Anyone current on attic ventilation for Climate Zone 1?

svetz

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The guy we bought the house off of was a fireman, and with the house came a 20' extension ladder. This is the most amazing ladder, it's not that heavy, super sturdy, has reversible feet with spikes to dig into dirt or flat feet for hard flat surfaces. It's fiberglass/aluminum. I'm pretty sure they left it because it was locked to the stairs and the lock had rusted (needed to cut if off).

Used it yesterday to inject foam in the attic vent holes. Today I'll cut off the bits of foam off that flowed out of the holes. Also sprayed the mold killer in the attic yesterday (fun times!).

My brother-in-law arrived yesterday for Thanksgiving (which is today for us, he has to work on Thanksgiving and is leaving on Tuesday) and helped out. Felt bad as he wanted to do more and I was doing the grungy stuff. But I figured out how to make it up to him. I'm going to let him clean the evaporator coils. I've been saving this as it's a bit of a contortionist act to get them from underneath. Need a board or something so he doesn't kill a vertebrae on the lip of the air intake (something like this).

They're not that bad, I figure a light brushing to get the dust out from the underside, then spray coil cleaner from the top, use a sprayer to rinse off, then the cleaner from the bottom and another spray from the top. What could go wrong?

We'll use a shop vacc to suck up the water/chemicals that spill over the drain pan. Probably need to clean the drain line too, yeah... perhaps I'll start there 😉.
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svetz

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The new roof is on, metal over insulation. So, the attic is closed up now and has a humidity sensor monitoring it.

With the secondary water barrier on the roof deck and with the vent holes plugged, no moisture can enter the attic other than from house below. Well, not precisely... it's not sealed... noticed some light cracks around the roof/wall joins while vacuuming out debris.

It's Florida, if water is going to condense and cause mold it'll happen on colder surfaces - now that the roof's insulated, that's most likely the cold interior walls between the conditioned space and the attic (where the prior mold was) and any AC ducting running through the attic. So the plan now is to monitor the humidity.

Hopefully whatever moisture accumulates will get sucked back into the conditioned space via the wood and then the AC can deal with it. But if not, will start to plan the next phase for the attic seal.
 

svetz

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Checked up on the attic today, humidity is around 61% and no signs of
moisture (not really expecting any issues until summer, should be the
opposite of most of the U.S.).

So, what am I looking for? I've seen the "general" wisdom is to keep
the attic under 70%. But does it work for this crazy climate zone?

The thermostat will be set 78°F, 1/2" drywall has an R-Value of .5,
the attic probably 100°F (doesn't get that hot as it's insulated above
the roof deck and loses heat to the house), so what would the attic
side temperature be? Since heat rises the interior air up high would
be over 78° and the interior wall warmer, say 82°, so the interior
attic wall around 84°? I can see I'll need my IR gun.

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Looking at the chart, if air at 100° and 70%, then a wall should start
having some condensation around 90°? At 84° the target humidity
should be 55% at 100°?
Dewpoint-RH.svg

The inside air currently is 60% at 78°, during summer the AC will run more and probably be a bit drier. Keeping the same amount of water in the air and adding heat to the air I believe pulls down the relative humidity. So, all that thinking and the conclusion is to have a beer and watch it sweat. ;)
Let me know if my thinking is all wet!
 

svetz

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The math to calculate the dew point is relatively straight forward, but the sensor won't
send alerts for that. There's no API for it, but possibly someone has a SmartThings
integration for it so might be able to rig something up yet.


But..., there might be a bigger problem. :cry:

The data for the last week to the right shows the humidity closely following the
temperature. If the mass of water was constant for the given volume, then the humidity
should be the reverse curve of the temperature.

So, that suggests the mass of water in the air is changing freely
2945f572903150ce31e87ffed35c7163.gif
1615821284693.png

I guess I need to measure the outside air relative to the inside air. But I have a sneaking suspicion its not sealed anywhere near good enough as is. Depends on if the humidity is coming from inside the house, or the outside air.
 

svetz

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I suspect mother nature is going to school me the hard way on this... so much for the humidity leaking in from the outside...

RH% Location
59% Attic
53% Kitchen
55% Outside

It must have something to do with the warmest air (attic) sucking in the moisture. Could also be moisture being driven out of the wood with increasing temperature, although the new roof went on about 8 weeks ago.
 
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svetz

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So, warm moist air is less dense, so that's probably why the attic has the most. Probably getting sucked in from the outside. No joy on Smartthings integration. I might get a second meter rather then hack the traffic.

I was looking for light leaks and spotted this...
1615928009879.png

Pretty cool huh? Turns out to be a wasp's nest, the wasps are from the nuclear power plant up the road.

Okay, so, not so much. It's the Styrofoam bulb that formed on the inside during the injection process to seal the old ventilation holes lit up by the reflected outside light. As you can see, there are some additional caulking opportunities. Leak looks big from inside, can't even see it outside.
 

Dr Mark

Solar Enthusiast
Enjoyed reading your account. I recently replaced my shingles with underlayment and metal. I am so glad I did. I had the roofers only cut 10 feet of the underlayment at the ridge (in the middle) for venting. I was concerned about driving rain up the roof to the ridge. They use this green sponging stuff to keep the water and critters out, but during a hurricane not sure how effective it would be (live in Daytona Beach). I have two attic vents at each gable and 4 (3" x 18") soffet vents. I thought it was important to have plenty of attic ventilation. The fact that metal cools more quickly than shingles is big help (putting shingles on shingles even worse). I haven't taken the temperature but the attic seems much cooler when I open the attic access. I do not pay much for power but it has lowered bill in summer. I was surprised to see an AC vent in my brother's newly built home in Texas. Now I understand the logic. Thanks! :)
 
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45North

Let it shine!
I was interested to note that on your Climate Map for HVAC purposes a bigger number means cooler.
This is the opposite of the USDA plant hardiness map for gardeners (that I am more familiar with) where a bigger number means warmer and Florida is about Zone 10.
Shouldn't cause confusion though. The uses are pretty distinct and different.
 

svetz

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I have two sensors now hooked up and recording data (images are amazon links).

The Govee was pretty much a mistake, it's WiFi, but only alerts on temperature or humidity
and shows the plots in #24.

What I wanted of course was something completely different, an alert when conditions might cause condensation.
Govee
Sonoff SNZB-02
The Sonoff sensor reports over Zigbee and works with the SmartThings (not natively, fortunately someone wrote a device handler for it.
From there I wrote a SmartApp to send text alerts should a surface temperature reach the condensation point (if anyone wants a copy let me know and I'll put it up on GoogleDocs).

No sooner did I complete that, then I started wondering, how close am I to
the danger point?

I know the interior wall is going to be no less than 80°F as the AC will be set
to 78°; but how's the dew point changing with the temperature and humidity?
In short, I wanted to see some trend lines.

Dug into that, turns out someone had written a data logger as a SmartThings
app, and they were putting the data into a GoogleDocs spreadsheet! Took
about an hour to setup, most annoying was typing the huge URL into the
cellphone app. Finally said heck with that (not precisely those words), and
copy/pasted the url so I could cut/paste on the cellphone.

Let it run overnight, and presto! I'm looking pretty safe (for now).
1616762608188.png


Enjoyed reading your account. ...Now I understand the logic. Thanks! :)
Thanks for the feeback, but keep in mind this is an experiment in progress and I'm learning as I go!

...This is the opposite of the USDA plant hardiness map for gardeners...
Wife loves it here... she's always loved to garden and has raised beds and planters. She twisted the "tops" off pineapples and they grew, best pineapples ever. The only downside is the yard critters love what she plants too. The iguanas taste test everything, somethings they devour like locusts.
 

Supervstech

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I just saw this pop up, sorry I didn’t see it last year!
Florida, mold, attic, sealing...
Yup, lotsa fun.
Do yourself a favor, and get a SantaFe dehumidifier and be happy up there.
 

svetz

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Did you insulate the vertical wall?
No, currently I'm just monitoring (it's cheaper ;-). There may be enough "attic leaks" to the interior I don't have to worry about it. 🤞
I'm also hoping the wood acts as a sponge to wick the moisture back into the house where the AC can eliminate it.

I did finish up the second pass at caulking, the only light leaks now are a knot in the exterior wood I missed (yeah, a 3rd pass is needed) and all along the the vaulted ceiling. I'm thinking air leaks to the interior should help (possibly not since moist air rises) so didn't seal there.

But yeah, watching it like a hawk. Don't want to have to go through the mold removal process again (benign mold, but hot and cramped working space up there with the odd nail/screw penetrating the deck to bang your head into). If it does build up, I've got a quote from a contractor to do spray-foam insulation on the walls and roof decking (or I might go DIY, I see HomeDepot sells kits). My main DIY concern is if I can get a long enough wand to spray (the attic isn't very high and getting to the outer edges is problematic, but a 4' wand would probably solve that).
 

svetz

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...Do yourself a favor, and get a SantaFe dehumidifier and be happy up there....
I see a few options if there is a problem at varying costs and escalating combinations. AFAIK, only the dehumidifier is guaranteed to fix the issue.
  1. Tightly Seal the attic envelope with closed-cell foam; this was the one I understood the least and spent the most time investigating. It's also what the Florida Building Code (FBC) calls for when converting an attic to a climate controlled space. While it should theoretically work, it's not guaranteed to solve the problem. Even if it doesn't dry up the humidity, it would raise the surface temperature reducing the potential for condensation and therefore mold. Expensive up front, but a passive solution and probably the cheapest in the long run. It also requires #2 and/or #3, although in practice there may already be more than sufficient leaks.
  2. Vent the attic to the interior with some AC grills, one in the adjacent wall to the kitchen and den (both have vaulted ceilings) would allow cross flow ventilation, Of course, if the moisture is coming from inside the house like a climate-zone >1 home that might just make it worse.
  3. Divert AC air into the attic space, combined with #2 will force air turn over in the attic.
  4. Add a dehumidifier into the attic and run a drain through the eave. Not covered by the FBC for attics. But as the rules are to protect from mold it seems reasonable.
I thought about #4 when I wrote the app for SmartThings - when it sends the text alert its also setup to activate/deactivate a WiFi outlet. I have a spare dehumidifier with a humidistat, but with the WiFi outlet the app could watch the trend and vary the runtime to ensure the attic was dry at 2 AM without the dehumidifier needing to come on and wake folks up.

As far as I know, #4 is the only way to guarantee no problems. It's probably also the way I'll start if a problem appears as it'd be pretty quick/easy to setup.

Let me know what you all think!
 
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Supervstech

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HVAC-talk.com has an ask the pros section where hundreds of contractors can help with problems like this. A member teddy bear on there is the highly rated humidity air quality tech, post a question on there and he will comment.
I am one of the mods over there too by the way...

attics in green grass states really should be sealed, and included in the load calc of the building.

any time a cold surface is poorly insulated touching a warm ventilated space, you WILL have moisture build up, and mold.

sealing the roof and perimeter locks out the humidity and heat from entering the home in the first place, so it works very well.
Then a suitably sized dehumidifier running, with a fresh air intake to positively pressurize the home will make a huge comfort improvement, and lower your energy bills to boot.
 

svetz

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HVAC-talk.com has an ask the pros section where hundreds of contractors can help with problems like this.
I looked over the site (really enjoying the wall of shame) but the rules make it pretty clear it's by professionals for professionals and DIYers aren't welcome:
  1. 2. Do-It-Yourself (DIY) - not here.
    This site is for industry professionals and folks seeking HVAC/R advice and knowledge. Please do not ask for step by step instructions on purchasing, installing or repairing your own equipment. This is our job and our livelihood. We are generous, but not to a fault.
    smile.gif
Apologies if at anytime I sounded professional, that's definitely not me. But no worries, I've watched Joseph Lstiburek videos a few times... what could go wrong? :ROFLMAO:
 

Supervstech

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I looked over the site (really enjoying the wall of shame) but the rules make it pretty clear it's by professionals for professionals and DIYers aren't welcome:

Apologies if at anytime I sounded professional, that's definitely not me. But no worries, I've watched Joseph Lstiburek videos a few times... what could go wrong? :ROFLMAO:
Oh, absolutely they do not assist DIY repair or install of HVAC equipment, but they ABSOLUTELY do help homeowners solve home design criteria, and make recommendations for the things your attic space needs.
 

svetz

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TeddyBear at HVAC-talk.com seems exceptionally nice/knowledgeable. Couldn't get logged in, but see where he recommends what I already knew, that 50% RH is the guideline (at least for normal climate zones, although he lives in Florida so is probably aware of CL1 issues).

I do see 50% as the upper humidity inside her house as you'd expect with a properly working ac. But obviously from the graphs above the attic is over that, between 50 and 60%. So that doesn't bode well. The air up there obviously has more water in it (if it was the same lbs/cuft as inside the house the RH% would be proportionally lower). Still, not an issue yet... I might try plotting the interior humidity against the attic humidity to see if I can get a sense of the flow.
 

svetz

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Wow! Glad I decided to plot that! Very informative. Also added outside RH% from a weather station 2 blocks away!

It was interesting to see the interior humidity gets rather high (57%) at night when it's cool and the AC is off, obviously leaking in from the outside. She has a programmable thermostat, pretty sure the temp goes up to 80° from 11pm to 6 am. From Midnight to 4 am you can see the house humidity going up, but the attic staying roughly the same (e.g., not leaking into the attic?).

1616863246388.png

The humidity in the Attic (blue line) looks like its following the interior (red line).

See the saw tooth pattern from 4 to 11 pm? Must have something to do with her programable thermostat coming on/off at a lower duty cycle (she has a big east facing window, so the AC has a higher morning duty). The blue line is a higher fidelity than the red line, so those flat parts on the red is where I just copied the last recorded value.

The question there is whether or not the negative AC pressure is pulling in outside humid air into the attic? Overall the trend is downwards, so a net positive. I wonder if I went up there with the AC on if I could "feel" any air leaks?

The downward dips show a marked decrease in humidity, so that seems to indicate something is going on when the AC is running. But the humidity also "snaps back" pretty quickly. Possible the sensor is near an air-leak (it is pretty close to the "hatch") from the house envelope into the attic? The ducting runs through the attic, so possibly air is flowing up around the hatch and back down to where the ducting penetrates the attic floor. If so, idea #2 from post #34 might make a huge difference.

The good news is that the AC coming on causes a net loss in the attic; so more dry air from the house interior rather than exterior moist air. I'm pretty sure the main leaks are to the interior, although she's getting new windows and a new door which will hopefully better seal those leaks. But the main mystery remains, is the bulk of the attic humidity coming from less dense moist air rising, or is it getting sucked in via the AC negative pressure (or something else)?
 

svetz

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Finally had a bit of rain (.2") and with it a big outdoor humidity swing ... great opportunity to see how it impacted the attic:

1618331019348.png
So far so good!
 
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