofing because that is the best choice for many reasons. Metal roofs last the longest, are virtually permanent, or require no maintenance, and ultimately are recyclable anyway. You can’t lose with metal roofs, better in every respect. Besides the lower initial cost of tab roofing, it has few other advantages. You’re buying garbage that is bad for your planet and your babies.
—-
Just cause – this got too interesting 🙂 My friend Joe in Port Townsend is a genius, so it’s fun to read what he has to say :
Joe: IMHO it is pretty good stuff. The major issue is that the way asphalt tar based roofing works is that it constantly reseals that gaps that form from expansion and contraction due to temp changes, by heating above the softening point of the asphalt. Defeating that mechanism, if you make the surface of your roof substantially cool, certainly invites leaks.
I ended up using a different product that I like better called SnowRoof that goes on in 2 applications, a basecoat primer and a topcoat. Brilliant engineering IMHO: it rolls on and then changes color pretty dramatically when it cures, which makes it VERY easy to see if you have adequate thickness.
Mark: Joe, I respectfully engage in a conversation with you about this issue. The conclusion you draw about inviting leaks is actually why we advocate for changing the color of a roof. I don’t mean to be argumentative because you may have a very good point, however when you paint the roof white it tends to stop the expansion and contraction affect that you mentioned. This is considered a good thing because expanding and Contracting breaks down the shingle. By keeping it one color it simply doesn’t expand and contract nearly as much if at all. You say that creates leaks, I say that it prevents them. It would be good to find literature that actually suggest that it encourages leaks, because that does not seem logical to me. Also the latex is a flexible seal so it Shields the surface of the shingle. Although I respect what you are saying, I would be very surprised if we have leaks in this old roof of ours that we’ve just painted for another decade
Joe: if it prevented expansion and contraction that would be a VERY different situation. It does not. The range of temps and the differential thermal expansion of materials used matters. The question is how much reduction you actually achieve, at both ends.
Plenty of research on the interior temperature of different color automobiles. I have lived under several colors of roof in the past, including gray, white and reflective (aluminized). I suppose I should go measure the temps of the skin of my car and the aluminum truck utility boxes and my white cargo trailer that are all parked within a feet of one another and post that here and you can calculate the differential expansion for roofing materials.
I am an empiricist and I measure shit, and built test fixtures, when in doubt. I have done a lot of research into the infrared emissivity of different colors, that was required because I could not find published relevant research.
I made a series of “patchwork” ripstop sleeping bags trying to find what color could go coldest w/o emitting IR to the point where it cooled the surface below the dew point (inside surface or outside surface) and started condensing. The reason people use elastomer roof treatments is to address thermal expansion, which is an issue any time you have penetrations in your membrane. Standing seam metal roofing was developed in an effort to address the leaks.
I am willing to wager that an attic fan can have a lot more impact than a bunch of white paint, But we ought to stop blathering and do the math, We do not need to find peer reviewed papers to evaluate stuff we can do with 5th grade arithmetic.
Fluke IR thermometers, here we come. Surface Temp readings will be added in a few minutes.
