Hello,
After getting estimates for around $600 to insulate my attic, I finally went over to Home depot and found that I can insulate my attic on my own for around $300.

I will be purchasing blow-in type insulation, and the blower comes free to use.

I have a couple questions:

Question (1)
My biggest concern right now is the "vapor barrier". As of right now there is about 7" of blown in insulation in the attic. I will be blowing in approximately another 10" to get an R38 value (I live in Wisconsin). I do not see a vapor barrier underneath the current insulation. From what I can tell, underneath the insulation is the ceiling of the rooms underneath, with no plastic or barrier of any kind. Would it be to my benefit to move the existing insulation and lay down some form of a vapor barrier? Do most attics have vapor barriers?

Question (2)
I know that I need to put in soffit baffles because there are none there. Should I put a baffle between every one of the rafters? Or do I just need them near the vents?

thanks

 

You can go to http://www.eren.doe.gov/consumerinfo/refbriefs/bd4.html and it discusses vapor barrier and air barriers. You do not need a vapor barrier. Several layers of paint on the ceiling would qualify as a vapor barrier. If you read the brief, it points out the major concern with moisture in insulation is air leakage. Since you already have insulation, if there was a moisture problem you probably would have noticed signs of it already. Like stains on the ceiling.

 

I guess that I should have mentioned that about 15 years ago, one of the rooms used to actually have problems with ice forming on the ceiling!!

To stop this, someone put a board over the soffit ventillation in the attic. This board has since been removed, and the house has been re-sided along with new soffits.

We havn't had any ceiling problems since then. I don't know what the insulation was like back then, if there was significantly more, or not. I don't suppose you could lose 10" of insultation in the attic over 15 years, could you?

But should I assume that the problem was due to the old soffit and siding and roofing?

Or was it possible that back then there was as much insulation that I am about to put in, and these problems may recurr?

 

Ice forms on ceiling or under roofing when warm air is introduced to a cold surface. By your description, it appears that there was a space between the insulation and the ceiling. This allowed cold air in the attic under the insulation and made the ceiling cold. Cold enough for the warm air to condense and then freeze. When the board was laid over the area, it probably closed the gap. The result is the ice on the ceiling did not occur again.

If the insulation blocked the soffit vents, it could cause ice to form on the roof underside. This is referred to as inadequate free venting. Basically what that does is dillute the heat that manages to get through the insulation. When you have inadequate free venting the heat lingers in the attic and finally condenses, usually on the coldest surface in the attic. Which is usually the roofing nails. Black stains around the roofing nails is a telltale sign.

 

Greetings,

Sorry guy, there is no such thing as R38.

You're another victim of the insulation industries rip-off scheme.

Your present system is rated at about R19+. Adding another R19 only increases effiiency about 7.6%. When you consider that you only lose about 20% of the heat throygh the ceiling it will probably never pay for its self. Too much bulk insulation can also increase a/c costs because you are storing more heat energy that is radiated into the house.

I would suggest that you buy a package of this material and inspect for its actual contents. Besides paper you'll find plastic, cloth and if you inspect close enough rodent droppings. Remember this stuff comes from recycle bins.

Now if you really want to lower your HVAC costs install a radiant barrier system over the top of your existing insulation.

Using google.com enter "radiant barriers"

If you want more detailed info contact me at "rbisys@juno.com"

Thank you for considering my opinion.

 

well, the amount of insulation that i have right now, is about 5" thick and in many spots, there is no insulation at all!! So I think it is a good idea to put something up there.

As far as the radiant barriers, go, I think it is a good idea. However, I disagree on one main point.

I went to school for electrical engineering, but had to take a few heat transfer courses. I am not trying to say that I know anything about the subject, but more that I can begin to understand it.

What I don't like about the radiant barrier, is that it should go on the outside of the house, above the shingles, and not inside the house!

If you think about it, the sun beats down on your house. When the sun's rays hit the black tiles on the roof, it heats them up. I would have to believe that most of the energy from the radiation of the sun is absorbed by the shingles. Afterall, your roof gets very hot in the summer!! (doesn't it?)

Now, while the singles are absorbing much of the energy, they are also converting the radiant energy to conductive heat energy. So now, the energy transferered from the roof to the attic is mostly conducted by conductive heat tranfer.

Granted, once the the shingles get hot enough, they would begin to radiate themselves, but I would think that the amount of ratiation would be much less than the conductive heat transfer.

 

Greetings,

Thank you for reply.

Don't feel cheated because you didn't get the full skinny on RBs when you took your classes. Most mechanical engineers and architects in particular get short changed too.

Putting RBs under shingles is the least preferred method.
Besides single layer sheets you also have 2 layer materials giving you 3 reflective airspaces and 3 layer giving 4 reflective spaces. These are designated type 3 and 4.

These materials are designed for wood construction and install in the framing cavities. Materials are also available for steel construction.

If you have older construction using 2x6 or 8s then you can install a type three above the old insulation after you LIGHTLY tamp down the existing. The results will far exceed any thing else you put up there.

If you have trusses I have a special 2 layer material I developed years ago that will lie on top of the existing. If you go this route I would just fill in the spots because any additional fiber type material will not give you any return value because the RB performance will exceed the fiber type by a considerable amount.

RBs are easy to install, they are more time consuming than others, but well worth the extra time. Depending on where you live and the size of your home, your pay back could be as little as 5 years or less. By the way you will find the home more comforable because you will not have hi levels of radiant energy radiating to your body in the summer. It is not unusual for the home owner to raise the summer thermostat when RBs are installed.

If you plan to side your home there are methods of installing RBs before the siding. If siding is out there are reflective interior paints that are very effective. I have reduced existing home hvac cost 50% or more on numerous occasions.

Thank you for considering my opinion.

 

can you point me to a picture of what a type 3 RB looks like? possibly by itself, as well as installed.

 

Greetings,

Thanks alot. OK I'll do my best.

Comes 16 and 24 . 500 sf rolls. You cut to lenght.

Materials constructed of a top or outer layer of aluminum bonded to craft paper with a no tear scrim between foil and paper.
The second layer is a plastic film electro coated.
The two layers are constructed so that when one side is stapled in and the material pulled across the cavity the 2 layers seperate (5/8-34") so there is an air space between them. The other side is then stapled in. For narrow cavities a single layer is used.

If you e-mail me your mailing address at rbisys@juno.com I'll send you a sample.

Thank you