Help identify exterior wall underlayment please.

[mannyrock]

Dear Guys,


   I have a main roof on my house, and then a side roof that is about 3 feet lower than the main roof.  On the side of the house, where the three foot drop occurs, the house is currently sheathed with 5/8 inch T-111.   It has held up pretty well for 32 years, but now needs to be ripped off and replaced.  The entire area is only about 3 feet tall by 12 feet long.  The upper roof has an overhang over this sheathing, with a perforated aluminum soffit.


   When I am in my attic, looking at the back of the sheathing, I see there there is some type of underlayment behind the T-111.   It is dark brown, fiberous, and looks like compressed hairy cardboard.  In areas where moisture has dripped down the inside of this stuff, the stuff has simply disintegrated.  You can pull it apart like damp cardboard with your fingers.




   My new roof goes up in about 2 weeks, so all leaks will be fixed.  The new T-111 will be put up at the same time.


   Here are my questions please:


   1.  What is this underlayment called?.


   2.  Why do I need it?   (It has zero structural strength, is not water resistant, and seems to have little insulation value.  Since the ridge vents of the upper and lower roofs are just inches above and below this material, why in the world would I need insulation here anyway?  The cold and hot air are always intruding into the attic via these vents just above and below this wall.)


   3.   Assuming I do need some type of underlayment for the T-111, is there something better I can use?  (I don't care how expensive it is, and there must be something better than this cardboard.)




   (The reason that the inside of the underlayment is damp, is that every time we get a hard blowing rain storm from the west, the high winds blow the rain up under the soffit, up through the ventilated aluminum soffit board, and then the raindrops drip down the inside of the wall, on the interior side of the underlayment.   I am replacing this ventilated soffit section with solid soffit to end this problem.)


  Thanks for all information and advice.




Mannyrock

[FPH]

Probably an ashault impregnated sheathing call Celotex (sp).  Used as insulationjn behind T 1-11.  I have literally put 1000's of sheets of it on spec homes, apartment,town homes, condos....you get it......cheap......... if using it on my own home today, I would use a house wrap over it.

[Old Syko]

Celotex fiberboard has gone through a lot of changes over the years.  The product you would buy under that name today is a lot different than it was many years ago.  The older stuff was black or dark brown and very poor quality and had a smell you remember.  The newer stuff is a light tan color or even white and usually foil backed and not nearly as susceptible to water damage.  A good house wrap is never a bad idea. 

[mannyrock]

  Thanks for your answers guys.


  Yes, the stuff that's up there has a smell like, . . . dried dog turds.  Especially when its damp.  So, it must be the old asphalt impregnated stuff.




  I'll get a few sheets of the new Celutex to go up under the T-111.  Guess it can't hurt.




Mannyrock

[hunt-m-up]

OSB sheathing is inexpensive, rip off the fiberboard crap, apply OSB then wrap and side it.

[FPH]

OSB sheathing is inexpensive, rip off the fiberboard crap, apply OSB then wrap and side it.

OSB will have no insulating value.

[Larry L]

[size=0px]OSB will have no insulating value.[/size]

That's not quite true. Wood itself is an insulator and darn good one. The R value of 1/2" OSB is 0.62 as manufactured (not installed in a wall cavity which adds R value). The 1/2" impregnated sheathing is better but it's still at a dismal 1.3 as manufactured. One of the best is the polyisocyanurates. But considering the location of the materials is on an end wall to the attic, it's not needed. Frankly, unless you just need for the siding to come out the same thickness to match an adjoining area, I wouldn't bother with any of it. Just put up the siding. Any 5/8" siding can easily be installed on studs at 24"OC with zero bracing or backer materials. Any of the T1-11's are certified to be used for bracing themselves, you obviously don't need to brace a bracing material. But this is like anything else about construction, there's a thousand ways to do it wrong and just as many to do it right. Give 10 builders the same plan and you'll have 10 differently built homes and all can be correct.

[FPH]

Any

[size=0px]OSB will have no insulating value.[/size]

That's not quite true. Wood itself is an insulator and darn good one. The R value of 1/2" OSB is 0.62 as manufactured (not installed in a wall cavity which adds R value). The 1/2" impregnated sheathing is better but it's still at a dismal 1.3 as manufactured. One of the best is the polyisocyanurates. But considering the location of the materials is on an end wall to the attic, it's not needed. Frankly, unless you just need for the siding to come out the same thickness to match an adjoining area, I wouldn't bother with any of it. Just put up the siding. Any 5/8" siding can easily be installed on studs at 24"OC with zero bracing or backer materials. Any of the T1-11's are certified to be used for bracing themselves, you obviously don't need to brace a bracing material. But this is like anything else about construction, there's a thousand ways to do it wrong and just as many to do it right. Give 10 builders the same plan and you'll have 10 differently built homes and all can be correct.

Any product has some R value, you are correct on that.    Neither OSB or Celutex are worth a hoot as insulation.  I would disagree with your contention that wood is a good insulator....in most jurisdictions it wont meet code.....what are you comparing it to?

[hunt-m-up]

[size=0px]OSB will have no insulating value.[/size]

That's not quite true. Wood itself is an insulator and darn good one. The R value of 1/2" OSB is 0.62 as manufactured (not installed in a wall cavity which adds R value). The 1/2" impregnated sheathing is better but it's still at a dismal 1.3 as manufactured. One of the best is the polyisocyanurates. But considering the location of the materials is on an end wall to the attic, it's not needed. Frankly, unless you just need for the siding to come out the same thickness to match an adjoining area, I wouldn't bother with any of it. Just put up the siding. Any 5/8" siding can easily be installed on studs at 24"OC with zero bracing or backer materials. Any of the T1-11's are certified to be used for bracing themselves, you obviously don't need to brace a bracing material. But this is like anything else about construction, there's a thousand ways to do it wrong and just as many to do it right. Give 10 builders the same plan and you'll have 10 differently built homes and all can be correct.

I would build a garden shed that way, but not a home, it would still get sheathing. There is no substitute for any of the products that are actually sold as insulation. You're exactly right, 10 contractors will each build it their own way.

[Larry L]

I would disagree with your contention that wood is a good insulator.

I can only assume that if you are in the industry, you didn't think before you posted. Have you ever picked up a hot fry pan with a wood handle? The handle wasn't hot because wood has very few free electrons therefore is a poor conductor of temperature. But to get to the meat here, are you familiar with what wood is? It's basically cellulose. Paper is made from wood fibers-cellulose, and cellulose insulation is used almost every where. We use a tons of it here for insulation and I'm sure it's used in your area as well.


Still the issue with this thread is why add insulation to an end wall panel that has attic on the other side? It's a waste of materials and provides zero benefits. Not using it would allow more heat to escape via conduction but that's only going to be marginal at best. Why provide insulation to a wall that has nothing to do with the living space? That's kinda like putting down porcelain tile on the floor and then covering it up with carpet or painting the trusses- a waste of materials.

[PowPow]

"painting the trusses"...I'm gonna remember that one.

[FPH]

I would disagree with your contention that wood is a good insulator.

I can only assume that if you are in the industry, you didn't think before you posted. Have you ever picked up a hot fry pan with a wood handle? The handle wasn't hot because wood has very few free electrons therefore is a poor conductor of temperature. But to get to the meat here, are you familiar with what wood is? It's basically cellulose. Paper is made from wood fibers-cellulose, and cellulose insulation is used almost every where. We use a tons of it here for insulation and I'm sure it's used in your area as well.


Still the issue with this thread is why add insulation to an end wall panel that has attic on the other side? It's a waste of materials and provides zero benefits. Not using it would allow more heat to escape via conduction but that's only going to be marginal at best. Why provide insulation to a wall that has nothing to do with the living space? That's kinda like putting down porcelain tile on the floor and then covering it up with carpet or painting the trusses- a waste of materials.

Operative word....good....wood is usually solid....a cellulose product will be artificially fluffed with air spacing.....this add a lot to the insulating factor.  I don't think you can argue that wood is a good insualtor say compared to a fiberglass product.  Attic fans or vents would facilitate heat and moisture exchange and  insulation could be warranted especially in witner months.

[mannyrock]

  Wonderful answers and exchanges of ideas here.  Just what I was looking for.


  Thanks,


Mannyrock

[Larry L]

Attic fans or vents would facilitate heat and moisture exchange and  insulation could be warranted especially in witner months.

Quite actually the opposite is true. If you want to get rid of the moisture and increase efficiency you'll be sealing the attic space from any outside air regardless of exterior environment. That means it doesn't matter if it's sub zero or plus 100F outside, a sealed attic will be more efficient. For this application and because the home is already built, a spray on radiant barrier would be in order otherwise a radiant barrier at time of construction would be speced. I live in Texas and we fight the heat here. Attic temps at 140F are common. Venting it does absolutely nothing as the heat build is still there. You can take a 48" fan and install it in the gable end and the temps of the attic materials do not change despite cooler ambient temps. Why? Because the radiant heat is still there and until you block it off, nothing is going to change the attic efficiency. If you use a laser probe you'll find the same thing on your own. Sealing the attic means no thermal loss from the interior penetrations like ceiling lights, fart fans, etc. To cut to the meat here, read the info at the link. If you've never attended one of Joes seminars, you need to. I've been to many across the years and all have been fascinating. Even better, I've been with him with the CEOs of several national builders to inspect the homes for energy efficiency. I've learned a lot from this crude but intelligent guy. If you've never looked thru Building Science website, you need to. These guys come up with some of the whackiest stuff but it works extremely good.
http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates/?searchterm=sealed%20attics


One of the attributes of cellulose is that it goes on wet. It gets in places and blocks air movement that fiberglas will never see. It fills all voids unlike fiberglas batts that have to go around a penetration/pipe. It will completely fill a wall cavity where fiberglas can't. In a wall cavity, fiberglas cannot match the performance of cellulose which is a wood product. In the attic, cellulose being a small grain type insulation will fall in places fiberglas will never see. It does a much better job at getting more insulation where it counts. But like with any product, while it may sound like a magic bullet, it isn't. To keep it from just being paper in the attic or walls which adds significantly to a house on fire, we add borates to it to make it fire resistant. Another great factor about the borates, at a 28% concentration, it's also certified as a termiticide. That's something you won't get with fiberglas. But unfortunately these borates deteriorate over time. Then you have issues with the fuel that is now packed all around you and your family. Once the borates have deteriorated it becomes subject to rot just like the wood it comes from. While it our performs fiberglas, it doesn't have the life of fiberglas which also has it's own issues like settlement and decreasing efficiency over time to where it's R value has fallen so bad it's near worthless.

[FPH]

Attic fans or vents would facilitate heat and moisture exchange and  insulation could be warranted especially in witner months.

Quite actually the opposite is true. If you want to get rid of the moisture and increase efficiency you'll be sealing the attic space from any outside air regardless of exterior environment. That means it doesn't matter if it's sub zero or plus 100F outside, a sealed attic will be more efficient. For this application and because the home is already built, a spray on radiant barrier would be in order otherwise a radiant barrier at time of construction would be speced. I live in Texas and we fight the heat here. Attic temps at 140F are common. Venting it does absolutely nothing as the heat build is still there. You can take a 48" fan and install it in the gable end and the temps of the attic materials do not change despite cooler ambient temps. Why? Because the radiant heat is still there and until you block it off, nothing is going to change the attic efficiency. If you use a laser probe you'll find the same thing on your own. Sealing the attic means no thermal loss from the interior penetrations like ceiling lights, fart fans, etc. To cut to the meat here, read the info at the link. If you've never attended one of Joes seminars, you need to. I've been to many across the years and all have been fascinating. Even better, I've been with him with the CEOs of several national builders to inspect the homes for energy efficiency. I've learned a lot from this crude but intelligent guy. If you've never looked thru Building Science website, you need to. These guys come up with some of the whackiest stuff but it works extremely good.
http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates/?searchterm=sealed%20attics


One of the attributes of cellulose is that it goes on wet. It gets in places and blocks air movement that fiberglas will never see. It fills all voids unlike fiberglas batts that have to go around a penetration/pipe. It will completely fill a wall cavity where fiberglas can't. In a wall cavity, fiberglas cannot match the performance of cellulose which is a wood product. In the attic, cellulose being a small grain type insulation will fall in places fiberglas will never see. It does a much better job at getting more insulation where it counts. But like with any product, while it may sound like a magic bullet, it isn't. To keep it from just being paper in the attic or walls which adds significantly to a house on fire, we add borates to it to make it fire resistant. Another great factor about the borates, at a 28% concentration, it's also certified as a termiticide. That's something you won't get with fiberglas. But unfortunately these borates deteriorate over time. Then you have issues with the fuel that is now packed all around you and your family. Once the borates have deteriorated it becomes subject to rot just like the wood it comes from. While it our performs fiberglas, it doesn't have the life of fiberglas which also has it's own issues like settlement and decreasing efficiency over time to where it's R value has fallen so bad it's near worthless.

I too live in TX.....West Tx area to be exact.( I have lived in E. TX.) If you don't think an attic fan or turbin vent will  decrease the attic temp.,they can dramatically do so, you are  sadly mistaken.(Why would a thermally controlled switch turn the fan on and off if you weren't causing the temp to change?)  Fiberglass does have it's settlement issues. 

[SHOOTALL]

just some thoughts , if you have studs insulate between them if you need to. Wrap what ever you put between the studs and exterior finish, Tyvex is good if can be used by itself if need be. If the space is unconditioned remember if the temp in the space is lower than out side you can cause a moisture problem if you bring in warm air as if it contains moisture it will cause dew as it cools on surfaces.

[Larry L]

[size=0px]If you don't think an attic fan or turbin vent will  decrease the attic temp.,they can dramatically do so, you are  sadly mistaken.(Why would a thermally controlled switch turn the fan on and off if you weren't causing the temp to change?)[/size]

There is a major difference between ambient temperature and surface temperature. I would suggest you buy a cheap laser probe from Harbor Freight and give this a try. Close up all of the vents and check the ambient temp at noon. Laser probe the insulation and wood members writing down the temps. Open all vents. Wait 1 hour....it should be getting hotter outside-right? Check the ambient temp. Yes, it will go down. Now check the insulation and wood members. It has gone up in temp, not down. The reason is the radiant heat- you got rid of the symptom but not the cause which continues to build. The members and insulation will continue to go up in temp all thru the day even if you were to cut the ridge back 12" each side of it. Due to conduction, the house will consume more energy than it would with a sealed attic. That's what the higher temps of the members and insulation bring to the drywall ceiling. In your old thinking, you assume that the deck is the cause of the heat- it's only a small part of it. Get rid of the hot air and the issue is solved. You have to know it can't be that easy. Radiant heat, like standing under a metal roof in the middle of a hot day, is the culprit.
I've been in vented and power vented attics many times. During the summer of most you can't be there more than 10 minutes or the world starts going around and around. But go in a sealed attic with zero ventilation and it's normally cooler than the outside temp and never hotter than the outside temps. I've been in attics on a 100F+ day and it's comfy in the attic. Doesn't sound right to old thinking but it works.


Obviously you didn't read anything at the linky. Building Science is THE top ranked construction consultant in the world. These are the mad scientists of building. There's very little that they haven't addressed in residential and commercial construction methodology. They build houses and building to different specs and experiment with what works and what doesn't. From roof systems, to plumbing, they pretty much cover it all. Anybody that does any kind of construction can benefit dramatically from reading their website.

[FPH]

 

[SHOOTALL]

Keep in mind the laser temp reading is not as accurate unless you are close. The farther away the surface is the less accurate the reading will be. What you get is the average between the instrument and the surface you are probing.

[mannyrock]

  Okay, now, having listened to all advice, here is what I'm gonna do.

  1.  My attic has a ridge vent cut along almost the entire ridge line top, and soffit vents between every set of rafters at the bottom of the roof, on front and back.  Therefore, whether this 3 foot by 12 foot section of siding is insulated or not will not have any material affect on the temperature or moisture rating of the attic space as a whole.




  2. When in doubt, I always go for greater ventilation and easier temperature exchange between inside and outside for attic spaces.




  3.  So, I have decided to put no insulation board between the T-111 siding and the underlying roof stud wall.


 4.  However, I will go up there once a week, for the next year, and run my hand along the inside of the siding.  If I feel any moisture, then I can always glue insulation board to the inside of the siding, between the upright chord supports, because these stud pieces are very easily accessible.


  Thanks for all of the great help.


Regards, Mannyrock


 
 

[SHOOTALL]

or just staple vapor barrier on the studs before nailing up the T-111

[Old Syko]

Funny thing about this thread is all the concern about attic temperatures and that is only a small part of why we ventilate an attic.  Moisture and humidity are the main issue where I live.  A "sealed" attic as mentioned earlier will not be permitted here or most other places as it goes against code unless there is another form of humidity control implemented.  Same goes for crawl spaces. 


+1 on the vapor barrier and do it as part of the original construction and not a later add on.

[mannyrock]

  Well, okay.   Please explain to me what the vapor barrier will do for me if I staple it to the framework before installing the T-111.  Also, exactly what vapor barrier material to use.  (Lots of times I see people using regular clear 6 mil plastic and calling it a vapor barrier.  Pretty popular underneath foundations.)


  Thanks for your help.




Mannyrock

[FPH]

This should explain it   6mil plastic should be fine.               .wikipedia.org/wiki/Vapor_barrier   

[hunt-m-up]

In this part of the world vapor barrier is on the interior side of studs under drywall and yes 6 mil is commonly used. As Old Syko said, sealed attics are not a generally accepted practice here.
Sounds like you have it under control Manny, good thing you did away with the fiberboard junk.

[FPH]

I think in his location, on the exterior would be better.  There is a reason only approx. 100,000 homes have been built with a sealed attic since 1995.

[Old Syko]

  Well, okay.   Please explain to me what the vapor barrier will do for me if I staple it to the framework before installing the T-111.  Also, exactly what vapor barrier material to use.  (Lots of times I see people using regular clear 6 mil plastic and calling it a vapor barrier.  Pretty popular underneath foundations.)


  Thanks for your help.




Mannyrock

Manny 6 mil plastic will serve as a vapor barrier only, since it will block moisture penetration.  Problem with using it as opposed to a foil backed or plastic coated insulation is that it won't prevent moisture from forming.  A product  such as the foil backed celotex or plastic coated polystyrene will aid in preventing the formation of condensation due to rapid temperature changes.  If it adds some support to the siding that's fine but that isn't it's intended use.  Temp and humidity control is.  Just going from direct sun to shade can cause condensation to form on the inside of a surface if conditions are right.  Moisture and wood are a bad mix and it pays off in spades to do everything possible to keep the 2 separated.  Think of it like dressing for the cold when you know it's going to get hot.  Multiple breathable layers are the way to go.  With home building you can't remove and replace the layers, so you have to use items that will work together.

[Larry L]

Well this thread will be printed for my fall Continuing Education classes that I teach. This should be labelled how to screw up a good house. NEVER use poly as a vapor barrier. Any architect that says use it- run as fast as you can away from this clown. I'll post a linky to the why rather than attempt to pontificate anything here. You cannot put a vapor barrier up in pieces-it's worthless if you do. That's why the materials that are used as a vapor barrier come in such long rolls- to keep overlaps at a minimum. In this application a vapor barrier would be like putting a 10 foot fence in the middle of a lake and expect the fish not to swim around it. It's absolutely worthless. Using a vapor barrier in this application would cause moisture to form on the barrier and it will puddle at the bottom causing the siding to rot. That's not speculation, that's fact as experienced by many now bankrupt builders. You might also want to know that using poly as a vapor barrier in any wall cavity, if it survives the rot, will have the poly in small pieces in the bottom of the wall cavity in less than 10 years. It decays rather quickly in a wall cavity.


Non Vented attics are recommended by IRC, ICC, BOCA, SFA, and all of the other code compliance associations. Apparently where ever you live if it's not recognized  they are out of step with the rest of the world. The reason why it's not a common methodology is that it is labor intensive. A crew of 6 will spend an additional 20 hours each of labor averagely making sure the attic is 100% tight. It does not build moisture per your opinion, it reduces moisture to the same level as the interior of the house per fact.


Here's the why you never use poly:
http://www.greenbuildingadvisor.com/blogs/dept/musings/when-sunshine-drives-moisture-walls

[hunt-m-up]

So I should be able to step outside and see/hear (hundreds of) thousands of homes crumbling as we speak. There are A LOT of poly vapor barriers installed over unfaced batts under drywall; faced batts are said to provide their own vapor barrier. From the exterior going inward: siding, house wrap(which is permeable and "breathes"),OSB or plywood sheathing, batts between studs, poly barrier, drywall. Builders went bankrupt here due to the economy or mismanagement, not their construction practices.

[FPH]

Never use poly as a vapor barrier.....Visqueen will be sad to hear that.  Same for Reef Industries maker of Grffolyn which is speced nationally by such corps as at&t.......Larry, I think you may be the one out of step.