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  1. #1
    Join Date
    Aug 2012
    Posts
    83

    Are roof shading nets economical to install? how about painting your roof white?

    http://specialtyfabricsreview.com/ar...ing_roofs.html

    Reduction in roof temperatures of 5.1C or about 10 degees F. Sounds significant, but does it really make your hvac bill lower, when you have a vented attic?
    not sure of cost per square foot.

    I was also researching cool roof paint, basically white paint. Is that worth the headache of applying? Seems like the cost per square foot is really high around 40 cents.
    henry's solar flex is one brand.

    http://www.homedepot.com/h_d1/N-5yc1...1#.UEJDQSJ2OSo

    obviously these products are only beneficial in southern climates. looking to apply in Carolinas.

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,064
    They make an attic radiant barrier paint and foil radiant barrier that would be more efficient

  3. #3
    Join Date
    Aug 2012
    Posts
    83
    http://hvac-talk.com/vbb/showthread....ighlight=white

    this thread seems to indicate it is better to block the heat build up before it even gets inside the attic. It is the only other thread I found on white roofs, couldn't find any threads on roof shading/netting.

  4. #4
    Join Date
    Aug 2012
    Posts
    83
    also found this article
    http://www.fsec.ucf.edu/en/publicati...0-00/index.htm

    seems like painting an asphalt roof only gets 3 to 5% improvement. White metal roof is very good at around 26%

    energy savings can be substantial
    Table 6
    Annual Cooling Energy Savings from Regression Analysis Method
    Site kWh kWh Savings (*)
    RGS 3679 0
    RWS 3471 208 (191)
    RSL 3242 437 (404)
    RTB 3570 109 (113)
    RWB 2809 870 (893)
    RWF 2859 820 (771)
    RWM 2584 1095 (1041)

    Over $100 per year. Can't figgure out if these savings are for an average sized home or the small (60% size of normal) home used in the study.

  5. #5
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,188
    what type roof do you currently have?
    will you be replacing the roof soon?

    every house is different, as are the plans (long or short range) for the
    homeowner and his/her budget.

    knowing where you are starting and what you hope
    to achieve in ______ years gives us more information
    to guide your choices.

    didn't you have the thread about ducts in conditioned space?

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  6. #6
    Join Date
    Aug 2012
    Posts
    83
    Yes I had a thread about ducts in conditioned space and my plan is to move them eventually.

    But this question is for my sister in Florida. She has ducts in her attic as well and it is unlikely they will move, so insulating them and putting in a radiant barrier is the first step and I'm seeing if painting the roof would be a good idea. according to that article the investment of $300 worth of paint would take over 10 years to break even, not really feasible.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,295
    Quote Originally Posted by newstudent View Post
    also found this article
    http://www.fsec.ucf.edu/en/publicati...0-00/index.htm

    seems like painting an asphalt roof only gets 3 to 5% improvement. Can't figure out if these savings are for an average sized home or the small (60% size of normal) home used in the study.
    If one makes 30% improvement to the ceiling load which is 15% of the total cooling load, one might save 5%.

    Seems like a lot of work to save $15.
    __ or you might _
    Turn your A/C off for about 4 or 5 days.
    Last edited by dan sw fl; 09-02-2012 at 07:12 AM.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,301
    When it comes time to replace the roof, use white shingles they cost the same as the dark ones in most areas. Odds are the roof will require replacement before any of the ideas you mentioned pay off.

  9. #9
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,967
    The Florida Solar Energy Center has some good information you may find helpful. Here is a link to one of their studies on Radian Barriers. http://www.fsec.ucf.edu/en/publicati...1-01/index.htm
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  10. #10
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,188
    don't know what happened to my previous post.
    oh well...
    "But this question is for my sister in Florida. She has ducts in her attic as well and it is unlikely they will move, so insulating them and putting in a radiant barrier is the first step and I'm seeing if painting the roof would be a good idea. according to that article the investment of $300 worth of paint would take over 10 years to break even, not really feasible."

    I have a radiant barrier. See attachedName:  my radiant barrier.jpg
Views: 172
Size:  42.6 KB
    first she would air seal from house into attic. recessed lights, electrical & plumbing
    penetrations. openings around bath fans, kitchen fans and any holes from attic
    into house.
    then seal ductwork. ducts to plenum, plenums to equipment, return air,
    and supply boxes to attic floor. the latter can be done from inside the house.
    again..see attached.
    Name:  how to seal supply box from inside with MASTIC tape only.jpg
Views: 279
Size:  46.0 KB
    the attic side work is done before rb install and before adding more insulation.
    the sealing of supply boxes can be done at anytime. I use hardcast brand 1402
    mastic tape. the only tape I've found to seal different materials like sheetrock
    wood metal etc.

    once this work is done, then installing rb. I used a single sided rb called fsk
    foil scrim kraft ..foil with nylon scrim on kraft paper. same thing used on duct
    wrap without the insulation.
    Ideally two people to install, one to measure and cut rb. I also used
    button cap nails to give more holding area. some people use staple gun,
    but with the ocassional hurricane I wanted more strength. the pic of
    my rb is after katrina and gustav..you can see a piece of fsk tape
    hanging down ..so when rb is installed you want to have an overlap
    of layers a minimum of 6-8". as you can see..in my solitary install
    my rb got crooked and I had to piece together between layers.

    there are different types of rb sold. but from the single sided foil that I used
    to the foil bubble foil also sold..there is little difference in performance.
    just a cost difference. so don't believe the sales hype and over spend on
    the product. the money is in the install. its a dirty difficult job. when
    installing next to eaves there comes a point where hammer or staple gun
    doesn't fit into the area. so you have to get creative as to how to
    attach rb. while rb doesn't have to be air tight..it should be continous.
    leaving a 3' section at eaves allows heat to enter, same at peak.
    I have collar braces, so instead of putting rb to peak, I came across
    the ceiling of the attic at the collar braces.

    I also have gable end venting, but the install I did wold also work
    for soffit ridge venting. if she has passive venting (turbines) then
    the rb install would still be the same. the air pathway for venting is
    between the rb and the roof decking.
    I see lots of people/companies get caught up in doing unnecessary
    detail work like cutting rb around turbines. this actually impeads
    air flow.

    on the south west facing gable wall of the attic rb is installed
    as it is the hot side. the north east side only gets morning sun...so
    I didn't do it.

    after rb is installed, then insulation. if you do it before hand it makes
    rb install difficult and compresses insulation.

    rb paints are easier to install, but the absorption of the paint into the
    roof deck decreases the value of the rb. in my testing of other peoples homes
    the rb paints fell far below the performance of roll rb.

    roof screens..in florida. don't you think that the wind would play havoc with them?

    if she replaces the roof, white metal. more costly, but a cool roof.
    when I replace the roof on my addition it will be reflective metal...just because
    I have the materials already. but under the metal will be 1" foil/foam sheathing
    with furring strips to maintain 3/4" air space. so on this roof the rb will
    be under the metal. better install, than on rest of roof.
    foil/foam sheating on top of rafters will stop thermal conductivity and add a
    continous R-7 to insulation.

    and white elastomeric like you linked from hd. we used this quite a bit back
    in my weatherization work. it works well if replacing roof isn't an option.
    on metal roofs..never did shingles, don't know if you can or not.
    the problems with elastomeric is again...install.
    temps have to be above 55 degrees, and two layres have to be applied.
    what works best...that the weatherization guys never could understand..
    is one layer painted across roofing..allowed 24 hours to dry. then second
    layer painted opposite direction of first.
    if its too cold, or it rains..the application suffers.

    also insulating ducts. you can't put insulation with a vapor barrier
    over insulation with a vapor barrier. in hot humid climates condensation will
    form between the two vb's. its best to mastic seal ducts always.
    but adding more insulation creates more problems unless the first vb
    is removed. I'd never recommend foam on ductwork. seen too many problems
    that are very very difficult to deal with once foam is sprayed on ductwork.
    does she have flex duct like you, or hard pipe ducts?

    sorry this is so long..had it put together better on post that got lost.
    these are the things I've learned over the past decade. hope some of
    it helps with your sister's situation.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  11. #11
    Join Date
    Aug 2012
    Posts
    83
    "also insulating ducts. you can't put insulation with a vapor barrier
    over insulation with a vapor barrier. in hot humid climates condensation will
    form between the two vb's. .......but adding more insulation creates more problems unless the first vb is removed. .........
    does she have flex duct like you, or hard pipe ducts?"


    I'm not sure what she has, but will find out in a week. I'm guessing flex duct since here heat pump is located inside conditioned space in a closet.

    I'll probably just take a razor and slit the exsisting flex duct to break up the vapor barrier, or just use roll insulation withOUT a vapor kraft paper barrier. What do you think will work better, deffinetely dont' want condesation problems due to a wrong install. That being said I insulated my ducts in Charlotte, NC and haven't noticed any moisture issues and our RHumidity is close, but lower than Central FL.

    I'm going to apply vapor barrier and insulate ducts, paint the roof white looks like a waste of time. in 15 years when the roof is replaced she can get a white metal one if her HOA allows it.

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