Air sealing, ventilation, and attic insulation project-need advice

[Badfish740]

Since the 90s are already here in NJ I am finally getting around to the air sealing/attic insulation project I've been putting off. I have a single story ranch with a simple gable roof. There are four ceiling fans, one ceiling light fixture, six recessed lights and one bathroom ventilation fan penetrating the ceiling so those all need to be sealed up which should be pretty straightforward. I'm going to use some plastic covers I found at Lowes along with Great Stuff to seal around the ceiling boxes for the fans, the hall light fixture, and the bathroom fan, but the recessed lights are going to be a challenge. I don't know whether they are IC rated or not and can't tell because the attic had a mold problem (due to poor ventilation) before we bought the home and it was sprayed to encapsulate what could not be removed-as a result the cans are completely coated with white paint. I have read about building a box out of drywall around the cans with 6" clearance all around to ensure that they don't get too hot and then caulking/taping the seams and joints. Does that sound like the best option? Besides the obvious ceiling penetrations what else should I be looking for in terms of leaks? The attic access is in the garage which is unconditioned space so I'm not going to worry about sealing it.

Once the ceiling is air tight I need to address the attic ventilation. Prior to our purchasing the house there was mold in the attic due to the fact that there was no ridge vent, soffit vents, or any type of mechanical ventilation-only two undersized gable vents. We got the seller to agree to have the mold taken care of, as well as install a ridge vent and two attic fans. The problem is that the attic fans now pull conditioned air from the house because there are still no soffit vents. The air sealing will help, but I still need to put in soffit vents of course. I was planning on installing the circular vents about every 4 feet.

Finally, I need to address insulation-the amount of insulation in the ceiling is a joke. I have about 6" of fiberglass and that's it. I figure the ceiling insulation is about R-15 and I want to get to R-60 in the hopes that it will lighten the load on my A/C this summer and keep more heat in during the winter. The question here is unfaced fiberglass batts or blown cellulose? I used the calculator on the Lowes website and found that I would need either 87 bags of cellulose or 32 bags of unfaced fiberglass in order to achieve R-60. Either option will cost about $1000 for the material. Lowes offers a free 24 hour blower rental with the purchase of the cellulose so there's no additional cost there. What is the better option? I'm leaning toward cellulose since it seems like it can really fill in where fiberglass would sort of just sit on top, but there's also the fact that it does settle over time.

 

[woodgeek]

Sounds like you are on the right track, but you may be missing some important air leaks in the attic floor. Most houses have the load bearing walls framed in first, then the drywall ceilings hung, then the rest of the walls framed. Thus, the load bearing walls have a top plate the breaches the air seal provided by the drywall. I had a couple hundred linear feet of ~1/8" gap, or several square feet of opening! Opinions differ whether these long gaps are better sealed with caulking (poor adhesion issues?) or spray foam (long-term durability?). Either way, it is a big enough job to research and do right. If you have any level changes in the attic floor, those are also potential locations of air leaks--I had six square feet along my split level.

It all likelihood, the airleaks in your attic could vent a lot more heat than the conduction through 6" of FG, seal the attic floor carefully before dropping more FG on top. With both improvements done right, you will see a big savings.

IF the attic previously had a mold problem it was almost certainly caused by a large-scale airleak, which imho is not due to a few can lights.

 

[midwestcoast]

+1 on woodgeeks likely sources of larger air leaks. I'll add bath fans & stove vent hoods vented direct to the attic or just leaky, and also look around the plumbing vent stack and chimney. Check for areas of dirty insulation to find other leaks (if it's not encapsulated?). Also seal air leaks in the basement (first) and main floor as those often connect to the attic & enhance the chimney effect.
The drywall boxes should be a good seal & insulation dam around the recessed lights.

In a ranch it's often tough to get access to the soffit areas in the attic due to low pitch of the roof. That makes blown-in easier to install than batts. It also makes it harder to get good insulation depth out there near the soffits OR to install the baffles/insulation dams that keep you air channel open to the soffit vents. You can try to solve both problems by making long baffles to fit in each rafter bay out of rigid foam insulation with a spacer block on the top, then push them under the roof decking down to the soffit and let them extend well up past your target cellulose depth to keep it from plugging them up. Use the thickness of foam + cellulose you need to get your target R-value out to the exterior wall. The downside to this is the foam is expensive.
With a ridge vent and fans I'd suggest a continuous soffit vent which would not be much more work to install & will give much more air-flow than the small round vents (basically you want to match the intake area to exhaust area). Also if you get flow in every bay it helps for roof cooling which is better for asphalt shingle life.

It's a job worth doing right the first time & sounds like you're doing it right. Don't pass out from the heat in that attic!

 

[Highbeam]

Since the 90s are already here in NJ I am finally getting around to the air sealing/attic insulation project I've been putting off. I have a single story ranch with a simple gable roof. There are four ceiling fans, one ceiling light fixture, six recessed lights and one bathroom ventilation fan penetrating the ceiling so those all need to be sealed up which should be pretty straightforward. I'm going to use some plastic covers I found at Lowes along with Great Stuff to seal around the ceiling boxes for the fans, the hall light fixture, and the bathroom fan, but the recessed lights are going to be a challenge. I don't know whether they are IC rated or not and can't tell because the attic had a mold problem (due to poor ventilation) before we bought the home and it was sprayed to encapsulate what could not be removed-as a result the cans are completely coated with white paint. I have read about building a box out of drywall around the cans with 6" clearance all around to ensure that they don't get too hot and then caulking/taping the seams and joints. Does that sound like the best option? Besides the obvious ceiling penetrations what else should I be looking for in terms of leaks? The attic access is in the garage which is unconditioned space so I'm not going to worry about sealing it.

Once the ceiling is air tight I need to address the attic ventilation. Prior to our purchasing the house there was mold in the attic due to the fact that there was no ridge vent, soffit vents, or any type of mechanical ventilation-only two undersized gable vents. We got the seller to agree to have the mold taken care of, as well as install a ridge vent and two attic fans. The problem is that the attic fans now pull conditioned air from the house because there are still no soffit vents. The air sealing will help, but I still need to put in soffit vents of course. I was planning on installing the circular vents about every 4 feet.

Finally, I need to address insulation-the amount of insulation in the ceiling is a joke. I have about 6" of fiberglass and that's it. I figure the ceiling insulation is about R-15 and I want to get to R-60 in the hopes that it will lighten the load on my A/C this summer and keep more heat in during the winter. The question here is unfaced fiberglass batts or blown cellulose? I used the calculator on the Lowes website and found that I would need either 87 bags of cellulose or 32 bags of unfaced fiberglass in order to achieve R-60. Either option will cost about $1000 for the material. Lowes offers a free 24 hour blower rental with the purchase of the cellulose so there's no additional cost there. What is the better option? I'm leaning toward cellulose since it seems like it can really fill in where fiberglass would sort of just sit on top, but there's also the fact that it does settle over time.

Big post. I just did this work to a 1963 built home.

1) Rip out the old cans and install new IC rated airtight cans. They are pretty cheap and you won't have to futz around with building boxes. Cans are easy to replace and you can even add more if you want to. There will never be an easier time to get rid of those old fashioned leaky can lights.

2) Look for wire penetrations and seal those holes in the top plate. A quick shot of foam or caulk will do. These are all over and the holes are often 3/4 inch to make room for a small romex wire. Big hole here.

3) I never understood people thinking that you need to seal along the entire edge of the top plate/sheetrock interface. In our area, we sheetrock the walls too and this joint is sealed very well on the room side by tape and mud, then paint. There is no gap to seal.

4) Also consider blown in fiberglass. Fiberglass won't burn or feed insects and mold. Cellulose is paper, it also ends in "ose" which makes it a sugar and a fuel source to bad things, think cotton candy. Educate yourself on both sides of this debate. Both products will work.

5) Absolutely blow in the attic insulation. The batts are a very inferior product in several ways, mostly labor costs for installation.

6) Bid the attic insulation with professionals doing the whole job. I couldn't buy the materials at home depot for what the installed price was. That way, the pros do this nasty job right.

7) Add adequate soffit vents and also make sure you add those baffles to prevent the insulation from blocking the air movement from the soffit to the ridge.

 

[semipro]

Since the 90s are already here in NJ I am finally getting around to the air sealing/attic insulation project I've been putting off. I have a single story ranch with a simple gable roof. There are four ceiling fans, one ceiling light fixture, six recessed lights and one bathroom ventilation fan penetrating the ceiling so those all need to be sealed up which should be pretty straightforward. I'm going to use some plastic covers I found at Lowes along with Great Stuff to seal around the ceiling boxes for the fans, the hall light fixture, and the bathroom fan, but the recessed lights are going to be a challenge. I don't know whether they are IC rated or not and can't tell because the attic had a mold problem (due to poor ventilation) before we bought the home and it was sprayed to encapsulate what could not be removed-as a result the cans are completely coated with white paint. I have read about building a box out of drywall around the cans with 6" clearance all around to ensure that they don't get too hot and then caulking/taping the seams and joints. Does that sound like the best option? Besides the obvious ceiling penetrations what else should I be looking for in terms of leaks? The attic access is in the garage which is unconditioned space so I'm not going to worry about sealing it.

Once the ceiling is air tight I need to address the attic ventilation. Prior to our purchasing the house there was mold in the attic due to the fact that there was no ridge vent, soffit vents, or any type of mechanical ventilation-only two undersized gable vents. We got the seller to agree to have the mold taken care of, as well as install a ridge vent and two attic fans. The problem is that the attic fans now pull conditioned air from the house because there are still no soffit vents. The air sealing will help, but I still need to put in soffit vents of course. I was planning on installing the circular vents about every 4 feet.

Finally, I need to address insulation-the amount of insulation in the ceiling is a joke. I have about 6" of fiberglass and that's it. I figure the ceiling insulation is about R-15 and I want to get to R-60 in the hopes that it will lighten the load on my A/C this summer and keep more heat in during the winter. The question here is unfaced fiberglass batts or blown cellulose? I used the calculator on the Lowes website and found that I would need either 87 bags of cellulose or 32 bags of unfaced fiberglass in order to achieve R-60. Either option will cost about $1000 for the material. Lowes offers a free 24 hour blower rental with the purchase of the cellulose so there's no additional cost there. What is the better option? I'm leaning toward cellulose since it seems like it can really fill in where fiberglass would sort of just sit on top, but there's also the fact that it does settle over time.

Big post. I just did this work to a 1963 built home.

1) Rip out the old cans and install new IC rated airtight cans. They are pretty cheap and you won't have to futz around with building boxes. Cans are easy to replace and you can even add more if you want to. There will never be an easier time to get rid of those old fashioned leaky can lights.

2) Look for wire penetrations and seal those holes in the top plate. A quick shot of foam or caulk will do. These are all over and the holes are often 3/4 inch to make room for a small romex wire. Big hole here.

3) I never understood people thinking that you need to seal along the entire edge of the top plate/sheetrock interface. In our area, we sheetrock the walls too and this joint is sealed very well on the room side by tape and mud, then paint. There is no gap to seal.

4) Also consider blown in fiberglass. Fiberglass won't burn or feed insects and mold. Cellulose is paper, it also ends in "ose" which makes it a sugar and a fuel source to bad things, think cotton candy. Educate yourself on both sides of this debate. Both products will work.

5) Absolutely blow in the attic insulation. The batts are a very inferior product in several ways, mostly labor costs for installation.

6) Bid the attic insulation with professionals doing the whole job. I couldn't buy the materials at home depot for what the installed price was. That way, the pros do this nasty job right.

7) Add adequate soffit vents and also make sure you add those baffles to prevent the insulation from blocking the air movement from the soffit to the ridge.

+1 on Items 1, 2, 5, 6, & 7. I think Oak Ridge Nat. Lab has some pretty good research on fiberglass versus cellulose but I'm not sure.

Also, ff you have a continuous ridge vent you should consider installing a continuous soffit. Round vents every 4 ft. probably won't be sufficient unless they're pretty big. The cross sectional area should be pretty close to the same at ridge and soffit. With adequate ridge and soffit vents you should no longer need the fans.

 

[woodgeek]

3) I never understood people thinking that you need to seal along the entire edge of the top plate/sheetrock interface. In our area, we sheetrock the walls too and this joint is sealed very well on the room side by tape and mud, then paint. There is no gap to seal.

I guess it depends on who is doing the drywall and what the framing below looks like. In my case I could see clearly down into the framed wall cavity (i.e. the wall sheetrock was not flush to the plate/studs at the ceiling). Of course if the wall below were sealed this would still be ok, I guess that there are enough gaps elsewhere between the cavity and the conditioned space to feed the leak. I could see staining and feel moisture (in the winter when I was doing this) on the FG above the gap, and 'see' that the FG over my tops plates was running a few degrees warmer (with my IR thermo).

I am also a measurement geek and determined by timing my heating system cycling that my heating demand dropped ~8% just from caulking all the top plates.

 

[laynes69]

We just did this also. We had a r-11 at most in our attic and I wanted to upgrade. For us we had a balloon framed home which we sealed over 32 open cavities our attic as well as a 1" gap around our whole top plates on our exterior walls. The tops of the walls on the interior top plates were also sealed. Sealing all the top plates won't take much, lay a bead of good caulk or use foam. Even though the drywall may be sealed inside and leaks in the top plates will carry air from elsewhere in the home. We ended up sealing a 6'+ diameter whole total in our attic which saved us a ton. After airsealing then we had to open all he overhangs and make baffles for the attic to breathe before blowing in insulation. Normally I would say blow in over the fiberglass, but if there was mold removal I would remove that and start from new. Doing it right the first time is much easier than trying again. After we airsealed, and created ventilation we blew in 14" of cellulose. I prefer cellulose over fiberglass for many reasons. After we insulated, our upstairs became 10 degrees warmer right away. Between the airsealing, we probably saved at least 15% and after insulation we probably seen a 20 to 25 percent reduction in heating with everything. High air leakage and lack of ventilation will wreak havoc on an attic. Also if possible I would stick with natural attic ventilation vs powered. That way no by products of combustion can be pulled through the home. Sounds like your on the right track. After your done you will have the benefits for years to come.

 

[coolidge]

Two inches closed cell foam for air sealing ,around can light boxes and fan boxes also and vapor barrier. Blow in 15" cellulose and REAP the savings. Be shure your bath exhaust is not the flex pipe, you should always use smooth bore for maximum cfm flow.

 

[velvetfoot]

A guy I know had foam sprayed on the underside of the roof deck on his old house. What's nice is that he still has a usable attic floor for storage, etc.

 

[Don2222]

Hello

If you want your house 10 degrees cooler in the summer:

1. Installing the Pink or light yellow Rafter Vents from HD or Lowe’s sometime called Proper Vents between the beams in the attic ceiling.


No electricity needed. Easy to install with a staple gun or a air stapler which is what I used!!
See 1st pic

2. Just staple Reflectix foil from Home Depot or Lowe’s to the rafter vents.
See 2nd pic

That is what I did, but for this to work you must have soffit vents. (easy to install yourself) and a ridge vent. (Roofers must install when re-roofing now because of the newer building codes)

I had the strip soffit vents put in with new primed wood. Works Great! See last pic!

 

[Highbeam]

That reflectix bubble wrap is not required or even needed. The goal of those attic baffles is to maintain a path for ventilation between the soffit and the attic space when you blow in insulation that would otherwise plug up the path.

Why did you choose to add the bubble wrap? Also, it looks like you ran the baffles all the way to the ridgevent. That would be a mistake as you would "short circuit" the attic ventilation. The baffles only need to be long enough to get past the blown in insulation. That's why they are sold in the 30" or so lengths. The soffit air then mixes with the attic air and ventilates through the ridgevent.

 

[Don2222]

That reflectix bubble wrap is not required or even needed. The goal of those attic baffles is to maintain a path for ventilation between the soffit and the attic space when you blow in insulation that would otherwise plug up the path.

Why did you choose to add the bubble wrap? Also, it looks like you ran the baffles all the way to the ridgevent. That would be a mistake as you would "short circuit" the attic ventilation. The baffles only need to be long enough to get past the blown in insulation. That's why they are sold in the 30" or so lengths. The soffit air then mixes with the attic air and ventilates through the ridgevent.

Hello Highbeam

It is not bubble wrap, it is the way the Reflextix foil comes. Next time your at Home Depot check it out.

You are right most contractors will only put the rafter vents down near the soffits to keep the insulation away. In Cathedral Ceilings the Rafter vents are required by code all the way up to the ridge vent.
The reason I did this also is:

1. It prevents most types of Ice Damns in the winter
2. It keeps the heat from escaping the living space in the winter but the roof stays cool!
Also by blocking up the gable vents the whole house stays 10 degrees warmer in the winter No Kidding!
That saves big bucks in heating fuel!!

See pic1 below where only the left half the roof had the rafter vents and foil
pic 2 of the insulated hatch door for the gable vent!

 

[gpcollen1]

That reflectix bubble wrap is not required or even needed. The goal of those attic baffles is to maintain a path for ventilation between the soffit and the attic space when you blow in insulation that would otherwise plug up the path.

Why did you choose to add the bubble wrap? Also, it looks like you ran the baffles all the way to the ridgevent. That would be a mistake as you would "short circuit" the attic ventilation. The baffles only need to be long enough to get past the blown in insulation. That's why they are sold in the 30" or so lengths. The soffit air then mixes with the attic air and ventilates through the ridgevent.

Hello Highbeam

It is not bubble wrap, it is the way the Reflextix foil comes. Next time your at Home Depot check it out.

You are right most contractors will only put the rafter vents down near the soffits to keep the insulation away. In Cathedral Ceilings the Rafter vents are required by code all the way up to the ridge vent.
The reason I did this also is:

1. It prevents most types of Ice Damns in the winter
2. It keeps the heat from escaping the living space in the winter but the roof stays cool!
Also by blocking up the gable vents the whole house stays 10 degrees warmer in the winter No Kidding!
That saves big bucks in heating fuel!!

See pic1 below where only the left half the roof had the rafter vents and foil
pic 2 of the insulated hatch door for the gable vent!

So the soffit to ridge vent is used solely for venting heat from the roof in the summer and for channeling the cold air in the winter AND the gable vent vents the attic in the summer but is closed up in the winter??

 

[Highbeam]

Sure looks like bubble wrap to me. You can see it in the photos. You still didn't say why you used the bubble wrap.

You mention a cathedral ceiling as the reason for your installation method but the photos show a flat ceiling and trusses as in a non-cathedral ceiling. I think this was an error. There are ways to build a non-vented attic but you haven't accomplished that either.

What you are doing is defeating your attic ventilation to gain extra warmth. It's like not running the bathroom fan when taking a hot shower, sure it works but it will get wet in there. I would not recommend that anyone do this. The cold parts of your roof that do not have the extra long attic baffles will be exposed to warmth and humidity from the non-vented attic space below. Water will condense on those bare plywood areas and you risk mold formation.

Hopefully you realize that you've chosen to do something that is not standard. Not becuase builders are cheap but because it fails to properly ventilate the attic.

 

[Don2222]

That reflectix bubble wrap is not required or even needed. The goal of those attic baffles is to maintain a path for ventilation between the soffit and the attic space when you blow in insulation that would otherwise plug up the path.

Why did you choose to add the bubble wrap? Also, it looks like you ran the baffles all the way to the ridgevent. That would be a mistake as you would "short circuit" the attic ventilation. The baffles only need to be long enough to get past the blown in insulation. That's why they are sold in the 30" or so lengths. The soffit air then mixes with the attic air and ventilates through the ridgevent.

Hello Highbeam

It is not bubble wrap, it is the way the Reflextix foil comes. Next time your at Home Depot check it out.

You are right most contractors will only put the rafter vents down near the soffits to keep the insulation away. In Cathedral Ceilings the Rafter vents are required by code all the way up to the ridge vent.
The reason I did this also is:

1. It prevents most types of Ice Damns in the winter
2. It keeps the heat from escaping the living space in the winter but the roof stays cool!
Also by blocking up the gable vents the whole house stays 10 degrees warmer in the winter No Kidding!
That saves big bucks in heating fuel!!

See pic1 below where only the left half the roof had the rafter vents and foil
pic 2 of the insulated hatch door for the gable vent!

So the soffit to ridge vent is used solely for venting heat from the roof in the summer and for channeling the cold air in the winter AND the gable vent vents the attic in the summer but is closed up in the winter??

Yes, Highbeam that is correct.

No bubble wrap just Reflectix foil. I will tell you when we closed those gables last winter we could just feel the extra warmth!!
It is tremendous! No mold because the ridge vent is still open to the attic air. But with those gable vents closed, old man winter does not blow fridgid air into the attic to really suck out the nice heat we pay dearly for

The 10% heat gain we get now in the winter has paid for the inexpensive foil and rafter vents over and over again Also we hardly ever use the air conditioning in the summer now!! We only turn on the air conditioning when it is too humid because it NEVER gets too hot anymore

Here is a video on something very similar
http://www.youtube.com/user/AtticFoil?blend=7&ob=5

As you can see in the last pic below, Reflectix is used in High Tech homes but maybe a little too much for the average household.

 

[laynes69]

Highbeam is correct, you pose a big risk of mold having inadequate attic ventilation. I wasn't sure exactly what you did until I seen this post. One of your other posts, you placed reflectix on top of the drywall before insulating. Having that and having it at the rafters will not allow the attic to breathe correctly. Your "10%" warmer has nothing to do with the foil. You are stopping the convective loops that occur within fiberglass insulation by stopping air flow. Its not worth the risk. Convection will reduce the r-value of the insulation because air travels through fiberglass. A attic that has adequate ventilation and the correct amount of cellulose will perform just as well as an attic with a radiant barrier and fiberglass. Cellulose does not lose its r-value as temperature drops and it will not allow for convective loops to occur within it. Also I didn't place a vapor barrier down before insulating our attic. I did not want moisure to get trapped between the drywall and attic. We live in a cold climate and any moisture that would migrate to the attic insulation would be dissapated and vented from the attic. There are some bogus claims on radiant barriers, and some of the most efficient homes don't use them. But then again they aren't insulated with fiberglass. Simply airsealing, venting and properly insulating an attic will have a huge effect on any home.

 

[Highbeam]

By "foil" you must mean bubble wrap with a shiny coating. That product IS bubble wrap.

 

[Don2222]

By "foil" you must mean bubble wrap with a shiny coating. That product IS bubble wrap.

Nope, It is foil encased in polypropylene

See the company and applications http://www.reflectixinc.com/ or go to the nearest Home Depot or Lowe's !! LOL

Home Depot
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

 

[gpcollen1]

By "foil" you must mean bubble wrap with a shiny coating. That product IS bubble wrap.

Nope, It is foil encased in polypropylene

See the company and applications http://www.reflectixinc.com/ or go to the nearest Home Depot or Lowe's !! LOL

Home Depot
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

The issue I see is in the video, the guy left the bottom near the soffit vent and the top at teh ridge vent open 6 inches or so. He said it was critical so it will breathe. You closed that entire system off. I am not saying it WILL as the other guys do but it definitely CAN lead to moisture issues. I may do this at some point as the guy int he video did but i will not do it like your looks - completely closed off.

 

[Don2222]

By "foil" you must mean bubble wrap with a shiny coating. That product IS bubble wrap.

Nope, It is foil encased in polypropylene

See the company and applications http://www.reflectixinc.com/ or go to the nearest Home Depot or Lowe's !! LOL

Home Depot
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

The issue I see is in the video, the guy left the bottom near the soffit vent and the top at teh ridge vent open 6 inches or so. He said it was critical so it will breathe. You closed that entire system off. I am not saying it WILL as the other guys do but it definitely CAN lead to moisture issues. I may do this at some point as the guy int he video did but i will not do it like your looks - completely closed off.

Like in the video, I left the top open so any very hot attic air can exit the house. However like the contractors, I blocked the bottom so no cold air from the soffits will get into the attic. Just like on Holmes on Homes when they put in the rafter vents down near the soffits, they also put in a piece of fiberglass to completely block the soffits from the attic air. Then when they blew in the insulation, no insulation would get into the soffits!

Also if soffit air gets into the attic space it will rob the house of heat in the winter, so I do not need that!

The reason a plastic moisture barrier is put down in the floor over the sheet rock is to PREVENT moisture and mold. The reason is that the warm air from the living space below will filter into the attic thru the sheetrock and when it heats the cooler air in the attic insulation moisture and mold will form!

I can understand the confusion so here is what I found.
In modern construction, vapor barriers have become controversial, but their use is legislated within the building code of some countries (such as the U.S., Canada, Ireland, England, Scotland & Wales)
Moisture barriers or Vapor retarders slow the rate of vapor diffusion into the thermal envelope of a structure.

The International Residential Code (IRC) defines vapor retarders as Class I, II or III based on how permeable they are to water vapor, the lower the permeability - the less water vapor that will pass through the vapor retarder.

Class I - Very low permeability vapor retarders - rated at 0.1 perms or less. Sheet polyethylene (visqueen) or unperforated aluminum foil (FSK) are Class I vapor retarders.
Class II - Low permeability vapor retarders - rated greater than 0.1 perms and less than or equal to 1.0 perms. The kraft facing on batts qualify as a Class II vapor retarder.
Class III - Medium permeability vapor retarders - rated greater than 1.0 perms and less than or equal to 10 perms. Latex or enamel paint qualify as Class III vapor retarders.

Another good definition from http://www.ashireporter.org/articles/articles.aspx?id=1722
A vapor retarder reduces the flow of water vapor contained in the air. A vapor retarder is required when warm, moisture-laden air may travel by convection into a cooler area such as the attic or a wall cavity. There, the water vapor may condense into liquid water and cause damage. Polyethylene sheeting is a common form of a Class I vapor retarder. Asphalt-saturated Kraft paper found on fiberglass batt insulation is a common form of a Class II vapor retarder. Latex and enamel paints are common forms of a Class III vapor retarder.

How to Install a Vapor Barrier in the Attic
http://www.associatedcontent.com/article/2028360/how_to_install_a_vapor_barrier_in_the.html

How to Add a Vapor Barrier to Attic Insulation
http://www.ehow.com/how_5888019_add-vapor-barrier-attic-insulation.html

Here is a great new product! Moisture barrier, insualtion and foil all in one http://www.insulation4less.com/

 

[woodgeek]

Don,

Not to rehash--but if your attic floor was actually airsealed and insulated to R-50, then nothing you did above that plane would do a darn thing to your energy loss, your attic could be freezing in the winter and 120°F in the summer, and the heat/AC loads on your house would be negligible. You would be free to vent the attic a little or a lot. Everything you are doing on your rafters, and the effects you are observing on your load are evidence that you are not effectively airsealed--apparently b/c you did not caulk/foam the cracks, just laid reflectix flat over the gaps.

The evidence is the AC load in the summer--if your attic is hot the hot air seeps into your top story. Your rafter work cools the attic space, and you see an improvement. In the winter, you close your gable vents (as described in another thread), and the attic space gets warmer (due to containing the hot air leaking from below), and your heat demand goes down b/c you have less air infiltration in the conditioned space. Push the numbers for how many BTUs are supposed to leak via conduction through a R-50 plane, it is BTU/h = sqft*Delta_T/R-value.

So, I am not denying that you can realize energy savings with your rafter work or gable vent closing, but instead I'm saying that you are suggesting methods that should not be generally applicable for folks with correctly done attic floor airsealing. The moisture concerns described by the other posters, are, I think, based on real-world experience. In my amateur opinion reading about current building science, the golden rule is to have the air-sealing plane and insulation in the same plane--in the winter you have the insulation in the floor, and the air-sealing plane, such as is it, on the cold roof deck (or the reflectix below it). With the exfiltration airflow you have through your FG batts, the perm rating of the building materials are the least of your concerns.

 

[laynes69]

Care has to be taken when placing a vapor barrier. If the vapor barrier isn't continous then it will do no good. Placing a faced batt of insulation over a vapor barrier is a no no. The photo you used for example is correct. Everything including the bottoms of the joists are sealed from above and taped before drywall. Here is a link to a video to show the temperature differences and airflow from fiberglass vs cellulose. Like woodgeek said, fiberglass will not stop the flow of air. Unless every crack was foamed or caulked air will leak into the attic space. If ventilation isn't present or enough the moisture in the form of vapor will condense and cause mold growth.

http://m.youtube.com/index?desktop_uri=/&gl=US#/watch?v=-Ybp93Jx6Tg

 

[Don2222]

Hello

I did air seal the wire holes with Great Stuff but then switched to DAP. Great Stuff works but too sticky and toxic! DAP does the same thing without the stickiness and toxicity!
http://www.dap.com/product_details.aspx?product_id=384

Also I agree a moisture barrier should be continuous.

I do respect your opinion. I did site known definitions, building codes and practices with links and videos to support my comments. So no matter how much insulation there is in the attic floor, if the attic is warmer in the winter, then the whole house stays warmer. The small wire holes are miniscule to leaving gable vents wide open! That is like leaving the front and back door open so the cold winter air can blow right thru! The air blowing thru the gable vents suck the heated air out of the house like a vacuum! Also if the soffit air is short circuited with the attic air, then that will suck the heat out of the house too!! I was up in the attic next to the gable vent and shivered when the zero degree air blew right in! Building a simple gable insulated door and closing it make a difference I could feel even downstairs in the living space!!
Also the radiant heat barrier in the rafters makes the attic about 20 degrees cooler in the summer and the living space 10 degrees cooler. It really is amazing!!

See Pic Below
Old man winter is not blowing thru this attic! In the summer the suns rays will not blaze thru the foil and the open gable will let the cool night air blow thru!

 

[Highbeam]

"The air blowing thru the gable vents suck the heated air out of the house like a vacuum! Also if the soffit air is short circuited with the attic air, then that will suck the heat out of the house too!!"

You have a very big misunderstanding about what you're doing. If anything happening in the attic sucks air and/or heat from your living space then you have problems with your air sealing and insulation. The only reason you even need a roof is to keep the rain off of your insulation.

It seems as though you took great efforts in building your home but you either misunderstood the documentation or you got bad advice from somewhere. You actually want air exchange in the attic, the whole attic, even if the outside air is cold air. It is a non-conditioned space.

 

[Don2222]

Hello

There is no misunderstanding here. You are correct that air flow is needed to prevent moisture. However moisture only happens when warm air rises and hits a cold mass. When these houses were first built with no soffit vents and no ridge vent, warm air would rise up and hit the cold inside of the roof and condense to form moisture. So back in the 60s they put in gable vents so the inside air in the attic would be cooler so when it hit the cold roof there would be no condensation. Now, we have soffit vents and ridge vents that work better because all of the roof is cooled. The gable vents are not really needed, however they do help cool the house in the summer. Also the newer technology shows in cathedral ceilings if there is a channel of air flow to keep the roof cool, then the space can be finished and used as living space. So what I am doing is applying the known technology of the cathedral ceiling and soffit vents and ridge vents with the air channel between them and closing the gables just like a cathedral ceiling. Then in the summer opening the gables for extra cooling and ventilation. Because this technique is based on known building practices that work, it indeed works very well! Hard to argue with success but I know there is still some controversy. That is fine but I am saving alot of heat and cooling costs in the meantime. LOL ~~

As the chart says, do nothing and more oil will be used and the price will go higher!