Anyone current on attic ventilation for Climate Zone 1?

svetz

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As we have members from all walks of life, thought I'd post this to see if anyone had knowledge on it....

Discovered the mother-in-law's house has mold in the attic. We had it tested and it's all benign. But, obviously want to do something about it before some strain takes root that requires a hazmat team to get rid of.

The rules are 1 sqft of ventilation per 300 sqft or 150 sqft if no vapor barrier or ridge cap. The idea being that good air circulation will prevent condensation as the temperature drops.

The house in question has a 1" diameter vent (a few of which are coated with paint) every rafter (24") for a total of 52, totaling 0.28 sqft. By the rules above she should have 4 or 8 sqft of ventilation space (house was built in the 90's).
IECCmap_Revised.jpg

To make things more complicated, the front and back have vaulted ceilings (they have 1" vents too, so assuming not filled). Of the 1280 sqft, there's only 275 sqft of actual attic space which is where the AC ducting lies. There is no ridge vent.

I would have thought "cold AC ducting" = sweating = mold, but the visible mold is on the drywall 3' away. The ducting is insulated, but one part looks damaged and needs more investigation.

Currently the inside roof panels have fiberglass batting stapled to them between the rafters, the attic is only slightly warm (approximately outside temperature) so the attic is being cooled by the AC, which is wrong for a vented attic as far as I know. The floor of the attic is plywood, I doubt there is insulation under the plywood but need to check.

While trying to figure this out, I came across a 2005 a paper that was submitted to the FBC (Florida building Commission) saying that:

M1. Although the rationale for attic ventilation is for moisture control, this was historically based on needs in cold climates and to prevent ice dams. The justification for attic ventilation for moisture control in hot humid climates is not scientifically defensible.
M2. Ventilated attics can introduce additional moisture loads into Florida homes by allowing moisture laden air in the attic that may communicate with the indoors.

Questions
  1. Regardless of code, should it be sealed? (still trying to figure out what the actual codes are) Update: Sealed is legal
  2. Currently the asphalt shingle roof needs replacing. A metal roof cools faster, would it need more ventilation? Update: not if not in roof contact
  3. If it should be vented, would adding a ridge cap count towards opening space, or do you still need 4 or 8 sqft in the soffit? Update: 4 sqft with ridge cap, 8 without
  4. Does soffit ventilation contribute to roof uplifting in a hurricane? Worried if I put in 4" diameter vent caps it'll weaken the soffit. Update: Yes
  5. I saw where some metal roofs were installed with insulation sandwiched between the metal and the roof panels, is that a good idea? Update: yes, also helps to deaden noise.
  6. If the attic part is sealed, what to do with the vaulted ceiling, should the vent size be increased?
Thanks in advance!
 
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svetz

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Found references to the FBC codes for a sealed attic, so it must be legal even if I haven't found the actual statutes yet. Looks like you need to spray closed-cell foam over the roof panels and rafters to create a complete air/moisture barrier. Has to be sprayed, batting or board won't get the air gaps and then its a moisture nightmare. Also needs an ignition or thermal barrier against the roof depending on attic usage.

With high velocity hurricane winds, sealed attics are indeed safer (ref - statement from president of Metal Roofing Association)

PDF for beginners on attic sealing: TL;DR: used closed-cell foam

The argument for sealed is that with AC on year-round the inside is drier than the outside. So, if the attic is vented it pulls humidity from the air into the living space (reverse of a normal house in winter).

Publication of data from two years of sealed attic exposure, seems to indicate a moisture buildup.

DoE checklist
 
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HRTKD

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Before you get too far along with ventilation, are you sure that you don't have a leak?

I have two solar powered roof vents in my roof. I haven't thought about them for years until this thread came up. I had them put in when the shingles were replaced. A subsequent modification was to add a module that shut the fans off below a certain temperature.
 

svetz

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#1 dumbest thing you can do building a house in the south: have a vented attic:

...Before you get too far along with ventilation, are you sure that you don't have a leak?
No, not sure. It's currently missing a couple of shingles too, but the tar paper looks intact and the it doesn't look like any of flashing should leak. But, as mentioned in the OP, there's fiberglass batting in-between the rafters so I can't see all the roof decking.

Also ran across something else...radiant barriers (e.g., expensive aluminum foil):

Now I just need to figure if foam board insulation sandwiched between the roof deck and radiant barrier make sense. Thermally it probably provides some benefit, but would need a counter-batten system which might not go well in a hurricane prone area.
 

svetz

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The house we built in Houston in 1997 had ridge vents. I think all the houses in the neighborhood had them.
Unless it's a High Velocity Hurricane Zone (HVHZ) issue, I see counter battens with a ridge vent to provide roof venting (not attic venting)... still working my way through stuff.
 

svetz

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As I was impressed with the AtticFoil guys from their youTube video I sent an inquiry:

Planning a metal roof install in climate zone 1 / HVHZ area.
There is a small attic (22% total area) that holds the AC ducting that I plan to convert into a sealed space with sprayed closed cell foam, the rest is cathedral ceilings and I'm unsure how it was originally done.
When installing the metal roof, is it advisable to put foam board insulation under the radiant barrier? That is the sandwich layers would be: roof decking, tar paper, foam board, Attic Foil, air-gap, metal roof. If so, what thickness of foam board would you recommend?
They responded just a couple of hours later...

No, you don’t need foam board on the roof. It wouldn’t add too much to the areas with the spray foam and even the areas with the cathedral ceiling probably won’t largely benefit from it. I’d skip it and proceed as usual with the install.

So, no need for counter battens!
 

svetz

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Asked more questions of the AtticFoil guy, specifically about usefulness with high reflectivity roofs and didn't the inevitable dust that settled out on them ruin them... never heard back so guessing it's snake oil.

Ran across Joseph Lstiburek who actually tests stuff and gets a lot of rule updates into the code, here's a video on it. The TL;DW: vented is best when you don't have mechanicals in the attic, conditioned is better after that. Those against conditioned are legion, the main argument is that if you have a conditioned attic you must have air changes with the rest of the house, and who wants to breath attic air (dusty, fiberglass fibers, etc)? There's also a fire issue that you shouldn't exchange air between floors (it's okay via code if you have a leaky attic, but not okay to purposely put in an air-return if your attic doesn't leak enough. Lstiburek has a solution and is getting it put into the code). Seemed to me a pipe going up to the peak (where the most moisture is) that had a check-valve in it would solve the fire issue too (aka, only one way air-flow).

Had one contractor come back and recommend a powered attic fan that was set on a humidistat. Considering the air outside is already moisture laden, it would create negative pressure and pull air from the house, and I'd be sucking in mold spores. I was dubious...but it's probably no worse than a normal vented attic - you just don't have to worry about hole diameters/quantity for natural convection. In Matt Risinger's 3 Remodel Rip-Offs powered attic fans were the #1 ripoff. Although his point was around remodeling to save energy as opposed to ventilation so it's probably an okay solution (not like the negative pressure is constant) for this situation. Waiting for another contractor to come out and give me their estimate.

Got a roof estimate, but there's no air-gap between the metal roof and the roof deck. On the other hand Lstiburek did some experiments and it seems water penetration isn't solar driven, it's moisture entering from the air through the house and accumulating in the attic. So, air ventilation underneath may only be important to eliminate thermal conductivity.

I can get 1.5" insulation under the metal roofing which is about R-6. Code calls for R-30, huge jump from the R-19 it used to be. So, it would need ~3.5" of closed cell foam to get to R-30. Seems wrong though, R-30 of the attic flooring has a smaller surface area, about 30% more surface area if you insulate the roof deck, more surface area more heat transmission - so seems insulating on the roof decks should be higher to hit an equivalent R-30 heat loss.

My thinking is with closed cell foam on the bottom, moisture can't get to the roof deck from below. Moisture shouldn't get to the roof deck through the metal roof/insulation/secondary water barrier (rubberized bitumen). So, that should prevent the roof deck from rotting. With a sealed attic, there would be moisture build up, but I might be leaky enough it isn't a problem. I have a humidity sensor on a "smart things" so it'll be easy to monitor and I could put a dehumidifier with a humidistat up there (who says you have to do air-changes to condition a space?).

For the roof areas with cathedral ceilings, we'll find out if there's any rot issues when the roof is replaced as the roof decking will have rotted, so that'll be my guide as to if there's enough roof ventilation under them.

But have to see what the next contractor says.
 

svetz

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Finally heard back from the other contractor...they're too busy.

So, I went to angie's list and found the top rated spray foam contractors figuring I could at least get an estimate for conditioning the attic. Two called back right away and I have appointments down to the day!

Best of all, both said the magic words... that might not be the best solution for your space, but we won't know until we get there and see it. Turns out they do more than spray foam.

One of them sounded like a snake-oil salesman, he was very against closed cell foam (fumes, popping/cracking sounds). Sounds like poppycock to me. From what I've read the new formulations don't have outgassing or dangerous fumes. He wanted to use open-cell foam, but it sounds like closed has a higher R rating. Both would need humidity controls, but opencell is like a moisture sponge; it mght work...but closed cell is definitely safe. He also brought up the "can't see a roof leak" with closed cell (which is also a debunked myth). I'll hear what the tech coming out has to say, possibly I was just talking to an idiot salesman spreading FUD, really hate that.
 
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ArthurEld

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I live in Tampa area and my house and all of my neighbors houses have ridge vents. They need vents in the soffits and the house needs to be sealed from the attic.
I'm not a roofer but I think the hot air pushes out the ridge vents and sucks outside air in the lower vents. My house has attic access in the garage and the hole just has a screen so it vents a lot of air into the roof.
That seems good to me and our air conditioning bills are low for this area. But someone who knows more than me might have reasons why it's not good.
 

svetz

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I live in Tampa area and my house and all of my neighbors houses have ridge vents. They need vents in the soffits and the house needs to be sealed from the attic.
I'm not a roofer but I think the hot air pushes out the ridge vents and sucks outside air in the lower vents. My house has attic access in the garage and the hole just has a screen so it vents a lot of air into the roof.
That's a great explanation of how a vented attic is suppose to work, supposedly they are good in every climate zone and the best thing you can do. It's what folks have done since they started building houses.

Now, this is where is gets interesting... what follows is what I've pieced together....

The first argument against a vented attic in Climate Zone 1 only (the dividing line is about at Miami) is that there's enough humidity outside for mold to grow. So, by venting your attic you're A) bringing in fresh moisture to feed the mold, B) bringing in new mold spores to start new colonies. A lot of places in Florida were having mold issues and in the 70/80's the solution to combat that was bigger air-vents and more air, but more air flow allows hurricanes to apply more suction to ripping your roof off. So, they made tie-downs mandatory in 1999. A Florida Building Code (FBC) study in 2015 (linked in a prior post) concluded vented attics just didn't work in Climate Zone 1. From the OP you can see my mother-in-laws house has only a fraction of the current FBC inlet ventilation square footage requirement (her problems are probably also largely due to the idiotic application of batting against the roof deck instead of the floor while also being vented).

Now the FBC allows "conditioned" attics.

Condition attics came along from energy conscientious folks who said it was an energy nightmare to put the AC ductwork and possibly the air-handler in the attic, as the attic is typically really hot. So, they started sealing the attic. Roughly half failed. They studied the problem and found that in the ones that succeeded, it was because the attic had a lot of air leaks from the AC system sucking the moisture out. Those without air leaks had roof rot.

So, they changed the code from "sealed" to "conditioned" attic space. The idea is moisture will build up there, so you have to remove it. But that's not easy to do via the code due to fire regulations and the argument against it is if you exchange house-air with attic-air, you're bringing crappy unhealthy air into the living space. Which leads me to think I just want to put a dehumidifier up there if needed (might have a leaky duct system) and call it a day.

But that's why I'm confused and seeking expert opinions. Is it a fad? Is it a better way to go here? Need to replace the roof too, so perhaps I should be doing something there (e.g., insulation above the roof)?
 
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svetz

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Open Cell
So, the case for Open Cell in walls in Florida (assuming you're okay with lower R value) seems to make sense.

The argument is the water vapor goes through the foam, but the interior is dry enough that by the time it gets through the foam there's no condensation.

Won't work for a roof though, there's no "drying" effect.

Update: Hmmm... if the attic space is conditioned, then there is a drying effect - so any roof water leaks might get pulled through... possibly not quick enough to prevent rot, but maybe. Shoot... might have to be more open minded with open-cell.
1603897996920.png
 
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svetz

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Gestalt!

I think I've finally figured out what's going on ... first some illustrations. The first is a top down view, the kitchen and living room have cathedral ceilings, the mold is in the attic walls adjacent to those two rooms. 1" air vents are about 1' apart on the right, on the left some air vents go into the attic space, some to the space above the cathedral ceiling:
1603980475765.png


This illustration is from the side with the left side of attic removed:

1603979077820.png

Obvious right? The inner walls probably aren't insulated... so where the inner attic wall corresponds to a cold wall, moisture forms and becomes a breeding ground for mold. Should be mold on the floors too, possibly there is and can't see it or the plywood is wicking the moisture away. Could be insulation under the plywood I guess.

So what about the roof decking and joists? Would it all be rotted? Possibly not...

1603979609891.png
 
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svetz

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Didn't I promise to put up some photos?
Eaves under the roof are 108,
underside of roof decking in attic is 114
1604003308393.png
From the living room,
looking at attic wall.1604003501755.png
Kitchen Left, LR right,
heat from attic.1604003607729.png
Kitchen wall from inside Attic,
1 degree delta with kitchen
1604003959379.png
cool how you can see the studs underneath the drywall.

So possibly the "true" need is to insulate in the walls between the attic and living space (yeah, still need the batts off the roof deck if its not conditioned). First "expert" will be out tomorrow.
 

svetz

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First inspector said the attic vents were blocked by failing insulation...and probably the same along the cathedral ceilings.
Also said the vents were too small, but suggested making it conditioned. Quoted $1k. To fix the cathedral ceilings need to take down the ceiling... he said you couldn't do injection foam through the roof deck (since I was getting it re-roofed)... pity. He also suggested open-foam, said it made it easier to find roof leaks. We'll see what the next guy says...
 

svetz

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<sigh> The materials in the last quote use a foam that has a 48 hour re-entry time and a class 2 fire rating.

Alternately I can DIY with a DOW "froth pack" from Lowes that has a Class 1 fire rating. Hiring a contractor shouldn't be this hard.
 

svetz

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So, the last guy came out and pretty much said you should do a conditioned attic... but he's not sending us a quote so that's the subtle way of saying the job is too small I guess.

So, DIY...

I got a respirator (did you know they want you to sign a statement that you're a professional and know how to use them now? that was weird - apparently you need to be professionally fitted now - weird because there are only 3 sizes and medium fits 80% of the people, also very easy to test if they seal properly) and a couple on N100 bayonette filters... boy was glad I did. Pulling out the old insulation was a really dirty job. In addition to the mold/mildew, a few decades of dust. Tomorrow I'll vacuum out the attic with the HEPA filter on my shop vac and then eliminate the mold on the drywall.

So, except for the gap between my long sleeves and gloves got away fairly unscathed. Quite surprisingly, a spray of hydrogen peroxide after a hot shower made the itch and angry red spots fade. Chalk one up for ole wives tales.

So stage 2 of the plan is plugging the existing ventilation holes. I suspect I'll have to do this from the outside, not quite sure how yet. Have a couple cans of loctite. Feels like a mess in the making. I know I have to work pretty quick with that stuff to keep the stuff from hardening in the tube, might be difficult with moving the ladder. Suppose I can jet some into a scrap bag every other minute.

Stage 3, knowing the age and condition of the existing insulation, we opted to get insulation on top of the roof deck when the metal roof is put on.

Stage 4 is to monitor the humidity and see if we need to do anything else... there's a lot of air leaks to the attic and a whole lot of wood, so might not need anything else. But if it does we'll seal the entire underside (stage 5!).

Inside the attic there's about a 4' rise for a 12' run (20 degrees?). Which means it's going to be really hard to get to the edge from the inside. If there were no obstructions I could probably scootch out, but naturally the ducting runs up there. So, need to pull and replace the ducting, or figure something out (assuming it gets to stage 5).
 
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