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Sunday, April 25, 2010

White Roof Coating, Ahead of Summer

After completing major tuckpointing and chimney rebuilding, we decided to apply a white elastomeric coat to our flat roof this month. This roof was a three-ply modified bitumen roof with a black, heat-trapping emulsion overcoat. The roof was old enough to coat but certainly not getting younger under the toll of ultraviolet rays. A mod-bit roof needs about one year to leech out oils before coating, and ours was well past that mark. Time to coat!

Now why would we go through the trouble of applying a white coat? There are two major reasons:

Energy efficiency and global warming. A white coat can reflect up to 80 percent of solar radiation, reducing overall planet temperature but more immediately reducing building, neighborhood and city temperature. One white roof is small local block against the urban "heat island" effect and many of them can have wide impact. The white roof will reduce the internal temperature and the need for air conditioning, which in turn reduces the electricity usage and so forth. (There is some question about possible heat loss effect of a white roof in winter. At St. Louis' latitude the sun's rays are vertical in the summer and at a low slant in the winter, so the available winter solar heat is much less than the summer heat. At other latitudes, a white roof might not be of such benefit as here and points southward.)

Longevity of the roof. An elastomeric coat will block ultraviolet rays that slowly break down asphalt roofing. Coats should be reapplied every 10 years or sooner if needed. With timely reapplication, the coverage can extend the life of the roof to 40-50 years, reducing cost as well as waste of nonrenewable roofing materials.

While the mason had the scaffolding set up, we used his pulley to hoist up the 5 gallon buckets of coating. We used five $72 buckets of Henry Solarflex 287, which completely covered our 1300 square foot roof. When the scaffolding was down, we used a tall ladder for travel to the roof.

Working with a friend, we spent about eight hours washing the roof and applying the coat. Since we had just had masonry work, the roof was dirty and required over two hours of scrubbing. The mod-bit roof dried quickly, however. We applied the coat with a 4" brush on the parapet sides and 9" rough rollers on the roof. We avoided a few new flashing repairs made around the rebuilt chimneys.

Most of the roof was covered with two coats, but some areas required three coats. (a one year old roof won't take this much work). We left a spot near the ladder for exit and came back to finish in a half-hour a day later. Now the roof is too bright to look at, just in time for summer. We're not big air conditioning users -- it's expensive and not very sustainable, although certainly necessary for a few weeks -- so we definitely look forward to the building heat reduction.


andy said...

Looks great, great post!

I wonder if it's cheaper to buy a black EPDM roof and coat it, or go straight to a white EPDM roof...

Anonymous said...

now that's a nice looking roof

samizdat said...

I had a white TPO roof installed in '08. I didn't ask about the price differential, but I doubt that the addition of titanium dioxide to the mix increased the price by a great amount. I'm betting that the same goes for EPDM. There are certainly a few more chemicals added to the mix in order for the titanium dioxide to fully disperse in the rubberised matrix, but a few grams per kilo of material shouldn't dent the pocket book too much. Congratulations, Mr. Allen, on a wise and energy-saving chouice. Your heat load will drop and your contribution to the heat-island affect will diminish significantly. I also installed rigid poly-iso insulation under the new roof. UE reports that I saved 25% on my electric bill in '09, as compared to '08. And of course, I can walk on my roof at the hieght of summer. FYI for those who remain doubtful: http://www.youtube.com/watch?v=5wDIkKroOUQ, http://www.youtube.com/watch?v=5wDIkKroOUQ, http://www.scientificblogging.com/news_articles/white_roofs_could_reduce_urban_heat_island_effect_33_percent, http://www.epa.gov/heatisland/index.htm, http://www.epa.gov/heatisland/resources/pdf/CoolRoofsCompendium.pdf

barbaroja said...

Great article. Just found this blog and plan to read all the way back to 2004, when I lived in STL on Russell in a house we brough back from the brink of rubbledom.

I Now live in Central Mexico (San Miguel de Allende) where roof coatings like this are a no-brainer. The most common brand here recommends annual re-coats with a thinned (5/1) solution of coating. Most of the roofs here are either reinforced concrete or brick bovedas and need recoating as much to fill hairline cracks as for overall protection.

My roof also happens to be covered with solar/electric and solar/water panels. I moved to Mexico in part to have the freedom to expiriment with living lightly on the land without having to jump through hoops in order to get permission to do things that make sense (eg: Grey Water recycling).
So far I think I made the right move.

Keep up the good work!

Rick (http://GreenMapSanMiguel.org)

samizdat said...

^^^Aaah, solar PV and water heating...some independence from the grid.

Doug Duckworth said...

It was a fun project, but this stuff does not wash off easily.

Roof Leaks said...

I think White EPDM Roof coating is cheaper than the black one. What do you think guys?