It Snows in Summer

If it were to snow in summer do you think it would cut down on the air conditioning costs? Can it snow in Atlanta in the summer? Why not….

IMG_7976

Knowing when the sun beats down on a roof it radiates into the attic and ultimately the house I knew an action on the roof would result in positive outcomes. Previously insulation was added to the attic and there was a foil radiant barrier put up against the roofing joist.

The Idea

After reading about a couple projects of cool roofing on the web site “builditsolar.com“, I decided to move forward with a cool roof plan. The first project I read about was from David M. Mundy, it was a plan to use hydrated lime to coat the roof with.

His idea was duplicated by Wolfgang in Sherman, Texas. The main idea of using hydrated lime was to cut the cost down from using elastomeric coating which is recommended from www.whiteroofproject.org .

The Risk

The idea has it’s controversy, an article from Maciek Rupar presented here states the manufacturers of asphalt shingles recommend against field application of elastometric coatings on asphalt shingles. There was even a law-suit in Florida pertaining to the coating. Florida Power and Light worked with local contractors to apply the coating to the houses in their area of service. 4,711 roofs were coated in south Florida. The law-suit was five homes in Hialeah, Florida installed by the same contractor who went out of business. There is another article on the same issue with good info. I also looked at the comments below this article. Five homes out of 4,711 is about .1% of the homes coated. One of the things in this lawsuit that looked interesting to me was the issue of leaking due to water being trapped under the coating which caused the issue with the houses. I have been to south Florida and I wonder if the contractor applied the coating during the rainy season there.

With the above caution of the coating I don’t recommend doing the same on their roof’s. In other words you are responsible for your roof if you coat it. (Just as I am responsible for my roof.)

I determined to move forward with my plan to coat my roof in spite of the warnings from the asphalt tile manufacturers for the following reasons:

  • The tiles on my roof were on there with the purchase of the house; I don’t know who made them so any warranty is unable to be collected anyway
  • The main risk I saw was the risk of trapping moisture; I have places where heat escapes at the peak of my roof and I was careful to not coat anything until the roof was dry for a few days
  • Elastometric coating have been used in Europe since the 60s; it seems to be a proven technology
  • The coating is virtually used on every other type of roofing and adds to the durability of the roof; I have no reason to believe this wouldn’t be the case with my roof
  • I was not fully in with the hydrated lime; I didn’t feel like mixing it and I thought the elastometric will last longer

Of course I’ll be inspecting the roof from time to time.

The Action

Before beginning I sealed all roofing issues to make sure I had the best possible roof to start with.

preseal

Progression of Temperatures:

I took measurements:

  • Outside temp 90 deg F
  • Attic temp 122 deg F
  • Inside temp 76 deg F
  • Surface temp roof 175 deg F

 

temp176

After about 1/2 of the roof done:

  • Outside temp 90 deg F
  • Attic temp 109 deg F
  • Inside temp 76 deg F
  • Surface temp roof coated 116 deg F
  • Surface temp roof without coating 178 deg F

temphalf

After 100 % of roof coated:

  • Outside temp 90 deg F
  • Attic temp 95 deg F
  • Inside temp 76 deg F
  • Surface temp roof 114 deg F

tempafter

All measurements were taken at 3pm on each day; in the same area of the roof. This was on three separate days with the same outside temperatures but I neglected to check the humidity. Also the last measurement was right after I completed the job so I suspect there is some built up heat in the attic.

Interestingly to note the first measurement was taken and the air conditioner was on while the next two the air conditioner was turned off.

Side Notes

Side by side comparisons:

temp116 temp178

Sneaker failure due to hot roof:

shoemelt1

Side Sliding

shoemelt2Total Blowout

Shading difference:

temp109shadeShade Un-Coated

temp108near shadeCoating near shade measurement

shadewcoatingCoated in shade

Half done

abouthalf

All done

haus100

The Bottom Line

The reason to go through such tasks is to get a reduction of energy usage for a reasonable price. I spent $1041 on the paint and supplies at Lowes (it was the 10 year version). I based the numbers on the 10 year usage. I did the work myself so the cost was zero to me.

The cost would be $104 per year if I divide up the total cost into the 10 years. My kWh usage is on track to be under 600 kWh this month. The same month last year was 1240 kWh. As full disclosure I have some family members on vacation this month which cuts down on the heated water usage. (laundry, showers, dishwasher, etc). The usage charge would be $48 if this holds out (plus $22 service fee and 6% tax). Comparing this to last year the usage charge was $109 (plus $21 service fee and 6% tax). This means in 2-3 months I’ll be making money back per year.

kWh per day compares last year 43.14 kWh to 17.85 kWh this year. Anything under 19 keeps the usage charge under $50. Anything over 29 kWh per day keeps the second tier pricing from kicking in which is a third more per kWh.

The big question for me is how much winter penalty is going to happen due to the sun not heating the roof. I suspect it won’t be much as the sun is lower on the horizon in the winter and there are less daylight hours in winter. Time will tell how well this works but, all I can say is so far so good.

 

 

 

 

 

 

 

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