The latest and greatest Florida houses are designed with closed cell spray foam insulation underneath the roof. This has the disadvantage that roof leaks are difficult to pinpoint, since the foam prevents the water from dripping directly down underneath the part of the roof that has failed, but seals the house against humidity because any attic space essentially becomes part of the air-conditioned and dehumidified internal space of the house.
Our house, sadly, dates to 2003. We thus have AC ducts in unconditioned attic spaces, which seems to work fine on the ground floor, but when we poke our heads up into the attic we find that it is moderately hot (85F) and extremely humid (80-85 percent relative humidity). The attic has soffit vents all around, which seem to do a good job of preventing super hot temps from developing, but they also allow humidity to intrude.
Current Florida code requires ducts insulated to R-8 inside unconditioned spaces. We have R-6 ducts. The air coming out of an air handler is typically about 20 degrees colder than the thermostat setting and we’ve measured about 52 degrees at a ceiling register. So let’s say that the duct temp is 50 degrees.
The Interweb doesn’t seem to have a simple formula for determining the outside temp of an R-6 duct given the inside temp. ChatGPT 4o, however, comes up with one:
Notice that, with this formula, the outside of the duct gets colder and colder with increased R value. A perfectly insulated duct, for example, would have an outside temperature exactly equal to the inside temp, a very curious result!
New prompt:
What if we increase the duct insulation to R-30? What would the outside temperature of the duct be? (the air inside the duct is still at 50 degrees)
Sheetrock has an R value of about 0.5, supposedly. Let’s see what happens when we plug that in:
What if we reduce the duct insulation to an R value of 0.5? What would the outside surface temperature of the duct then be?
Our future AI overlord has determined that putting cold air inside a duct will raise the temperature of the outside of the duct above the ambient temperature of the attic.
What is the solution to the sweating duct problem, you might ask? A quarter-baked approach, from the energy and building envelope expert who did our Manual J calculation:
You probably have too much ventilation in your attic. I had a similar problem in my house. I blocked off more than half of the soffit vents. The temperature in the attic went up a few degrees while the humidity came down dramatically because not as much humid air was coming in from the outside.
(He didn’t say this explicitly, but I am guessing that the relatively dry attic was due to the attic being exposed to dried-out cooled-off conditioned air from the conditioned space below.)
The half-baked approach:
Install a dehumidifier with a fresh air inlet on one or more of the house AC systems. Each dehumidifier can bring in at least 100 cfm of fresh air, thus creating a positive pressure within the conditioned spaces of the house. The result will be conditioned air being pushed up into the attic and, eventually, being exhausted through the soffit vents. Expensively dehumidified air goes out of the house via the attic instead of humid air coming into the attic. A dehumidifier consumes about 700 watts of power, so this will consume about $1000 per year in electricity at 15 cents/kWh (per dehumidifier).
The fully-baked approach:
- Remove all ceilings on the top floor of the house and the fiberglass insulation on top of those ceilings.
- Bring in a spray foam company to block off the soffit vents and spray foam over them and the entire underside of the roof
- Have the AC contractor put some small supplies and a return into the attic so that there is nowhere for humid air to hide (humid air is lighter than dry air so it will tend to rise to the top of a house)
- Have a drywall contractor come back to put new ceilings up
- Paint
Circling back to artificial intelligence, as embodied by the latest paid ChatGPT model (4o)… I’m impressed with how confident and erudite the machine sounds when making these simple physics calculations!
Do your homework before spraying attic insulation, summarized by AI:
Many insurance companies are becoming reluctant to insure homes with spray foam insulation in the roof or attic space. This is due to several concerns:
– Potential structural risks from trapped moisture leading to timber decay and roof damage
– Difficulty in visually inspecting the roof structure
– Fire risks associated with some spray foam products
Some homeowners have reported being refused building insurance entirely because of spray foam insulation in their lofts.
Anon: I hate to disagree with AI, but spray foam is quite standard in new construction here in Florida so it would be odd if the results were uninsurable.
I’m wondering if the AI treats all English-language content equally and doesn’t factor in whether a web page relates to a house in Florida or a house in the Dar al-Islam (e.g., Michigan or the UK).
When I do a Google search about people rejected for mortgage/insurance due to spray foam, all of the top results are from the UK.
https://thinkplutus.com/learn/spray-foam-insulation/
https://propertyinspect.com/uk/blog/spray-foam-insulation-guide-2024/
https://www.ftadviser.com/property/2022/12/13/advisers-issue-mortgage-warning-against-use-of-spray-foam-insulation/
I think most of the issues relate to moisture and situations in which a space was completely sealed up without ventilation. So if we push through with our plans to add a small supply and return to the three attic spaces on that top floor (total cubic footage maybe only about as much as a large bathroom) we should avoid the problems that plagued people in England.
Although rich in Islamic observance and customs, England is a pretty terrible country in general. If it were part of the U.S. it would be poorer than Mississippi. I think part of that relative poverty is that they don’t have much in the way of air conditioning or forced air heating. So their houses just sit and stew in the damp British environment. Of course, it is at least as humid here in Florida but everyone has literally tons of air conditioning.
Google’s AI preface if you search for “is closed cell spray foam standard in attics florida”:
Closed cell spray foam is a popular choice for attic insulation in Florida because it can help keep attics cool and prevent moisture and mold. Here are some reasons why closed cell spray foam is a good choice for Florida attics:
Air barrier
Closed cell spray foam can create an effective air barrier that prevents hot, humid air from entering the attic through vents and heat from the sun from beating down on the roof. This can help keep the attic from becoming unbearably hot.
Vapor barrier
Closed cell spray foam is water impermeable and can act as a vapor barrier, preventing moisture, mildew, and mold from entering the attic.
Structural strength
Closed cell spray foam is dense and can improve the structural strength of the roof deck, ceiling, or wall where it’s installed. This can be important in Florida, which is threatened by hurricanes.
Flood resistance
Closed cell spray foam can reject bulk water and won’t deteriorate in areas prone to flooding.
Tile and metal roofs
Closed cell spray foam is a good choice for tile and metal roofs because these types of roofing don’t absorb as much heat as asphalt shingles, which can cause shingles to rise in temperature and become weaker.
However, closed cell spray foam is more expensive than open cell spray foam. Open cell spray foam is less expensive and more flexible, which can make it easier to spot hard-to-reach areas in the attic. It can also help minimize noise. However, open cell spray foam is not moisture-proof and doesn’t stand up to harsh weather as well as closed cell spray foam
Unsurprising that something developed by the Extreme Left would be “often wrong, but never in doubt.”
We prompted CHAT gpt to format a petition pro se for summary judgement to open a small estate probate case in a Florida District Court. My first filing made it past the clerk of the court but was rejected by the judge for some kind of formatting she wasn’t used to. Her court, her rules. I had to resort to US Legal Forms to get it exactly right and a month later the petition was granted, saving us at least $1500 in legal fees. There was no substantive discrepancy between the ai doc and the USForms version.
So CHATgpt was an almost good paralegal for us.
I’m use gab.ai and Perplexity these days.
You’re not seriously considering living in that house instead of staying on the road while using the house to preserve wealth.
Sustainable energy solved! Spontaneous movement of heat against a temperature gradient! You’ll be rich!
Heat the attic!
Out of curiosity I asked the same question on various models available within DuckDuckGo AI chat and the results are similarly hallucinogenic. From 167.9°F to 41.7°F. One came to a plausible 57.5°F
I was alse also impressed how confident and erudite ChatGPT 4o sounded while delivering wrong results to some (relatively simple) trigonometry problem. After I pointed the mistake out, it sounded very reasonable while admitting mistake, and very confident and erudite while offering new (wrong) solution. After several tries, I tried to shut it up, and it was not easy, it wanted to keep trying, and offering new (wrong) solutions.
Earlier, free ChatGPT 3 version offered wrong solutions for program calculating relative humidity, wet-bulb temperature and dew-point temperature from each other. Algorithm was wrong, not code itself. It also offered wrong solutions to doing some image processing in Gimp. In all those cases, my main problem was confidence with which wrong solutions were presented, and this confidence fooled me.
It is just stochastic probabilistic engine whose developers used symbolic logic and some form of gradient walk to.mimize some greatly simplified fit function.
What happens if you ask Wolfram? They have a rather confusing product structure but I think there is one thar allows natural language queries. Possibly Wolfram One?