Attic insulation

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dorlando

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We have a gable style roof and had insulation blown in a few years back. It was certainteed so I don’t think it was Celluose. They got it to the height that was needed for R 30 but our house gets hot very quickly after the air turns off. I live in Florida and get full sun all day long.

at what point does it not make sense to add more insulation? I had read that at some point there’s no value and that if you blow in too much it can cause moisture issues.

i’m trying to determine if it would be worth me blowing in more without causing any problems. Thanks
 

Stuff

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May not help much. More likely you have air leaks that need sealed. Get a blower door test to see how bad things are. You can also use an infrared thermometer to measure your ceiling temps.
 

Fitter30

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Attic have a ridge vent or power exhaust? Gable vents normally has window screen mounted on the inside are they clean. Window and door weather stripping in good shape?
 

dorlando

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Attic does have vents. My ac run cycle times haven’t increased but the time between cycles is shorter, meaning the unit comes on faster and doesn’t stay off as long. I am comparing against similar days in temp outside
 

HudsonDIY

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It's obviously hotter than hades in Florida right now. Just my personal observation but the rear of my house faces Northwest and has two huge glass sliding doors. The rear of the house becomes a huge thermal mass in the afternoon and this may be what you are experiencing. I find it helps to keep all the curtains closed on that side of the house on extra hot afternoons. I'm considering some kind of film on those sliders but I don't want to reduce the nice view either. Back in the day all the Florida houses had awnings over all the windows to reduce the amount of sun shining directly on the windows. They've become out of style but they weren't so dumb. The struggle is real.
 

Dana

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We have a gable style roof and had insulation blown in a few years back. It was certainteed so I don’t think it was Celluose. They got it to the height that was needed for R 30 but our house gets hot very quickly after the air turns off. I live in Florida and get full sun all day long.

at what point does it not make sense to add more insulation? I had read that at some point there’s no value and that if you blow in too much it can cause moisture issues.

i’m trying to determine if it would be worth me blowing in more without causing any problems. Thanks

How much hotter is the ceiling temp compared to the room temperature?

What color & type is your roofing?

What type of attic venting do you have? (Soffit to ridge? Gable vents? Actively powered vents? Other?)

Do you have sufficient clearance between the top plates of the exterior walls and the roof deck at the eaves to add 3 more inches of insulation?

Did the insulation contractors meticulously air seal the ceiling/attic floor plane before adding insulation?

Are the ducts & air handler up in the attic, above the insulation?

Low density fiberglass is somewhat translucent to infra-red radiation. The temperature an inch or so below the top of the fiberglass is often hotter than the attic's air temperature due to it's absorbing the IR coming off a blistering hot roof deck, so you're effectively insulating against a higher temperature using slightly less insulation thickness. Many higher-density fiberglass blowing wools have additives that reduce that effect, but even with additives a low-density installation will still have that issue.

If the ceiling still leaks like a sieve you 'll have a significant stack effect pulling air out of your conditioned space up into the attic, which then draws in outdoor air from all other leaks in the house. The hotter the attic is, the greater the stack effect draw. So even if the ceiling temperature is fine, it's still going to draw heat and humidity into the house whenever the roof deck is hot.

Adding more insulation doesn't necessarily create moisture issues, but it can make some defects in the building envelope more obvious. In FL the summertime outdoor dew points are higher than the indoor air temperature. With low insulation levels the ceiling will usually be above the outdoor air's dew point, but at higher levels the ceiling temp can approach or drop below the dew point and take on moisture. The rate of moisture uptake is higher with low-density fiber than with high density or hygroscopic fiber (such as cellulose). But even with higher density/lower air-retardency fiber insulation chronically running the indoor air temp well below the outdoor dewpoint temp will cause moisture accumulation UNLESS there is a good air-barrier on TOP of the insulation. Even if the air barrier is permeable to water vapor it's still pretty effective. Standard latex ceiling paint on gypsum board runs about 3-5 perms- it's semi-permeable, and the much drier indoor-air will pull moisture (but not air) through the ceiling a fast enough rate to keep up in most houses.

Ventilating the attic with outdoor air in Florida usually ends up adding more moisture to the house than it purges, and is a generally bad idea even though it's built into code. Under IRC 2018 it's now code-legal to build the attics air-tight to the exterior, using a "diffusion vent" along the ridge for purging moisture. (Take a free trial subscription to read the whole article in that link, or do some internet searches for "diffusion port" or "diffusion vent" for other sources.) While diffusion vents will still add some moisture to the attic during the cooling season, it's an order of magnitude less moisture to manage than when the attic is vented to the outdoors.
 
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