Hi – New to this forum but it came highly recommended and at a time when I really need some advice. I own an old home (1845ish) – Plank construction. Am currently doing a major remodel and have removed all walls down to the plank. My carpenter has studded out all walls so we can put insulation on the exterior walls. So far so good… Now the question. After installing insulation but before drywall there seems to be different opinions about use of a plastic Vapor Barrier over the kraft paper backing. My Architect and My Carpenter are in favor – my drywaller (also an experienced carpenter) is opposed as he says this simply traps moisture between the drywall and insulation and will lead to mildew/mold, etc.
Perhaps an unbiased opinion will help us make the call. Thanks in advance.
Replies
First, I assume you are talking about fiberglass insulation with kraft facing. The kraft paper IS a vapor barrier and to add plastic would be 2 vapor barriers and a definite no-no because you could end up with moisture trapped between the two.
Second, plastic vapor barrier is "out of vogue" because of mold concerns - the possibility of trapping moisture in the wall could result in mold. One of the reasons for installing plastic was to form a air barrier, since the leakage of (winter/summer)hot/cold air is greatest where air leaks occur. If you feel you must use a plastic vaporbarrier, and fiberglass insulation use unfaced insulation and check out a product from Certaineed called MemBrain: http://www.certainteed.com/CertainTeed/Pro/Builder/Insulation/Prodindex/Residential/MemBrainProdIndex.htm
Personally, I'd just use the kraft faced insulation, but in ether case, make sure the insulation is detailed PERFECTLY, (behind all electrical boxes, pipes, etc, and install backer rod around the windows and doors. Then, air leakage is dealt with at the sheetrock, again around plumbing fittings, electrical, etc.
Now some guys are gonna flame me for saying to use fiberglass, because there are some other, better alternatives such as cellulose or foam which is rather expensive.
Not going to flame you, I use f/g too when there are budget constaints.
The purpose of the vapor barrier is to stop migration of moisture into the wall cavity.
The problems with newer homes is the tightness of both the inside and outside wall cover does not allow the wall cavity to dry out. No vp is perfect, so at some point moisture will get into the cavity.
In a house that old, and with plank sheathing, the will not be so tight that the wall can not dry to the outside.
My preferance would be as you sugested, unfaced f/g if dense pack cellulose or foam are not in the budget, and a 6 mil poly vp.
That of course is depends on the area of the country,i.e. predomently heating or cooling climate. Different techniques need for different climates.
A good site for the vp use and placement is Building Science Corp.
Gabe, I would somewhat agree with you except my experience with local builders and many of the archys tell me most of them don't keep up around here. A little research outside of the guys that are taking his money can't hurt, and may help him get a better job.
Dave
Gabe, I would somewhat agree with you except my experience with local builders and many of the archys tell me most of them don't keep up around here. A little research outside of the guys that are taking his money can't hurt, and may help him get a better job.
Except that in this case, the advice was accurate. Highly unlikely that the exterior will be air tight. Kraft paper is not a very good VB.
Drywallers don't like installing over both because if it's not properly applied, it bunches between the stud and drywall making lumps.
Gabe
Agree about the kraft paper. Try as I might, I have never been able to install it tight in every stud bay. That is why I would use unfaced bats and a poly vp.
In the northern climate, mostly heating, any moisture getting into the wall from sources within the house will tend to move to the colder outside of the wall, where it could condense. The vp inside is the barrier to prevent as much as of that moisture from getting in the wall in the first place. Since the cold outside air is also a lot drier, the wall will also tend to dry to the outside.
The reverse of this occurs in the hot and humid south, where central ac makes the inside of the house the cold wall.
In mixed climates, it is best to choose one side or the other as the drying side. It is a compromise, based on knowledge of the local conditions.
Having this knowledge, when faced with conflicting recomendation, will at least let the HO ask some question as to why they are suggesting a certin placement/type of vp.
In old homes the choices are often dictated by how far one is going to go with tightening up the house.
I agree he got the correct advice about placement, but not the poly over kraft face. Why pay for the labor to install kraft face when it is poor to start with, then cut it up , and pay to install poly? Just use unfaced and the poly.
Dave
My Architect and My Carpenter are in favor
If you're not going to take their advice, why did you hire them if you have no confidence in their experience and honesty?
They are there, on site, we are here, at home. Who best to judge the needs of the house and client?
Gabe
Would help to know where you are. Are you in a heating or cooling area?
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Put up the plastic, but slit each section of kraft backing first. Just a simple diagonal slit 8-10 inches long at the top and bottom of each bay should be plenty.
Even without the slits I's unlikely that you'd have trouble, but it's cheap insurance.
You're very, very unlikely to have "trapped moisture" problems in an old house, and even if you did, avoiding the vapor barrier is not the way to solve them. Some sort of air exchange would be the way to go.
You said:
>>Put up the plastic, but slit each section of kraft backing first. Just a simple diagonal slit 8-10 inches long at the top and bottom of each bay should be plenty. <<
Why even use the kraft insulation at all? Why not go with unfaced batts? The only thing the kraft paper would do is help to create air pockets between the the sheetrock and the insulation which would only aid in the circulation of unconditioned air... Matt
The kraft also provides a convenient way to fasten the batts in place, and if the fit is a little loose, it keeps them from sagging.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
You don't have to fasten the batts in place. You just buy "friction fit" ones
I can offer some insight here.
We live in Fairbanks Alaska where the temps can get down to 60 below F. and much of the winter is in the 20 to 30 below range. There are no options regarding vapor barrier. It is mandatory that some sort of VB be installed on the warm side of the wall (the inside). 100% of the builders here use 6 mil visqueen throughout the whole envelope of the house. Any seams in the visqueen are sealed with an acoustic sealant such as Tremco and any seams that don't align over a stud or backing are taped with "red tape" as are any holes caused during construction. Special flanged electrical boxes are used and the VB is sealed to the flange. It is highly important that the VB be completely sealed. Failure to do so will result in the moist inside air migrating through the wall, through the insulation till it reaches the freezing front inside the wall where the moisture will turn to ice. Eight months of this will result in satruated insulation when things start warming up outside. Granted, not many on this forum live in an environment such as this but the principles are the same. We use unfaced insulation. Using craft faced insulation is unheard of here...the facing does not provide the level of vapor resistance required here and if you were to use visqueen over the craft faced insulation, you would create a double vapor barrier which could also spell disaster by potentially getting moisture trapped between the layers. Don't know if any of this helps for your location but it's what we do here.
>> ... does not provide the level of vapor resistance required here ...
What is the required level?
A perm rating of .06 is required. I don't know what the perm rating of craft faced insulation is but I doubt that it meets this requirement.
Friction fit batts work great, as long as the studs are exactly right, and for any odd bays the insulation is cut to proper width.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
I was assuming that they were "married" to the kraft-faced insulation. Unfaced batts would obviously be an option.
The DW guy doesn't want the poly because he won't be able to glue to the studs.
You're assuming that he would use glue ... that's unheard of down here.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
For my information, can you clarify what you mean by plank construction? Someone else mentioned plank sheathing, but is that what you mean? If so, what is meant by 'studding out' the walls? What have you stripped off (siding? interior finishes?).
Most folks here would use tyvek over the sheathing as the air barrier, and faced batts with the kraft facing to the interior. The drywall, when painted, forms a fairly efficient vapor barrier itself. I have only seen poly sheeting applied over cellulose insulation, which obviously does not have a facing. If you are not in a position to put a good air barrier over the exterior sheathing (i.e. siding is already in place) then you may want to consider trying to create an air barrier from the inside, but my understanding is that the foam insulation materials are the best at that.
I agree with Gabe that you should hopefully have some trust in your guys on that end, but I double-check stuff here all the time that local tradespeople and designers tell me. I mean... why wouldn't you?
dave.. by plank i assume he means there are ( or were ) no studs.. it probably has a post & beam frame.. and the vertical planks run from the top of the wall to the bottom of the wall.. on the interior, lath was nailed to this and plastered..
on the exterior, the siding ( usually clapboards ) was nailed to the planks..
the windows had their own frame..
the whole wall thickness was about 2" with no cavity for insulation
Mike Smith Rhode Island : Design / Build / Repair / Restore
No matter which route you go, be sure to foam all the penetrations in the plates from pipes, ducts, wires and poor craftsmanship (if it's balloon framed, install blocking and then foam the little holes) to prevent air moving into the walls from the inside of the house. Air infiltration is by a huge margin the chief source of water in framing cavities. Vapor pressure might account for one percent of what air infiltration can bring you. Definitely visit buildingscience.com. The further north you are, the more important vapor barriers become. Go far enough south, and they can rot your house from the inside out. Present company excepted, most tradesmen and architects that I've met have a poor understanding of the mechanisms at play here.
Andy
Arguing with a Breaktimer is like mud-wrestling a pig -- Sooner or later you find out the pig loves it.
It's trouble asking about vapor barriers here. Sort of like asking folks to express their religious beliefs.
Assuming you live in a heating climate...
Just to throw you a curve, look into "airtight drywall" or "airtight drywall approach".
Of course, only my way is the righteous way...
So, after all this discussion, why are you using fiberglass, especially if you are going to pay someone to install?
this Q really can't be answered till we find out where you live ...
mostly heating .. mostly cooling .... mostly mix?
But the easy generic answer has been given .... unfaced batts ... and put the poly on which ever side of the wall it's needed ... is the moisture coming in or going out.
Jeff
Buck Construction, llc Pittsburgh,PA
Artistry in Carpentry
Heating, cooling, ?? there's no difference.
Area? ,? no difference. the cold air of 40 Degrees in California is no different from the 40 Degree cold air in Siberia.
Edited 9/21/2004 10:19 am ET by Hube
U could not be more wrong.
JeffBuck Construction, llc Pittsburgh,PA
Artistry in Carpentry
40 degrees F is the same in any country or language and is also 8 degrees above freezing temperature anywhere. Savvy?
in warmer climates where there are more cooling days than heating ...
like say .. Houston TX ... there is more moisture outside the house.
in cooler climates where there are more heating days than cooling ...
like say ... Pittsburgh PA ... there is more moisture inside the house.
in Houston .. the VB ... which protects the insulation from moisture ...
goes on the outside of the studs.
in Pittsburgh ... the VB ... which protects the insulation from moisture ...
goes on the inside of the studs.
savvy?
maybe answering vapor barrier questions in the const tech's section isn't your forte?
stick to meteorology and world geography.
JeffBuck Construction, llc Pittsburgh,PA
Artistry in Carpentry