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My son's attic is running about ~30 deg F hotter than the outside temp in the peak of day and makes the AC work overtime to cool the house. The previous owner re-did the attic/roof, and there are only three vents (on the N, S and West sides) of about 3-4 sqft each. (ie no soffit vents). The home is in southern Arizona where daytime outside temps reach 100-110F. On such days, the home's interior gets to about 85 with AC running 100%, but the attic space hits 135F!. (he has four transducers measuring temperature throughout the 1200 sqft home.) Ive checked all 4 instruments, and they are all reading correct. Even worst, at night once the outside temp drops to a "comfortable" 80F, the attic remains above 100 till morning. I told him he need to add a vent fan to pull the hot air out of the attic; but is there something else he should be looking at doing?

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    It is like sitting in a car with windows closed, it heats up very quickly. Without adequate vents, you may consider creating forced airflow through the HVAC system or add roof deck insulation material.
    – r13
    Aug 3, 2021 at 0:31
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    a gable vent and a ridge/turbine vent would help.
    – dandavis
    Aug 3, 2021 at 0:48
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    The primary protection from attic heat is insulation sitting on the ceiling , although ventilation is always good . Aug 3, 2021 at 1:03
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    Indeed - how much insulation is on the ceiling? Options for moving air are various, and depend on what sorts of things you can or are willing to attach to the roof. The old-fashioned cupola(s), the new-fashioned ridge vent, the presently missing soffit vents, the powered (solar or not) fan vent, the turtle vent(s), the turbine vent(s), the solar chimney(ies)...
    – Ecnerwal
    Aug 3, 2021 at 2:12
  • Thanks all, there is currently about 8-12 inches of blown in insulation sitting above the ceiling in the attic "isolating" the living space. the Roof is roofed with black roofing felt/tiles which certainly dosnt help... Ill try to get some gable vents added and the exhaust fan. I think ridge vents are the best at venting a roof, but they are better added when you build or recover.
    – mark f
    Aug 3, 2021 at 14:47

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I don't know what the pest situation is in Arizona, but I am bewildered that either the house was built with no soffit vents, or the prior owner closed them up. Either one would be a terrible mistake, unless the intent was to make the attic part of the conditioned space.

Please be aware that this is at least somewhat possible. If the roof is constructed appropriately (which your son's is currently not) it is possible for the attic to be conditioned along with the other rooms. It would involve making I suspect a lot of changes to the current setup, but those changes may have been made in the opposite direction in the past. It would help if you had pictures/plans/drawings of the house prior to when the old owner "fixed" it.

Assuming that you now have a "simple" plywood or tongue & groove sheathed roof over wooden trusses or rafters, and you have a somewhat limited budget, I would suggest the following options:

  1. Sell the house and move elsewhere. (This isn't as snarkastic as you might think -- if the prior owner screwed up the roof, who knows what other things may have been done poorly or wrong?)

  2. Rebuild the roof. This is the most expensive option, but will likely pay off the most. You could redo the roof with the attic either in or out of the conditioned space, and address many of the below suggestions at the same time.

  3. Recover the roof. This is cheaper but not cheap. Replace whatever roof you have now with a more reflective roof, such as a "cool metal" roof: for esxample https://sheffieldmetals.com/learning-center/cool-metal-roofing-and-sri/. Note that there are competing metal roofs from other vendors, and also competing "cool roof" solutions that are non-metal.

  4. "Paint" the roof. There are various fluid-applied reflective roof coatings available that reduce solar heating, usually by reflecting some or all of the sun's rays. Here's an example from a big box web site. These are all fairly new products, so you might see new products arrive and old ones discontinue between the time you decide to start a project and when you try to buy the products. Just keep researching. Beware, however, that the lifespan on these coatings can be very short! You may have to re-apply the coatings on a 10-year cycle or worse. That can be a challenge, but if the coatings work it will be worth the hassle.

  5. Add a radiant barrier. I'm talking about the rolls of shiny plastic that want to be installed with an air gap between the plastic and the inside of the roof or trusses or rafters.

  6. Add soffit vents! The "standard" way to cool attics is to create air flow from beneath the soffits to a ridge vent or some other up-high ventilation exhaust (perhaps a gable end vent?). You can make your own, or buy a variety of cheap vent solutions from a big box store. (Obviously, you can buy un-cheap solutions too.)

  7. Add passive vents to the attic, such as gable or eave vents. These would be just a hole in the wall with screen and a decorative cover, positioned to hopefully catch any breezes in the neighborhood. Be sure and seek guidance on the size (sq footage) of the vents versus the total roof size or attic volume.

  8. Add a ridge vent at the peak(s) of the roof. This is a form of passive vent, but it is the "expected" complement to soffit vents. Here's a video, and a warning from I Like to Make Stuff. Note that if you don't have a ridge vent, it can effect your ability to use radiant barrier and soffit vents together.

  9. Add active vents to the gables and/or roof. These would be electrically powered vent fans, either driven from solar or from hard-wired AC power, or both. These will potentially increase your electric bill, but may also lower your climate control expenses. Again, be sure and get guidance on size/number of vents/fans versus roof/attic size.

  10. Air-seal your ceilings! This should probably be earlier because you probably should do this first. Sealing your attic from air flow up from below will actually tend to make your attic hotter. But it reduces your A/C losses due to airflow out the top of the conditioned space. You should do this step before doing any "blocking" work in the attic -- work that might prevent you going around on your knees wearing long sleeves, goggles, respirator and stirring up the insulation :->. Yeah, doing this will suck in the winter, and be a hellish nightmare in the summer.

  11. Block the sun. There are several ways you could do this. Maybe sell the rights to install a giant billboard in front of the house to cast a shadow on the roof? Or take up hot-air ballooning as a hobby, I understand that is big in the southwest. Or a trellis or arbor with vines on it? Or buy some trees. This is very low-tech, but one or more nice deciduous trees positioned in the right place can provide shade in the summer and heat in the winter.

  12. Install solar panels. In many states this can be arranged through a 3rd party company that handles the installation and collects state and federal incentive funds for the system, thus lowering the costs quite considerably. This is really just another version of "Block the sun" since the point would be to put solar panels between the sun and your roof, absorbing some or all of the heat before it gets to your attic.

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  • I think the powered roof or gable mounted fan is probably the most bang for the buck. $100 for the fan + installation, which is something many DIYers can do. Get a licensed electrician to run the power for it to be safe and legal.
    – SteveSh
    Jul 15, 2022 at 11:21
  • The practical and cost effective solutions start at #6.
    – FreeMan
    Jul 15, 2022 at 12:40
  • Some more detail: black asphalt shingles. I like your comments, I think ridge vents seems doorbells and adding back in some soffit vents.
    – mark f
    Jul 17, 2022 at 16:01

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