I would like to insulate my attic with blown in cellulose. The problem is that I would like to rehab the second floor next year and that will entail taking out the ceiling and all that insulation will fall out all over me.
My question is, what type of material could I possibly use to lay over the joists to hold the insulation up after demo and not become a vapor barrier?
“It is what it is.”
Learn more about the pros and cons of single-room ERVs.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Insulmesh, Mike Smith can tell you if I got it wrong.
it doesn't already have a vapor barrier? it should. I can think of a few things I would try. If you don't have insulation yet or removed it, you could may be staple down plastic over ceiling joists, draped into the bays then fill in with cellulose. Or if you have existing insulation with it's vapor barrier intact, you could staple a cheap breathable fabric to the joists. The insulmesh is good but anything will work...old bedsheets, rolled canvas, or burlap. A third idea is to use an attic blanket; which is basically just a wide, thin roll of fiberglass insulation that is rolled out perpendicular to ceiling joists. It could be stapled down and blown on.
Good Luck
gk
Check with your building insp., most of upstate do not use a vapor barrier.
Yeah, vapor barriers are not really running rampant around here. I have seen more damage from having them then not. From what I have seen, I am personally against them.
If the vapor barrier isn't 100% (think balloon) than there are small areas where the vapor will go and be concentrated at that point. So, I guess I would be comfortable with vapor going everywhere than it all going to very small locations throughout the home.
I plan on having a very aggressive exhaust system in the baths and kitchens with energy recovery and make up air.
"It is what it is."
> If the vapor barrier isn't 100% (think balloon) than there are small areas where the vapor will go and be concentrated at that point.Actually, this is not true, assuming that the humidity in the structure is reasonably well controlled. However, if the vapor barrier is also the infiltration barrier then airflow will be concentrated at defects in the barrier, and that can result in pockets of condensation.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
This may be specific to upstate NY, but nobody that I know of does vapor barriers anymore.
Are you guys talking vapor barrier (non-permeable...plastic sheeting) or vapor retarders ( Tyvek, kraft paper on fiberglass)?
either or.
Well, then vapor retarders are a good thing. Example, assume unpainted drywall, 4x8 sheet 70F and 40%rh (relative humidity), in one heating season 1/3 of a quart of water will "pass", diffuse, through the drywall to get to the other side. If you cut a 1" sq. hole in that same sheet 30 quarts of water transport through! Without a vapor retarder, that vapor will pass through the insulation and condense on the first cold surface it can find. In a heating zone most of the moisture comes from the inside during the heating season, therefore unless you can a very , very tight house, that water will get through and condense on the sheathing (fiberglass is an awful vapor retarder. Vapor barrier on the other hand is Class I vapor retarder, and is impermeable. If used you must make sure is is air tight, because if any vapor gets through it will be hard for it to eventually dry.
We used to use "vapor retarders" but not any longer. This, at the direction of the energy star people, who are basically building scientists. That is for where I live. Don't know anything about where you live.
I live in Maine....where do you live and why no VR's?
click on my name to see where I live.
Why no vapor retarders? They want wall assemblies to be able to dry as quickly as possible to prevent the possibility of mold - weather it is to the inside or the outside. Here, the current practices dictate sealing the inside of the building envelope with a tight air barrier. Most of this is accomplished via the drywall and sealing around penetrations. No air leakage = no (or little) vapor transfer. I believe that mold occurs for other reasons though - like a leakly exterior.
Edited 8/9/2008 12:34 pm ET by Matt
"Most of this is accomplished via the drywall"And what is finished drywall?The problem is that a neither a vapor barrier or a vapor barrier has be some separeate item with a BIG RED STAMP saying VAPOR BARRIER or VAPOR RETARDER.And as you said ability to dryout is part of the equation.And everything that is put on walls and is a vapor barrier is not labeled as such.One of the 10 worst thing to do in the south, according the the Building Science website, is to install vinyl wallpaper on the inside of an exterior wall. It is both a vapor barrier and water barrier.Thus moisture moving from the outside in will condense on the backside and grow mold..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
and your point is....?
"and your point is....?"You mean that these messages are suppose to have a point? I just checked the rule book and could not find that requirment. And I have lots of proof that there is such a rule that it has never been enforced before. <G>.Actually I have one."We used to use "vapor retarders" but not any longer."That is BS. I don't know a single building product that is not a class 1, 2, or 3 vapor retarder.This explains it some more.http://forums.taunton.com/tp-breaktime/messages?msg=108067.35.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I'm aware that all different kinds of stuff can act as a vapor retarder - paint, sheet goods, etc, etc, etc. My point was we no longer install craft or aluminum faced insulation, poly, etc that has the sole purpose of a vapor retarder/barmier - possibly partially, as you say, because there are other vapor retarders in almost any modern wall assembly. Hence, no need for the purpose specific vapor barrier the guy a few posts back referred to. I think you got that but were just adding some supplemental information.
BTW - 5 or 8 years ago the local inspection dept was still requiring some kind of (sole purpose) retarder/barrier. As instructed by the ES guys we were using craft faced insulation (that has a bituminous mastic onthe back) as it was about the least effective available.
What about housewrap, like Tyvek?
Awful expensive for this application.