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Community and Q&A

Painting Asphalt Shingles

First Last | Posted in Energy Efficiency and Durability on

We have an and old (1910) house, single story with partial basement.  I’ve foam-sealed and weatherstripped everything i can find, and done a first pass at attic insulation with ~R20 blown cellulose (this was all they had in stock when i purchased, or i would have done at least R30).  IECC climate zone 5B~6B.

The windows are single pane, the walls/floor/foundation remain un-insulated, (and I don’t believe there is anything cost effective to do about that until we can perform a full-gut remodel and/or new construction).  Realistically the house also still leaks like a sieve even with my sealing efforts.  At some point we plan to do a large remodel and/or new construction to accommodate a growing family.

I have some prel1minary energy consumption data after adding the attic insulation, and while _comfort_ has improved substantially (important as we WFH), overall energy usage is still extremely high (~60kwh on 105high/90average day, 49kwh on 95high/80average day).  As the HVAC is still outmatched by demand (temperature peaked inside around 80degrees on the 105degree day), summer energy usage is not actually reduced much with the attic insulation.

Which leads me to consider other relatively easy energy-saving measures i could apply.  Such as white paint over my asphalt shingles.

It seems there are two classes of product for asphalt shingles:
– “paint” (with primer), which doesn’t change waterproofness (or breathing) and has a shorter useful life.  Cost for ~800sqft of roof is approx $100-$200
– “coatings” / applied elastomeric membranes – form a fully waterproof layer.  Cost seems to be roughy $1000 (3-4 coats required, 50sqft/gal, and $15/gal), but it does last longer.

The cost of the later is high enough I highly doubt it’s more effective than going crazy with ~R60 of cellulose.  I’d also have serious concerns about freeze/water damage as the membrane inevitably leaks between itself and shingles over time, in a climate that freezes regularly in winter and shoulder seasons overnight.

So, mostly for the simple paint approach, and given i have non-nill air exchange with the attic despite the cellulose – how performant is it?  Any way to compare apples to apples?  Given the paint’s lifespan, it sounds like a similar lifetime cost of a large powered attic fan (?).

Note that while I’m not a professional in construction or energy efficiency, i have a solid amount of remodeling experience and am interested primarily in projects i can tackle myself.   Any other related ideas welcome as well.

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Replies

  1. First Last | | #1

    Also, related to this question - what about exterior WALL paint?

    The house is a simple rectangle, roofline & long-dimension east-west. Both the south roof and wall get mostly full sun.

  2. Expert Member
    Zephyr7 | | #2

    I will warn you, again mentioning that I've actually done this before (but on a commercial flat pitch roof), the paint will look crappy after less than one season. It will get all splotchy and look like a condemed property. On a flat roof, this doesn't matter -- no one can see it from the ground (in my case anyway, where I tried it), but on a regular residential roof EVERYONE will see it. Are you sure that's a tradeoff you're willing to accept for a degree or two at best of cooling performance improvement?

    When I did this, and had lots of sensors to document performance (it was a project for a paying customer), the temperature change due to the paint was minimal, maybe 1 or 2 degrees or so. What we noticed most, and were least expecting, was that the peak temperature inside the building was delayed further into the day compared to where it peaked (relative to the time the outdoor temperature peaked) later in the day.

    There is a benefit, but it's small.

    Bill

  3. Expert Member
    DCContrarian | | #3

    You're in a heating-dominated climate. You have to factor in the loss of heat in the winter too.

    I have no idea how to do that calculation though.

    1. First Last | | #5

      Definitely technically true, but two complicating issues here:
      - being uninsulated, we have two problems: first comfort** (the HVAC can't keep up in general) and second we'd like to conserve energy and don't mind spending some money to do so. The current furnace has no problem keeping up in the winter; the AC cannot for the hot months of the summer
      - we don't ask as much of the system, relatively, in the winter. We can always wear more clothes, and for my wife WFH she can deploy a small couple hundred watt heater or heating pad just when she gets very cold, for shorter times. In contrast, i have a tough time falling asleep when it's 80 inside, even with the fan on high, and I can only take off so many clothes :)

      1. Expert Member
        DCContrarian | | #7

        Don't discount comfort. The only reason to heat above the freezing point of your pipes is comfort, and it's the only reason for AC at all.

  4. Expert Member
    DCContrarian | | #4

    > I’ve foam-sealed and weatherstripped everything i can find, and done a first pass at attic insulation with ~R20 blown cellulose (this was all they had in stock when i purchased, or i would have done at least R30).

    This is a curious statement. Blown cellulose gives an R-value for however thick you blow it. I know the big-box stores will label the package as "R20" but then the fine print says "at 6-inch thickness." It's just marketing, and I'm not sure why they do it.

    1. First Last | | #6

      whats curious here? I installed somewhere around 6, maybe a little more (and surely some un evenness to counteract) . So i'm roughly estimating ~r20

      1. Expert Member
        DCContrarian | | #8

        I read it to mean that R-20 blown insulation was the only type they had in stock or you would have done R-30. If the store only had enough bags for you to do R-20 then it makes sense.

  5. Jon R | | #9

    > still leaks like a sieve even with my sealing efforts

    If you haven't used blower directed air sealing, you should.

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