HVAC question...or two

I've been reading the links provided along with others for a mixed humid climate which it seems I live in ...

Some say vented others say unvented with foam board on top of sheathing...but from what I can tell with my situation it calls for vented. My roof is finished and the air handler is installed in the attic at this point so whatever I do will be around those definite's.

The rafters in my home are 10" and my roof consist's of metal,roof wrap, osb then rafters. From what I can tell it looks like I can insulate the walls with R16, ceilings with R38 and use 2-3" thick full length baffles from eve to ridge vent. The attic area in my home is only 12' x 20'.
If a heat pump working properly is supposed to control humidity then maybe to help with moisture up there a register could be installed to help control temps. From the way the whole house return is positioned 1' away from the conditioned living room would it need a seperate return if interior walls and ceilings were not air tight?
 
braxton357 said:
What am I missing? Seems like he's arguing for un-vented attic and crawl spaces rather than the "more ventilation" argued here.
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Unvented attic requires continuous board insulation and a ridge vent.
hunterdan said:
use 2-3" thick full length baffles from eve to ridge vent.
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The air space probably needs to be 6" high, continuous from the soffit vent to the ridge vent. More air space is better.

hunterdan said:
then maybe to help with moisture up there a register could be installed to help control temps
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That's like saying you're going to dump conditioned air into the stud cavity to prevent condensation. If anything, it'll make the problem worse. It's not just about humidity, but relative humidity. If the roof is warm and damp, blowing cold air on it is going to cause condensation.
 
braxton357 said:
What am I missing? Seems like he's arguing for un-vented attic and crawl spaces rather than the "more ventilation" argued here.
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That's what I mean. One says vented other says unvented. the unvented says any moisture that accumulates in winter overnight will be evaporated through some kind of thermal reaction from sun on metal roof and abilities of osb to adsorb and discharge also...
Another thread says a properly done vented roof can work in Florida or arctic home. But there's always a disclaimer with any method that involves a air handler or ductwork in an attic....unless...it's conditioned...unless:)
 
The roof is already on, you didn't install continuous insulation, you can't do a sealed attic.

Do you have ridge vents?

Don't forget that OSB is MUCH more susceptible to mold growth than plywood, so this is a big issue.
 
I guess in the end warm or cold air hitting cold or warm air is bad.
I need to make the roof sheathing warm in the winter and cool in the summer? Considering my situation how would I do that? I just figured conditioning the attic to be somewhat warm in winter and cool in summer would kill two birds....
 
shawn said:
The roof is already on, you didn't install continuous insulation, you can't do a sealed attic.

Do you have ridge vents?

Don't forget that OSB is MUCH more susceptible to mold growth than plywood, so this is a big issue.
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I must admit sometimes I say to myself "XXXX Tucker and these guys" but then I realize your just trying to help. I'm sure if ya'll saw a way for to put no insulation you would tell me....or at least that's what I'll tell myself.:)

As far as sealing everything like a ziploc bag I really don't care. I've been told that I should sheetrock tape and mud the entire house and then install tongue and groove but I don't want to and can't afford to. I intend on sealing every possible exterior wall and ceiling crack or hole and insulating but that's it. I've read that modern homes are too sealed and many need some kind of venting for walls/ceilings... I don't want to have to open a window to light the fireplace.

I do have eve and ridge vents. Since I don't have foam board on top of the sheathing I believe a vented roof is my only option...just how is my predicament.
 
braxton357 said:
What am I missing? Seems like he's arguing for un-vented attic and crawl spaces rather than the "more ventilation" argued here.
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If it’s going to be vented, then it needs to be vented correctly, and not half vented/ or vent restricted.

Im just pointing out , the same as others, regardless of attic type,

If the sheathing is below the dew point temp, condensation will occur, then mold will grow and rot the wood.

So to alleviate you either,

have to remove the moisture, to effectively lower the dew point,

Increase the temperature of the products to above the dew point temp,

Or a combination of both.


In a vented attic, during the cooling season condensation typically occurs on the hvac unit and duct system. Generally the temperature is so great during the day, it’s above the dew point, but not at night.

In the winter, the roof sheathing cools at night, and the humid air in the attic condenses on the sheathing. The south side may dry during the daytime, on sunny days.

The other areas of concern is any hole from the attic to the ceiling where the humid attic air can leak into the living space and condense.

As well as the massive amount of heat loss/gain through the duct system in the attic. For that I’d suggest double insulating all ducts, now that you know it’s all Air sealed.

That and build a plenum box from rigid foam board around the air handler if it’s in the attic.

The big point to understand you either remove the moisture, or change the temp. Whichever is easier and more practical. Only way to avoid condensation.
 
hunterdan said:
I need to make the roof sheathing warm in the winter and cool in the summer? Considering my situation how would I do that? I just figured conditioning the attic to be somewhat warm in winter and cool in summer would kill two birds.
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You're on the right track. What you've identified is the insulation is the source of the problem. If you didn't insulate, there wouldn't be any risk of condensation. But clearly that's not an option either.

You've got the vents, so the air can move. The trick now is making sure that the batts you put in the rafters allow for a sufficient amount of air to move between those vents. If it were me, I'd hang 2x4s off straps below the structural rafters, put the batts between them, and then hang sheetrock from the 2x4s. The reason I say sheetrock is because it's a vapor permeable interior air barrier, t&g wood sheathing is not.
 
Mac5005 said:
As well as the massive amount of heat loss/gain through the duct system in the attic. For that I’d suggest double insulating all ducts, now that you know it’s all Air sealed.
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It sounds like all the ducts and equipment are going to stay inside conditioned space, but I might have misunderstood.
 
shawn said:
You're on the right track. What you've identified is the insulation is the source of the problem. If you didn't insulate, there wouldn't be any risk of condensation. But clearly that's not an option either.

You've got the vents, so the air can move. The trick now is making sure that the batts you put in the rafters allow for a sufficient amount of air to move between those vents. If it were me, I'd hang 2x4s off straps below the structural rafters, put the batts between them, and then hang sheetrock from the 2x4s. The reason I say sheetrock is because it's a vapor permeable interior air barrier, t&g wood sheathing is not.
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Problem is I'll never install shitrock in my house. I think we discussed this before. I'll have to think of another option or just replace the house in 10 years.
 
basically, I have paid 400 dollar power bills in the winter and made due when living in a really non airtight doublewide. If I have to do the same in a newly constructed home because it's not GREEN or wrapped in shitrock so be it. Sorry to be so blunt but that has been my demand since the beginning. I'm so serious about not using shitrock that I will gladly watch my heat go out the roof than install it. Hopefully, "there's more than one way to skin a cat" as my Dad used to say.
 
Why do you call it "shitrock"?
 
Because it's fragile, prone to mold (I've seen it) It's hard to erase what I have seen first hand. I saw black mold in my previous home (double wide) (bathrooms and laundry)and in my fathers new home ( a newly constructed home in a high end neighborhood by a high end builder) Supposedly he got some Chinese sheetrock from lowes that caused the mold problem. I personally believe mold can grow on gypsum because like I said because I have seen it. One thing I know is that mentally they were fine when building the home but after 1 yr he and my mother both got alzheimer's and I blame it on the home. I'm not sure where their health issues came from but they both fell apart the minute they moved into that home. I blame it on all the caustic chemicals in modern homes. Many modern building materials mention formaldehyde and such chemicals... I think one day we will find out that the people are a test rat. I imagine that one day I'll see lawyers running ads for lawsuits against some building materials and methods.
Sorry to ramble but when I was a kid an occasional elderly person was considered "Senile". Now it's about as common a cause of death as cancer and senility is called Alzheimers

Wow, I guess I have some issues with sheet rock and skepticism with some modern conveniences.
 
Wood grows mold way better than drywall. I'm not understanding your logic here...

Stop the moisture issue and you'll avoid mold regardless of what material you use.


Listen to @Mac5005 and @shawn they are professionals in the industry and know what they are talking about.


If you are worried about mold, the first people you need to listen to are those two. Next is to reconsider you wall coating since wood harbors mold extremely well, much more than drywall.


Double wides are extremely prone to leaking and growing mold because they are poorly built and use crap materials. If the drywall was growing mold, try to imagine what the wood looked like!!!!
 
I'm pretty sure that Alzheimer's onset takes much longer than a year. It's a terrible affliction (I've lost family members to it), but blaming it on a years worth of drywall exposure in a new home seems pretty tenuous.
 
FYI, section 402.4 of the 2012 NC Energy Code requires an air barrier behind tongue and groove planking as it is specifically noted as not being a sufficient air barrier by itself. Taped house wrap is listed as a possible alternative to drywall.
 
Mac5005 said:
If you want a good read to dive into information that directly applies to our climate start here.

Info-015: Top Ten Dumb Things To Do In the South

There is plenty to study on that site, just browse around.
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Is that guy a professor? I'm working with a retired professor from NCSU on a wastewater project ihave going on and he, just like this guy, is so sarcastic at times that I can't tell if he's serious or not :lol:
 
Fabrik8 said:
I'm pretty sure that Alzheimer's onset takes much longer than a year. It's a terrible affliction (I've lost family members to it), but blaming it on a years worth of drywall exposure in a new home seems pretty tenuous.
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We went thru several years of dementia as caregivers for my uncle. Any major life change caused a 'plateau' change in his mental status. Moving down here to an assisted living facility. Major change. He had a pipe burst...ended up moving to another apartment...another major drop in mental status. Moved back several months later....yep, another (unrecoverable) drop. Happens a lot...moves, death of a spouse, even retirement....
 
paradisePWoffrd said:
Maybe I'm missing something but why not insulate under the heat pump/ducts and leave the underside of the rafters/roof open?
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Unconditioned attic is the worst place you can put an HVAC unit and ducts.

Also, no coincidence that there was mold in the bathroom and the laundry. I'm betting there either weren't exhaust fans in those rooms, or they weren't used to maintain a proper humidity level.
 
shawn said:
If it were me, I'd hang 2x4s off straps below the structural rafters, put the batts between them, and then hang sheetrock from the 2x4s. The reason I say sheetrock is because it's a vapor permeable interior air barrier, t&g wood sheathing is not.
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This is darn good advice, and a darn good solution.

Don't be a Fuller!


As to the sheetrock/shitrock, here is a quick read: You Don't Need a Vapor Barrier (Probably)

T&G will have a lot of air leakage...

Seal the air leakage pathways.
Seal the air leakage pathways.
Seal the air leakage pathways.
 
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