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How to reduce heat in Florida attic *without* using spray foam?

AnnieL | Posted in General Questions on

I am a new owner of a very old leaky home in Tampa FL.  Air handler & Ducts are in attic — no alternative.  Nasty old insulation recently vacuumed out (allergies).  I had spray foam job lined up, but after further research I just don’t trust local installers to do a good job given cramped roof heal, crawl space, etc.  Many disastrous foam results in old houses here (humidity).  If I knew the right team to spray foam, I would choose that — but I don’t, so I’m not ((unless — quality contacts from here??)).  Current plan is air seal job; blown insulation; and a radiant barrier to help attic/AC equipment.  I need to act quickly (remember… zero insulation right now). Please advise:  1) is there a downside to radiant barrier?  I’ve heard the perforated holes don’t always let the moisture breathe as intended… ie, risk of moisture problems in Florida (true/false?)   Is there a specific radiant barrier that is best for humid climates?  2) I prefer blown cellulose (green)… but I was told to stick with blown fiberglass as it’s less prone to mold in Florida (how likely is this a concern?)  I need to get this insulation job done ASAP … I want to be efficient/smart/green; but I will probably own this house for 3 to 5 years.  I’m not cheap; but this property is also not worth “high end” solutions. It could very well be scraped one day, who knows…  I’m looking for smart/basic solutions for an entry-level home.  Advice??  Much appreciated!!

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  1. Expert Member
    DCcontrarian | | #1

    The downside of radiant barriers is that they don't do much, radiation isn't a significant source of heat transfer within the attic.

    The big question is whether the attic is vented or ventless, which is determined by whether the insulation is between the floor of the attic and the ceiling above (vented) or along the underside of the roof (ventless). It's a bad idea to have the HVAC equipment in a vented attic, you're basically cooling the outdoors.

    In your climate the vapor drive is going to be entirely from the outside to the inside, so venting the attic isn't as critical as it is in a heating climate. To the extent you get condensation happening, it's going to happen on the interior of the house when hot humid air from the outside comes in contact with a cool surface. The better you make your air sealing the less chance of that happening. To the extent you have vapor barriers or vapor retarders, you want them to the exterior of the insulation. You want any moisture that gets into the insulation to dry to the interior and be removed by the air conditioning. If you have interior vapor barriers the moisture will never dry, it will accumulate and cause mold and rot.

  2. walta100 | | #2

    With only 3 -5 years anything over R4 is unlikely to have any payback. What is your local code minimum?

    The only thing that pays back that quickly is air sealing.

    I think you should do it yourself as it is a low skill task that requires lots of hours.

    The most important leaks are the supply duct work. Turn on the AC blower and hold a burning incense stick and a bright flashlight near all the joints any leaks will disturb the smoke fix the leaks. The return ducts are next but they will suck in your smoke making it harder to see. Then you can tape a box fan into a window so it blows air into the house this will blow air out of the house into the attic use the smoke again to find the leaks and fill them with caulking.

    If the old AC unit happens to fail consider replacing it with a ductless system.


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