is vapour barrier needed when replacing siding?

Hi everyone, we are replacing the wood siding on an older home with vinyl. In the process I want to add insulation from the outside, since the home likely has very poor insulation. I plan to tear off the wood siding, add fiberglass batt insulation, nail 4x8 OSB to the studs, housewrap and then vinyl. My question: do I need to put on vapour barrier as a first step? This would be awkward since it would have to go over the studs. Doing anything from inside is not practical since it is all lathe and plaster. Any ideas, tips?

Sounds like a good idea but your question is confusing me a little. the house wrap is your vabor barrier and will go on your osb.

Did you price blowing in insulation. could save alot of time and maybe money.

Fortunately, house wrap is not a vapor barrier.

The vapor barrier belongs on the warm side (usually inside) of the insulation. Never on the outside.

Easy...as you remove siding, replace any existing insulation with craft faced r-13. The paper will face and actually touch the sheetrock/plaster, interior wall. You should see nothing but insulation....pink stuff. From there install your plywood...or OSB. Then your house wrap, I would use 15lb felt/tar paper starting from the bottom of the house and install over each piece as you go up at least 3 inches. It is less expensive than tyvek or other wraps. Then install your insulation board and tape all seams with the recommended tape product. Not duct tape.
Then install your siding, and think like water. Where would you go if you where traveling down the house.

What I mean is "don't tuck your raincoat into your pants...your substructure will get watered."

Do not use plastic on an old house anywhere, it will cost you....guaranteed.

I have to go with Guyod on this one. Blow insulation into the walls and leave the siding in place. Use the fan-fold foam insulation and vinyl siding.
Stripping down and using batt insulation is very expensive and, in my humble and accurate opinion, is overkill.
Glenn

I would not trust the suggestions regarding vapor barriers and "moisture barriers" if they think a house wrap is a vapor barrier and that the vapor barrier goes on the outside of the insulation.

Mudslingin.
An explanation would work better to clear it up.
A house wrap (tar paper, tyvek, typar, ect)belongs on the exterior side of a home, this is called a moisture barrier.
A vapor barrier goes on the interior. This is kraft face paper, plastic(terrible) or some paints on older homes.

Rigid foam insulation has nothing to do with either, this is not integrated with the windows barriers and relies on adheasive tape for joints, so it does nothing but keep the house a bit tighter.
Read my suggestion carefully and explain the areas which need clarification.
So I understand what it is I need to fix.

The mudslinging apparently started as a dispute over where the Vapor barrier belongs and why winnepegreno would want to replace the wood siding on his home with osb before he covers it with vinyl siding....

I gotta say, I'm with the Inspector on this one. The vapor barrier is already on the batts if you buy the kraft faced batts. tearing off the old siding and replacing it with osb will lend strength to the walls but it does seem like overkill. Unlike inspectorD though, I consider plastic a good thing in certain situations. As in, flashing from under the wall sheathing, down and out to the weeps in a brick wall. BUT I agree that felt paper is an adequate choice for an exterior moisture barrier. Foam board is always a good choice behind vinyl siding and tyvec is... well, in my opinion, not worth the extra money and should actually be free because the manufacturer or the supplier certainly uses it to advertise themselves all over your home until the finished siding covers it all

So repeat after old Square Eye
"Drywall, vapor barrier, insulation, wall sheathing, moisture barrier, foam insulation, vinyl siding."

winnepegreno, you do not have to try to apply a visqueen from outside to get an effective vapor barrier.

Sheet plastic is only useful as an interior vapor barrier or at or below grade for a moisture barrier or flashing.

Thanks everyone for your input. It raises a couple more questions though. I know that Tyvek or other housewrap is a moisture barrier and not a vapour barrier. My questions: even though the insulation batts have the kraft paper backing, that doesn't create a continuous vapour barrier, because of the studs between. Second, what the heck is visqueen???

Visqueen is a thin, light plastic sheet that makes an excellent vapor barrier. The name comes from an old manufacturer's brand name.
Anyway, you insulate then cover the walls with visqueen before you drywall.

AND

No, kraft paper can't provide a continuous vapor barrier but neither will anything else. The only way to get a continuous vapor barrier would be to open the interior walls and apply it from inside.

And...if you want to get really "scrutinize-ding" Is that really a word?? You wont get a vapor barrier on a lot of places besides the studs. The joists and box areas between the floors never have it. And any outlets which get cut out...all throughout the outside walls. Moisture will evacuate itself from the house. This Kraft faced paper just helps to collect it and actually store some moisture and release it as it needs to.
A house will breath, that is why I disagree with plastic on the inside of homes. It will not let anything through...at all ,and will collect at the bottom of the sheet. I have fixed to many new homes were they have humidifiers in the system which are doing nothing but causing serious damage , and health concerns. All because of plastic vapor barriers.

Do it like Square Eye and I suggested and be done, then enjoy the greater comforts of home.

Probably over 40 years of experience between the 2 of us. I'm on 24 myself at 40 years old.
Still young enough to boast about it, and old enough to know I'm just foolin myself.

The purpose of a vapor barrier is to prevent warmer (and more moist) INTERIOR air from reaching colder surfaces and resulting in moisture from condensation. As such, it is applied on the inner WARM side of a wall, not the outside.

BustMyBum said:

The purpose of a vapor barrier is to prevent warmer (and more moist) INTERIOR air from reaching colder surfaces and resulting in moisture from condensation. As such, it is applied on the inner WARM side of a wall, not the outside.

Click to expand...

Welcome to the site and good info but check the dates, answering ther real old question is a waiste of time.

As well as the information not being quite right either.

Vapor barrier placements in hot humid climates (if at all) would be the exterior walls surfaces.