Reflectix radiant barrier

[ChrisJM981 924]

Anybody have experience with Reflectix? I was thinking of doing the ceiling in my garage with it instead of drywall. It's a raised ranch with bedrooms over the garage. I know it's class I/A fire rated.

[djg0770 481]

If you Google it and have an even rudimentary understanding of heat transfer you'll realize that it's smoke and mirrors, but by all means, do what you like so I can say "I told you so" in the middle of February.

[ChrisJM981 924]

I have fiberglass insulation in between the joists, I just didn't get around to putting up a vapor barrier and fire rated covering. Trying to kill two birds with one stone.

[raz-0 1,260]

If you Google it and have an even rudimentary understanding of heat transfer you'll realize that it's smoke and mirrors, but by all means, do what you like so I can say "I told you so" in the middle of February.

 

How so. It's a radiant barrier? You have to air gap it. And it does push heat into the gapped space. Most of what I have read up on radiant barriers is for keeping heat down in converted attics though. Radiant barriers usually do so at the cost of shortened roof shingle life. DoE has done evaluations of it and does say it lowers temps. As far as I can tell, claims of it saving you jack are largely BS unless you have been silly enough to try and cool a poorly insulated attic 24-7, it's a matter of improving livability.  It's pretty useless for cold, which would be my main concern with a garage under living space. 

 

From what I have read, anything other than in the attic is a waste of money in our climate, and in the attic, it's a small return with an unfinished attic, with a finished attic you might gain livability, but unless the way you finished it leaves room to vent the heated air, you are just going to shift a chunk of the costs to cooking your shingles. 

[djg0770 481]

http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/29497/The-Foil-Faced-Bubble-Wrap-Sham-Understanding-Radiant-Barriers

 

http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/bubble-wrap-duct-insulation-good-idea

 

 

 

Foil-faced bubble wrap "is not Energy Star or Manual D approved," he wrote, "and is generally viewed as snake oil by reputable builders."

[djg0770 481]

Furthermore, what "radiant" energy will it trap in the summer in the ceiling of a garage with living space above? 

[Howard 538]

I hear radiant barriers make sense in FL and TX but waste of money in NJ area.

[ChrisJM981 924]

So my understanding is that the barrier should be on the warm side. What would make an effective vapor barrier? My concern is more so with carbon monoxide and gasoline vapors than moisture.

[DeerSlayer 241]

Don't waste your money. Go double 5/8" rock if your looking for fire ratings. If you want warm rooms in the living space above your garage, invest in high end thermal garage doors, and heat the garage in the winter to about 50/55 deg F. I've added a zone of heat to many garages for customers for exactly that reason. They were all happy for having done so.

[djg0770 481]

Don't waste your money. Go double 5/8" rock if your looking for fire ratings. If you want warm rooms in the living space above your garage, invest in high end thermal garage doors, and heat the garage in the winter to about 50/55 deg F. I've added a zone of heat to many garages for customers for exactly that reason. They were all happy for having done so.

 

I'd be wary of extending a hot air system to a garage due the (albeit remote) possibility of CO migration back to the unit or home.  Hot water, no problem other than the potential for someone to freeze the branch lines inadvertently.  With a hot air system, I'd rather lean toward a gas fired (or electric if you're brave) unit heater in the garage, but that's me with a belt, suspenders, and a rope in my pocket, JUST IN CASE.

[DeerSlayer 241]

I'd be wary of extending a hot air system to a garage due the (albeit remote) possibility of CO migration back to the unit or home. Hot water, no problem other than the potential for someone to freeze the branch lines inadvertently. With a hot air system, I'd rather lean toward a gas fired (or electric if you're brave) unit heater in the garage, but that's me with a belt, suspenders, and a rope in my pocket, JUST IN CASE.

I'm pretty sure he has a boiler, I kinda remember from another post. Add a zone run a supply and return hang a unit heater, mount a thermostat, dump 5 gallons of anti freeze in the boiler. As far as forced air goes, I completely agree. I'm not a fan of that idea either. I would rather see something electric, or a stand alone direct vent gas or lp unit in that case. Maybe even a mini split with a heat pump depending on budget.

[Zeke 5,504]

I have fiberglass insulation in between the joists, I just didn't get around to putting up a vapor barrier and fire rated covering. Trying to kill two birds with one stone.

You need 2x 5/8 on the ceiling if there is living space above.

Vapor transmission up? Same level garage floor/ living space need a min of a 4" curb for vapor.

 

I'm not a chemist,but, the molar weight of co1 is heavier than that of air.

[Zeke 5,504]

Yank out your bat insulation.

Have deerslayer run radiant.

Foam it.

Fire rock it for code.

Everything will then be honky dory

[ChrisJM981 924]

I have a raised ranch with 2 bedrooms over the garage. Hot water heat with a boiler. I ripped out the entire ceiling after I had a toilet leak and drip through the insulation, spawning mold. I got it in my head that I was going to solve the cold bedroom issue by spray foaming the ceiling with a base layer of foam to act as a barrier, then put in fiberglass insulation. I ran out of product and missed some spots. I put up the fiberglass insulation to get through the winter and spring but never got around to finishing the job.

 

I already have hot water pipes running through the garage, but they go up into the bedrooms.

[Zeke 5,504]

Bat insulation no worky with moving air. Like every time you open a garage door.

[Zeke 5,504]

If your house catches on fire, I would not want to be you disputing with the insurance company. Rent a Sheetrock lift and rock your ceiling. You should tape between layers. They have new sticky fire tape you don't have to spackle. It's purple.

[Zeke 5,504]

Bud, the easy way never ends up being the best/right way

[10X 3,321]

You need 2x 5/8 on the ceiling if there is living space above.

Vapor transmission up? Same level garage floor/ living space need a min of a 4" curb for vapor.

 

I'm not a chemist,but, the molar weight of co1 is heavier than that of air.

 

 

I'm a chemist.  The MW of CO is lighter than that of oxygen (as O_2, the form in which it exists in the atmosphere).   It's the same as that of nitrogen (N₂).   So CO is lighter than the average molecular weight of 'air'.

 

But that doesn't matter, as the gasses diffuse very efficiently, and CO, N₂, and O₂ aren't going to stratify even a little bit.  Even the little bit of Argon in the atmosphere doesn't settle out, and it's a friggin heavy gas atom.

[Zeke 5,504]

I'm a chemist. The MW of CO is lighter than that of oxygen (as O_2, the form in which it exists in the atmosphere). It's the same as that of nitrogen (N₂). So CO is lighter than the average molecular weight of 'air'.

 

But that doesn't matter, as the gasses diffuse very efficiently, and CO, N₂, and O₂ aren't going to stratify even a little bit. Even the little bit of Argon in the atmosphere doesn't settle out, and it's a friggin heavy gas atom.

Ok then, why do I have put in "gas curbs "

[10X 3,321]

Ok then, why do I have put in "gas curbs "

 

No idea.   A lot of places don't require them, but that doesn't help if you live somewhere that does.

[ChrisJM981 924]

Bat insulation no worky with moving air. Like every time you open a garage door.

I planned on putting up 5/8" drywall, just not sure what I need to do as far as a vapor barrier first.

[Zeke 5,504]

How much does octane vapor weigh vs air? Since I have you on the horn

[10X 3,321]

How much does octane vapor weigh vs air? Since I have you on the horn

 

 

Googling around, I found a value of 3.3 grams per liter under standard conditions, or about 3.9 times as dense as air.    I didn't quickly find a value for the vapor density of gasoline, which has all kinds of volatile stuff in it in addition to octane, but the vapor will still be denser than that of air.   But it will still diffuse pretty quickly, because the entropy of the gas won't let it stratify for long.   A balloon filled with octane vapor will sink; the unconfined gas, not so much.

 

If you spill a little gas on the floor, think of how quickly the smell gets to your nose.

[Zeke 5,504]

Googling around, I found a value of 3.3 grams per liter under standard conditions, or about 3.9 times as dense as air. I didn't quickly find a value for the vapor density of gasoline, which has all kinds of volatile stuff in it in addition to octane, but the vapor will still be denser than that of air. But it will still diffuse pretty quickly, because the entropy of the gas won't let it stratify for long. A balloon filled with octane vapor will sink; the unconfined gas, not so much.

 

If you spill a little gas on the floor, think of how quickly the smell gets to your nose.

Thank you. I was in error of the purpose of curbs. It's the venting of the gas tank. Doors closed it's confined space.

[DeerSlayer 241]

Yank out your bat insulation.

Have deerslayer run radiant.

Foam it.

Fire rock it for code.

Everything will then be honky dory

I can do staple up radiant. But we usually use foil face insulation with the foil side up to reflect the heat back. And we need a 4" air gap between the insulation and pipe. If you foamed it, it would insulate the pipe from being able to penetrate upward effectively.

 

Here's a staple down I just did.

[DeerSlayer 241]

I have a raised ranch with 2 bedrooms over the garage. Hot water heat with a boiler. I ripped out the entire ceiling after I had a toilet leak and drip through the insulation, spawning mold. I got it in my head that I was going to solve the cold bedroom issue by spray foaming the ceiling with a base layer of foam to act as a barrier, then put in fiberglass insulation. I ran out of product and missed some spots. I put up the fiberglass insulation to get through the winter and spring but never got around to finishing the job.

 

I already have hot water pipes running through the garage, but they go up into the bedrooms.

With multiple outside walls in those rooms, and unheated space below, you could put R-890987655772 in the garage ceiling, and it's still going to be cold upstairs above the garage.