Attic Insulation Type

Reply

  #1  
Old 03-15-03, 08:41 AM
tlunn
Visiting Guest
Posts: n/a
Question Attic Insulation Type

Hello,

I am in the process of building a garage/workshop at the rear of our home. I am at the point where I would like to insulate the walls and attic space.

I am going to use R-13 with vapor barrier in the walls. I am not quite sure what I am going to use in the attic. I have decided I do not want to have insulation blown in the attic. I would rather just purchase batts for the attic and roll it into place.

I have been looking at a product by Owens Corning called Miraflex. It is rated R-25 (which would be fine for garage in S.C.), comes in 25 foot rolls and is virtually itch free. However, the info tag posted by Lowe's underneath the product states the product is to be used over existing insulation. Does this mean Miraflex is not intended to be used alone or as the primary insulation???? Or is this product fine as the ONLY insulation in an attic space???

Also, if I change my mind and go with just the standard pink insulation for the attic, should it be backed with paper or not? I am assuming that if blown insualtion has no vapor barrier, then I really do not need paper backed insulation for the attic.

Thanks.

TL
 
Sponsored Links
  #2  
Old 03-15-03, 11:44 AM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Received 0 Votes on 0 Posts
insulation

Yes you dooooooo.If you go with the paper back for the ceiling. You want to put it on the down side of the ceiling. If you want to have it blown in Do that but you want to put a 2mil poly on the rafters first before you drywall Then blow on top of all that. WE put that 2 mil poly on the room side of the wall and ceiling insulation all the time even if we use the paper back kind. It cost just penneys. Do the ceiling with the paper batts first then put the poly up let it hang down some on the walls over the poly on the walls this helps keep the room tight then put the drywall up ED
 
  #3  
Old 03-17-03, 05:46 AM
tlunn
Visiting Guest
Posts: n/a
More Info Needed

Hello again!

I posted a question a few days back and need further clarification.

As stated earlier, I am in the process of building a garage/workshop at the rear of our home. I am planning to insulate the walls and attic. From reading info at other sites, it seems vapor barriers in attics are a tossup for my area (mid S.C.)
Some seem to think it is not good to use the vapor barrier, while others seem to think it is necessary.

I called the county planning and zonning commission and they stated vapor barriers in attics was not a requirement nor in the building code for our county. Does this mean it is not necessary and probably best not to use one??? I just want to do the correct thing first go around, but I do not want to introduce a problem by adding OR not adding a vapor barrier. Any insight would be helpful!

Thanks,

TL
 
  #4  
Old 03-17-03, 08:23 AM
R
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
A very confusing subject.

On the "Energy & Weather-stripping" forum read Sick Building Syndrome (SBS) & Energy Conservation. This post also discusses "Air Transported Moisture" and ErH% and how it removes humidity from your home to avoid moisture problems. Though it does not discuss the process in the cooling season, I will shortly.

It also gives you some Government sites that will answer your question, especially the brief on Vapor Diffuser Retarders (VDR) and Air Barriers. This brief actually discusses your situation concerning vapor barriers in areas where heating degree days are around 2,000. Or if you prefer, areas where they experience mild winters. My site also discusses your problem briefly. You can access it by clicking on the www icon at the bottom of this message and then in the "Topics" click on and read Insulation, Thermal Boundary, Air Boundary and Ventilation.

Actually all of the above information does not specifically address your answer, at least not to my satisfaction. The information does give you an idea why most people if not all including experts in this industry will not be specific concerning vapor barriers in areas of warm humid climates. The Dept. of Energy, Oak Ridge National Laboratory, Tennessee Valley Association, Architects of America, ASHREA and even the EPA have taken very vague stances on this subject. Your county commission's reply to vapor barrier use in your area is in direct response to SBS. I do not agree with this blanketed approach to an apparent serious moisture problem.

I wish to make clear at this point, that my reply is SPECIFIC to your question and concerns your AREA!!! In other words my reply may not apply to other areas of this country or the world.

In the cooling season, unlike in the heating season where the primary concern is the expansion and contraction of air within the structure and the moisture content of this air, the primary concern is how high pressure areas are attracted to low pressure areas and not vice-versa. Condensation is influenced by only condensing on cooler surfaces which are located inside the structure during the cooling season and how humidity is transported in the air the surrounds the structure. It is obvious what separates these 2 areas and it is the thermal boundary. In this case your attic. Vapor barriers reduce the amount of humidity in heat by diffusion or if your prefer slows down the transfer of humidity from one area to another. This reduces the probability of condensation occurring inside the insulation cooler surfaces during the transfer. Heat transfer in the winter is from inside the home to the outside and outside the home to the inside during the summer. The determining factor on where to install the vapor barrier is the amount of humidity involved and which season dominates. In the northeast, heating dominates and the amount of humidity associated with heating justifies the vapor barrier being install on the ceiling side of the insulation. In the south where heat and humidity is present and cooling dominates, the installation of the vapor barrier being on top of the insulation is justified. In areas, like yours, where the heat load (winter) and heat gain (summer) are almost equal putting a vapor barrier on either side of the insulation creates more moisture related problems than it prohibits. Hence the blanketed approach to recommending no vapor barrier installation.

What this does is completely ignore the insulation material itself. For example, fiberglass insulation has a very slow absorbancy and fast expulsion rate towards moisture. For this reason it is unwise to install fiberglass insulation without a vapor barrier under any circumstance. Furthermore, when it comes to opposing pressure areas being attracted to each other air transported moisture plays an important role. Fiberglass does not deal with this problem well.

On the other hand blown-in cellulose insulation does well on all accounts. It has a faster absorbancy and slow expulsion rate towards moisture. One might think that this is a disadvantage when it comes to moisture. They are wrong because Equilibrium Relative Humidity (ErH%) is the process in which material not only absorb humidity, it also expels it or if you prefer drys out the material. The ability to retain moisture and release it slowly provides the time required to accomplish it. Whereas fiberglass is not so forgiving. Dense packing of cellulose insulation is used in the air sealing industry, not only for the increased resistance value per inch but as a qualified air barrier. This makes this application superior to all other for your area. Remember the major concern with moisture related problems with cooling is air transported moisture. This will work well in both the heating and cooling seasons in the avoidance of moisture related problems.

I do realize that this is a complicated subject and some jargon was unavoidable. If there is anything with the information on the sites or what I have said here, I am more than willing and able to explain it further to you.
 
  #5  
Old 03-17-03, 09:15 AM
tlunn
Visiting Guest
Posts: n/a
Thanks Resercon !!!!!!!!

Resercon,

Thanks for the detailed information and your TIME for answering!!

Our home does have blown cellulose in the attic and we have never had a problem of any kind.

Back to the garage/workshop. It is 36 x24 and will not have central air and heating. At some point in time, it most probably will have a window AC ...... probably use a propane heater in the cold months. Of course, the only time I will have either the heater or AC running is when I am actually in the building doing prolonged work. I am primarily installing insulation to hopefully help control heat gain/loss. In other words, I am hoping insulation will make the building more comfortable without the need to use a heater or AC very much at all.

Having said that and based on your reply, it appears cellulose may be the better insulation. But, I had planned to use fiberglass batts all along because I could easily roll them out in the attic. Since I never installed air baffles at the eaves, blowing cellulose in the attic space now may create problems with attic ventilation, if one is not very careful. As a note, I have eave vents and a ridge vent across the entire 36 foot rofline.

1 - Now, with all this in mind, I would still rather use insulation batts. If I did, would I use insulation with a paper backing or without ...... and which side goes toward the room below???

2 - In your expert opinion, do you feel it would be a mistake to go ahead with insulation batts and if so, please elaborate. I know many people use fiberglass in South Carolina, but I am not aware of their problems, if any exist.

Thanks again!

TL
 
  #6  
Old 03-17-03, 11:39 AM
R
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
Mixing of different types of insulation.

This is done almost everywhere in the world. This is especialy true when it comes to contractors who install insulation for a living. I do not agree with this practice. Even though many studies have shown that this does not cause a moisture problem.

Diffusion is the dominant heat transfer mechanism and diffusion is how moisture permeates materials. It is easy to confuse the difference between energy transfer and fluid transfer. But they are not the same. So I can take 2 different types of insulation that have exactly the same R-value but the rate in which fluid transfers through will more than likely be different. The difference many agrue is so small that it does not make a difference. This is true in most cases. Yet the probability that a moisture problem could occur is higher with mixing than keeping with the same material.

Under laboratory conditions where most if not all of these studies are done, excludes other applications within an average structure that will clearly interact with the insulation and its properties. Even using solvents in the garage can have an adverse affect on the performance of the insulation and combined with other applications can cause a moisture problem. Though many will argue with me based on the fact that the probability is so low, it does increase the probability and we do not know what all the different applications will behave within a confined area. In my opinion it is worth the inconvenience to installing the cellulose because it reduces the probability of a moisture problem from occurring.

You don't have to have it blown-in, you could do it yourself. As far as the eaves are concerned you could lay in a strip of fiberglass insulation near the eaves to prevent the cellulose from falling into them and then lay the cellulose up to it. Shop around and even on the web and you'll find some, cellulose comes in bags. All you have to do is take the bag where you want the insulation, rip it open and use a small board or rake to level it. It is quicker and easier to do than laying batt insulation. The amount of fiberglass insulation is neglible and it will be close to ventilation.

Fiberglass insulation is widely used throughout this country. As discussed in the other post, air transported moisture is a concern. One way of dealing with this potential problem is an air barrier. The most common type of product used is Tyvec. For attics, another type of application is used and this is usually induced ventilation. Here a fan is used to create convective transfer by forcing air to move above the material. This is turn transfers the humidity to the moving air and then out of the house. So with fiberglass you have to introduce other applications to assure moisture will not become a problem.

In most cases people don't have a choice on what type of insulation they'll have in their homes. It is usually there when they buy the home. It is not the type of insulation that is causing the moisture problems in homes today, it is in fact the way we live in our homes today. Because of this, we must control the humidity in our homes and avoid doing things that may create unnecessary humidity levels. No, I do not consider fiberglass applications in your area a problem, I just see cellulose as a superior application for your area.
 
  #7  
Old 03-17-03, 01:17 PM
tlunn
Visiting Guest
Posts: n/a
Resercon - One Last Question

Thanks again for your time in answering my concerns!!!!

I am going to look around and check all the possibilities BEFORE insulating the attic. But, according to your last post, I have already done several things correctly:

1- Adequate ventilation - Ample eave vents AND full ridge vent
2- Entire building, including gable ends, wrapped in tyvek
3- Installed insulated garage doors (R value of 8.7)
4- The two windows and entry door have Low-E insulated glass

Now for the last two questions:

1 - If I decide to go ahead with fiberglass batts, should I purchase batts with or without paper backing?

2 - If the answer to question #1 is with backing, which side should go towards the room below?

Thanks again!

TL
 
  #8  
Old 03-17-03, 01:23 PM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389
Received 0 Votes on 0 Posts
insulation

just my 2 cents I would put down just R13 paper side down to get a vapor barrier there in the ceiling. Then come in with a blow of the cellulose on top for fire and to fill all holes up. Time back sold cellulose. If it looked like we might have lost the job we would do this( try it) Take a piece of the fiberglass and just a small LP torch hold it to the FG it will melt right away. In a fire it wont burn but it will let the fire get through. Now we would take some cellulose in our hand and put a penney on it take the Lp torch and melt the penney some the cellulose would turn black and get a red glow to it but that was all.....We'd get the job ED
 
  #9  
Old 03-17-03, 08:24 PM
R
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
Ed's input concerning insulation properties is worth noting.

If your intent is to use fiberglass insulation in this application it must be unfaced. Installing a vapor barrier between layers of insulation or on top of the 2 different insulating materials will increase the probability of condensation occurring. Again, if you are installing fiberglass insulation over cellulose insulation, it is unwise to apply a vapor under these circumstances.
 
  #10  
Old 03-18-03, 03:57 AM
tlunn
Visiting Guest
Posts: n/a
For Resercon

Resercon,

I am not sure we are all on the same page. Your last post stated if I was going to use fiberglass over existing cellulose, use unfaced. The building I am referring to is new and unfinished. There is absoulutely nothing in the attic except for sheetrock. Whatever insulation type I use, I will use it as the only type .... no mixing.

With that said, I would like to get your opinion on questions from my last post. I will include the facts once again:

1- My area is mid South Carolina
2- Adequate ventilation - Ample eave vents AND full ridge vent
3- Entire building, including gable ends, wrapped in tyvek
4- Installed insulated garage doors (R value of 8.7)
5- The two windows and entry door have Low-E insulated glass

Now for the last two questions:

1 - If I decide to use fiberglass batts, should I purchase batts with or without paper backing?

2 - If the answer to question #1 is with backing, which side should go towards the room below?

PS: Since this is a workshop and storage area, I am not overly concerned about the fire protection properties of one insulation over another, as I would if this were being installed in our home. My main objective is to get the ceiling insulated, being careful NOT to introduce a moisture problem later.

I do thank you for your time and input to these questions. Thanks for helping!!!

TL
 
  #11  
Old 03-18-03, 06:39 AM
R
Banned. Rule And/Or Policy Violation
Join Date: Nov 2001
Location: USA
Posts: 1,875
Received 0 Votes on 0 Posts
If you decide to use fiberglass you have to use a vapor barrier and from the attic, the vapor barrier would face downwards.

If you use cellulose do not use a vapor barrier.
 
  #12  
Old 03-19-03, 09:28 AM
P
Member
Join Date: Feb 2003
Posts: 150
Received 0 Votes on 0 Posts
The kraft paper facing will act as a vapor barrier. Place the paper side facing down (i.e. facing the room below).
 
  #13  
Old 03-25-03, 08:19 AM
Sharp Advice's Avatar
Admin Emeritus
Join Date: Feb 1998
Location: The Shake and Bake State USA
Posts: 10,440
Received 5 Votes on 4 Posts
Arrow Topics Have Been Merged

Hello: T Lunn

You said we are not all on the same page.

We all could stay on the same page. Actually & Literally.

Please use the "REPLY" button to add any additional information or ask additional questions on this same subject of attic insulation type.

Doing so keeps the entire thread together and makes it much easier to follow along.

Thanks,
Web Host and Multiple Topic Moderator.
Tom_B
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: