Wall insulation

[pinsky190]

I'm getting a 24x24 gambrel garage built next week. Initially I was going to get 3/4" T1-11 paneling for the exterior but decided on getting the Duratemp product instead...which seems to hold up better. I want to finish off the inside and eventually make a home office out of the upstairs.
So if I was to insulate between the 2X4s with some R-13 batts and then throw up sheetrock, would that be enough insulation? Do I need a vapor barrier? Do I need housewrap?

 

[Torque1st]

Welcome to the forum!

I would use a housewrap. It will not be as effective on a garage because of the big door but it may help especially with the office space. Buy the faced insulation bats with a vapor barrier, R-13 or R-15 would be OK with 2x4 studs in the wall. Since you are doing an office I assume you are heating and AC the space.

Some of the manufacturer's websites have good how-to information:
http://insulation.owenscorning.com/homeowners/

Some people use sheetrock on the garage walls and others use OSB. There are pros and cons to each. Personally I prefer OSB.

Check this thread:
http://www.garagejournal.com/forum/showthread.php?t=46306

 

[kbs2244]

You will need both.
You are, in effect, building a residential space.
You need to follow those practices.

 

[Costner]

Depending upon local codes, I doubt R-13 will be enough - it surely isn't in my area. You may need to install some rigid insulation on the outside to add R-value or you might even have to step up to a 2x6 exterior wall to get sufficient space for the insulation required (assuming you stick with batt insulation).

Also, if you plan on using the office and want finished space, take the time to install a proper vapor barrier and don't rely upon paper faced batt insulation. Unless you take the time to use sheathing tape to seal every joint, you will never get a good seal. so you're just wasting your time.

Housewrap is good building practice regardless as it helps prevent driving rain and moisure from penetrating the structure and therefore reduces the chance of rot or future moisture damage. Considering the cost to do a garage is probably about $100 worth of material it is a no-brainer. I'd do that even if you have no plans to heat or cool the space.

 

[tcorns]

My 24x24 has 2x4 walls with house wrap and is easily heated with a small heater. i also had to insulate my garage door and make sure the door seals were in good shape. i have a room upstairs that i insulated with r-19 and heat with a small electric heater.

trev

 

[pcmeiners]

Agree with Costner, unless your vapor seal is close to air tight, the insulation you use will not live up to it's R valve, particularly fiberglass.
To add to this, if you seal well from the inside at the craft face that helps considerably, but you still would have considerable air flow over the fiberglass face if not sealed from the exterior. Fiberglass manufacturers should have two R factor rating printed on their product, one for air tight building envelopes (to be generous 10% of new buildings), and one for average construction/workmanship envelope...R value rating would drop like a rock.

 

[tcianci]

I know I'm gonna get whacked again but my experience with anything made of hardboard outdoors has not been good. I tried to find installation details for the product but the links wouldn't work. The detail I was looking for was the house wrap issue. I have never seen house wrap applied to studs and then have a sheet-goods sidewall material applied to it although it is possible. The suggestion about the kraft paper vapor barrier being no good is no good itself. The kraft paper vapor barrier is designed by the insulation manufacturer to allow the insulation to achieve its rated R value in a typical installation. There is an unbelievable amount of theory, conjecture and sheer hocus pocus on this subject. It's just like going to a speed shop and buying all kinds of go-faster stuff for your car. You are attempting to out engineer the designers and manufacturers by bolting all kinds of **** onto your engine in your driveway, like you're going to beat them at their own game.

The statement that the insulation will not live up to it's R value if the vapor seal is not close to tight is not true. While water vapor condensing in the insulation will reduce the R value, as I stated earlier, thats the situation that the designers of the insulation take into account when designing the vapor barrier. All you need to do is install it according to the manufacturers instructions. There is usually the possibility of air/water vapor leakage around boxes and guys go through hoops to seal the daylights out of them while the very wiring devices and the boxes themselves are far from airtight.
I think some people have this vision of an invisible garden hose being turned onto every electrical box and penetration in the building 24/7 rotting and molding its way through everything in site like some sort of plague of locusts. Did you ever open up an existing wall to move an outlet or something? Did you find the hideous aftermath of death and destruction that all these people fear? Not a chance.
Now all of that little rant was about vapor barriers, which by the way can be something as simple as a good coat of paint on your drywall. One of the real culprits in reducing the R value in fiberglass insulation is air movement in the wall cavity. The principle that the insulation functions under is that of "dead air". The fiberglass batts hold the air "dead" and that resists the transfer of heat. The actual fiberglass strands are really conductors of heat but you can't get the air still totally on its own. This is why spray foam insulation works so well. The dead air is contained within the bubbles or "cells" of the foam and the dead air is maintained regardless of whether there is any air leakage in the wall cavity or not.

To the comment about the R13 being insufficient...If the OP has been issued a building permit then the specifics of his construction conform to the current regulations for his locality. However, R15 insulation is available in a 3 1/2 inch form factor so why not use it. Gong to R38 or more in your ceilings will give you the biggest bang for the buck.

T-111 or Dura-temp carefully installed should be a sufficient air infiltration barrier for keeping the air movement in the wall cavities to a minimum. No one likes to hear this but there is a serious risk in making the wall cavities too tight. It goes back to my hod rod analogy... when you go too far in any aspect of the construction, you may get the building to work well as far as annual heating costs go, but what happens in 10 or 15 years when stuff rots out from the inside because it can't breathe? You will spend everything you saved on fuel costs and then some fixing your deteriorated structure.
I know I just painted another bulls eye on my *** but go ahead, take your shots!

 

[pcmeiners]

Not getting on anyone's ***, different opinions are important, there are many points to be considered surrounding insulation... ways to do it correctly and many ways to foul it up. The entire insulation industry can't release two papers stating exact same thing, insulation is like politicians, great promises until installed.

I am from NYC, my pet peeve is the lack of workmanship in the building trade (in general), leading to among other things, for R-19 fiberglass to become less then R-13.7 here.

" “R-19” labeled fiberglass batts have an R-value of
17.4 before they are installed.
 “R-19” fiberglass batts have an R-value of 17.0 when
installed perfectly (the scientists installed the batts
before installing the exterior sheathing to precisely fit
the batts in place from both sides).
 “R-19” fiberglass batts have an R-value of 13.7 when
installed as commonly found in actual walls."

http://www.demilecusa.com/Repositor...Articles/Actual performance of fiberglass.pdf

 

[Daniel Dudley]

I had the second floor of my barn foamed after insulating the garage portion the usual way wit fiberglass batts. Cost me about 30% more, but there is no comparison as to how well it works. A big plus for me was that I didn't have to handle fiberglass, and I have handled way too much of that in my lifetime. Comparing the R value of fiberglass to foam doesn't really give you the true picture. Think about holding a styrofoam cup full of hot coffee, and you will get the idea.

 

[gesoffen]

Not to move this to a debate on the efficiency of different insulation methods but the biggest enemy to any insulation is air penetration/movement within or across the insulation barrier. If you had a vinyl sided house with no or poor wind barrier (house wrap), all the batt insulation in the world would be useless as the driven and convective winds would infiltrate the insulating space - in effect your drywall would become your insulation barrier. That is why most of batt insulation systems are done in conjunction with an air barrier house wrap. Also, keep in mind that the house wrap is not a moisture/vapor barrier - it prevents air movement through the membrane but allows vapor/humidty to pass through.

The benefit of a spray in foam insulation is that it also acts as a vapor and air barrier. Also, due to its application method, there is only a single step to install a durable insulation, vapor barrier and air barrier. Fiberglass batts involve multiple steps (exterior barrier, batt, cavity sealing, vapor barrier, etc.) that count on the quality of previous step. Not to mention, each of the parts of the system are relatively fragile and easily subject to damage in the typical construction environment.

 

[Costner]

The suggestion about the kraft paper vapor barrier being no good is no good itself. The kraft paper vapor barrier is designed by the insulation manufacturer to allow the insulation to achieve its rated R value in a typical installation.

When I speak of a vapor barrier, I'm not worried about the R-value. The vapor barrier (as the name implies) is to restrict the flow of vapor into the wall cavity from the interior. If someone relies upon the craft paper face alone, they are leaving open seams between every single piece of insulation - and even the paper face itself isn't a great VB. Rather than spending hours taping every seam, it is faster, cheaper, and more effective to simply install a proper 6mil poly VB and be done with it.

The statement that the insulation will not live up to it's R value if the vapor seal is not close to tight is not true. While water vapor condensing in the insulation will reduce the R value, as I stated earlier, thats the situation that the designers of the insulation take into account when designing the vapor barrier.

I'm not sure if you are confusing the vapor barrier issue (interior) with housewrap (exterior) or if your comment is based upon the comments of another poster, but I will tell you that paper faced or unfaced fiberglass batt insulation will have a much lower effective R-value if a housewrap is not used on the exterior due to wind penetrating the structure.

In truth, fiberglass batt insulation has a much lower R-value when the wind factor is taken into effect, but in the lab where no wind is included, the stated R value can be acheived. This is not an opinion, but industry fact - all R-value testing is done with zero air movement. Controlling air infiltration is one of the primary benefits of a housewrap, and to a lesser degree the vapor barrier as well.

I recommend anyone who is interested in building a solid, energy-efficient structure review the following sources:

http://www.buildingscience.com/docu...-assemblies/advanced-frame-wall-construction/

http://www.bpi.org/documents/Yellow_Sheet.pdf

http://www.buildinggreen.com/auth/article.cfm?fileName=070401a.xml

To the comment about the R13 being insufficient...If the OP has been issued a building permit then the specifics of his construction conform to the current regulations for his locality.

According to the OP's post, he is having a "garage" built, and that he might "eventually" finish off an office on the inside. His future plans are most likely not even considered when he obtains a building permit, so his local permits are based upon the structure being a garage and nothing more.

I don't want to assume anything which is why I made the comment about local codes. We all know codes vary, but in most areas R-13 would not be sufficient for wall insulation. Granted if he never goes back and gets a second building permit to finish that interior space nobody will know, but if you want to build things the way they are supposed to be built - then you need to know and follow local code.

 

[Costner]

The benefit of a spray in foam insulation is that it also acts as a vapor and air barrier.

I'm a big proponent of spray foam, but you need to be sure you specify closed-cell foam. The open-cell spray foams can still allow water vapor to pass through them easily.

If using a closed-cell foam, most manufacturers such as Dow recommend at least 2" of foam to get a true vapor barrier, but even less is required to control air.

Of course there are many other positives of foam such as how it conforms to the wall structure, how it seals gaps and penetrations, and even the fact that it strengthens the structure itself due to how it adheres to the sheathing and studs etc.

About the only negative to it is the cost - which can be 3 to 4 times more expensive as fiberglass batts.

 

[tcianci]

I wasn't confusing the housewrap and the vapor barrier. I use this stuff every day, I know the difference. The kraft vapor barrier on the face of the insulation is provided by the manufacturer to allow the insulation to maintain its effectiveness that would otherwise be ruined by the transmission of interior moisture into the wall cavity. It's adequate. The seams at each stud are adequately sealed by the pressure applied by the drywall. You can improve the vapor barrier by sealing around boxes and such but the boxes them selves are not air tight nor are the wiring devices installed in them. As I stated in my first post, painted drywall is a good vapor barrier. As I and others stated, with fiberglass insulation, air infiltration must be keept to a minimum for the insulation to work correctly. In most cases, properly applied sheathing, nailed correctly with the horizontal seams eather taped or breaking over blocking creates 99% of your air infiltration barrier. The big culprits are window and door openings, but they typically admit air to the building itself, not the wall cavities.

 

[Costner]

The kraft vapor barrier on the face of the insulation is provided by the manufacturer to allow the insulation to maintain its effectiveness that would otherwise be ruined by the transmission of interior moisture into the wall cavity. It's adequate.

Unfortunately many contractors would agree with you, and if you want to go with the mindset that it is adequate that is your choice. I don't tend to build things that are merely adequate, because merely meeting code is rarely good enough, and I don't tend to take the word of the manufacturer unless there has been indepenent testing.

Whats that old saying? A team of engineers built the Titanic, but a lone man built the Arc.... or something like that.

Case in point - kraft paper is not a true vapor barrier, but merely a vapor retarder.

"A kraft-faced fiberglass batt is a Class II vapor retarder"
http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design

The seams at each stud are adequately sealed by the pressure applied by the drywall.

Do you have any information to support that theory? I disagree because unless your drywall and studs are perfectly straight and true, there will be gaps. Besides, as we have already discussed kraft paper isn't even a good vapor barrier in the first place.

Here is one excerpt that explains it better than I could: "kraft-facing is impregnated with bitumen and the paper-bitumen composite is hygroscopic. It adsorbs water as the relative humidity it is exposed to rises"
http://www.buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers

Do you really want a so-called vapor barrier that absorbs water?

You can improve the vapor barrier by sealing around boxes and such but the boxes them selves are not air tight nor are the wiring devices installed in them.

I agree - although best practices would dictate the usage of lessco boxes or a sealed box anytime it is on an outside wall. If such a device is used, the VB can be sealedto the box, and the wires can be sealed with silicone or acoustical sealant to create a 100% airtight electrical box.

Does this happen? Yes, but it isn't very common and contractors aren't about to do it unless the client mandates it. This is why it is a good thing for consumers to educate themselves, because a sloppy job of installing a VB where it is just cut around electrical boxes and where seams aren't sealed is essentially worthless.

As I stated in my first post, painted drywall is a good vapor barrier.

I wouldn't go so far as to say it is good, and I would be more apt to call it a vapor retarder rather than a true vapor barrier (technically latex paint is a class III vapor retarder), but I understand what you're saying. In some areas paint is all that is required and in fact the addition of a secondary VB isn't recommened. However if someone is in a colder or northern climate, then paint alone won't be sufficient.

 

[walrus]

"A kraft-faced fiberglass batt is a Class II vapor retarder"
http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design



Do you have any information to support that theory? I disagree because unless your drywall and studs are perfectly straight and true, there will be gaps. Besides, as we have already discussed kraft paper isn't even a good vapor barrier in the first place.

Here is one excerpt that explains it better than I could: "kraft-facing is impregnated with bitumen and the paper-bitumen composite is hygroscopic. It adsorbs water as the relative humidity it is exposed to rises"
http://www.buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers

Do you really want a so-called vapor barrier that absorbs water?

More people should read www.Buildingscience.com

 

[pinsky190]

Wow lot's of good information. If I was turning my second floor into living space then according to my township I need 2X6 walls, and a proper exterior. However, it is just an office that I'll spend a few hours in a day, plus it is relatively small space. Like someone said, a small electric heater was enough to heat up the floor.

For me to add sheathing, housewrap, and vinyl it would cost me a good penny. What I think I'll do is just stick with the 2X4 > Duratemp combo. I'll seal the seems as best as possible and then add the batts of R15 insulation between the 2X4s, and then sheetrock the inside. For the upstair I'll install roof baffles between the roof rafters from the soffit to the ridgevent and then use R19 batts between the rafters, and then sheetrock. My upstairs has no knee walls at all, so all the walls are just roof rafters.

Do you think I'll have sufficient insulation with this set up?

 

[hansen1]

This thread has been very informative. I am starting to understand the differences and the challenges with various approaches to insulating.

What I have not seen is much mention of the outside properties impact what you should do on the inside. I have OSB sheeted outside with on layer of 15 lb felt and then it was stucco'd. Does the felt act as the vapor barrier or do I need to put another 6 mil vp on the inside. I will probably be using kraft faced fiberglass which I have learned is probably not the best vp.

 

[tcianci]

Hansen, yeah you need a vapor barrier on the inside if you are in a part of the country where you typically heat more often than cool. The felt acts as a weather and water barrier and it does retard the transmission of water vapor through it but the idea is to reduce the movement of water vapor form both sides.
Now, on with the rant...So, the guys who design insulation don't know enough about their product to provide an adequate vapor barrier when they manufacture it? It's the hot rod mentality I see here time and time again. You make a few quick shoot from the hip observations and suddenly you know everything that the product manufacturers and their multi million dollar research efforts can't possibly tell them. Like I said earlier, it's like a guy buying a bunch of go-faster **** from Summit or someone like that and then setting out to out-engineer the manufacturer in his driveway. Well, go right ahead and improve anything you want, and then try to file a warranty claim with anybody when your materials fail.
There are many guys here that cannot distinguish between the real world constraints of building construction and their dream world buildings that they think will last forever and be heated with a freakin Bic lighter.
The biggest problem with the installation of vapor barriers is that it is IMPOSSIBLE to create a site built vapor barrier that will completely inhibit the transmission of water vapor into the wall cavities of a structure. The closer you get to that goal, the more risk you run of creating a situation where the vapor that does enter the walls will be there plenty long enough to to the very type of damage all you guys are ******* your pants over. You are far better off in the long term to let your structure breathe a little, get some professional counseling for your water vapor and fuel-use anxieties and call it a day.

 

[walrus]

The biggest problem with the installation of vapor barriers is that it is IMPOSSIBLE to create a site built vapor barrier that will completely inhibit the transmission of water vapor into the wall cavities of a structure..

Closed cell foam, complete fill, not impossible

 

[tcianci]

Of course a complete fill of closed cell foam is great. I was talking in respect to fiberglass batts. Point well taken!

 

[Costner]

So, the guys who design insulation don't know enough about their product to provide an adequate vapor barrier when they manufacture it?

The "guys" who design insulation don't advertise kraft paper as being a true vapor barrier, because it doesn't meet the legal definition of the term.

Is it better than nothing? Maybe - but kraft paper does serve other purposes. In spaces that are unfinished (such as garages) kraft paper helps prevent dirt from collecting in the insulation. It also allows the insulation to be stapled to the studs which prevents it from falling out. In the case of insulating a ceiling or floor above a crawlspace, kraft paper covered insulation is often used just because of this benefit - but not because people think it is a great vapor barrier.

The biggest problem with the installation of vapor barriers is that it is IMPOSSIBLE to create a site built vapor barrier that will completely inhibit the transmission of water vapor into the wall cavities of a structure.

To some degree I would agree with that. The problem is, no matter how well someone installs a VB, the second they start hanging drywall there will be penetrations at every screw hole. If they miss a stud or two, those holes will be there a lifetime. Heck, most VB is hung using staple guns, and unless someone took the time to tape over every staple hole, there will be holes. Even if they did a perfect job with the VB and drywall - the minute they move in and pound a nail in the wall to hang a picture - they will puncture the VB.

However, this isn't to say we shouldn't do our best to create a true vapor barrier. If you can limit the gaps and seams it will go a long way to prevent air infiltration around electrical boxes and other penetrations. A little sheathing tape and some acoustical sealant might not give you a 100% perfect VB, but it is better than the alternative.

I sort of equate your statement to the theory that all concrete will eventually crack. Sure that might be true, but does that mean we should just skip the rebar and wire mesh or forget about the fiberglass? I mean if you can't get it perfect why bother right? Of course not - because even if it can't be perfect for a lifetime, you would still take the time to do the best job you could wouldn't you?

The same holds true with a proper VB. We aren't talking about over-engineering anything and this isn't rocket science, but if you can limit the airflow and ability of water vapor to hit your insulation it will pay you back in the end in terms of energy efficiency and in terms of the longevity of the structure, and that isn't even factoring in the issues with carbon monoxide that exist in a garage environment.